MTB Tech Rumors and Innovation

w4s wrote:

doesnt the stumpjumper use a digressive damper tune to account for the spring rate of the flex stays?

BigNubbs wrote:

On the DPS from Fox yes it does. Both comp and reb stacks

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

Velocipedestrian wrote:

I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place.  Seems like...

I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place. 

Seems like a good idea in theory. 

boozed wrote:

This Pivot prototype suspension design looks very similar to Polygon's "IFS", just with a flexible seat-stay rather than a seat-stay pivot?

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

Primoz wrote:

Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel...

Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?

In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.

How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.

Primoz wrote:

Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel...

Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?

In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.

How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.

RonJon wrote:

 Hopefully this works. The horizontal link is right on the brink of inverting but not sure it gets there before stroke runs out.

 Hopefully this works. The horizontal link is right on the brink of inverting but not sure it gets there before stroke runs out.

Primoz wrote:

No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring...

No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring. You would need to add a separate damper to the frame (mount it to who knows where) for it to have an effect. 

barryjenson wrote:

Looks more like a Pirelli scorpion M 

Looks more like a Pirelli scorpion M 

krabo83 wrote:

speaking of pirelli, anyone seen what tires loris really was on? :D

parnifel wrote:

Maxxis DHRll by the looks of this…      

Maxxis DHRll by the looks of this…

 

 

 

austin-NC wrote:

I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they...

I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires. 

austin-NC wrote:

I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they...

I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires. 

Jrp wrote:

It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them...

It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them. His results are very important to the team and he’s notoriously fussy so I’d imagine come race week he’s free to run blacked out tyres he trusts. The % of people who notice his tyre has no logo would be tiny in comparison to the people who notice the pirelli logo on his shirt 

paddydigital wrote:

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...

All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.*  This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup. 

 

This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping. 

 

Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position. 

 

In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?  

 

Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling. 

 

Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***

 

All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'. 

 

*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable. 

 

**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on. 

 

*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.

 

TEAMROBOT wrote:

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX...

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.

Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.

TEAMROBOT wrote:

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX...

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.

Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.

TEAMROBOT wrote:

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX...

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.

Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.

yahmon wrote:

Loris' mechanic said in the Vital Pit Bits from Lenzerheide when asked about the Pirellis: "It's good, still need a bit more improvement to be ready...

Loris' mechanic said in the Vital Pit Bits from Lenzerheide when asked about the Pirellis:

"It's good, still need a bit more improvement to be ready to win races but... the guys want to have tires that win races."

Kind of a crazy admission from someone on the team payroll.

ORTOGONAL555 wrote:

Related to Jordan Williams not being on the new proto, I'd say they are fully custom frames and they have to figure out his ideal geos...

Related to Jordan Williams not being on the new proto, I'd say they are fully custom frames and they have to figure out his ideal geos before giving it to him. But he most likely is on a longer reach frame, as the Demo is quite small (465 on the bigger size)

TEAMROBOT wrote:

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX...

Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.

Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.

yahmon wrote:

Loris' mechanic said in the Vital Pit Bits from Lenzerheide when asked about the Pirellis: "It's good, still need a bit more improvement to be ready...

Loris' mechanic said in the Vital Pit Bits from Lenzerheide when asked about the Pirellis:

"It's good, still need a bit more improvement to be ready to win races but... the guys want to have tires that win races."

Kind of a crazy admission from someone on the team payroll.

Sonofbovril2 wrote:

Interesting that Pirelli have sponsored so many DH teams when they don’t yet have a DH tire that is competitive? Besides Trek, they sponsor one of...

Interesting that Pirelli have sponsored so many DH teams when they don’t yet have a DH tire that is competitive? Besides Trek, they sponsor one of the Commencal teams and a Canyon team possibly?

wasn’t Fabian Barrel heavily involved in the Pirelli development?

TEAMROBOT wrote:

I agree that the Pirelli DH tires appear to be at least rideable. The Canyon/Pirelli team has some serious young racers like Dante Silva, Antoine Pierron...

I agree that the Pirelli DH tires appear to be at least rideable. The Canyon/Pirelli team has some serious young racers like Dante Silva, Antoine Pierron, and Loris Revelli who are consistently getting top 30 results on the Pirellis.

Regarding what's inside the racers tires- who knows? I wonder the same thing about the new Conti's, because in my mind there's no way a 1200 gram 29" DH tire is winning Snowshoe or Hardline or Lenzerheide or even getting to the bottom of the track with air in it. Meanwhile Minnaar got two flats this weekend running 1400 gram Maxxis tires, or even heavier if he's running the prototype "Breaker" pinch flat barrier in them. With Michelin and Schwalbe getting good results by moving up to 1500 gram DH casings, and with 1300-1400 DD and DH casing Maxxis tires serving as the norm on the EWS, I think the stock 1200 gram Conti tires are pretty unbelievable as World Cup DH tires. But who knows.

TEAMROBOT wrote:

I agree that the Pirelli DH tires appear to be at least rideable. The Canyon/Pirelli team has some serious young racers like Dante Silva, Antoine Pierron...

I agree that the Pirelli DH tires appear to be at least rideable. The Canyon/Pirelli team has some serious young racers like Dante Silva, Antoine Pierron, and Loris Revelli who are consistently getting top 30 results on the Pirellis.

Regarding what's inside the racers tires- who knows? I wonder the same thing about the new Conti's, because in my mind there's no way a 1200 gram 29" DH tire is winning Snowshoe or Hardline or Lenzerheide or even getting to the bottom of the track with air in it. Meanwhile Minnaar got two flats this weekend running 1400 gram Maxxis tires, or even heavier if he's running the prototype "Breaker" pinch flat barrier in them. With Michelin and Schwalbe getting good results by moving up to 1500 gram DH casings, and with 1300-1400 DD and DH casing Maxxis tires serving as the norm on the EWS, I think the stock 1200 gram Conti tires are pretty unbelievable as World Cup DH tires. But who knows.