Modern Geo Talk: Chainstays, Stack, Reach, and Bitching About It

2/5/2026 2:04pm
I wouldn’t even want the same rad on two very differently balanced bikes. Consistent rad across bikes makes zero sense as there are very different geo...

I wouldn’t even want the same rad on two very differently balanced bikes. Consistent rad across bikes makes zero sense as there are very different geo and body positioning needs depending on terrain and discipline. I would love the same fc/rc ratio AND rad on all my bikes, but if I could only choose one consistent variable it would be fc/rc ratio. Let the rad change depending on how I’m riding the bike.

So you haven’t tried it. 

RAD is the worst addition to this thread. horrible derail.

RAD is really just the concept of spread, with extra steps. Spread (somewhat used before rad) is just the length of the hypotenuse of the triangle formed by reach and stack. 

Its important as it determines "fit" and overall body position, but without FC/RC head angles, BB drop etc, it is useless by itself. 

 

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seanfisseli
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2/5/2026 3:19pm

So you haven’t tried it. 

RAD is the worst addition to this thread. horrible derail.

RAD is really just the concept of spread, with extra steps. Spread (somewhat used before rad) is just the length of the hypotenuse of the triangle...

RAD is really just the concept of spread, with extra steps. Spread (somewhat used before rad) is just the length of the hypotenuse of the triangle formed by reach and stack. 

Its important as it determines "fit" and overall body position, but without FC/RC head angles, BB drop etc, it is useless by itself. 

 

Upon further reflection, I can see that rad actually belongs in here, even though it mainly relates to ergonomics

sethimus
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2/7/2026 8:51am Edited Date/Time 2/7/2026 8:53am

i‘m sorry, but he also invented the riprow…

 

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2/9/2026 8:37am

I always thought that the idea behind the RAD measurements were to get s similar cockpit feel between different bikes..

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2/9/2026 11:51am

it sounds like RAD is like getting your ski boots fit and knowing exactly what size you are. 

fC/RC ratio is what style of ski boot you want, in that size. 

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seanfisseli
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2/9/2026 12:51pm
it sounds like RAD is like getting your ski boots fit and knowing exactly what size you are. fC/RC ratio is what style of ski boot you...

it sounds like RAD is like getting your ski boots fit and knowing exactly what size you are. 

fC/RC ratio is what style of ski boot you want, in that size. 

RAD is boot fitting. FC/RC is mounting location of bindings

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Dave_Camp
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2/9/2026 5:34pm

Got a good ride in on the short bike... I'm surprised at how much different it feels even though in my head 48mm (difference in wheelbase from my normal bike) is not that big of a % change.

 

Anyway- this thing feels great to me- seems to be able to carve switchbacks (we have a lot) instead of just steering around them.  Also more poppy and fun to ride.

 

Will have to do more setup work to get comfortable- needs grips, taller bars and more gears.  After I'm comfy- will try to do a real back to back with my other bike and time some sections. 

IMG 1411 0
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AgrAde
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2/9/2026 9:51pm Edited Date/Time 2/9/2026 9:58pm

But what if I like centre-mounted skis but my bike's F:R ratio is 1.89 and I like that too?

Primoz
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2/9/2026 10:33pm
Dave_Camp wrote:
Got a good ride in on the short bike... I'm surprised at how much different it feels even though in my head 48mm (difference in wheelbase...

Got a good ride in on the short bike... I'm surprised at how much different it feels even though in my head 48mm (difference in wheelbase from my normal bike) is not that big of a % change.

 

Anyway- this thing feels great to me- seems to be able to carve switchbacks (we have a lot) instead of just steering around them.  Also more poppy and fun to ride.

 

Will have to do more setup work to get comfortable- needs grips, taller bars and more gears.  After I'm comfy- will try to do a real back to back with my other bike and time some sections. 

IMG 1411 0

What's up with that rear derailleur 😁

seanfisseli
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2/10/2026 8:10am
AgrAde wrote:

But what if I like centre-mounted skis but my bike's F:R ratio is 1.89 and I like that too?

How tall are you?

AgrAde
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2/10/2026 8:23pm

5'11"

seanfisseli
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2/10/2026 10:49pm
AgrAde wrote:

5'11"

I think skis being center mounted is easier for people to understand. Like, if you want to ski park and ski switch center mounted for sure. If you like the way a ski carves when it’s center mounted that’s a little more esoteric. Same with bikes. People who like a more centered stance like the way that the bike carves when your weight is more balanced. I feel like the front end of long front center bikes “swing around” similar to how a long stem feels on a road bike. There isn’t really a riding switch equivalent on mountain bikes and so the difference between the ratios is a little more subjective I suppose.

AgrAde
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2/10/2026 11:15pm

Yeah I was being silly. Centre mounted skis and long chain stays don't have a lot in common.

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Primoz
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2/11/2026 1:03am

You still don't mount the bindings all the way back on carving skis. You need a bit of tail to give you support from behind. It's analogous to the front and rear end of a bike, maybe a bit different due to the bike having two contact points while a ski has a surface contact and bends. 

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seanfisseli
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2/11/2026 8:18am
AgrAde wrote:

Yeah I was being silly. Centre mounted skis and long chain stays don't have a lot in common.

I’ve had ski shops give me a lot of shit for mounting my bindings further forward than manufacturer recommended, just like we hear lots of people complaining about long chainstays making bikes unrideable 

Eae903
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Fantasy
2/15/2026 9:42am Edited Date/Time 2/15/2026 9:43am
Primoz wrote:
You still don't mount the bindings all the way back on carving skis. You need a bit of tail to give you support from behind. It's...

You still don't mount the bindings all the way back on carving skis. You need a bit of tail to give you support from behind. It's analogous to the front and rear end of a bike, maybe a bit different due to the bike having two contact points while a ski has a surface contact and bends. 

I don't know, I've found that some pairs of Skis handled a lot better when the binding was set back a bit from the recommended mounting point (a pair of Salomon QST 85s that I demoed for a few days come to mind), not many but some. Depends on the ski, the terrain, and who's using them. Same with bikes. I should check to see what the tip to tail ratio is on my current skis (icelantic Nomad 105s), see how close it is to the bikes fc/rc ratio. 

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2/15/2026 1:20pm

Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski ahead or behind the recommended mount point is to compensate for your style of weight distribution (forward or upright). The goal is to always put the weight through the mounting line. 

Long chainstays are equivalent to traditionally mounted skis > more stability. 

But yes, it all comes down to how you like to out your weight into the ground and what characteristics you want out of the equipment. 

 

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seanfisseli
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2/15/2026 3:36pm
Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski...

Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski ahead or behind the recommended mount point is to compensate for your style of weight distribution (forward or upright). The goal is to always put the weight through the mounting line. 

Long chainstays are equivalent to traditionally mounted skis > more stability. 

But yes, it all comes down to how you like to out your weight into the ground and what characteristics you want out of the equipment. 

 

100% wrong as far as I understand it. I like a more center biased ski because I don’t want to have work the front of the ski. I like being in the center of the ski can carving from there. Normal mounting forces you to apply a lot more force through your shins to press forward and into the tips of the skis. This is similar to short CS bikes forcing you to weight the bars to get traction on the front wheel.

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seanfisseli
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2/15/2026 3:37pm

I clicked through really thinking I might find a thread over there about mountain bikes lol

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2/15/2026 8:44pm
Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski...

Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski ahead or behind the recommended mount point is to compensate for your style of weight distribution (forward or upright). The goal is to always put the weight through the mounting line. 

Long chainstays are equivalent to traditionally mounted skis > more stability. 

But yes, it all comes down to how you like to out your weight into the ground and what characteristics you want out of the equipment. 

 

100% wrong as far as I understand it. I like a more center biased ski because I don’t want to have work the front of the...

100% wrong as far as I understand it. I like a more center biased ski because I don’t want to have work the front of the ski. I like being in the center of the ski can carving from there. Normal mounting forces you to apply a lot more force through your shins to press forward and into the tips of the skis. This is similar to short CS bikes forcing you to weight the bars to get traction on the front wheel.

Definitely not wrong, and you agreed with me with your reasoning. I think we can agree that it is an analogy that can be taken a few ways. Sure Short CS and trad mounted skis make you shift your weight forwards but they also produce two opposing characteristics. Short chainstays = more flickable, Short front of skis (centre mounted)= more pivotable. 

Anyways...

seanfisseli
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2/16/2026 12:02am
Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski...

Some skis have a more forward mount to make them more playful by reducing swing weight and leverage the front has over you. Mounting a ski ahead or behind the recommended mount point is to compensate for your style of weight distribution (forward or upright). The goal is to always put the weight through the mounting line. 

Long chainstays are equivalent to traditionally mounted skis > more stability. 

But yes, it all comes down to how you like to out your weight into the ground and what characteristics you want out of the equipment. 

 

100% wrong as far as I understand it. I like a more center biased ski because I don’t want to have work the front of the...

100% wrong as far as I understand it. I like a more center biased ski because I don’t want to have work the front of the ski. I like being in the center of the ski can carving from there. Normal mounting forces you to apply a lot more force through your shins to press forward and into the tips of the skis. This is similar to short CS bikes forcing you to weight the bars to get traction on the front wheel.

Definitely not wrong, and you agreed with me with your reasoning. I think we can agree that it is an analogy that can be taken a...

Definitely not wrong, and you agreed with me with your reasoning. I think we can agree that it is an analogy that can be taken a few ways. Sure Short CS and trad mounted skis make you shift your weight forwards but they also produce two opposing characteristics. Short chainstays = more flickable, Short front of skis (centre mounted)= more pivotable. 

Anyways...

“Flickable” as a quality imparted by short chainstays is nonsense. Riding from a centered position and through the feet makes any wheelbase/chainstay length more flickable

7
2/16/2026 3:57am

“Flickable” as a quality imparted by short chainstays is nonsense. Riding from a centered position and through the feet makes any wheelbase/chainstay length more flickable

Remember , our sport is full of ideas that have stuck around due to a notion of how things are perceived. Kinda like some roadies who will tell up that a 23c tire at 105psi feels faster. Even though every pro team is running wider tires at a lower pressure..

The shorter rear feels more nimble because the FC was still short.. And, that was based on thinking that went back to the early MTB days where geometry was based on road bike knowledge..

I've wondered what the next big geometry debate/ change would be.. I'm thinking ive now found it..

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seanfisseli
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2/16/2026 8:52am

“Flickable” as a quality imparted by short chainstays is nonsense. Riding from a centered position and through the feet makes any wheelbase/chainstay length more flickable

Remember , our sport is full of ideas that have stuck around due to a notion of how things are perceived. Kinda like some roadies who...

Remember , our sport is full of ideas that have stuck around due to a notion of how things are perceived. Kinda like some roadies who will tell up that a 23c tire at 105psi feels faster. Even though every pro team is running wider tires at a lower pressure..

The shorter rear feels more nimble because the FC was still short.. And, that was based on thinking that went back to the early MTB days where geometry was based on road bike knowledge..

I've wondered what the next big geometry debate/ change would be.. I'm thinking ive now found it..

Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to change the road world has been. As soon as I stumbled into long chainstays I realized it would be the same thing. 

On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?

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storm.racing
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2/16/2026 9:39am

“Flickable” as a quality imparted by short chainstays is nonsense. Riding from a centered position and through the feet makes any wheelbase/chainstay length more flickable

Remember , our sport is full of ideas that have stuck around due to a notion of how things are perceived. Kinda like some roadies who...

Remember , our sport is full of ideas that have stuck around due to a notion of how things are perceived. Kinda like some roadies who will tell up that a 23c tire at 105psi feels faster. Even though every pro team is running wider tires at a lower pressure..

The shorter rear feels more nimble because the FC was still short.. And, that was based on thinking that went back to the early MTB days where geometry was based on road bike knowledge..

I've wondered what the next big geometry debate/ change would be.. I'm thinking ive now found it..

Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to...

Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to change the road world has been. As soon as I stumbled into long chainstays I realized it would be the same thing. 

On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?

"On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?"
this. I want to see too. I have always been curious about this whole flickable side of biking that only short chainstays can do

1
2/16/2026 3:30pm
Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to...

Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to change the road world has been. As soon as I stumbled into long chainstays I realized it would be the same thing. 

On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?

1
seanfisseli
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2/16/2026 10:19pm
Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to...

Oh I know! I was on wide road tires 10+ years ago and it was a real eye opener to see how slow and resistant to change the road world has been. As soon as I stumbled into long chainstays I realized it would be the same thing. 

On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?

I don’t think that’s what “flickable” is referring to but if it is it’s not worth the trade off AND I have seen plenty of people on long CS bikes do those “flicks.” I will also take this opportunity to admit that I have never been able to figure out how to do those, long or short chainstays 

bigbrett
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2/17/2026 6:43am Edited Date/Time 2/17/2026 6:43am
"On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?"this. I want to see too. I...

"On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?"
this. I want to see too. I have always been curious about this whole flickable side of biking that only short chainstays can do

Cmon man it’s a vital segment and even in the title 

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seanfisseli
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2/17/2026 9:11am
"On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?"this. I want to see too. I...

"On the flickable note… can someone link to a video of this “flicking” that’s happening on the short chainstay bikes?"
this. I want to see too. I have always been curious about this whole flickable side of biking that only short chainstays can do

bigbrett wrote:

Cmon man it’s a vital segment and even in the title 

What am I looking at here? What about this riding necessitates short chance days?

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