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David.Max
11/15/2017 10:58am
11/15/2017 10:58am
Edited Date/Time
11/30/2017 5:33am
This is just a little side project that I've been toying with, but I've been wondering if with the advent of tire inserts (CushCore etc.) it might make sense to take a new look at how tires are designed. If we conceptualize and design wheels, tires, and inserts as part of an integrated system, instead of as individual components, I think that there might be some real weight and performance gains available. And maybe, just maybe, we would see less World Cup and EWS races being decided by flat tires.
The tire has a variety of roles that are fulfilled by the tread and carcass. The tread is responsible for maintaining traction with the ground, but its ability to do that is directly tied to the performance of the carcass.
Meanwhile the carcass is responsible for:
1. Keeping air in the tire
2. Protecting the rim from damage
3. Providing sidewall support
4. Damping the rebound of the tire
Currently, most of the these design goals are accomplished by adding more material (and more weight) to the tire to create a more supportive and durable carcass.
Adding tire inserts to the wheel/tire system adds a new element into the system that overlaps with a lot of the same roles as the tire carcass. The insert also:
1. Protects the rim from damage
2. Provides sidewall support
3. Damps the rebound of the tire
I'm wondering if you could make a tire that would be both lighter and more resistant to slashes and punctures by designing it specifically to work with an insert. If you assume that insert will provide the majority of sidewall support, rim protection, and rebound damping that are normally a large portion of the tire casing's responsibilities, that frees up the design of the casing to focus solely on keeping air in the tire.
In essence, I'm wondering if you could make a casing that is made almost entirely out of a para-armamid, or an UHMWPE material like dyneema with just enough rubber built into it to provide for air holding. I've used dyneema slings quite a bit for rock climbing and in that application it can be woven into a fabric that is highly cut resistant and very flexible. If it was possible to build a casing this way you would end up with a casing that is very compliant and highly cut resistant, but it would offer very little sidewall support or rebound damping. However, if you can assume that these aspects of the design criteria are going to be carried out by the insert then that's not really an issue.
To take it a step further, if you design the rim to specifically work with a tire insert as well than you can eliminate some of the installation struggles that seem to be an issue at the moment. Based on Jeff Brines review of the Santa Cruz Reserve wheels it is certainly possible to create a rim design that is way less of a headache when installing an insert.
https://www.vitalmtb.com/product/guide/Wheelsets,44/Santa-Cruz/Reserve-….
Beyond that, I would think that you could shave some weight from the rim if you knew that it was always going to be used with an insert in place to provide impact protection. I'm not entirely sure about this notion given the fact that EWS racers are still destroying carbon wheels with CushCore in place. That said, the recent video of Danny MacAskill bashing the heck out of pair of the Reserve wheels without a tire certainly makes it seem like it would be possible to build them with a bit less material if the designer could assume that they would only be used with a tire insert installed.
https://www.vitalmtb.com/videos/member/Can-Danny-MacAskill-Break-the-Ne…
According to Flat Tire Defender using their insert means that a rim can handle 20% more force without suffering damage and I would imagine that CushCore would offer a similar level of protection. From an engineering standpoint a 1/5 reduction in the forces that a structure has to withstand is pretty significant and I would think that it would allow for a rim that could be somewhat lighter to compensate for the weight of the insert.
This has turned into a bit of an essay and there are obviously some complications involved with the idea like getting a rim, insert, and tire manufacturer lined up to work together; and bringing even more proprietary products into the market place. However, when you consider the fact that races at the absolute pinnacle of our sport are still being decided by the fact that we can't seem to keep air in a f#*%&ing tire, it seem like its something thats worth some discussion and outside of the box thinking.
The tire has a variety of roles that are fulfilled by the tread and carcass. The tread is responsible for maintaining traction with the ground, but its ability to do that is directly tied to the performance of the carcass.
Meanwhile the carcass is responsible for:
1. Keeping air in the tire
2. Protecting the rim from damage
3. Providing sidewall support
4. Damping the rebound of the tire
Currently, most of the these design goals are accomplished by adding more material (and more weight) to the tire to create a more supportive and durable carcass.
Adding tire inserts to the wheel/tire system adds a new element into the system that overlaps with a lot of the same roles as the tire carcass. The insert also:
1. Protects the rim from damage
2. Provides sidewall support
3. Damps the rebound of the tire
I'm wondering if you could make a tire that would be both lighter and more resistant to slashes and punctures by designing it specifically to work with an insert. If you assume that insert will provide the majority of sidewall support, rim protection, and rebound damping that are normally a large portion of the tire casing's responsibilities, that frees up the design of the casing to focus solely on keeping air in the tire.
In essence, I'm wondering if you could make a casing that is made almost entirely out of a para-armamid, or an UHMWPE material like dyneema with just enough rubber built into it to provide for air holding. I've used dyneema slings quite a bit for rock climbing and in that application it can be woven into a fabric that is highly cut resistant and very flexible. If it was possible to build a casing this way you would end up with a casing that is very compliant and highly cut resistant, but it would offer very little sidewall support or rebound damping. However, if you can assume that these aspects of the design criteria are going to be carried out by the insert then that's not really an issue.
To take it a step further, if you design the rim to specifically work with a tire insert as well than you can eliminate some of the installation struggles that seem to be an issue at the moment. Based on Jeff Brines review of the Santa Cruz Reserve wheels it is certainly possible to create a rim design that is way less of a headache when installing an insert.
https://www.vitalmtb.com/product/guide/Wheelsets,44/Santa-Cruz/Reserve-….
Beyond that, I would think that you could shave some weight from the rim if you knew that it was always going to be used with an insert in place to provide impact protection. I'm not entirely sure about this notion given the fact that EWS racers are still destroying carbon wheels with CushCore in place. That said, the recent video of Danny MacAskill bashing the heck out of pair of the Reserve wheels without a tire certainly makes it seem like it would be possible to build them with a bit less material if the designer could assume that they would only be used with a tire insert installed.
https://www.vitalmtb.com/videos/member/Can-Danny-MacAskill-Break-the-Ne…
According to Flat Tire Defender using their insert means that a rim can handle 20% more force without suffering damage and I would imagine that CushCore would offer a similar level of protection. From an engineering standpoint a 1/5 reduction in the forces that a structure has to withstand is pretty significant and I would think that it would allow for a rim that could be somewhat lighter to compensate for the weight of the insert.
This has turned into a bit of an essay and there are obviously some complications involved with the idea like getting a rim, insert, and tire manufacturer lined up to work together; and bringing even more proprietary products into the market place. However, when you consider the fact that races at the absolute pinnacle of our sport are still being decided by the fact that we can't seem to keep air in a f#*%&ing tire, it seem like its something thats worth some discussion and outside of the box thinking.
For those unfamiliar with tire inserts or CushCore, here's a primer: https://www.vitalmtb.com/features/Vital-MTB-Face-Off-The-Best-Tire-Inse…
I do find it rather odd that people are putting a ton of weight into carbon wheels with these inserts and ending up with larger rotational weights at a higher price. You are probably better off getting cheap alloy rims and smoking them on a regular basis.
Are we now basically talking about tubular mountain bike tires?
Spomer said it awhile ago, but the number of races over the years (and overal championships) decided by losing air out of a tire is far (far) too many. Its an obvious problem, and something that has more or less gone un-addressed.
Heck, we rarely even see tire companies playing with new casing, let alone something entirely new. Until the recent slew of inserts, there was really no development in this area.
As I posted in my wheel review, I expect to see a wheel that has some form of insert integrated from the factory. This will make for easier tire installs and the engineers to pull material where it really isn't needed.
Considering we are already seeing $100 tires, I'm not sure there is enough room in the market for an insert-based tire. EG: It'd just be too expensive for something you throw away in a month or two due to wear, but I could be wrong.
Oh, and to anyone that thinks the whole insert thing is just about keeping air in the tires, think again. Its the single most impressive thing I've put on my bike when it comes to improving ride quality and handling when really pushing my bike in rugged terrain...
My first post was pretty long so I'll see if I can clarify what I'm thinking and pull out some of the main points.
At the moment this is definitely a performance focused idea, something for racing and other mission critical applications were traction and keeping air the tire are the highest priority. One of the things that really got me thinking about this is the frustration of seeing races at the highest level of our sport being decided by flat tires. If I was going to list priorities they would be:
1. Keeping air in the tire air
2. Ride quality/traction (as a very close 2cnd)
3. Weight
4. Price
I know those aren't everybody's priority, but from a racing perspective it makes sense.
The insert and the tire would still separate elements from each other, but the tire would be a squirmy, undamped mess if you rode it at low pressures without the insert.
Essentially this a a thought exercise. All tires are currently designed with the notion that they should be able to perform at high level without an insert. The insert is a new and significant structural element that was never taken into account in the original design of any tire that is currently on the market.
I'm asking what might be possible if a tire was specifically designed with the knowledge that an insert would be a part of the overall system of the wheel/tire? Right now the tire designer has to come up with a tire that is able to offer a significant degree of sidewall support, ride damping, and pinch flat protection. If the tire doesn't have to deal with those roles because they are being handled by the insert would that free up resources -i.e. material constraints and hence weight- that could then be redirected towards keeping air in the tire?
There are already a variety of ballistic materials that are used in tire construction. If we reconsider the design brief of the tire based on the use of an insert could we come up with something that is significantly more slash and puncture proof, while also offering an improved ride quality?
You have my attention. BUT these were my exact thoughts when I first used Maxxis DH casings.
So I have to ask, what tyres do you choose to run under said circumstances?
Genuinely curious here because I keep getting laughed at when I tell people how much of a difference the DH and DD tyres have made. I even think the weight aids stability as well as the damping characteristics. But it could all just be me. And I’m tryna figure that out...
I could run my pressure as low as 18-19psi and still not get the tire to roll off the rim. To me that's amazing. Side note, I didn't actually run tire pressure that low, but it was cool to be able to play with it. I generally run 28-30psi-ish front and rear. 29" wheels. 30mm rim width. 2.4-2.5" tires.
With Cushcore I dropped to 23-26psi. YMMV
J
Edit: I'm 200lbs. And I hit shit. Hard.
_MK
- Carbon rims crack instead of bend
- Carbon rims are probably less elastic than aluminum and absorb less force
Inserts seem a temporary solution to a not fully mature technology. And a solution to the problem brought on by ourselves for putting on the carbon rims.
- The biggest issue I've seen are cut casings, pinches are rare compared to cuts.
I have to wonder if the bikes have become so good, and we can now ride so fast, that the tires are playing catch up in durability. I used to be able to ride 600g tires, but now have to run 900+g tires for durability (however the tires are bigger and 26 --> 27.5)
- Pro DHers do not ride like us
Perhaps to solve their issues, tire manufacturers make Pro-level tires that their pros won't rip off in competition. I would not want one, as it would probably ride like a brick for my level of riding. Not unlike the air spring rates the pros run are waaay beyond what we ride. Or maybe pros run moto style bead locks to keep their tires on.
What I want: a cut protected tire that is still supple.
The inserts solve issues I do not have.
Not so sure I agree with the latter part of this statement, as its a bit too general for my liking. I have seen some carbon wheels that seem infinitely more durable than their alloy counterpart...
I don't disagree that we need some serious work on the tire front, especially with respect to casing durability. Cuts are very much a problem for all riders (pro or not). Still, with Double Downs, I do experience a much lower cut rate than I had in the past.
Most importantly...
"The inserts solve issues I do not have."
I don't agree with this. You are asking for a more supple tire. You can have this! Throw Cushcore into your tire/rim combo, run less pressure. Boom! You have what you are asking for. Nothing is going to be fully "cut protected" unless we ditch air all together, but something like Cushcore with a Double Down tire will be an improvement in everything except weight
Integrated air bladder = innertube
On a separate note, it seems that rim bead is the weakest link of any rim and the part which does the most tire and tube slicing. Maybe the rim should become just the support structure for the insert wrapped in tire with the beadlock attaching to the support to retain the tire. In effect, the rim would become totally beadless.
Spokes would lace up to the rim support, everything else would attach to it.
_MK
For me the issue isn't so much pinch flats or sidewall cuts, it is protecting the rims from damage.
I'm 92kg (200lbs) and race downhill. I generally run around 28psi in Maxxis DH casings front and rear on the DH rig
Main mode of flat tyres is rim damage causing the bead to leak, then the tyre gets trashed as the pressure goes down.
I recently added a DH spec Huck Norris to the rear tyre. I cased a 30' double in a race last weekend, landing on the log at the top of the downramp. Bent both pedals and exploded the bash guard/chain device but the rear wheel stayed inflated, round and straight. An insert definitely solves that problem for me and I'm happy to add 70g to the bike to do it!
We might better concentrate on rethinking the rim profile, with better lateral support for the tire. Maybe creating an inner channel with tubular shape instead of the sharp hookless profiles we got used to see in the actual carbon craps these days would both improve lateral support and minimize the pinch flatting risk.
Nothing prior to these purpose built inserts has compared to what it can do to the overall feel of your tire interacting with the ground. Is it the end all be all? Heck no. But its the most groundbreaking thing I've tried with respect to actually keeping traction while not flatting in the last decade...
I personally thing the top notch wheel manufacturers have the rim profile thing pretty well dialed. Its all about adding an intermediate layer, tuning the volume of the tire and playing with casing technology that'll bring us the most gains in the shortest amount of time (and money)
But hey, be skeptical. I was!
EDIT: Put another way, a full DH tire can be compared to a heavy coilover. Its linear and offers no bottom out control.
An insert with a lighter tire is more like an air spring. It really isn't THAT much lighter (or any) than a good coil (dh tire) but it is more progressive, does have a different feel, and infinitely better when it comes to bottom out control...
Heck, like someone said on Ridemonkey, the problem with properly designed tires is somebody will put them on a kitchen scale an bitch about them on the internet even before mounting them on their bikes.
EDIT: When talking about the rim profile, I was thinking of having it shaped like a toroid instead of being mostly laminar. That way you could still retain the vertical inner surface perpendicular to the rim bed -where the tire bead contacts the rim- while blending the outer surface of the rim in a semicircular way with it. It'll give the lower tire bead a greater surface to dissipate the impacts and from my limited knowledge in structural analysis I'm thinking it'll also increase the rim's strength, all without driving the weight through the roof.
For me, hard trail riding, tires are just about there.
For pro competitive DH and Enduro (almost DH), tires seem to a have a ways to go. I hate to see races decided by a tire issue. But top level pros are so beyond how we are riding.
Perhaps the trail tire, DH UCI pro tire conversation should be separated as they are really two separate issues. Reliability riding vs. finishing a pinned race with no tire issues.
I’m interested how an exo tyre with an insert feels compared to a DH tyre with none, I just can’t imagine it being as good and for me at 62kg a DH tyre AND insert would be overkill.
Thanks for that analogy Jeff, interesting. I need to try myself before I can contribute more to the discussion.
I am looking at this from a Enduro and DH perspective, but I do wonder about whether this is something that could work for lighter duty tires as well. I know that CushCore are working on cyclocross insert as well, as someone that has raced cross bikes in the past that sounds like and epic idea and something that I would grab in a second if I was still racing.
My main point remains: If the tire designer doesn't need to focus on designing as much sidewall stability and damping into the casing of the tire, does this allow them to bring more resources to bear on making the tire cut and puncture proof?
I have no idea what these tire would weigh. I would hope for something between the weight of an exo tire and DD, but so long as the overall system offered a performance advantage I think there would be market even if it wasn't lighter. Tire and wheel tech has improved over the years, but I don't think its anywhere close to being all the way there yet.
If someone did manufacture a product along the lines of what I'm describing it might start as a race only product, but if it had merit it would filter down to general trail use for some riders. No, I definitely don't ride as hard a pro, but like Jeff I'm heavy (6'3, 195lbs), and I move pretty quick on a bike at times. To some extent I'm probably harder on my gear because I push hard, but I don't always have the skills to back it up all the way and I slam my wheels through chunder that I should be getting light and skipping over. Without a doubt racing pushes tech forward, there is a clear relation between the rise of enduro racing and the fact trail/enduro bikes, like the Transition Sentinel, hitting the market this year with head angles as slack as 64 degrees.
Cost is definitely an issue, I'm Canadian and I really don't love walking into a bike shop and throwing down $120 for a new tire. There is a good chance that weaving more high tech material into the casing would push that up even more. Something that I've been thinking about a bit is whether there could be some kind of system put in place for re-treading a bike tire. From the research I've done it looks there aren't really any real technical obstacles to doing it with a single compound of rubber, although it would likely be more complicated to do it with multiple compounds in the tread. I think the bigger the challenge would be putting a system in place where it made economic sense for the riders, the tire companies, and the re-treaders.
I know this probably sounds like a wacky idea to most of you, but consider that there were no shops tuning and servicing suspension forks and shocks until they became a widespread technology. What if you could buy tires that performed significantly better than what we currently have for $150, but when the tread was worn out you could send them away to your authorized Maxxis retreading centre and get and get a new tread on them for $40? If the new "wonder" casings that this idea is based around were tough enough to allow for 5 or 6 retreads (in areas that are less rocky and more loamy you might be able to get even more than that) you'd be coming out well ahead and we would be sending less material to the landfill in the process. Assuming 6 retreads per casing is possible, lifetime cost per tire would be about $55 and overall tire performance would be up.
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