For every 32" or 36" bike we've covered on Pinkbike, there has always been one big drawback, tires. Trek's Travis Brown
politely put it as, "the quality compared to what enthusiasts are accustomed to of those tires is pretty low, so that kind of influences the impressions," while 36pollici described them
as a limit of their carbon 36er project.
An increase of 7 inches in the diameter of the tire means an increase in the circumference of more than 21 inches. That's a lot more rubber and a lot more bead and that brings with it a lot of issues. The larger diameter tires are also a very specialist bit of kit. As a lot of vendors simply don't have the oven drums to go larger than 29", those wanting to build larger wheeled bikes have to go to more economy-based manufacturers who can't provide the same quality as the brands we may be more used to.
The most popular choice for larger diameter wheels at the moment is the Vee T-Monster 36x2.25 from Vee Rubber. While we previously enjoyed riding Vee Tire Co's dedicated mtb options
, Vee Rubber's 36er is from their mass-market focused parent company and is reported to leave a lot to desired, despite being the best option on the market.
Although this is a Vee branded tire, it was actually designed by Walt Wehner
of Waltworks, a custom frame builder based out of Park City
, Utah who claimed at one point to have built more 36ers than anyone else on the planet. He approached Vee to make the tire as a contract job and says, "Vee did not design the tire (or particularly want to make it), I designed the tire and then we argued about minimums and bead characteristics and such."
The tire is now around 15 years old and was, and still probably remains, the lightest and most mountain bike worthy option among larger wheeled tires. It has also been adopted by unicyclists who use it as an off-road option on large wheeled touring unicycles. We caught up with Walt to understand what the biggest issues are in designing larger tires and what that might mean for the future of mountain bikes with larger diameter tires (answers edited for clarity).
What are the key characteristics you want in a 36” tire? are they different to a 29” tire?The key characteristics really aren't much different if designing purely for bikes (more on that in a minute). This is a 15-year-old tire at this point and 36ers were (and still are) basically XC bikes, so the design was XC oriented.
What considerations do you have to make to a tire to work with both unicycles and bicycles?Unicycles suffer from something called camber steer - essentially this means that on uneven terrain, the tire tries to "climb" into/up the ramp, because the side of the tire is moving slower than the bottom of the tire as the wheel spins. This means that (on a unicycle) it's very hard to ride on off-camber surfaces, especially at low pressures with flimsy/flexible sidewalls. So unicycle-specific tires have a MUCH stiffer carcass in general. It's worth noting that bikes camber steer too (if you've ever had your front wheel try to climb up out of a rut you've experienced it) but having 2 wheels on the ground makes the problem much more manageable.
What are the difficulties in designing a tire larger than 36”?The biggest difficulty is keeping the tire on the rim. As the bead gets longer and longer, a little bit of stretch matters more and more because the bead stretches more in absolute terms on a bigger tire even if it's the same as a percentage. Once there's enough absolute stretch, the tire can come off the rim. So the 36er tire bead has to be crazy burly.
What are the biggest limitations of tires larger than 29”?The beefy bead and resulting weight is the biggest drawback/limitation, probably, setting aside the relatively tiny market for the tires which is obviously a bit limiting factor.
What are the biggest advantages of tires larger than 29"?The advantages are the same as with any other wheel. Bigger is more efficient as the terrain gets rougher. Believe it or not, the US government studied this with tractors during WWII when trying to save fuel. They found that basically there was no size too big for tractor tires (confirming what farmers had already figured out, of course).
How much lighter could a 36” tire be made?I can't be sure how much lighter a 36" tire could be made but I'd guess the lower limit would be around 1000g? Until someone puts a lot of effort into it and there's a market, I'd guess we'll be stuck with the Vee tires.
You mentioned you would rather the tires be wider than lighter, why is this?The existing tire is a 2.25" which is pretty skinny by modern standards, and to be honest I don't give a rat's ass about bike weight anyway, so I'd rather see the tires get more capable than lighter. If you ever get a chance to ride that Vee tire, it's just fine in most situations (as intended) but it gets in over its head pretty quickly on anything rough/loose/etc. To take full advantage of the 36" rollover on rough stuff, it would be nice to have a more aggressive tire.
Do you think larger tires will be adopted by the industry in future?There are a lot of problems fitting even average-sized riders onto 36" wheels (suspension is mostly impractical, for example) but the longer/slacker trend is a good thing - wheelbases on 36ers are now right in line with normal trail bikes, when back in the day they were crazy long. If I were a betting man I'd bet we'll see 32" wheels on mainstream bikes in the next decade, but 36" will probably remain a niche/unicycle item.
So, there we have it, as it stands there's a chicken and egg situation going on. Tire manufacturers aren't willing to invest in the technology to produce bigger tires until here's demand for them and currently demand is stifled by a lack of suitable tires. Travis Brown said, "People are definitely going to be messing with this for a while and depending on what happens with tires, I see that as kind of the biggest restriction on really feeling into what the potential is of larger diameters than 29. I would bet that when one of the quality tire manufacturers or someone commissions a prototype of a really high-quality tire, our understanding of what the potential is will experience another breakthrough. And that'll be fun." Until that time, it looks 29ers will be the biggest common wheel size we'll be seeing for a while.