I’m clear on the value of larger wheel size for rolling more easily over bumpy stuff. This has advantages for both speed and less-need-to-worry-about-line-choice, for a given course. As I understand it, this value mechanism is the main reason that mountain bike wheels went from 26 to 27.5 to 29, and that trend is just continuing.
The part that doesn’t make sense to me is @Josh_Weinberg and @Ronan_Mc_Laughlin both mentioning the value/future for gravel bikes. Apart from particularly bumpy washboard (where the smoother rollover of larger wheel size would seem applicable) I don’t understand what the advantage would be. Would the larger wheel size be beneficial for speed, or for handling confidence? What am I missing here?
We may have evidence that it’s beneficial (empirical/experiential data that speed or comfort-while-riding is improved), reason to think that it might be beneficial (theoretical reasoning), or both; I’m just not familiar with the reasons or evidence.
I’m 6’5” (196 cm) and would mostly avoid bike-fit tradeoffs of larger wheels, but am still curious about this. (I also have a 650b rando/allroad bike with 42mm tires.)
I’m a similar height and drawn to the frame proportions that a larger wheel could offer. As for the washboard roads, the guys at curve did their 36’er for just that reason and I don’t think it had the effect they were looking for.
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I think it depends what terrain you are picturing when you talk about “gravel”. Category 1 or 2 gravel, 32” makes very little sense. But if you’re looking at Category 3, 4 or even beyond then "the benefit of rolling over bumpy stuff” becomes increasingly relevant.
And I think we have seen “gravel” bikes moving in that direction. Tyre clearance has been growing - a few years ago having 35mm tyres would be classed as a gravel bike; now people expect a minimum of 50mm. Gravel suspension is coming too - just the other day, Trek released the CheckOut full suspension gravel bike.
I think this is because mountain bikes, and mountain bike trails, are becoming increasingly technical. Which is great in some ways, but also means MTBs are increasingly only used on artificial trails with features deliberately built in to keep things interesting.
This is left a gap in the market for bikes to use more challenging terrain that falls short of technical mountain biking (footpaths, goat tracks, mountain trails etc.). Where as once that terrain would have been within the remit of an old fashioned XC mountain bike, on a modern XC bike you’d feel overbiked. So “gravel” bikes are moving into that gap.
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True, less-underbiking when using a gravel bike on rougher stuff would have rollover advantages But I don’t think this applies to, say, Unbound/Kanza gravel, or really any gravel roads apart from abandoned logging roads that haven’t been graded or used by logging trucks for a decade or more.
But my perception was that the comments from Josh and Ronan (on separate venues) were envisioning middle-of-the-gravel-category riding as having potential benefit from the larger wheel size, for some reason/mechanism (or just empirical evidence even if we don’t yet know the “why”) other than rollover.
A larger wheel would have also have a larger contact patch (more rubber on the ground). This gives you more control and stability. Again, a big benefit on cat 2 and 3 gravel.
The contact patch will have the same area at the same pressure, but will be longer, which should increase both stability and cornering grip. Then there’s rollover and greater moment of insrtia, the latter a bit of a two edged sword.
Personally, I can’t imagine acceptable geometry with >622BSD wheels, and there would also be issues with gearing being too high, etc. Maybe the UCI will do everyone a favour and ban 32” wheels as has been mooted, but that didn’t happen this month.
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Coming from the MTB side, I do struggle to wrap my head around this new wheel standard for anything else other than hardtails and short travel FS. Anything above 100 mm would require a regressive or at least perfectly straight wheel path to avoid contacting the seat-tube. This would greatly narrow - if not void entirely - the use of some of the best suspension platforms that we are accustomed to. Kinking the seat tube would prevent the use of long dropper posts, while smaller sizes would likely have their saddle touching the rear-wheel when they drop it. I really can’t see how they could pull it off.
On the other hand the latest trek Checkout and similar bikes would prove more suited to the benefits of a 32” wheel. Bigger tires have more mass and therefore more inertia, which is just what you want for a bike that is supposed to keep momentum and and a steady pace over changing terrain for hours on.
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