dangle wrote:
I think that misses my first point. Due to the larger tire circumference, the chainring is effectively 4-5% larger.
4% is a fairly small jump, about half the size of a gear step in the straight block of a road cassette. And people on gravel bikes are sometimes running smaller rim diameters anyhow:
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A quick Sheldon Brown reference says that a 50 mm tire in 650B has a wider diameter than a 700 x 44.
That's not right. The width increase will change inflated wheel diameter by something in the ballpark of a centimeter, but 650b wheels are nearly four centimeters smaller than 700c.
My 53mm 26ers are smaller than the 700x25s on my Trek.
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If somebody is riding gravel tires at the lower pressures they are supposed to be, the rolling resistance gets pretty high at fast speeds.
Depends on the tire.
Actually, one of things I like about my 53s being so wide is that they can be squishy without being terribly underinflated. Narrow tires need to be run at comparatively high drop to get the same amount of squishiness, and this also increases the exposure of the sidewall to the riding surface, which encourages people to get tires with lots of protection. The result is, frequently, a heck of a lot slower on smooth sections than my supple fat tires.
I was on a gravel ride last summer with a guy who was about my equal on road rides, but he was on toughened 35s. I was cruising along paved sections with nigh-indistinguishable performance from my road riding, and he was having a hard time even staying in my draft.
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A simplified comparison would be to take some numbers from Jarno Bierman and apply them. A 25 mm 4000sII with a butyl tube at 80 psi has a CRR of .00411 and he measured the Bon Jon Pass with a similar butyl tube (the only gravel tire he has published, so our only comparison) at 30 psi at .00842.
Fat road tires can actually roll just fine, but BJP roller data is an anomaly. TomA also saw very high numbers for the BJP on his drum,
including compared to Compass's wider Snoqualmie Pass. I wouldn't necessarily assume anything about gravel tires in general based on that test.
It is true that most gravel tires are slower than most road tires... they're often more protection, knobs can slow them down on paved sections, and there are aerodynamic disadvantages. But there's a huge amount of variety in what people ride.
But I also think you're looking at this wrong:
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Even if you could pedal in the 52/53 x 11/12/13/14 with a true gravel tire.......it seems wasteful.
It's not that a gravel tire is better for the jobs where you need a 53-11 than a high-performance road setup is. It's that some people might come across those situations occasionally while riding their gravel bikes.
