Help on choosing tire size for crit racing

Hey guys!
I’m trying to decide between the 25c and 28c size of the Continental GP5000tl.
It will be used mainly for crit racing. The wheels are Reynolds strike disc, 17mm internal and 25mm external. The bike will be a specialized allez sprint.

I would go with 25mm. Especially with that rim will match well and you can run low pressure.


Yea def 25 with that internal width, I’d be concerned during hard cornering with a 28c that will surely lightbulb on that rim and probably feel squirmy too.

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First thing, it probably depends on your size. If you’re 130 go with the 25s. If you’re 225, go with the 28s.

Second. 28mm tires on 17mm / 25mm rims won’t lightbulb that much and they won’t squirm. Plenty of folks have ridden that size tire on narrower rims and done so hard. I’m one of them. IIRC Mavic Open Pros were 15mm / 19mm internal/external and I rode those during early season crits and down technical stuff all day long on. My current early-season crit wheels are H+Son Archetypes which are 17mm / 23mm. At 165lb I’m racing 28mm GP5000s on them (not tubeless though) with 65/70 psi

Third, I’ve been told that aero is all the things. 28mm tires on a 25mm rim will not be as aero-awesome as 25mm tires on 25mm rims. 23mm tires on 25mm rims will be even more aero-awesome. (See Josh Portner’s 105% Rule)

Fourth, I like bigger contact patches and lower tire pressure around corners with crappy tarmac. Same thing goes when descending technical stuff.

What does the tire actually measure to, because on my 17.5 internal clinchers, my 25c GP4000 is 28mm. The 5000 is a bit more true to size but continentals still run big

Ya I’m 5’8” 139lbs. Thanks for the input!

Aero matters most on the front wheel, especially on a frame with a cutout like the Allez. Why not run 25 front, 28 rear?” Bigger contact patch where your weight is; probably better aero where it matters.

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