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TT bike tires, 24mm vs 26mm

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TT bike tires, 24mm vs 26mm

Old 08-09-20, 10:45 PM
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cybirr 
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TT bike tires, 24mm vs 26mm

I am a new TT bike rider who recently stumbled on a heck of a deal for a TT bike. I must confess my reason for owning a TT bike is just for the fun of going as fast as I can. Actually entering a Time Trial event might be a year away for me as I learn.

By way of example the 2020 Specialized Shiv models are spec'd with 700x24mm tires. With all the emphasis on wider tires, lower pressure, why are TT bikes like this still going with 24mm?

The Shiv Elite has caliper brakes, I'm guessing it would top out at 26mm if a rider did want to go larger?

For someone like me, a new TT bike rider, would there be value in starting with 26mm and when more confident on the bike go back to 24mm?

Thank you for any help in exploring this new type of riding.
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Old 08-10-20, 06:54 AM
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Rides4Beer
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Bigger tires with lower pressure are great for all around riding, I'll never go smaller than 32s for daily riding now, love 'em. But for a TT/Tri setup, the goal is to maximize every marginal gain that you can, and smaller tires, when appropriately matched to the rim, will be faster. My local TT loop is pretty smooth, you could run super skinny tires at high pressure with no issues. But out on the country roads here, you'd get beat up, so bigger tires actually end up being faster.

I would match the tire size to the size of your rim, which probably means 23/24mm. Need to know the wheel model, or at least the internal & external widths.
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Old 08-10-20, 07:31 AM
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That's right. Aero matters enough in TT that you should match the tire size to the profile of the wheelset that you own. If you can't match it because the roads suck or because of rider weight.......reassess the wheelset to get one that works with wider tires. 3 to 5w gained in CRR of some massive tire will be more than lost in disrupting the airflow around the rim.

If you have a 23 or 25mm rim at the brake track.....run 23's on the 23mm rim and 23's or 25's on the 25mm rim. With 27's, 25's would be optimal on aero and maybe train in comfort on 28's. Etc......

Given you're rim brake, yes, there may be a max tire size to fit. However, with wider rims the tires don't balloon like with the old narrow internal width rims.

Given that is a rim-brake bike, in the long run I would probably gravitate toward something like the classic HED Jet plus lineup. 25mm at the brakes. Run a 23 up front for optimal aero or still be fine with a 25. Andy at HED told me that they are quickest on a 23, but the 25 isn't much penalty.

Also, you can always run a size larger in the back as the rear wheel is shielded by the frameset some and there isn't' the same aero penalty.
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Old 08-10-20, 10:41 AM
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Originally Posted by burnthesheep View Post
That's right. Aero matters enough in TT that you should match the tire size to the profile of the wheelset that you own. If you can't match it because the roads suck or because of rider weight.......reassess the wheelset to get one that works with wider tires. 3 to 5w gained in CRR of some massive tire will be more than lost in disrupting the airflow around the rim.

If you have a 23 or 25mm rim at the brake track.....run 23's on the 23mm rim and 23's or 25's on the 25mm rim. With 27's, 25's would be optimal on aero and maybe train in comfort on 28's. Etc......

Given you're rim brake, yes, there may be a max tire size to fit. However, with wider rims the tires don't balloon like with the old narrow internal width rims.

Given that is a rim-brake bike, in the long run I would probably gravitate toward something like the classic HED Jet plus lineup. 25mm at the brakes. Run a 23 up front for optimal aero or still be fine with a 25. Andy at HED told me that they are quickest on a 23, but the 25 isn't much penalty.

Also, you can always run a size larger in the back as the rear wheel is shielded by the frameset some and there isn't' the same aero penalty.
Good answer.
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