25mm tires too thick for my fork?

[bkingva]

Hi everybody -- longtime reader, first-time poster. Anyway, I needed to replace my 23mm tires in a pinch, but the bike shop I went to didn't have anything thinner than 25mm. That seemed OK at first, but I just noticed that the top of the tire is rubbing up against the inside of the crown of the fork -- the thickness of the tire plus the diameter of the wheel add up to a total diameter just barely too much for this length of fork, apparently.

Do I just need to go back to 23mm or is there some way to make this work? I tried clamping the wheel slightly farther out from the edge of the dropouts, but that feels like an unsatisfactory (and not necessarily terribly safe) solution. A millimeter or two added clearance would be enough.

I've also noticed I suddenly have more trouble shifting into the highest gear without slipping. Is that possibly related to using a slightly thicker tire? Do I need to adjust something else? (The tire clearance appears to be fine in the back.)

Thanks all.

[Raymo853]

I can see no way that tires could effect the shifting, unless, the tire is interfering with the front derailleur. This usually only occurs on mountainb bikes when people switch to way too large tires, say like 2.4" aka 61 mm tires, on frames deisgned around 2.1, aka 53 mm tires. I suspect when the rear wheel was placed into the rear dropouts slightly off, and that is causing the shifting issue. Try making sure the rear wheel is in there straight and fully. It may also be totally unrelated and just an unfortunate correlation.

Regarding putting the front wheel in dropouts slightly oddly, DO NOT DO THAT. Do not ride the bike that way. That is a easy way to crash very badly. Yes, you need to go back to 23 or narrow tires at least on the front.

[mstone]

Yes, you need to go back to 23 or narrow tires at least on the front.

And now you know for n+1 to make sure that your new bike can take reasonably wide tires.

[bkingva]

Thanks everybody! I appreciate the advice. Is there any drawback to running 23" on the front and 28" on the back?

[DismalScientist]

Excessive torque can cause front end to rise uncontrollably.

[bkingva]

Seriously? And I meant to say: 23" on the front and 25" on the back.

[DismalScientist]

No. Some people, if they notice, might think it looks funny.

I would think you have a pretty racy bike with so little clearance with the front fork. Is the frame designed that you will have any problems getting 25s on your rear wheel as well?

[bkingva]

I have a 25-year-old Cannondale road bike. The 25mm tire appears to fit just fine on the back, or at least the clearance appears to be fine. (I'm still puzzled by my sudden shifting difficulties, which began immediately after the new tires went on.) But on the front, the top of the 25s rubs the inside of the fork, with a noticeable increase in friction.

[mstone]

Seriously? And I meant to say: 23" on the front and 25" on the back.

I've had that problem, but I chalk it up more to my quads than the tires. The biggest problem is that the small, high pressure front tire will beat you up through the handlebars. But there's nothing different than there is if both tires were 23.