I have a 17C clincher (BDOP diy kit) with a 25mm (Conti GP4000). In 2015, I built the wheels but couldn't use them because the tire was rubbing against the rear fork (upper - where the breaks are screwed in). At the beginning of this season, I tried them again and this time there was no issue. I was quite puzzled and wondered if the tires aged and caused it to shrink in size. I was using the tire on a second bike I do not have anymore. The fork had more clearance on it so I had the opportunity to put some kms on the tires.

However, this last week end was quite hot in quebec and now the tire rubs against the fork again... and it is clearly bigger than what it was at first. I use the same pressure - between 80 and 90.
I am very surprised that temperature can induce such a big difference. I can't use my nearly brand new set of wheel due to that
I guess my only option left is to sell the bike and get a new one with more clearance.

I agree, get a new bike is the only viable solution.

rubs the brake bridge? or the brake caliper arm?

either way, it could just be the way you mount the axle/wheel when you put it back on the bike.

my bike also has minimal clearance on the rear. so little so that a fresh tire wore away a bit of the caliper.



just repositioned the axle slightly and locked it down tight and happened no longer.

Definitely more likely to be about how you're mounting the tire than about heat. You could try 23mm tires. Or a new bicycle.

I had a 2005 Trek 2100 some time ago that was supposed to have clearance to run a 25mm tire, but couldn't. The seat stays were a "Y" type just after the brake mount, and the tire would rub at that junction. I ran 23mm tires until I got a new bike.

You could always try an experiment to confirm or rule out your theory. On a cool morning when the tire looks normal, check the clearance then let about 5 pounds out (since you're concerned about the rubber not the pressure) and use a hair dryer or heat gun on the tire. See if the shape has changed enough to make it rub.

I'd advise using some caution with this experiment, monitoring the temperature of the tire, rim etc to avoid damaging something or a potentially dangerous blowout.

Rear fork? I think you put your bicycle together wrong!

But seriously, is it rubbing on the brake bridge or the brake calipers? If only on the caliper, you could possibly space it out a little further from the bridge and see if it has enough clearance then.

For gases, like air in tyres, temperature and pressure are related. Increase the temperature and the air molecules bounce around faster which increases the pressure. I think this comes under the Gay-Lussac gas law.

For example, pump your tyres to 90psi at 68 deg F then go outside and ride around in 104 deg F weather and the heat will increase the pressure to 97psi

https://en.m.wikipedia.org/wiki/Cold_inflation_pressure

The change should not be permanent. What is happening is that the tire is softening at the elevated temperature and is expanding more due to a given pressure than when it is cold. Think of the tire like a very stiff balloon when it is cold and a more flexible balloon when warm. The tire blows up more at the same pressure when hot than when cold.

Oh, and BTW, it is "dilation", not "dilatation".

Sorry, yes I did mean rear brake bridge. The only solution I can think of is to put some sort of spacer where the wheel is attached to the frame (see picture - btw not my bike).



I really love my bike but I've been thinking buying a new one for a while. The only issue is that money is quite tight at the moment. A temporary solution would be very great.

That I know, this is why I made it clear that the pressure was kept between 80-90 psi. The pressure does NOT vary since I inflate the tire at a given (supposed constant) temperature (outside).
My bet is that the rubber and/or the wires are dilating which increase the volume of the chamber.