Tube sizes

gmk77

Hi,
I'm a bit of a novice so apologies if this is a dumb question.
I just bought a road bike and the original tubes were 700 x 18/23 and they fit just fine.
However, most of the time when I get spares from my bike shop they give me 700 x 20/25 which in theory are the same diameter, but slightly wider.

However, I find that these tubes are way too big for the rims/tires - not too wide but too big in diameter. I find it hard to slot them into the tires without excess trying to pop out. Even when I do manage to get them in, there's a bulge and so there's a bump when I ride.

Am I missing something here? I thought all road bike wheels were the same diameter (700) and that therefore any 700 tube would fit (within reason).

Thanks

Raam

Do you put some air into the tubes before installing them on the rim? I use similar sized tubes all the time and it is fine.

Cee-Jay-Cee

Inflate the tubes very slightly before putting them into the tyre.

Tubes generally are slightly longer in circumference than the space they have to fill but when inflated to 100+ psi they will fill the space entirely and evenly. I don't know what your doing to have a bump in the wheel as everyone's tubes are the same and it's not something I've ever heard happening before unless the tube has an actual bulge in it which happened me once. It was a defect in the tube from the factory as the tube was brand new. I ditched it and fitted a new one.

To be sure you don't have a defective tube inflate it before you fit it to see if there are any bulges appearing in it.

gmk77

Yes, I am inflating the tubes a bit.
Replacement tubes are definitely a bit bigger than the originals (which were Kenda). When I inflate them both there is a visible difference.

Maybe there is just some variation between different manufacturers although you would think 700 would mean 700.

Anyway, I'll keep trying. Thanks for the replies.