spiritfirst

I have a 1998 Trek 7500 hybrid with 700cm wheels that I use for commuting. I'd like to put skinnier tires on it, but I think someone told me that they had to be 35's or so. It came with 38's. Can I put any road tires on them? I'd like to put maybe 25's or 28's. And can I use the same tubes (Schrader) or do I need to get new tubes as well?

Thanks,
Mike

LóFarkas

You mean this one?



700C rims take almost any sized 700C tyre, but it's beneficial to stay within certain limits, cuz the tyre may take a bad shape, or a too wide tyre might roll off the rim.

https://www.sheldonbrown.com/tire_sizing.html <= scroll down to the red-green table

Al1943

They're not cm. 700 is mm the "c" is the rim type designation.

halfspeed

Almost right.

"700" is the outside diameter of a particular historical french tire size that had a 622mm bead seat diameter and a wide cross section. 700C tires can have very different outside diameters because the "C" width doesn't mean anything any more. So at this point in history, it's pretty much an arbitrary designation.

Al1943

What do you mean almost right. I said it was mm not cm. They're not known as "622 wheels". The 700 includes an assumed tire size.

Al the anal retentive.

moxfyre

I don't think there are any 700C tires actually in production that have a diameter as large as 700 mm Maybe some 29'er tires, but even then 700 mm is pretty huge.

Most 700C road tires have a diameter more like 650-670 mm. By the way, I think it *would be* preferable to refer to them by the bead seat diameter, to avoid confusion. That way we wouldn't confuse 26 inch (559 mm) tires with 26 inch (591 mm) tires or 26 inch (597 mm) tires .

Al1943

True, but that's where the 700 number originated, the approximate overall wheel diameter, same with 27 inch or 26 inch.

Al

halfspeed

And all those "sizes" ought to be ditched in favor of iso sizes because they cause more confusion than enlightenment.

2372ighost

Back to the OP, Your hybrid will do well with 700x28's in about 115psi tires. Made mine fell like different bike.
go here:
https://sheldonbrown.com/tire-sizing.html#width

Nigeyy

It sounds to me like you should be ok, though there is a limit on some rims for the width of tyre. Going from 700cx38 to 25 might be too big of a jump depending on the width of your rim (see Sheldon's page already referenced). And yes, I'd get new inner tubes as well -that's not to say your existing ones might not work, just that I'd be conservative with something as crucial as the interface between you and the ground. Better to get the right size.

A little example here, I looked at putting 26x1.25s on Sun Rhynolite rims, but decided the rim was just too wide. You've got to do a little eyeballing here and use common sense -again, err on the cautious side!