# Tube sizing



## stevo4 (Jun 25, 2007)

Couldn't find what i was looking for with the search featrue.

Can someone re-state what the sizes refer to in a 700 x 18 x 23c tire and tube. I see that my Conti 4000's say 700 x23 but the tubes i used at one point were 25's. What does the 'c' designation mean. And what does 48mm mean when talking about the Presta Valves?

Just want to keep it all straight. 

Lastly, are there any other tricks to avoid a blow out due to a pinch when changing a tube? I inflated the tube a little today before i started to replace someone's flat and then used a C02 cartridge to inflate the tire. I did check the bead before inflation but it still blew. 


Thanks!

Stevo


----------



## JCavilia (Sep 12, 2005)

*700c*

http://www.sheldonbrown.com/tire-sizing.html
I'll let Sheldon explain the arcane tire sizing designations. That 700c/23 tire is designated 23-622 in the modern system, but everybody uses the old shorthand.

The 23 or 25 is width of the tire (in mm). You can fit a 25mm tube in a 23mm tire -- it just won't stretch as much. It also might be a little more likely to get caught under the bead, which may explain the problem you experienced.

48mm is the length of the valve. They vary, to accomodate rims of different shapes.

Check more carefully, inflate more slowly. Inflate a little, go around and squeege the bead all the way around (don't just look), inflate some more and squeeze again, then inflate the rest of the way, not too fast. Some tire/rim combinations are looser than others, and can blow off more easily if not seated perfectly. So your blowout may have been a result of the bead lifting off the rim, rather than the tube being pinched initially.

Here's a recent thread with more discusison of the blowoff issue.
http://forums.roadbikereview.com/showthread.php?t=108913


----------



## Mr. Versatile (Nov 24, 2005)

"_You can fit a 25mm tube in a 23mm tire -- it just won't stretch as much"_

While this can probably be done, I think I'd do it only under emergency situations. Tubes are pretty flexible. Buying a tube perfectly sized for your tire is the best way to go. If you can't do that, I'd suggest going one tube size smaller, rather than larger.


----------



## Dave_Stohler (Jan 22, 2004)

http://www.sheldonbrown.com/tyres.html
http://en.wikipedia.org/wiki/Bicycle_wheel


----------



## lawrence (May 17, 2005)

The tubes that I buy say 18-25 so they will fit 23 and 25 tires.


----------



## Kerry Irons (Feb 25, 2002)

*Tube size clarity*

In addition to what has already been said, it should be noted that there are virtually no tubes for sale that are a "single" size. Typically, there are 3 or 4 sizes of 700c tube. The "small" size fits most road tires up to 25 mm, medium tubes fit tires up to 32 mm, and large or XL tubes fit tires up into the 40+ mm width.

What you don't want to do is put a too-large tube into a tire, because it will tend to wrinkle and that can lead to flats. Putting a too-small tube in usually means more rapid pressure loss because the rubber is stretched thin, and that MAY result in more flats, but it is not a major issue. The size marked on the tube, or on the tube box, usually is stated as a range, with the biggest number semi-meaningless. Don't put a tube in a tire where the smallest number on the tube is bigger than the tire size.


----------

