Digital Gee

(Remember that phrase?)

With my new bike I have 700x38 tires. Can I use the unused tubes I already have that were purchased for 700x23 tires, or do I need new ones for the new bike?

Allegheny Jet

My cycle cross bike has 32's on it and I was told by the LBS to use tubes to fit that size tire. Most of the tubes I buy for my road bike are for 21 to 25 tires. I wouldn't use a road tire tube except as a emergency spare.

roadfix

I wouldn't hesitate to use a larger tube on a narrower tire (done it many times) but not the other way around for the most part.

Tom Bombadil

There is a HUGE difference in the volume of air contained in a 700x38 tube as opposed to a 700x23 tube. The 23mm tube would have to be stretched way out of spec and would certainly have weak spots, if it didn't outright burst.

You could possibly get away with a 700x32 tube, but I wouldn't try anything smaller than that. You may even find tubes labeled as 700x32-38, or 700x35-42. It doesn't have to be an exact fit to the tire, but it needs to be within a reasonable range.

Retro Grouch 

I'm just the opposite - given the choice I'll always choose a slightly too small tube over one that's slightly too big. It's too easy to pinch a 700 X 32c tube in a 700 X 23c tire.

Having said that, stretching a 23mm tube to fit a 38mm tire is more push than I'm willing to do unless there's simply no other choice. It's a $5.00 inner tube, deege, don't be so cheap!

stapfam

I'd buy new tyres to go with your unused 700x23 tubes.

Digital Gee

Okay, okay. I'll pick up some larger tubes. I prefer the label "frugal," but whatever!

Floyd

With my brother, who thinks like you, I use the word 'eccentric' ...but the older I get I am giving myself the same title.
I tooo sometimes ''cheat'' on a tube size but there are times when one has to admit defeat and give in to buying..........................

oldbobcat

Saw this last week when a customer brought in a flat to be repaired. The tire was a standard 2" MTB tire, and the tube was a 1.25-1.75" thorn resistant heavyweight, with a presta valve. The tube had stretched to fill the tire, but there was a puncture at the base of the valve stem. The heavier, less flexible rubber at the base of the valve stem had not stretched with the rest of the tube it split.

In a pinch I might stretch an 18-23c tube to fill a 25c tire, but any greater difference is probably asking too much of a butyl tube.

europa

Just think of the really neat slingshot you'll be able to make now that you have two tubes you don't have any legitimate use for

Richard

Rowan

Go get a pump and inflate a 23C tubes for, say, 50 strokes. Then compare the tube against your 38C tyre and the cross-sectional diameter. I'd say the tube will exceed the tyre cross-section.

I use 23-25C tubes up to 32. I'd probably go to 38C without qualms, but I have absolutely no need to use 700C tyres that wide on pavement.

Tom Bombadil

It may well stretch to fit, but that rubber wall is going to be stretched thin. Could be prone to popping when riding over a hard bump.

A 23mm circle has a circumference of 72.2 mm. That's what a 23mm tube is optimized for.

A 38mm circle has a circumference of 119.4 mm. The rubber walls will be stretched that extra 47mm to fill the inside of a 38mm tire. They may work for a while, but I wouldn't take that risk to save $8-$10.

staehpj1

+1 on all counts

jppe

Oh com'n guys.......let him try it. The best lessons are those learned from person experience!!!

But if you do try it, please don't rocket down a hill at 40+ mph!!

Tom Bombadil

Doesn't that Vienna 2 have Schrader valves/rims?

And doesn't your Roubaix wheels use Presta valves?

Rowan

The diameter and circumference don't have the ultimate say on the integrity of the tube. It's the thickness of the tube material at the given inflation pressure.

I'll relate a story again I heard about six years ago. A competition was held to estimate the number of pumps to get a standard tube to burst. People punted on 50, 100... but something like more than 1,000 piumps later the tube finally burst its seams.

The irony of this discussion is that 23-25C tubes are designed for high pressure (140psi is not unheard of). The 38C tyre probably has a recommended psi limit of around 80. Tubes also come in welterweight and lightweight configurations -- meaning the weight-saving is in the thinness of the tube material... yet they have not trouble maintaining the ultra-high pressures for racing.

Heck, I've even used a 700C tube in a 26" MTB tyre to get over a lack of spare carried by the owner. It's not something that's a great idea because the tube moves around inside the casing a lot, as we found. But it was effective for the 15km we had to ride.

People should experiment with things. That way, they find out!

Digital Gee

Yep.