Is This Normal?
 

Hi everyone,

I'm a newbie roadie, getting back on my bike this summer. I'm sure a lot have changed since 10 years ago. (Yes, I'm old :lol:)

I bought a Continental tube (700x20-25c) as a spare in my emergency kit, and I had to use it a few days ago. For some reason, this tube was WAY way bigger. It practically folded itself as I was tucking my tube inside my tire. I only inflated it to 60psi for the ride back home, since I thought pinching was inevitable...

When I came home, I took out the tube and measured the diameter. It was 39.5 inches (>1000mm)! Is it normal? or did I just get a lemmon?

http://bikeforums.net/attachment.php...hmentid=465474

Wrong size tube would be my guess.

Box says:

Continental Race 28 (700c)
20-622 to 25-630
27x3/4 to 27x1.00
700x20c to 700x25c

My tire is 700x26c.

That's not how you measure diameter—you're measuring half the circumference. The circumference is pi*d, so half of it is pi/2*d. Dividing your result (39.5" ~= 1003mm) by pi/2, we get a diameter of 638.5mm. Does that sound better?

Outer circumference of an inflated tire is around 2100mm so 1000mm for 1/2 the tube seems reasonable.

+1, it looks spot on.

do the math

the tube ID inflated in the wheel would be about 622, add 25mm to get to the center of the tube, and it's 650 or so X 3.14 = 2050, and half that is a bit over 1,000mm.

The mistake you made was probably (guessing) that you didn't inflate the tube to an unstretched sausage before installing. That allowed you to cut to the inside of the diameter along the rim when you started and ending up with "excess" at the end. Had you inflated the tube first it would have spread itself nicely around the rim at the central diameter between the rim and the outside of the tire, and life would have been easier.