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Discussion Starter · #1 ·
I built up a set of tubular wheels - WI T-11's w/ HED Belgium C2 rims. I got some Continental Sprinter Gatorskin tires in 25mm. I dry mounted the tires and inflated them for a few days, but i seem to have a hump at the valve stem. The hump starts a couple inches on either side of the stem. I figured that the stem was hanging up on the inner stem hole, or that there was a little extra material buildup on the tire right at the stem, so I filed the hole a little to help relieve binding. But it hasn't seemed to make a difference. The hump is still there when I spin the wheel.

So I'm here to seek the help of the experts. Any thoughts - am I missing something obvious?
 

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You've got the right approach - we countersink valve stem holes on tubulars as a matter of course. We don't have any HED tubulars on hand at the moment but I just measured the valve stem holes in a few clincher HED rims - 8.4mm diameter. That's actually on the big side compared to many. BUT... tubular tires don't exert any outward pressure on the rim like a clincher does, if you get what I'm not saying to you.

Some tires just plain have a hop. The cloth backing tape overlap is usually the culprit on road tires.
 

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Discussion Starter · #3 ·
Thanks for the info Dave. I may pull the tires off, and gently relieve the valve stem hole with a countersink bit with my power drill. GENTLY.
 

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No harm should come from relieving the stem hole a little. It might improve the situation a little bit, but I doubt it will solve the problem. In 45 years, I've never needed to enlarge a stem hole for any tubular rim.

Do you have the hump even when the tubular has been inflated to at least 100psi? If so, you likely have a second rate tubular. For many years, I refused to ride Conti tubulars, as too many of the North American sourced Conti tubulars had defects (which usually means they have an unacceptable hump at the stem). For many years, I rode hand made Vitoria's, for which I never encountered a defective tire. Since I don't race anymore, I can't really justify the cost of Vitoria's. I've not had any problems with the UK sourced Conti Sprinters or 4000's in recent years.

Many tubulars will have a hump at the stem when new and the tire has not been inflated enough. The main reason for the hump is that if you were to peal back the cloth on the bottom side of the tire, you will see that the joint in the tubular casing passes around the sides of the valve stem. The stem does not pass through a hole in the casing, and the casing is not cut to form around the stem. There is a real art to stitching a tubular casing around the stem area so that the tire does not have a hump when the tire settles in after being properly inflated. Cheap tubulars almost always have a bulge and/or a jog by the valve stem, even after the tire has been ridden a while. But even higher quality first rate tires will appear to have a hump when initially mounted until they have been fully inflated and have time to settle in - after which they should ride perfectly round on any unmodified tubular rim.
 

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Discussion Starter · #5 ·
This is all good detailed info, thanks for taking the time RH. I've had the tires for a few months, and purchased them from one of the U.K. sites. I bought three tires, so may try and swap the spare onto the front wheel. The back isn't bad, but not hop free. I may invest in some higher quality Veloflex or Vittorias.
 
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