I'm new to tubular wheels and tyres, just had some new wheels built, done lots of reading on the subject. I've just put my Vredestein Fortezza Pro Tricomp tubular tyres on the rims 'stretch' (700c).

They slipped on so easily I'm not convinced there's much stretching actually happening. I was under the impression it would require some effort to get them on the rim the first time. I've put 100psi of air in them which keeps them in place, but I'm concerned... shouldn't it be harder than that? When there's about 20psi in the tyres I can still pull them clear of the rim bed. I've also tried putting the same tyres on a clincher rim - they slip over the lip just as easily. Does this sound OK or might something be up here?

Looking forward to doing some gluing over the weekend, just wanna make sure these tyres are OK.

They're fine - inflate higher and you won't have such an easy time, and yes, even at full pressure they can be forced off - that's why they're glued on!

Oh good, full speed ahead then.

Cheers!

There's a tremendous variation in ease of fit among tubulars. Usually, but not always, lighter tires fit better. I've seen tires that fit so easily they seem too big, and others so short that I suspected they were for smaller rims.

Either way it doesn't matter because all tubulars are built with bias plies and work on the same principle as the Chinese finger puzzle so that pressure inside makes the tire fatter and shorter, constricting onto the rim. It's this bi-axial helix action which holds tires on, with the glue only providing traction so it cannot shift.

Note: pump them up off the rim and they shrink in diameter,inside, when inflated, that and the glue work together .

" It's this bi-axial helix action" Francis

WOW! This is the quote of the year. Andy

I always reference the chinese finger trap when I explain how tubulars work, but some time after I was a child, these went out of fashion, and many of those I speak to using the analogy have never seen one. For years I used to meet people who had no idea what a Slinky was, but they're back, though the modern plastic version is a poor imitation of the original steel ones.

Agreed. Some are incredibly easy to fit, others are a royal pain.

So how does this principle hold up when I have 20psi in my cyclocross tubulars?

At 20psi you're 100% dependent on a good glue job. This is acceptable because because you won't be doing a field repair. Also speeds and conditions are different than on the road where you might be speeding down a steep grade at 50+ mph, and going into a hairpin turn, with a 1,000 drop off on the outside.

Try this experiment if you have a tire and unglued rim or wheel. Mount dry, and inflate to 100psi, and try to push the tire over the side aka "roll the tire". Try the same with 20psi, and you'll see a significant difference.

Before team support caravans, cyclists of Fausto Coppi's generation carried spares and did their own repairs mid race. Obviously they weren't going to wait for glue to dry before screaming down out of an alpine pass.

+1, Hope the Glue Job is good, that's what you are relying on , in the corners..

at least rolling a tire an falling in the mud wont hurt, as much,
like losing it descending a hairpin on the road, can.

Yes the sound of a now bare rim scrapping on the pavement is only eased by the pain of the body's impact... I rode sew ups for 25+ years on more then one bike a year. Only had two roll offs, both were with spares I had mounted earlier while in mid ride each day. I hope to never have a strike three! Andy.