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-   -   Pre-Stretching a tubular tire, but NOT on a rim (http://www.bikeforums.net/bicycle-mechanics/935932-pre-stretching-tubular-tire-but-not-rim.html)

Syncmaster 02-27-14 07:11 AM

Pre-Stretching a tubular tire, but NOT on a rim
 
Hey everyone,

I know it's common practice to pre stretch tubs pumped up on a rim overnight, and this is what I've always done in the past, but recently I saw this video where they mentioned you could stretch the tires by just inflating them with air, NOT on a rim, and that would stretch them. Is this enough? I am going to go hunt down a clincher rim to stretch out my new tires at the moment but it'd be nice to know if I could just stretch them without a rim in the future. It's in this vid:


Ex Pres 02-27-14 08:31 AM

Never tried it myself, but have thought about it. I just have old unused tubular rims around. They're cheap as dirt.

JohnDThompson 02-27-14 09:42 AM

I couldn't get your video to work, but I'd avoid trying to stretch tubular tires off the rim: they'll twist so the base tape is on the outside and the base tape will start to separate from the tire. As Ex Pres notes, used tubular rims are abundantly available. It doesn't matter if they're out of round, dented, or otherwise unusable on the road; for stretching they'll work just fine and such derelict rims can often be had for free.

FBinNY 02-27-14 10:13 AM

Quote:

Originally Posted by JohnDThompson (Post 16531913)
.... I'd avoid trying to stretch tubular tires off the rim: they'll twist so the base tape is on the outside and the base tape will start to separate from the tire. ...

+1, inflating to pressure off the rim is a good way to destroy a tubular. Tires are built of 2 bias plies laid at right angles to each other. Internal pressure makes the tube get fatter and shorter. This is what holds the tire in place on a rim. But off the rim the tire distorts beyond it's means weakening the glue bonds in the walls, tread & base tape, and if the pressure is high enough can tear the stitching out.

Some 40 years ago we used to use some tires that were nearly impossible to mount, even just to stretch without glue. In the end, we pulled apart a dead rim, removed an inch or so and splice it back together. This gave us a slightly undersized rim we could easily mount the tire on and inflate for stretching without risking the tire's integrity.

Homebrew01 02-27-14 10:46 AM

I can't see how stretching without a rim could be very effective. I think stretching on a clincher rim would be better than nothing.

FBinNY 02-27-14 10:50 AM

Quote:

Originally Posted by Homebrew01 (Post 16532111)
I can't see how stretching without a rim could be very effective. I think stretching on a clincher rim would be better than nothing.

I haven't looked in decades, but I believe that the flanges of clinch rims are higher than the diameter of a tubular rim, so mount a tight tire there may be more difficult.

FWIW- I don't know anybody that's been riding tubulars a while and didn't end up with an extra front wheel, or a dented and replaced rear.

Syncmaster 02-27-14 01:18 PM

Quote:

Originally Posted by FBinNY (Post 16532122)
I haven't looked in decades, but I believe that the flanges of clinch rims are higher than the diameter of a tubular rim, so mount a tight tire there may be more difficult.

FWIW- I don't know anybody that's been riding tubulars a while and didn't end up with an extra front wheel, or a dented and replaced rear.

Thanks for the comments. I think that video I linked to actually encourages other bad habits so it's not the best resource. Glad I asked here. I actually DO have an extra defective tubular rim laying around, but it's a deep section rim, and I only have 2 valve extenders, both of which are being used! So I can't inflate my new tires on the old tubular rim I have. I always tell myself to get another extender but... alas.

I ended up mounting them to a set of clinchers and they're stretching on those now. I've read that plenty of people use clincher rims to stretch tubs without issue (as long as there isn't anything that could poke into the tire).

Homebrew01 02-27-14 01:39 PM

Quote:

Originally Posted by Syncmaster (Post 16532610)
. I actually DO have an extra defective tubular rim laying around, but it's a deep section rim, and I only have 2 valve extenders, both of which are being used! So I can't inflate my new tires on the old tubular rim I have. I always tell myself to get another extender but... alas.

If it is defective beyond use, you could hacksaw a section out of the rim so you can get at the valve without an extender.

look566 rider 02-27-14 01:46 PM

If you can, leave them on your driveway in the sun for 30 minutes or so. Let the heat expand them. This is how I mount tires that give me trouble.

Andrew R Stewart 02-27-14 05:15 PM

One can stretch a sew up with body strength. But doing do can also cause damage from too much tension. Ask me how i know :) I've never tried the heating method, not sure how much expansion would happen. When we use to mount semi pneumatic tires we would place them on a hot black top or on the radiator mostly to soften them not expand them. I have used 27" clincher rims to store tires before. Not too much stretching would happen. The rim's spoke base is usually a smaller diameter then a 700 sew up rim's tire base is. Just find an old racer who is also a pack rat. He will have lots of old and likely dented rims to use a a stretcher. Andy.


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