Bicycle Mechanics - Are modern tires compatable with 1970 Mavic rim?
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02-21-06, 11:26 AM
I have an old low mileage 531 bike with original 1970 Mavic Monthlery rims. Last time I rode it was 1992. I put new Hutchinson tires on last week (carefully following all standard procedures). I slowly pumped up the tire always checking for bulges or a tube stuck between the wire bead and rim. Everything was fine until I reached 80 psi. The tire slipped off the rim and the tube exploded. After jump starting my heart, I checked the rims and tires for defects. The wire bead looked to have a small crimp in it so I bought a pair of Panaracer Pasela that looked perfect. But once again as I pumped at 80 psi the tire slipped off and the tube exploded. So, what am I doing wrong or are new tires incompatable with these rims?
02-21-06, 11:49 AM
Do the rims have a lip on the inside?
The 'lip' is desgned to hold the bead of the tire and create a friction lock.
If the lip is worn and/or missing then you have a rim that is not as safe as modern rims.
There are tires that are made to the low end of the tolerance range that will fit tightly over the rim and may be a bit safer to use if you do not want to purchase a new rim.
Clincher rims of that era where designed for pressure fit of the tire against the inside of the rim. As Powers says in the '80s a new design was introduced that had a stepoff inside the upper part of the rim wall, and the tires have a corresponding bulge at the edge of the bead. The bulge locks into the stepoff and in theory under inflation pressure locks the tire onto the rim. In practice it is possible to blow the tire off but nowhere near as easily as it used to be. You will have a hard time finding non
lipped bead tires. They are obsolete. If the rim does have the lip inside and is not smooth, then you need to take care assembling the tire to be sure the lip has engaged the rim all the way around, you can roll the tire across the floor for a full revolution pushing down on the tire or just squeeze it into the rim while rotating the wheel by hand (off the bike is easier). Check to make sure the tube is not visible between the edge of the tire and the rim. Inflate slowly looking for signs of tire edge lift off from the rim as the pressure goes above 40-50#, look at both sides of the rim.
This happens to everybody at least once, and when you are up to 80-100# sounds like a gun going off, ruins the tube too....
02-22-06, 07:59 AM
Excellent replys. Thanks. Anybody know a source for non-lipped bead tires for my ancient rims?
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