Wednesday, Feb 05, 2003 at 17:52
Voxson, perhaps I can explain although I think this is a technique for advanced players. In my student days when I used to work at a service station - yes SERVICE station (we used to pump your petrol,
check your oil & wipe your windscreen) and we had a rubber ring of about 15" diameter and about 2" in cross section. If a tubeless tyre was being stubborn in reseating, with the tyre already on the rim we'd also stretch this "donut" onto the rim so it fitted between the flange of the rim (the bit the
bead usually abuts ) and the
bead/sidewall of the tyre. It was like mounting an inflated 16" bike tube on the rim next to the tyre. The donut fitted snugly around the rim and pressed up against the sidewall of the tyre, and when done properly, formed a seal between the tyre and rim. This also helped push the inner
bead onto the inner flange of the rim. Pumping air in first sealed the inner
bead and as pressure built up the outer sidewall started to squish the donut onto the flange. The tricky bit was to stop inflation before the donut got so completely squashed between tyre and rim that it couldn't be removed without letting air out of the tyre. However, if you pulled the donut out before the outer
bead had seated properly you just broke the seal but at least by that stage you would have had the inner
bead seated. It's harder to get both sides of the tyre to seal at the same time, hence the need for the "whoosh" of air so if you sealed only one side that was still a help.
Had to be bloody careful when pulling out the donut to avoid getting the fingers stuck betwen the
bead and flange.
The donut technique was useful when trying to reseat narrowish tyres on wide rims because the tyre beads wouldn't naturally span the rim to form a seal.
Hope this explains it.
MikeyS
FollowupID:
7332