Service

SERVICE

Tubeless tires and spoked wheels

Those of us who have motorcycles with spoked wheels appear to be at a great disadvantage when it comes to new tires—Michelin Hi-Sports, for instance, may not be used with a tube. Can you tell me if D.I.D., Sun, Akront, or anyone else plans to market a tubeless rim for spoked wheels in the near future?

Eiden Carl La Mesa, California

To our knowledge, no company plans to market a rim that can be used without a tube and spoked to standard hubs. Honda is using tubeless spoked wheels on the XL600LM dual-purpose model intended for the European market, but it uses a unique wheel design that seats the spoke nipples in a special hub rather than in the rim.

But don 7 despair; at least in some cases, tubeless tires can be used with tubes. Formerly, some tire companies hesitated to recommend this usage because the combination of a tube's extra weight and the friction of it rubbing against a tubeless tire's leak-proof inner lining increased heat buildup and sometimes reduced the speed capability of the tire below the rating on the sidewall. Newer tire linings manage to hold air without generating so much friction when used with a tube, and several tire companies, including Dunlop and Metzeler, accept the usage of tubes within their tubeless street tires with no reduction in speed rating.

Unfortunately, there is one other potential problem with the use of tubeless tires on spoked wheels: a mismatch between tire bead and rim profile. Tubeless rims have a different contour (Motorcycle Tubeless, or “MT") than the WM-profile rims that are common on spoked wheels, and a tire designed for the best fit with an MT-profile rim will be very difficult to seat on a WM rim. The tire companies that allow the use of tubeless tires with tubes have designed a compromised tire bead that will seat on either rim profile. Michelin tubeless tires do not fall into that category, however, and a Michelin spokesman stated strongly that Hi-Sport tires should not be used with a WM rim because of the diffi-

culty in properly seating the bead.

Ón the other hand, the Michelin representative also acknowledged that Michelin tubeless tires would seat correctly on spoked wheels with rims that use an MT or TL profile and no safety humps, that Hi-Sports should have no problems with heat build-up when used with a tube, and that it's not unusual in club racing to find HiSports mounted on spoked wheels. So while Michelin doesn 7 recommend using tubes with Hi-Sports, there's at least tacit recognition that it can be done.

There is a catch, though: Rims with the necessary MT or TL profile are very rare indeed, and most of the racers who are mounting Hi-Sports on spoked wheels seem to be resorting to fairly desperate measures to seat the bead, such as inflating the tire to 80 psi or more. That's a dangerous practice in itself, and Michelin claims that's it 's no guarantee of proper mounting. So, realistically, you 'll have to be satisfied with the use of Michelin tube-type tires, or tubeless tires from other companies that specifically allow them to be used either with or without a tube.

If anyone knows of a source for rims with either the TL or MT profile, please let us know, and we'll print that information in this column.

Crankshaft repair

I recently rebuilt and repainted a 1972 Yamaha LT2 Enduro for my oldest boy to ride. Unfortunately, the crankshaft recently broke, almost flush with the crankthrow on the flywheel side. My question is

this: Is it practical for me to weld the crankshaft and then turn it down to its original O.D. on a lathe? If so, what type of welding rod should I use. It’s a great-running bike, so I would hate to have to junk it.

Jeff G. Paradis Truman, Montana

Welding the crankshaft back together is unlikely to offer a satisfactory repair; the welded area would almost certainly be weaker than the original crank, and subject to breaking again, and tolerances and alignment on the crank would be difficult to maintain as it was welded and re-machined.

As an alternative, we'd suggest trying to find a replacement crank at a motorcycle salvage yard. The closest salvage company to you that we're aware of is Cycle Salvage, Inc., 3008 Garrity Blvd., Nampa, Idaho 83651; (208) 465-4455. If Cycle Salvage doesn 7 have the crarik, someone there may be able to locate one at another salvage yard. B3