Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
To tube or not to tube
Q: My question involves switching from tube to tubeless tires. I have read a few articles that discussed the problems involved in trying to use tubeless tires on spoked rims. The consensus seems to be that tubes should definitely be used, for a long list of good reasons. Most of these articles go on to say running tubeless on alloys that were originally fitted with tube tires is OK “in most cases.” That seems a little vague, considering the result of popping a bead going 60mph (or faster). I would like to make the switch on a 1980 Suzuki GS450. There is no problem finding 18-inch tires for the rims. Is there anything I should look for on these alloys other than bends, warpage, cracks, etc., which should be checked anyway, that would make going tubeless a bad idea? — Eric Schmidt/Cincinnati, Ohio
A: Unfortunately, this is a question that is most easily answered by saying it works “in most cases.” Dunlop Tires has this to say about your question: “Only mount tires as tubeless when recommended by the wheel manufacturer. Some spokeless rims require tubes. With a tube inserted, a tubeless tire may be fitted to a tube-type wheel.” I did a little digging and found that there are three basic rim profiles used today: the WM series usually found on old British bikes, the MT or TL series in common use now and the CP contour. Both the WM and CP profiles were meant to be used with tubes and should be used with tubes. You may be able to use a tubeless tire on them, but it should be tubed. Also, when using a tube in a tubeless tire you should downgrade the speed rating by one to compensate for the increased heat due to friction between the tube and the tire carcass. The MT or TL profile was designed to run a tubeless tire, though some of the earlier examples of this came with tubed tires, possibly due to lack of tubeless motorcycle tires when they were introduced. There is an organization that regulates tire bead/rim bead seat designs so they are all compatible with each other. The bead design should be the same for both tube and tubeless tires, and most manufacturers say that their tires will fit properly to all three of the rim designs. No one is going to say it is OK to run tubeless where there once was a tube — it’s just too great a liability exposure. As an added impediment to going tubeless on tube-type rims, the valve stem hole in the rim is larger on tubeless rims than on tube-type rims. To use a proper tubeless valve stem you have to enlarge the hole in the rim. Once you do that, I’d think you’d never be able to go back to a tube in that rim. I hope this helps with your decision. MC