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Car tire on stock rear rim of my 1974 BMW R90/6
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Dr. Raoul Duke
Posted 10/18/2004 3:56 PM (#5061)
Subject: Car tire on stock rear rim of my 1974 BMW R90/6

After looking at the poll I ran I think this is a must project over the coming winter. "Can" I put a radial automotive tire on the stock rear rim on a 1974 BMW R90/6. If so does anybody have any recommendations? If not, what do I need to do to the rim to accomodate an automboile tire?

Thanks in Advance,
Dr. Raoul Duke
AKA The Circus Bear
AKA Jim Kelleher
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Posted 10/18/2004 6:46 PM (#5064 - in reply to #5061)
Subject: RE: Car tire on stock rear rim of my 1974 BMW R90/6


Posts: 4833
Location: Boise, Idaho
Several vendors furnish a wheel (wheels) for Beemers (and other bikes) that have a rim that is the correct size to accomodate automobile tires. Automobile and motorcycle tires do not actually share the same diameter. The 14", 15" 16" size designation is only approximate to identify sizes between tires of the same genre. The difference in the actual rim diameters is enough to kill you if the tires and rims are mismatched in some instances. Is risking your life worth saving a few bucks on a tire replacement? Most of the wheels designed for auto tire use are expensive enough that they will not produce a significant saving or perhaps any saving unless you are a long rider. They will produce a difference in handling characteristics however, wanting to follow seams in the pavement or hopping over them.
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claude #3563
Posted 10/18/2004 10:22 PM (#5068 - in reply to #5061)
Subject: RE: Car tire on stock rear rim of my 1974 BMW R90/6


Posts: 2498
Location: Middleburg, Pa
Give Harry Tarzian a call at (814)349-2414. Harry makes auto wheel conversions. For the Beemer the size to go to would be 15". The tire could be a 135R15 thru a 165R15. The 135s at this time are available throug Coker tire and soem other places. The 165 can sometimes be found at a conventional tire shop. The 165 is typically less expensive. It may have around a 26" rolling diameter where the 135 will have around a 23" dismeter when mounted. The smaller diameter helps the final gearing when pulling a chair.
Lonnie is correct in that some car tires do followw the imperfections in the road. I do not find this to be the case too much with these size tires,from my experience anyhow.
A lot depends on the tread pattern and even moreso on the air pressure in the tires. I have 135R15s on the front and the rear at this time. The front does wander a little when the road varies but it is not objectionable when you get used to it. With a motorcycle tire on the front and a car tire on just the rear I found the rig to run straight no matter what the road surface was like.
The last 165 I bought was on sale for 38 bucks. Compare prices with a 491 Dunlop motorcycle tire9which wears prettywell for sidecar usage) and you may find the wheel conversion to be pretty appealing. If, as Lonnie stated, you plan to keep the bike long enough to make it wothwhile.

Edited by claude #3563 10/18/2004 10:33 PM
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