The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: crocket on July 31, 2012, 04:45:30 PM
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just had a BT45 100/90x18 h fitted .Itshows direction of rotation on tyre and the words "front use only " Is it ok for rear?
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I think I've read that you can but mount with the arrow going the "wrong" way...
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The difference between front and rear has to do with the tire construction - it handles the forces one way better than the other. The front has mostly braking forces to contend with, but the rear is mostly drive torque. They're opposite directions.
A 100/90 might be a bit small for the rear.
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As well as being too narrow a 100/90 on the rear will be approx. 1.4" smaller in diameter than the original 4.00 x 18 which will lower your ride height and affect the gearing/speedo accuracy. Also the centre stand will become more difficult to use.
I wouldn't think of using it on the rear for those reasons.
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Took it back and the got me a BT 45 4.00x18 64H have put it on bike (1981 twin shock )and very little clearance on side of s/arm. Worried it may rub when tyre hot ? Anyone used same tyre?
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That should be the correct size. How much clearance is there?
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Would say about 1mm clearance without measuring just about slid a cable tie down side,.Took a bit of getting wheel back in between brake shoes and s/arm. worried tyre may rub on s/arm when hot?
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I would suggest confirming correct "stack height" of the rear wheel's axle and bearing assembly. A 1mm clearance does sound too tight, especially with a close-to-OEM sized tire... Manufacturer's variances.
The rear wheel has a specific pre-load requirement as you snug down the axle nut. This correctly positions the tapered wheel bearings and insures long and trouble free life. Too tight or too loose, not good.
You may want to confirm the rear wheel bearing stack, compression rings (2) and the spacer tube along with the rear axle's correct thick washer under the axle nut itself.
Over/under torquing the rear axle shortens bearing life. Sounds as if something may be missing, worn or incorrectly sized.
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Just measured clearance,slipped a 2mm plastic tie past it ok.Wondered if I could maybe space it a little?Or is 2mm OK?
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My last tire had something like 2mm and that was fine. I doubt many tires have much more than 3 or 4mm. My present tire is about as narrow as they come for a 4.00 X 18 and that has 4.5mm clearance. 78-80 R65's had a different swinging arm to the 81- bikes so there may be differences in running clearance.
I measure the gap with the shank of a metric drill bit. The narrowest gap may not necessarily be at the widest part of the tire wall. Due to the shape of the swinging arm it can be a little further back towards the wheel rim.