The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: ridefar on August 15, 2011, 05:54:40 PM
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Anyone have any info on making the r65 trans have a taller 5th gear?
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This comes up once in a while, the transmission is the same for all of the bikes made from '81 through the end of the airheads, which I think is around '95.
The real difference with the R65, is the final drive ratio, I think it's a 3:56 on the '81 through '95 bikes, the larger bikes have a different ratio .
You could change the final drive, but performance would be degraded .
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Actually, I believe that there are gearsets with taller 5th gear available for racing use for the 5 speed transmissions, though one may have to replace the entire gear cluster at the same time, and the 1st, second, and third gears are also a bit taller than the non-racing version. For whatever reason, 4th gear is the same ratio in both.
This is not a common or inexpensive change though, and you'd likely be talking with folks like Tom Cutter or Anton Largiader to do the job.
While it would reduce your acceleration ability across the board, you could probably simply swap the final drive from an R80 (look for 37/11 ratio for decent balance between making your gearing taller without going alot taller) without too much trouble, and lower RPMs on the interstate. Just plan on downshifting for brisk overtaking on the freeway.
You will need to get a matching speedometer, or pay ~$200+ to re-gear and calibrate your speedometer to match the new final drive. But, I think the 37/11 ratio was common on the R80RT through the 80s, so used speedos that match shouldn't be super-hard to find.
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You don't have to replace the gear clusters, only the 5th gear. 1-4 ratios would stay the same.
Source for the gear:
http://www.beemershop.com/catalog/index.php?manufacturers_id=51&osCsid=8b39bc4c9cd10e4934e476d13c6ae4f4
A thread on the MOA forum from around one year ago:
http://www.bmwmoa.org/forum/showthread.php?t=48013
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Rob is correct, and the gear costs about $125 - the installation will run a bunch more.
If you're not a heavy guy, a 3.36 final drive will work just fine. The standard drive was either a 3.56 or 3.44. The 3.36 isn't much taller at all. I even know a guy who mounted 3.20s on both of his R65s. But it's possible he doesn't have many hills to climb, which could make a difference.
Swapping the final drive would definitely be cheaper than adding a taller fifth.
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People say changing the final drive is cheaper but I think they are wrong.
When you change the final drive you also have to include the cost of changing the speedometer as it will no longer be acurate. If you change the 5th gear the speedo will remain the same.
At one time I thought about doing this but with the load that I carry I decided against. If it was a naked bike then I might consider this.
Just use ~5000 rpms as your max long distance RPM and be happy with what it is. 8-)
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I wouldn't have to change MY speedometer... a Vector, similar to Monte's Vapor. ;D
But I don't need higher gears.
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Thanks for that link, Rob. I thought that one would possibly have to replace the gear cluster if the racing gear 5th gear tooth cut didn't match that of one's existing transmission (there were 15 degree and 17.5 degree gear angle cuts over the lifespan of the 5 speed airhead gearbox. But, I see on your link that they have both cuts available (X on the gear marks the difference). Good to know!
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Thanks for the info. It is appreciated.
Bill