The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: MR.E on January 24, 2012, 04:15:41 PM
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Hello
I've been thinking, back to the few days i got to take the R65 out this year, is it possible to change the gearing in the gearbox?
looking for lower revs and a little higher cruising speed!!
any advice welcome
thanks
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Yes it can be done.
Two options:
1. Put in the 6% taller fifth gear in the gear box.
2. Change the rear end to one with taller gearing (and then change your speedo to the same).
Your choice.
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I like the sound of the taller 5th gear.
The stock 4th and 5th are so close.
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I know a guy who loves the 3/20 final drive on his R65s. Not sure what kind of riding he does, though. I've converted to the 3/36 on mine, but could stand to go even taller. Next step would be the 3/20 for me.
Unless you need to open the transmission for some reason, you're money ahead swapping final drives.
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Cracking open the gearbox is generally a ~$500 minimum proposition, whether it is to replace a bearing or change a gear cluster (though gear cluster parts add alot more $$ to the bill than a bearing).
As indicated, you could change the stock final drive gearing from 3.56:1 or 3.44:1 to either a 3.36:1 or 3.2:1, but your speedometer will be off by a percentage corresponding to the ratio (e.g. going from 3.44 to 3.2 will net a 3.44/3.2 = +7.5% error in your odometer and speedometer readings, if you don't change them to match. Getting a replacement one (and possibly having to repair it) will then sometimes eat up most of the difference in savings from going the gearbox route, but at least the final drive/speedo change is something you can do yourself, versus pulling your transmission out and sending it to a specialist, like Anton Largiader, Tom Cutter, etc.
On the other hand, having the taller overdrive 5th gear in the transmission will still preserve your acceleration capability, which will be reduced across the board if you swap out to a taller final drive. Or, if you are changing to a 3rd part speedometer with front wheel sensor anyway, then the BMW part speedo-swap is a non issue and you can use whatever final drive you like.
Lastly, don't be put off/frightened by the 5000 RPM on the speedo when travelling on the interstate with the stock gearing - these engines are actually quite happy spinning like that, and you can cause alot more damage to it if you lug it around town in top gear at 2200 RPM..
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I know a guy who loves the 3/20 final drive on his R65s. Not sure what kind of riding he does, though. I've converted to the 3/36 on mine, but could stand to go even taller. Next step would be the 3/20 for me.
Unless you need to open the transmission for some reason, you're money ahead swapping final drives.
Whaaa-huugh?
I think I have a 31/9 final drive on my 1980. Never heard of a 3/20 final drive. What did I miss?
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Lastly, don't be put off/frightened by the 5000 RPM on the speedo when travelling on the interstate with the stock gearing - these engines are actually quite happy spinning like that, and you can cause alot more damage to it if you lug it around town in top gear at 2200 RPM..
Hmmmm
I was thinking it'd be better to keep the revs lower than not.
What kind of cruising speed will i get at 5000 revs comfortably??
At the minute i sit around 60mph which is fine but thought i'd be better lowering the revs.
Think i'll look into the taller 5th gear (just incase i decide to go ahead) so i keep the acceleration etc.
Thanks
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I know a guy who loves the 3/20 final drive on his R65s. Not sure what kind of riding he does, though. I've converted to the 3/36 on mine, but could stand to go even taller. Next step would be the 3/20 for me.
Unless you need to open the transmission for some reason, you're money ahead swapping final drives.
Whaaa-huugh?
I think I have a 31/9 final drive on my 1980. Never heard of a 3/20 final drive. What did I miss?
My question, too, Gumby. Both my R65s have the OEM 31/9 finals.
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Monte/Gumby - I think that was just a typo in his message - he actually meant a 3.20 final drive ratio, which was standard on the earlier R75/6 and which one could often get optionally for the R75 or R80 when they switched to a 3.36 (37/11) ratio.
Mr. E - Assuming you have a standard/stock profile rear tire, 5000 RPM will net you 70 MPH with a 32/9 final drive (3.56:1) or 73 MPH with a 31/9 (3.44:1) final drive ratio. A common misunderstanding by folks new to airheads is they think "big twin" and assume that means it should be driven like a Harley-Davidson.. not so. These bikes are designed to hum along, and will do so happily at 5000 RPM all day. The R248 engines (short stroke R45/R65 design) are also especially more eager to rev than the longer stroke R247 engine design on the R75/80/90/100.
Just don't over rev it - they don't like that. But the BMW engine design is very robust for handling high RPM conditions for extended time.
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We have had a lot of discussion in the past on this very topic. Here's a link to a thread entitled "70/75MPH all day long" which says it all really.
The thread includes some tables which illustrate the changes to revs/MPH for different final drive ratios.
http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1271977389/21#21
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ok so a numpty's question
how do i find out the ratios of the bike?
Are they stamped into the engine somewhere?
Thanks
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Right - I meant 3.20. Sorry.
Can you see a pinion gear with three teeth? :D
The only reason I haven't tried a 3.20 yet is because I'm getting close to 50mpg as it is with the 3.36.
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Mr E - top of the final drive, where the gray alloy part bolts onto the black swingarm, ahead of where the lower end of the shock absorber is bolted on - there is a stamping in the metal which would be either "31/9" or "32/9", etc.
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If you change the final drive ratio you will need a matching speedo ratio. The speedo ratio printed on the face of Airhead speedos is the number of cable revolutions for 1 mile traveled and as it is driven by the gearbox the correct ratio depends on which final drive you have. Here's a list.(http://)
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Fitting a 6% taller 5th gear was mentioned early on in this thread. Came across this web site with a very good write up by someone who had one fitted.
http://www.gunsmoke.com/motorcycling/r100gs/tranny/index.html