Which year/model final drive units are candidates?

[bjamesw]

Want to raise the ratio from the constantly irritating 32/9 to something more useful (to me) like 37/11 32/10.   I'm under 160lbs, never carry more than a medium sized tank bag, and ride 95 percent solo.

First gear usually gets me forty feet or so beyond the stop light and then sometimes I'm into fifth at moderate city speeds.  I raised the topic at advrider and a couple of members there have owned or ridden R65's thus modified and encouraged me to do the same after describing my riding habits and style.  

One comment was interesting

[size=12]"9:32? That is the ratio that was used in the R50/5 models! 11:37 was used in the R60/5's.

What were the R65 designers thinking???" [/size][/b]

Ebay is full of final drives from a variety of years.  Anyone know which ones bolt onto the R65?

[nhmaf]

Most of them will work, though ideally you do want to try to use ones within the same "generation", so to speak, as I am not sure if BMW changed the cut of the mating splines or not - I tend to think not though.   BMW first tested out the "cush drive" (spring loaded driveshaft) on the R65 models in the 1979 model year run, and by 1980 or 1981 they had incorporated this into the other bikes.  I think it looks better to either keep the smooth/rounded final drive units with the pre-1981 bikes, and the more angular, ribbed final drive units with the 1981-> bikes, as that maintains the factory appearance, but that is just my opinion.

The R65 - especially the 1981-1985 models - were tuned to rev up faster and have their torque and HP peaks higher up in the rev range than the R80/R100 bikes.  Consequently, if you keep them "on the boil" the R65 will keep up pretty darn well with the R100, and outhandle it in the twisty sections.  

some folks do swap out with a 32/10 final drive, but I think that many use the 37/11 (3.36) one which was used on the R80RT bikes (and thus is quite common).   BMW originally used the 32/10 final drive unit on the R75/6, but later changed it to 37/11 on the R75/7 to improve the get-up-and-go factor, especially when riding 2-up.   Going from 32/9 to 37/11 will give you about 6% taller gearing, which will drop your RPMs by about 300 or so at 65 MPH.   I think that is a pretty good compromise as it wouldn't too badly impact your acceleration.  The 32/10 is definitely the tallest I would go, otherwise you'll have to be dropping down to 4th gear a whole lot more often, I think.

With most of the airheads, I believe, the designers intended for the bike to be able to just pull redline RPMs at top speed.   The taller you make your final drive, the more likely that you will tend to top out at a bit lower top speed, as the bike won't quite have the HP to pull the top end - though that generally isn't a concern with street riding.

Don't lug the engine, either!

[Luca]

Don't lug the engine, either!

Ditto.  The cam chain and sprocket are the last things to get oiled in the engine... by a straw that spits excess oil them.  They like a few revs.  Air cooled engines don't like getting lugged anyhow.

Out of curiosity, where do you shift/cruise on the tach?

[georgesgiralt]

Hello !
I've my user manual in front of me.
In 82 for European market, BMW fitted :
8:34 to the R45 (20kW)
9:35 for the "normal" 26kW R45
9:31 for the R65 (normal and LS)
You may find the missing information in Clymer's or Hayne's spec pages.

[Barry]

Here a comparison between the 32/9 and 37/11