Vintage BMW Motorcycle Owners

A friend I ride with has a 82 R65. And at 65 MPH the tachometer says 4700 RPM. He says the engine sounds like it also. We think that is really to high RPM. It just came from a BMW shop where they adjusted the carbs for him. He has only had the bike for a few months, as far as I know has always been that way. He knows its a 5 speed so I assume he has it in 5th gear. My R100RT at 65 mph is 3500 RPM. We think that is more where his should be rpm wise.
Any help?

It likely has to do with the final drive ratio. Anton Largiader has a web page that compares gear ratios...it doesn't work for me for some reason...maybe it will on your computer:

http://largiader.com/articles/gearing/

I had developed a spreadsheet a while back to figure out RPM for my /2 and adapted it for my /7 as well. When I put in the final drive ratio for an R65 (3.44 or 31/9), I compute an RPM a little above 4400. Computations are based on standard measurement of the rear tire circumference so there can be some various. Given that, your observed 4700 is in the ball park.

My /7 has a 33/11 final drive and my spreadsheet computes around 3850 for RPM which is pretty much what I see on the tach.

The 31/9 rear end is the one he has I believe. Ill let him know that the 4700 is not to far out there. Just not a bike I would want to take on the autobahn. But it is a nice old Boxer anyway.

The R65 was a bit of an odd duck. Airheads are known as Type 247 engine/bikes. The R65, while being a twin cylinder, is a Type 248.

What you have is the difference in final drive gearing between airheads.

The R65 is the lowest gear.
Next is the R80RT
Then is the R100RS
Highest gear is the R100RT

This was done to have the engine turn the proper RPM for crusing, torque, and HP for each of the engines.

So for an example, my R80RT at 60mph runs at 4200RPM. My R100RS at 60mph reads 3200RPM. An RT will read a bit lower than the RS.

So yes, an R65 is busier at cruise than an R100RT..

You have to make up for the lack of HP and torque somehow. St.

BMW's like to rev. I've spent many thousands of mile at 5000 rpm or more on my twins. While in Europe we mostly traveled at redline! Never could convince my friend to slow down to 150kph (from 210 kph) to get there faster. At 150 we would travel more than twice as far before needing to refuel. At 210 we were getting 15mpg and stopping every every 30 minutes or less.

Don't worry about the revs; keep it below redline and enjoy the ride.

Mike

Thanks guys, Ill tell him to ride it below the red paint on the tach. LOL
Good info.

Keep it above 3000RPM, never lug the engine. St.