Speedometer

[RandyN]

I bought a new to me '86 R65 with about 53,000Km. It is in pretty decent condition and runs well. I know I am going to have a number of question as I get to know it. The speedo is my first one. It seems to read very high, indicating 140KMH at about 4500 RPM. The odometer checks fairly close compared to google maps. I do have a GPS tht I wil check it against this weekend, but thought I would ask for some feedback. Is it a calibration issue or ?

Thanks
Randy

[Barry]

As someone once said "BMW Speedo Accuracy" is a contradiction in terms.  They are at least predictable reading deliberately high typically by something like 5 - 7 mph and that is considered acceptable by BMW. To be more specific they consider a high reading of 10% + 2.4 mph to be acceptable.

If you tell me your final drive ratio I can calculate what the true speed should be at 4500RPM and also what your speedo ratio should be to checke it's the correct one to match the final drive.

[Bob_W]

On my oilhead, I noticed a seven mile distance according to the road signs showed 7.7 miles on the odometer. I later got on a straight US highway 17 for 8 or 10 miles and noticed the same 10% high readings. Surprisingly, the airhead with an 85 mph speedo is very close to the mile markers. I have no easy way to measure speed.

Bob

[Barry]

There is no reason for BMW to have deliberately made the odometer inaccurate in the same way they did for the speed reading. Some will say odometers should be spot on but that can't be given variations in tire size. Even so the odometer is usually nothing like that far out.  My odometer actually under reads by 2 % but I have a tire with a particularly large diameter. Metric 110/90 tires would make it over read but again only by a very small amount.

Car tires are more consistent in dimensions so I'm not surprised that my car odometer is more accurate.