Optimistic speedometer

[winklerrob5]

Airhead newbie here.... Just picked up a 1976 R75/6 survivor with about 38K original miles. This bike has won a couple Antique Motorcycle Club of America awards, and I'm thrilled to be its new steward. I'm busy working through through electrical gremlins in between rides (shocker...), but that's not the subject of this request.

The speedometer/odometer is wildly optimistic on this bike (about 25%), and I would like to hear folk's experiences. The Final Drive housing is stamped 33/11, and the "original" state of the bike makes me doubt that is incorrect. Any suggestions about wrong gears in the speedometer drive or in the actual speedo? Indicated 50mph = 40mph actual. Indicated 70mph = just over 55.

Thanks in advance for any advice!

[Kurt in S.A.]

Welcome to the forum! First, from the factory the speedometers were somewhat "fast" in a way that keeps the rider out of getting a visit by some LEO. But yours sounds way too high. I think the R75/6 came with a 32/10 or 37/11 rear drive so likely yours is not original. Also it's important that the final drive and the speedometer must be a matched pair. There's a little number written on the face of the dial. My /7 with a 33/11 has W=1.112 written on the dial for a MPH speedo. See what yours says.

Kurt

[winklerrob5]

Well, this post is paying off already! Thanks Kurt, rubbing a little road grime off the final drive shows that it is indeed 37/11. Speedo is marked 1.186.
Based on some other references, it looks like my bike is fitted with a non-standard final drive somewhere along the line (32/10 was "normal" for USA bikes) but retains the standard speedometer at 1.186. Shorter than standard gearing would explain everything (including the 36-39 mpg I've been getting).

[Kurt in S.A.]

For the 37/11, the speedometer number should be 1.244. Not sure which is easier...find the proper drive or get a new speedometer. Or maybe just mount a GPS!!

Kurt

[melville]

I have two 1975 R75/6 and they both have the 32/10 final drive. The one that still has a speedo has the 1.186 version.

All Airhead speedos I've dealt with read high even if the odo is correct. Actually, with a fresh tire, the odo tends to be about 1 or 2% understating the thing but it lines up with a little tire wear. The R75/6 was about 11% high. My R100/7 is worse--indicated 80 was maybe an actual 67, or about 20% high. My RS is the closest to correct, and even it is 10% fast.

The R75/6 speedo has been serviced and recalibrated by a guy with a great rep and I expect it will be a shock to me when an indicated 80 is actually 80! Before, I'd get to 80 on the slab and I'd have to keep sharp eyes on the mirrors.