Topic: Speedometer Drive Gear

[Grabcon]

When I built my 1974 CB750 K4 I used the front wheel off a CB750A. This is a spoked wheel with aluminum rim. Not sure of year. I am using a standard tire size 100/90V19. I also used the speedometer gear drive from the CB750A.

The Speed on this setup just didn't seem right. So I am validating my speedometer against a Garmin GPS unit. This shows that my speedometer is off by at least 10mph depending on what speed. Garmin says 60 and the speedometer says 70 mph. So the question is "Is there a difference between the CB750A and the 1974 CB750 K4 Speedometer gear drive on the front wheel?"

I am running a 120/80V17 on the back. This really should not affect the speedometer, but potentially could affect the RPMs and speed ratio.

[Bankerdanny]

I would think the same year bike would use the same ratios. You don't say what year 750A provided the front wheel.

And you are right that the rear tire size only affects rpms at a given speed. It would have no impact on speedometer accuracy.

FWIW, my speedometer is off by as much as 5-7mph depending on the speed, and thats the original wheel/speedometer combo.