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Speedo setting up

Posted: Tue Apr 23, 2019 11:49 pm
by Allan
I have a working Corbin speedo on my 1925 roadster. I even had the swivel assembly nickel plated as they were when new.
20190421_104020.jpg
However, at a steady 35 mph on the dial, I was doing a GPS verified 38 mph. Currently it is fitted with a 68 tooth road gear and 18 tooth fibre gear. I can change the fibre gear. How much closer to an accurate indication would a 17 tooth fibre gear would I get?

Allan from down under.

Re: Speedo setting up

Posted: Tue Apr 23, 2019 11:57 pm
by rodelljunior
I don't have speedometer experience, but it makes sense that the small gear would turn 1/18th faster with one less tooth, which would give you about 2 mph higher reading at 35 mph, which would be closer to your GPS reading of 38 mph.

Re: Speedo setting up

Posted: Wed Apr 24, 2019 9:45 am
by Adam
What size tire do you have? A slightly oversize tire might be the issue. Using the next smaller gear like Jim recommends makes sense.

Re: Speedo setting up

Posted: Wed Apr 24, 2019 6:46 pm
by Corey Walker
The speedometer on my 14 reads fast as well. It has the correct gearing for a Stewart Model 100. If you put a different gear to make the chain spin slower then it seems like it would mess up the odometer reading, or at least in my case I think the problem is with the speedometer head. The mileage checks out good, which is determined by the gearing whereas the speed indicator is determined by the magnet rotating in the speed drum. I thought about turning the dial with numbers backwards one revolution against the stop to put more pressure on the spring that makes it return to zero. I’m not sure if that would work or not. I put the speedometer on mainly for the odometer.