The Atlas Thread

Is there a drive ratio difference between a speedo drive gearbox for an 18" rear wheel and a speedo drive gearbox for an 19" rear wheel?

If so, what is the Part No. for a speedo drive gearbox for an 18" rear wheel?

And, what is the correct drive ratio? eg. 2:1 or 12/15 (1.25:1) drive ratio
 
Possum said:
Is there a drive ratio difference between a speedo drive gearbox for an 18" rear wheel and a speedo drive gearbox for an 19" rear wheel?
Click to expand...

No.
Or they would be in the parts books.

And how could there be, the difference is only fractional.
If you measure the rolling diam of 18" and 19" tyres, there is very little difference,
a 4.00 x 18 and a 3.50 x 19 are not too far different at all..

All you have a choice of is the one in the Atlas/dommie parts book 2:1 P/N 22888
https://andover-norton.co.uk/en/shop-details/17341
http://www.rgmnorton.co.uk/dept/instrum ... d01124.htm

The Commando uses the 15:12 ones, and different speedos.

I'm sure there will be more complexity to it, there always is.
Like c/w and anticlock rotations...
hth
 
When the two prototype Commandos were built, they got speedo drives that weren't the correct ones. For some screwball reason, the Commando instruments were calibrated for drives with (I think) half the number of cable rpm/mph compared to the Atlas. It was a three months or more before we got the correct ones and we had to rely on the tachometer for speed indications. The speedo went off scale high at 50 mph.
 
Just make sure you have the proper top hat spacer that fits the axel in a 2:1 drive ratio and it should work given you're using the original clock.
 
kernel65 said:
Just make sure you have the proper top hat spacer that fits the axel in a 2:1 drive ratio and it should work given you're using the original clock.
Click to expand...

Agree!

Thanks to Time Warp who made me a top hat spacer so I could adapt a NOS 2:1 drive to my axle. Works fine.

Slick
 
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