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-   -   Speedo Gear Selection (http://www.clubcobra.com/forums/era-speak-bob-putnam/99834-speedo-gear-selection.html)

Excaliber 09-23-2009 04:57 PM
Speedo Gear Selection
 
I'm currently running the PINK driven speedo gear in my Top Loader. My speedometer reads about 6 to 7 mph slower than I'm really going. 60 mph indicated is actually 66-67. Checking ERA's web site indicates PINK is 19 tooth. So, do I go with an 18 or a 17 tooth to get close to my real world mph reading?

Here's a link to ERA's chart: My tires are Goodyear Eagle II, 295X50X15 which I THINK is 26", maybe slightly smaller?

http://www.erareplicas.com/427man/gearing/spd_gears.htm

Chaplain 09-23-2009 07:09 PM
The speedometer gear wants to turn 1000 revolutions per mile. Using your tire diameter and final drive ratio solve for what the speedometer drive to driven gear ratio should be to get as close to 1000 revolutions as possible.

strictlypersonl 09-23-2009 07:23 PM
If your speedometer is indicating 10% low, you want to change your cable drive gear by 10% also. So 90% of 19T is approximately 17T.

Excaliber 09-23-2009 07:48 PM
There ya go! I was concerned that 18 might not quite enough, based on the chart. I'd rather read slightly fast than to slow, so 17 it is!

Thanks guys.


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