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Busted-have a question about speedo ratios

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longhorn
Posts: 61
Joined: Sun Jul 15, 2007 11:58 am
Bikes: 58 servi-car
64 panhead
65 panhead
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Location: SE Minnesota

Busted-have a question about speedo ratios

#1

Post by longhorn » Sun Jul 26, 2009 3:39 am

Got popped today, 73 in a 55. I knew my speedo was off, it said 55. I had the cop follow me, and signal me when I got to 55, my speedo said around 43mph. I think my speedo is a 2-1. Where is my problem in the speedo, or the drive gear in the tranny?
Wonder how fast I was going on the hi-way, when my speedo said 70? LOL
Thanks Jim



51Hog
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Joined: Fri May 20, 2005 7:29 pm
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Location: Wasilla, Alaska

Re: Busted-have a question about speedo ratios

#2

Post by 51Hog » Sun Jul 26, 2009 4:08 am

Need more info---
What year bike?
Probably running a 25 tooth sprocket on the tranny?
A 23 tooth will get the speedo closer.
Stock back sprocket?

longhorn
Posts: 61
Joined: Sun Jul 15, 2007 11:58 am
Bikes: 58 servi-car
64 panhead
65 panhead
70 shovel
Location: SE Minnesota

Re: Busted-have a question about speedo ratios

#3

Post by longhorn » Sun Jul 26, 2009 3:42 pm

I don't understand why changing the countershaft sprocket would change the speedo readout? I can see where it would change the speed, but not the readout.
Here goes anyway.
The bike is licensed as a 64, because of the cases, but the parts range from 51-02. It's a mutt. Couldn't tell you what year the tranny is.
The countershaft sprocket is a 24 tooth. I didn't count the rear wheel sprocket, the old lady was having a hard enough time with the tranny sprocket. LOL
I'm thinking that the 2-1 is the correct ratio for a 64.
Even if it wasn't, couldn't a guy just change the speedometer drive gear, to correspond with the 2-1 ratio speedo? Or, would there be clearance/assembly problems?
Thanks Jim

51Hog
Posts: 664
Joined: Fri May 20, 2005 7:29 pm
Bikes: 1951 Fl
Location: Wasilla, Alaska

Re: Busted-have a question about speedo ratios

#4

Post by 51Hog » Sun Jul 26, 2009 4:17 pm

This post will explain the sprockets.
Check out Jacks calculator a few posts from the top.

viewtopic.php?f=5&t=5134&hilit=calculator

The output sprocket on the tranny, and the rear wheel sprocket, are after the tranny gear. Any change in them will change the revolutions of the rear wheel at a given rpm which will affect the speedo. It will also affect the power available at the rear wheel. A 22 tooth on the output will get you close to being correct on the speedo. It will also raise the rpm on your engine for a given rear wheel speed. (It will pull stronger)
I do not know if you can put a different speedo gear into your tranny.
HTH--Dale

RUBONE
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Re: Busted-have a question about speedo ratios

#5

Post by RUBONE » Mon Jul 27, 2009 6:25 am

The info on sprocket changes is correct. They are calibrated for a 22 trans and 51 rear. Any variation on those ratios will affect the readout. You CANNOT change the drive gear without changing the mating gear WITHIN the gearbox, a major task, as the tooth count is different and the gears will chew each other apart. The only way around the sprocket issue is a front or rear wheel drive unit that reads only wheel revolutions. Or have someone pace you with a known correct speedometer and make note of actual speed and remember it or mark the glass on yours!
Robbie

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