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Re: what trans speedo gear?
[Re: stickman]
#605351
02/05/10 08:31 PM
02/05/10 08:31 PM
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Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
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You need a 34 tooth pinion.
The INTERNET, the MISinformation superhighway
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Re: what trans speedo gear?
[Re: stickman]
#605353
02/06/10 11:23 AM
02/06/10 11:23 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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Might put a piece of flat stock on top of one of your rear tires and measure underneath it to ground & see if your actual dia matches what the listed dia for that tire is. Plus if it isn't a whole # it could nudge you one way or the other on your tooth count choice.
live every 24 hour block of time like it's your last day on earth
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Re: what trans speedo gear?
[Re: RapidRobert]
#605357
02/06/10 09:16 PM
02/06/10 09:16 PM
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Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
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OK, if you apply a small slow-drying paint daub on the center of the tread on a rear tire and roll the car forward, the paint daub will make two marks on the ground, measure between them and this is the actual rollout on the tire.
If the tire is 85 inches in circumferance (the rollout) the working diameter will be 27.056". If you use your "lay a stick on top of the tire and measure to the ground" you will likely get a smaller measurement of the diameter than the actual 27" due to that flat spot on the bottom of the tire but the rollout will still be 85" and that's what the odometer needs to see.
If the flat spot is 1/2" your measured diameter will be 26 1/2" which will make the rollout 1 3/4" too short which will result in a 2% error. In the real world you'd be lucky to come within 2% accuracy from one pinion to the next larger/smaller size but the point is the "stick on top" measurement is not the correct diameter for computations especially considering that many tires will have more than 1/2" squat.
The INTERNET, the MISinformation superhighway
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Re: what trans speedo gear?
[Re: John_Kunkel]
#605358
02/06/10 09:25 PM
02/06/10 09:25 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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Alright, Pi divided into the rollout to get the actual diameter
live every 24 hour block of time like it's your last day on earth
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& I was thinking you'd let me slide on that after a period of time. So much for me thinking huh 
. Alright here goes: My reasoning is that my tires are almost perfectly round so the diameter spec in the archives works in my case and when I used the chart w my dia and my ratio it made my odo spot on (checked @ interstate mile markers) and luckily my speedo also was correct (checked by a digital roadside MPH sign and measuring rollout would require a helper to drive the car for a few feet as I watch for the stem to hit 12 0'clock again then tape measure the distance then a bunch of math 
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