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speedometer gear???

4005 Views 7 Replies 6 Participants Last post by  Ram
speedometer gear or whatever it is called that you can change to correct the speedometer after getting different gears. anyway would the dealer have what i need to get my speedometer accurate after going from 235/75/15 tires and 3.55 gears to 33inch tires with 4.56 gears???

thanks for any help
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When I changed up from 29 inch diameter tires to 31's, I "swagged" the teeth count that my speedo gear should change and posted it on the board. Some one came back with a formula as to what gear it should be and I was not off. I just came to the size I needed differently! I seem to remember that the formula had the teeth count of the speedo gear. Do you know what size you have now that went with the last set of tires which ran accurately? I'll try and find that post.
Ok, I know that my post was back between Aug 2003 and Jan 2004 and I can't get the search, or page back feature to get that far back in time. Sorry! Hopefully some one who has answered my post in the past will chime in and let us know again!
Duffy said:
Here's the fomula that you requested
first you need to figure the driveshaft rpm at 60
speed x gear ratio x 336 / tire diameter
60 x 4.56 x 336 / 33 = 2786 ( or about )
take that number and devide it by 75
2786 / 75 = 37 tooth gear needed
each tooth on the speedometer gear is equal to about 3 mph.
speedometers cost about $12 at the dealership.
Thats it, Thank you Duffy :)
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