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I have changed up my tranny gear ratios and am quite satisfied with the current rear gear ratio of 3.31 for around town, but I am looking for a track change up to 3.73 by changing the diameter of the rear tires. Based on my calculations our stock tires have a diameter of 28.098 inches so I would need new tires with a diameter of 31.70 inches. Whether I can find such an animal is yet to be accomplished with the stock 18" rims as I have a second set. Does anyone have any input?
 

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I have changed up my tranny gear ratios and am quite satisfied with the current rear gear ratio of 3.31 for around town, but I am looking for a track change up to 3.73 by changing the diameter of the rear tires. Based on my calculations our stock tires have a diameter of 28.098 inches so I would need new tires with a diameter of 31.70 inches. Whether I can find such an animal is yet to be accomplished with the stock 18" rims as I have a second set. Does anyone have any input?
Not sure I understand what you are saying here....if you are saying you want the same ratio as a 3.73 rear end by using the stock 3.31 and changing it with tire size to achieve a "3.73" you need smaller tires not bigger and I am not aware of anything that small that would be an 18" tire. You would need to drop to a 17"....this seems like a poor decision, just change the read end to 3.73 and be done with it; considering both 5th and 6th are OD you are not going to run out of RPM for daily street use.
 

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The tire height (diameter) for the gt500 is 26.98
Thanks for the information. I just used a tire calculator based on the stock size of 285-45-18. That changes my new tire diameter to 30.40.
 

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Not sure I understand what you are saying here....if you are saying you want the same ratio as a 3.73 rear end by using the stock 3.31 and changing it with tire size to achieve a "3.73" you need smaller tires not bigger and I am not aware of anything that small that would be an 18" tire. You would need to drop to a 17"....this seems like a poor decision, just change the read end to 3.73 and be done with it; considering both 5th and 6th are OD you are not going to run out of RPM for daily street use.
That was my initial thought but based on the calculator I was using, that is not the case. I must be missing some thing. Think you are right and just go for the 3.73's.

http://www.ramblerman.com/blazer/gearcalc.htm
 

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