# Final drive ratio

**URL:** <https://community.cartalk.com/t/final-drive-ratio/21806>\
**Category:** Maintenance/Repairs\
**Created:** [November 7, 2008, 11:04pm UTC](https://community.cartalk.com/t/final-drive-ratio/21806 "2008-11-07T23:04:33Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dseroka](https://avatars.discourse-cdn.com/v4/letter/d/7ab992/32.png) [@dseroka](https://community.cartalk.com/u/dseroka)\
**Post date:** [November 7, 2008, 11:04pm UTC](https://community.cartalk.com/t/final-drive-ratio/21806/1 "2008-11-07T23:04:33Z")

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what would be the rpm difference at 70mph with a 3.23 versus a 3.73 on similar vehicles with same tire sizes?

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**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\
**Post date:** [November 7, 2008, 11:19pm UTC](https://community.cartalk.com/t/final-drive-ratio/21806/2 "2008-11-07T23:19:11Z")

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If the vehicles are IDENTICAL except for axle ratio, just divide the two ratios. Otherwise, no way to know without knowing the transmission ratios.

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**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\
**Post date:** [November 7, 2008, 11:40pm UTC](https://community.cartalk.com/t/final-drive-ratio/21806/3 "2008-11-07T23:40:57Z")

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Looks like an 11.5% difference in RPM at any speed. These sound like common Ford RWD ratios…

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**Author:** ![oldschool](https://avatars.discourse-cdn.com/v4/letter/o/e19adc/32.png) [@oldschool](https://community.cartalk.com/u/oldschool)\
**Post date:** [November 7, 2008, 11:52pm UTC](https://community.cartalk.com/t/final-drive-ratio/21806/4 "2008-11-07T23:52:22Z")

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I have it at 13.5% reduction 3.73(.135)=.503 3.73-.503=3.227

These are common GM rear ratios.