Gear Ratio
Melting Slicks
Joined: Aug 2016
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From: CLEVELAND STUCK IN OHIO
2024 C3 of the Year Finalist- Modified
Le Mans Master
Joined: Nov 2016
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From: Lake Tahoe, CA
Thread Starter
Intermediate
Joined: Jun 2018
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Thanks a million what a great resource!!!
Instructor
Joined: Feb 2013
Posts: 228
Likes: 67
From: Kennewick WA
Hi all, haven't been on here for a while, long story...
So my Vette (73 L82 w/Auto) came from the factory with 3.08 rear gears and the numbers on the diff confirm, however, when I'm running 60 mph the tach is at 2700 rpms and it feels like it needs to shift to another gear. Car has BFG TAs that website says the are 27.4" tall but when I put the tape on them they measure 26.5" tall from ground to top of tire. So found this website that seemed to work the best in calculating diff ratios based on tire height http://www.advanced-ev.com/Calculators/TireSize/ and it comes out to be 3.549 so 3.55 gear set which makes more sense to me.
Also I've got a doc named "Vette Diff Ratio" from somewhere but don't remember that says:You can multiply miles per hour times 1000 and divide by the engine RPM. For a 3.08:1 the ratio is 25.6, for 3.36:1 is 23.1, for 3.55:1 is 22.2, for 3.70:1 is 21.3, for 4.11:1 is 19.2, and for 4.56;1 is 17.0. Do it at different speeds and in different gears and you should get a pretty good average.
Using this info 1000x60=60000/2700=22.222... so from this info my ratio should be 3.55:1 which matches the website's calc.
Anyway, food for thought.
So my Vette (73 L82 w/Auto) came from the factory with 3.08 rear gears and the numbers on the diff confirm, however, when I'm running 60 mph the tach is at 2700 rpms and it feels like it needs to shift to another gear. Car has BFG TAs that website says the are 27.4" tall but when I put the tape on them they measure 26.5" tall from ground to top of tire. So found this website that seemed to work the best in calculating diff ratios based on tire height http://www.advanced-ev.com/Calculators/TireSize/ and it comes out to be 3.549 so 3.55 gear set which makes more sense to me.
Also I've got a doc named "Vette Diff Ratio" from somewhere but don't remember that says:You can multiply miles per hour times 1000 and divide by the engine RPM. For a 3.08:1 the ratio is 25.6, for 3.36:1 is 23.1, for 3.55:1 is 22.2, for 3.70:1 is 21.3, for 4.11:1 is 19.2, and for 4.56;1 is 17.0. Do it at different speeds and in different gears and you should get a pretty good average.
Using this info 1000x60=60000/2700=22.222... so from this info my ratio should be 3.55:1 which matches the website's calc.
Anyway, food for thought.
