Final drive ratio question!
Thread Starter
Burning Brakes
Joined: May 2009
Posts: 1,014
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From: Ft Wayne IN
Final drive ratio question!
I had 275/40/18 rears and just went to 285/40/18. I have 3:07 gears and a 700r4. My question is I know I lost a little lowend and am looking into a Dana 36 to 44 swap. Not sure what ratio would get me back to the same final drive that I had with the smaller dia. tires. I would think 3:45's would be close? Then I was thinking sense I am going to the trouble and cost I would like even a little higher final drive ratio than I originaly had i.e. taller gear. Would 3:55's do the trick or is the diffrence between 3:45 and 3:55 not noticable?
1.) What was my original final drive with 275/40/17's and then with the new 285/40/18's?
2.) What will 3:45's/3:55's/3:73's change my current final drive too and is there a way to equate a change in final drive ratio to rpm change?
3.) Recomendations ?
THANKS!
1.) What was my original final drive with 275/40/17's and then with the new 285/40/18's?
2.) What will 3:45's/3:55's/3:73's change my current final drive too and is there a way to equate a change in final drive ratio to rpm change?
3.) Recomendations ?
THANKS!
Last edited by C4vettrn; Sep 29, 2012 at 09:12 PM.
Safety Car
Joined: Aug 2009
Posts: 3,751
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From: Melbourne, Victoria, Australia
Hi the T700 has a great first gear for standing starts, that would suit a tractor pulling tree stumps.
I have 275/40/17 all round with 3:07 gears. Even before adding the blower she would break traction first and second gear very easily, if you have a 275/40/17 tire compare it to your 18 inch tire heights.
There should be little difference, also check your RPM at a particular speed or check your actual speed with a GPS it should only change a small amount.
My vette sits at 1900 rpm at 100 kmh (around 62mph) and 2100-2200 rpm at 110 kmh (68/70 mph with the 275/40/17 tires and dash shows the exact same speed as my GPS.
I have 275/40/17 all round with 3:07 gears. Even before adding the blower she would break traction first and second gear very easily, if you have a 275/40/17 tire compare it to your 18 inch tire heights.
There should be little difference, also check your RPM at a particular speed or check your actual speed with a GPS it should only change a small amount.
My vette sits at 1900 rpm at 100 kmh (around 62mph) and 2100-2200 rpm at 110 kmh (68/70 mph with the 275/40/17 tires and dash shows the exact same speed as my GPS.
Last edited by gerardvg; Sep 29, 2012 at 09:32 PM. Reason: more info
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http://www.angelfire.com/fl/procrastination/rear.html
Instructor
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From: Reno Nv
Tire Size Comparison
Specification. Sidewall. Radius. Diameter. Circumference. Revs/Mile. Difference
275/40-18. 4.3in. 13.3in. 26.7in. 83.8in. 756. 0.0%
285/40-18. 4.5in. 13.5in. 27.0in. 84.7in. 748. 1.2%
Specification. Sidewall. Radius. Diameter. Circumference. Revs/Mile. Difference
275/40-18. 4.3in. 13.3in. 26.7in. 83.8in. 756. 0.0%
285/40-18. 4.5in. 13.5in. 27.0in. 84.7in. 748. 1.2%
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I had 275/40/18 rears and just went to 285/40/18. I have 3:07 gears and a 700r4. My question is I know I lost a little lowend and am looking into a Dana 36 to 44 swap. Not sure what ratio would get me back to the same final drive that I had with the smaller dia. tires. I would think 3:45's would be close? Then I was thinking sense I am going to the trouble and cost I would like even a little higher final drive ratio than I originaly had i.e. taller gear. Would 3:55's do the trick or is the diffrence between 3:45 and 3:55 not noticable?
1.) What was my original final drive with 275/40/17's and then with the new 285/40/18's?
2.) What will 3:45's/3:55's/3:73's change my current final drive too and is there a way to equate a change in final drive ratio to rpm change?
3.) Recomendations ?
THANKS!
1.) What was my original final drive with 275/40/17's and then with the new 285/40/18's?
2.) What will 3:45's/3:55's/3:73's change my current final drive too and is there a way to equate a change in final drive ratio to rpm change?
3.) Recomendations ?
THANKS!
You "felt" I doubt any difference - everything is "assumed"!
The calculators in post #3 should entertain you sufficiently for some time!
Something you didn't ask and if you've corrected it already fine but I believe a 40 tooth driven will correct your speedometer as closely as possible without changing the VSS. That's based on a very rough calculation of "rolling radius" of the 285/18. You can't use "advertised" diameters for accurate speedometer calibrations.
Last edited by WVZR-1; Sep 30, 2012 at 06:03 AM.
