C4vettrn

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!

gerardvg

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.

bjankuski

The difference is 5 percent so 3.23 would be the same ratio.

vetteoz

Play with the numbers
http://www.bgsoflex.com/rpmmph.html

http://www.angelfire.com/fl/procrastination/rear.html

envirotrans

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%

WVZR-1

Your text "comments" don't match the "numbers" in your questions but with complete disregard to your "text" and using that in question #1 - Your original final drive was 3.07 and the introduction of the larger nearly 27" tall tire your current final drive is 3.04.

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.

C4vettrn

I Had 275/40/17's and went to 285/40/18's.
I will play with the thread sent, thanks for the help guys.