195/75/14 and 2.41s to 255/60/15 with 3.23s Questions.

[MrSony]

Hello. I've been doing the math, and currently at 75mph with 2.41 gears and 195/75/14 tires I'm at 2500rpm on the highway in third gear (Drive). Eventually, hopefully even this year, I want to beef up my rear end (7.5) with a girdle, 28 spline axles, and 3.23 gears. Along with getting 235/60/15 cooper cobra tires up front and 255s out back with the 15x7 aluminum t type buick wheels. With the gear change and going to a larger tire, my math puts me at 2500 rpm on the highway, just like before. Because the gear is still steeper, will there be any difference at all? One would think that if the rpm at speed is the same, at low speeds it would be the same as well. IS this true? Also, is 255 to big for that wheel? I'd go 235s all around if it is. I'm not a fan of sidewall bulge or stretching tires. Nice and even is my thing.

 

[MrSony]

DISCLAIMER: I am very tired. My math may be very wrong.

 

[Streetbu]

It will act exactly the same, just with more traction. A 255 is too much for that wheel. It will fit, but you'll find the middle of the tire will wear out first. I've done it with Z28 wheels and that size tire. I recommend lowering the tire pressure to about 25psi and it helps.

 

[motorheadmike]

A 255 is a great tire for that wheel, do you know what is even better? A 275/60R15, that's what.

I have run both with great success on 15x7 T-type wheels.

 

[UNGN]

255/60's work fine on a 7" wheel as will 275/60's (but not as well as 255/60's). I wouldn't recommend either if you want to get 30K miles out of them, but my tires generally time out before they mile out.

275/60 are without a doubt, the ABSOLUTE best Drag Radial tire size for a turbo Regal with stock T-type wheels for straight line traction and 1/4 mile ET/MPH.

255/60's work better on the street for everyday driving.

If you are currently @ 2500 RPM at 75 mph with 2.41 gears and 195/75R14's (814 Revs/mile), you'll be at 3,165 RPM with 3.23 gears and 255/60R15's (769 revs/mile)

Math: 2500 X (3.23/2.41) X (769/814) = New RPM

 

[MrSony]

255/60's work fine on a 7" wheel as will 275/60's (but not as well as 255/60's). I wouldn't recommend either if you want to get 30K miles out of them, but my tires generally time out before they mile out.

275/60 are without a doubt, the ABSOLUTE best Drag Radial tire size for a turbo Regal with stock T-type wheels for straight line traction and 1/4 mile ET/MPH.

255/60's work better on the street for everyday driving.

If you are currently @ 2500 RPM at 75 mph with 2.41 gears and 195/75R14's (814 Revs/mile), you'll be at 3,165 RPM with 3.23 gears and 255/60R15's (769 revs/mile)

Math: 2500 X (3.23/2.41) X (769/814) = New RPM

Thanks man.

 

[motorheadmike]

My all-time budget tire and wheel combo are T-type wheels with 215/65s and 275/60s.

 

[gbodytoys]

RPM Calculator

Also gives you a final gear ration number based on what transmission you run

https://www.ringpinion.com/calculators/Calc_RPM.aspx

 

[SRD art]

I've run both 275-60 BFGs and 275-50 Drag radials on 15x7 rallies without issue. The wider the tire the more a 7" wheel will suck it in. 235s are about perfect for that wheel.

If I'm understanding your question you want to know if performance will change down low? I had 2.41s in Pumkinator's stock rear. The engine was a little bit warmed over 406 small block backed by a stock TH350 and 1800 stall converter, and the car weighs 3700 with me. I ran consistent 14.60s @ 97 mph at ~ 3000 ft altitude on the 275-50 Drag radials. When I swapped in the 3.42 GN rear the car ran 13.90 @ 98 with no other changes. I went from about 2200 around 65 mph to 3000 at the same speed.

A 195-75-14 is 25.5" while a 255 is 27.1". If you kept the 195s you'd be at 78 mph at 2500 w/ 2.41s compared to 58 mph with the steeper 3.23 gears. With the 255s and steeper gears you'd be at 62 mph @ 2500 and about 3200 for 78mph, so even with the taller tires you gain about 700 rpms to match speeds between the 2.41s and 3.23s. The taller 255s final gear ratio drops to about 3.05 gear compared to a 195 with 3.23 gears. The difference is roughly 5% if all my math checks out.

This website has a bunch of cool calculators. http://www.wallaceracing.com/Calculators.htm