Picking rear gears

[Tc77]

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator

That’s what I am getting with the spicer calculator. Maybe the math is off.

 

[fleming442]

Wallace racing says 2500 would be 82mph, so have at it.
What tire is 29.5, though?

 

[CaliWagon83]

Well, I’m coming from the context of 26” tires. 29” tires change (lower) the overall RPMs.

 

[olds307 and 403]

I ain't buying it. Something isn't right. My 4L60e is at 2500 at 80 on 26.4" tires with a 3.42

Exactly, about 300 rpm too high even at 2800 rpm with a 29.2" tall tire. Try this calculator, very accurate with the converter locked up.
http://tech.oldsgmail.com/axle_RPM.php

 

[Qdub24]

I've used these calculators for mine in the past

www.summitracing.com/newsandevents/calcsandtools/gear-ratio-calculator

www.randysworldwide.com/calculators/rpm

 

[airboatgreg]

I just did this and I put a 3:70 to pair with my Muncie 4 speed. I drive 60 miles a day to work and back but my car is not a daily driver. I went from a about a 2:80 stock and it made a new car out of it. What do you want? Mileage, performance? You have overdrive so that is a plus. Hard to beat a 370ish gear but with OD you easily can go a 342ish.
Do you drive in a hilly area? Downshifting an issue? or is terrain flat? Gas is relatively cheap now but I expect it to increase so that may be a consideration.

 

[MrSony]

At 75mph with my 26.1 tires and 3.42s I'm at 3300rpm, and it's not bad, sound wise, but it's annoying and puts unnecessary stress on an otherwise low strung engine. .67 O/D of a 200r4 would put it at 2200. Much More livable.
29.2" tire, .67 O/D, 4.30 at 75mph calculates out to 2486rpm for this calculator. Always been accurate +/-100 rpm for me.
https://www.crawlpedia.com/rpm_gear_calculator.htm

 

[Bonnewagon]

What tire is 29.5, though?

This. https://www.jegs.com/i/Mickey-Thompson/672/3455/10002/-1 A BIG tire for sure. Still would not justify 4 series gears though.

 

[Texas82GP]

I calculate 2790 RPM at 85 assuming 0.67 overdrive (please confirm), 29.5" tires, and a 4.30 rear gear. I think that's about right. My daily driver turns 2500 at 80 and 3000 at 95. It's a truck with 4.11 rear and nearly 32" tall tires (275/55/20). It has a 3400 stall and I mush it down the highway at 85+ with no issues.

2.74x4.30=11.72 final drive ratio in first, seems steep but that really tall tire will mitigate it. Looks like a reasonable setup to me.

 

[565bbchevy]

This. https://www.jegs.com/i/Mickey-Thompson/672/3455/10002/-1 A BIG tire for sure. Still would not justify 4 series gears though.

If they are M/T 295/65R15 then they are 30" tall, I had them on the back of Monte but felt they were too tall and that was with 28" front runners.