31x10.5 with 3:73 gears.700R4 trans. What RPM will I have at 70MPH?

[Nasty-LSX]

I know the final gear ratio on the 700R4 is 0.696. Or 0.70
So I got a k10 with 350 and 700R4 with a rear axle
ratio of 3.73. I would Like to see 1800 to 2000 RPM
at 70/75 MPH. So looking to get the right tires. Thanks!!

 

[Camar068]

online calculators

 

[waterpirate]

Any side street. lol
Eric

 

[Bloodhound1981]

About 1970 RPM at 70mph. That's the exact setup I have. Works great.

 

[Hunter79764]

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

2000 RPM is 71 MPH. Your exact tire will affect it of course, and that assumes you have the lockup working, as well. Going to a 33" gets 75 mph @2000 rpm, for example.

 

[Nasty-LSX]

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

2000 RPM is 71 MPH. Your exact tire will affect it of course, and that assumes you have the lockup working, as well. Going to a 33" gets 75 mph @2000 rpm, for example.

Awesome man, Thanks!!

 

[gmbellew]

This is the best calculator I have found

Gear Ratio Calculator

 

[justhorns]

Its simple. For each 1 engine rotation, the driveshaft will turn 1/0.696=1.43 times
The rear end lowers the rotation from 1.43 to .383 wheel rotations (1.43/3.73). So, multiply your 0.383 by the circumference of the tire 97.4" for a 31 (approximately, but go and measure your own with a tape measure). So 1 rotation of the crankshaft will take you 37.3". 2000 rotations take you (2000*37.3") or 74,608 INCHES. How many inches in a mile? (5280*12=63,360 inches) so, 74608/63360 is 1.17 miles. 2000 rpm will take you 1.17 miles, or 2000 rpm is 60/1.17 or 51.2 mph at 2000 rpm (the minutes drop out in the calculation). Put your own tire circumference, overdrive ratio and rear end in this calculation and there you go. Tell me how math compares with the online calculators.. Ha!
Did I screwup somewhere?

 

[justhorns]

Oh, you want RPM at 70-
(70/51.2 mph)*2000= 2734 RPM at 70 mph

 

[justhorns]

Your rear end should be (2000/2734) * 3.73 = you need a 2.72:1 rear end for 70 mph at 2000 rpm. Look at tire circumference to refine this calculation.

 

[Bloodhound1981]

Oh, you want RPM at 70-
(70/51.2 mph)*2000= 2734 RPM at 70 mph

I got lost in your math, but I assure you that with 3.73s, 31in tire, and a 700R4, it is 1950-2000 rpms at 70mph. I know because I have it.

 

[gmbellew]

I got lost in your math, but I assure you that with 3.73s, 31in tire, and a 700R4, it is 1950-2000 rpms at 70mph. I know because I have it.

I have 33x10.5 (spec is 32.5in, probably actually 32in, or a little less rolling diameter), 3.73 ratio, and a 700r4. my RPM at 70mph is about 1950rpm and at 75mph is about 2100rpm for flat land cruising.

Using the grimjeeper calculator, 31in tires (rolling diameter might be 30.5in?), the rpms at 70mph will be 2013rpm and at 75mph will be 2157rpm.

 

[Old Guy Bill]

It’s not the height of the tire it’s the circumference