Final drive calculator

[Astro]

Hey guys,

How can I accurately calculate my rpms and final drive?

I want to gear my truck, but want to make sure I put in the right gears and not sacrifice too much too end. Want to see what my rpms would be like around 75 mph.

I have 35's, a 4L80, and 3.73s at the moment and was thinking of swapping to 4.56.

Thoughts and advice?

 

[Caman96]

Google a final drive calculator.

 

[Sean Buick 76]

Engine RPM / Engine Speed Calculator

Crawlpedia's RPM and Engine Speed Calculator will find your engine RPM at any speed given your transmission ratio, ring and pinion gear ratios, and vehicle speed.

www.crawlpedia.com

The 4L80E 4th gear ratio is listed on here as well.

You would be at 2400 rpm at 75 MPH with the 4.56 and 2200 rpm with a 4.10 gear.