Calculator for drivetrain setups to give RPMs at given speeds

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New member
Nov 5, 2011
Kelowna, BC. Canada

This is a great site for figuring out tire size, gear ratios, and trans setups. You can put in the trans, transfercase, underdrive if you have one then put in tire size and gear ratio hit calculate and it shows rpms at given speeds, speeds given at rpms for each gear. Its a pretty sweet tool.



96 Bronco 5.0
Staff member
Oct 18, 2005
Coronado, CA
yo MIKE, thanks!

And your post reminds me that I have to try & recover more Cals from my archived Site @

select a LINK, Right Click & Hit Properties; copy the the second HTTP address; paste in a new browser to see current page

Here are some for example;

Automotive Calculations By Bowling & Grippo

Aerodynamic and Rolling HP Loss Calculation

Compression Ratio Calculation

Miles-Per-Gallon Estimation Calculation

Speedometer Gear Calibration

RPM & MPH Correlation

Best Differential Gear

Best Header

Battery Cold-Cranking Amp Estimation

Battery Cold-Cranking Amp Temperature Adjustment

Compression Ratio Influence

Engine Displacement Calculation

Driveshaft Velocity Calculation

Roadway Vehicle Dynamometer

ET and MPH Environmental Correction

Cylinder Head Flow Correction

Holley Carburetor Jet Program

Intake Runner Harmonic Pulse Prediction

Fuel Injector Sizing Program

Rough Engine Horsepower Estimation Program

RPM Range Program

Optimum Shifter Program


Gear Ratio Guide for Larger Tires; Scroll Down or Click, Another RPM/Gear Ratio/Tire chart if site reverts to main page; MIESK5 NOTE, Rough Country® removed this same chart from their site in FEB 2011 & company rep said it isn't there anymore.
Source: by Rough Country® via broncocity chart


Pit Bull Tire Company

Crawl Ratio
Gear Ratio (new tire diameter & gear ratio)
Metric Tire Conversion

Miles Per Hour (MPH) (tire diameter, RPMs, axle ratio, transmission & transfer case ratios)

RPM (axle ratio, transmission & transfer case, tire diameter)
Speedometer Calculator, by Tire Diameter

Kelly's Hotrod

Note: Calculator forms tested under MS Explorer 4.0 and 5+. Operation unsure under NetscapeCompression Ratio/Displacement

Calculate Air Requirements in CFM

Estimated Optimum 1/4 ET from 1/4 mile speed

Estimate HP from 1/4 mile speed and weight

Estimated 1/4 ET from rear wheel HP and weight

Estimated 1/4 speed from rear wheel HP and weight

Estimate HP from 1/8 mile speed and weight

Estimated 1/8 speed from rear wheel HP and weight


Currie Enterprises

3rd Member Calculator
Build your Custom Third Member online using our Third Member Calculator! Works for any 9" application!

Ring Gear/Pinion Gear Teeth to Gear Ratio
Enter the # of Pinion Gear teeth and the # of Ring Gear teeth to find the correct Rearend Gear Ratio for your Rig!
Differential Gear Ratio Calculator
Calculate your differential gear ratio from RPM, tire size and desired MPH.

Find Overall Crawl Ratio
Figure out your off-road 4x4 crawl ratio based on transmission, axle and transfer case ratios.

Find out your engine's Revolutions Per Minute based on other engine criteria, tire size and rearend ratios.Find MPH
Find out how fast your vehicle can move based on engine criteria, rearend ratios and tire size.

Speedometer Converter
When you buy bigger or smaller tires, your speed will change. Enter the diameters of your new and old tires, then enter a speed and see the difference!

Find New Gear Ratio with New Tire Size
Buying bigger or smaller tires? Then you might need to change your gear ratio to keep up! Enter your new tire diameter, your old tire diameter and your present gear ratio to find out your new gear ratio.

Convert P-Metric Tire to Tire Diameter Inches
Convert the funky P-Metric Tire # (Example: 195/75R15) on the side of your tires to Inches, so you can use more of these rearend calculators!

West Coast Differentials

Differential Gear Ratio Calculator - Enter the number of teeth on your ring and pinion gear set to find the gear ratio. Example: Ring Gear / Pinion Gear = Ratio

RPM Calculator - Use the RPM calculator to determine what RPM your engine will run based on gear ratio, tire diameter, transmission and MPH.

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