Axle Ratio/Tire Size Calculators - Version 1.4 - - Off-Road.com

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Axle Ratio/Tire Size Calculators - Version 1.4

Publish date: Dec 1, 2005
By: Mark Medina
Source: Off-Road.com

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Updated: Feb 12, 1998
By Mark Medina, http://www.4lo.com

I've made a few changes to these calcs. By popular request I've made the majority of these work to find any one value if the other values are known. By doing this I've combined the MPH/RPM/CrawlRatio calcs into one. Also, I've included some of the tran smission/transfercase ratios that I could find. This page uses JavaScript and thus should be compatible with Netscape 3.x and MSIE 3.x or higher. If you notice problems, send me Email with a description of the problem and the browser name and version being used.

Don't have a JavaScript capable browser?
Jump over to the
Gear Table - Transmission Ratios - Transfer Case Ratios
for similar information in printable form.

These calculators are color coded by function
All Blanks Required	Find Any (one) Missing Value	Output Only

I've spend a bunch of time trying to WAG (wild ass guess) my actual MPH when going down the road. By knowing your gear ratios and tire size you'll get a more accurate idea here. Enter all values exce pt the one you are trying to find (in green section). If you'd like to find your overall crawl ratio, enter the Diff/Trans/TransfCase ratios. This calc can be used to find any missing value.

Now that you have your truck lifted, you want bigger meats. They look cool and have the potential of being very functional, but they may also be robbing you of power/gas mileage. This calculator will get you back to a ratio that's closer to your original. Enter your old and new tire diameters and your current (stock) differential gear ratio. The values on the right (in yellow section) will show the "actual" gear ratio before upgrading gears and the recommended new gear ratio. The recommended New Ratio is based on getting the vehicle back to a stock gear ratio. If you do mostly city/highway driving the "hi" value may be best. If you tow, go rock crawling, or just want more low end power then use t he "lo" ratio.

Most of the formulas on this page use tire diameters (in inches). This formula is a nice way to get the tire diameter of those metric tires that are common on just about everything stock. For example a 265/75R16 would be around 31.6 inches tall. Enter the numbers into this form in the order you read them from the tire.

Example: 195/75R15
/ R = Tire Diameter:

Okay, so you've torn your pumpkin apart and have the ring gear and pinion gear teeth count. This calculator will give you the gear ratio, just plug in the numbers.

Ever wonder how far off your speedometer is with your new bigger tires? I'm using a simple ratio calculation, so this info will only approximate your corrected speed and depends on the accuracy of tir e size diameters (assumimg nothing but tire size has changed). If you know specific information about your vehicle's gear ratios, RPM, etc., then use the "Find Gear Ratios, Find MPH, Find RPM" calculator above.

Send me your formulas for "useful" calculators and I'll build em.

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