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Axle Ratio/Tire Size Calculators - Version 1.4


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.
  Find Gear Ratios, Find MPH, Find RPM

RPM: Tire Diameter:
Diff Ratio: Trans Ratio: TransfCase Ratio:

MPH:
  Crawl
  
  Ratio

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.
  Find New Differential Ratio (with tire size change)
New Tire Diameter:
Old Tire Diameter:
  Current Gear Ratio:   Actual
  
  Ratio

Hi Ratio:   
New Ratio:   
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.
  Convert P-Metric tire to Tire Diameter (inches)
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.
  Ring and Pinion

# Ring Gear Teeth: # Pinion Gear Teeth: = Gear Ratio:


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 tire size diameters (assuming 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.
  Speedometer Check

Original Tire Diameter:
New Tire Diameter:
  Speedometer (MPH): Actual (MPH):