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Axle Ratio/Tire Size Calulator

Convert Metric Tire to Inches : The tire manufacturers played a nice trick on us when they converted tire sizes to metric size - they left out the tire height! So how tall is that new metric tire you bought or want to buy? Will it be near as tall as the 33's you had? This calculator aims to put that right again.

  Convert Metric Tire to Inches

P-Metric Style
Example: 215/75R15
/ R

Inch Style
Example: 31 x 10.50 / 15
x /

Speedo converter : It is common knowledge that your speedo will change if you fit different sized tires, but by how much? This table uses 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).
When purchasing something like Aviva car insurance for your car, it is important to stay safe, legal and covered. The Speedo converter assists you in all three.

  Speedo converter 

Original Tire Diameter:  
New Tire Diameter:    
Speedometer Reading (MPH):  Corrected Speed (MPH): 

Find new Gear Ratio with new tire size : If you fit bigger tires the overall gearing of your truck change - sometimes so much that you loose power and the truck is not happy going uphill or when towing. This calculator will get you back to a ratio that's closer to your original.  

  Find new Gear Ratio with new tire size

New Tire Diameter:  
Old Tire Diameter:  
Current Gear Ratio:  New Gear Ratio: 
 

Crawl Ratio : Crawling is how slow you can go offroad - this is especially "helpful" on rocks - thus the name "rock-crawling". As a rule of thumb you can say you have a decent low range when your crawl ratio is over 40:1, but if you are into real offroading and run bigger tires the aim is to go over a ratio of 70:1. It is not strange to have specialized rock crawlers with crawl ratios in the 200:1 region!. Enter your values on the left side, press Compute and your answer will be on the right. 

 Crawl Ratio

Transmis Ratio:  
TransCase Ratio:  
Axle Ratio:  
Overall Ratio: 

Find MPH : Ever gone down the highway wondering how high the fine will be if you get caught? Or then: ever wondered if you are really traveling the speed your speedo shows? This table will help you get a better idea on the speed you travel at a certain engine speed - bare in mind that the end result will depend on the accuracy of your tire measurements. By knowing your gear ratios and tire size you'll get a more accurate idea here. Enter the value on the left, press Compute. 

 Find MPH

RPM:  
Tire Diameter:   
Axle Ratio: 
Transmis Ratio: 
TransCas Ratio: 
MPH: 

Find RPM : It is always handy to know how fast your engine is turning - even if it is only to know when you approach terminal velocity…Because some of the older vehicles have no rev-counter it might be handy to use this calculator to give you some indication what your engine is dong at certain road speeds.

  Find RPM

MPH: 
Axle Ratio: 
Transmis Ratio: 
TransCas Ratio: 
Tire Diameter:  
RPM: 

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