This calculates the effect of tire size on the speedo.

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

What is the proper ratio needed to correct for those tires, and since none are available it is more like a how far off will I be. 

  Find new Gear Ratio with new tire size 
New Tire Diameter:  
Old Tire Diameter:  
Current Gear Ratio:  New Gear Ratio: 

This still applies to us. If using large tires you may be more effective engaging low ratio permanently and shifting 2wd and 4wd alone.

  Find Overall Crawl Ratio 
Transmis Ratio: TransCase Ratio: Axle Ratio:  Overall Ratio: 

Another speed calculator, helpful for making a new speedo face.

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

And for you DL folks with no Tach.


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

Convert the stock tire to 23 inches all day long.


  Convert P-Metric tire to Tire Diameter inches 
Example: 195/75R15 
/  R 
Tire Diameter: 

Coded by the good folks at 4Lo!