How many mph does 38 inch tires throw off a speedometer? the truck is a 93 ford ranger?

3 Responses to How many mph does 38 inch tires throw off a speedometer? the truck is a 93 ford ranger?

1. Tony H says:

   December 12, 2011 at 11:37 am

   about 15 mph

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2. Ron H says:

   December 12, 2011 at 11:47 am

   The r on the tires is for radius. You need the original and new radii.

   Use the r from the original equipment tire. Let’s say r1 is original and r2 is the new tire radius.

   (r2)/(r1) = k

   Multiply each number by k, write it down the adjusted number and tape it to your dash board.

   Make a MPH table

   speedometer, actual speed
   10, k*10
   20, k*20
   30, k*30
   40, k*40
   50, k*50
   60, k*60

   Reply
3. MUSTANG_MAN says:

   December 12, 2011 at 12:30 pm

   I would need the diameter or height of the old tires too.. I ‘m guessing add over 20mph. another way is check it against a GPS unit, they are very accurate.
   but you can use this calculator to find it..

   27 to 36 makes 19 mph faster

   http://www.csgnetwork.com/speedocalibcalc.html

   Reply