Speed difference

PoPo8 · #1 (**permalink**) 07-05-2010, 11:49 AM

When I put 305/70/16 on my 2001 f350 how far off will my speedo be off?

**cubalz** · #2 (**permalink**) 07-07-2010, 05:42 AM

It really depends on what came stock on the truck. I am going to say a fair amount but you can go to the Ford dealer and they can recalibrate it for a couple of bucks.

kylev90 · #3 (**permalink**) 07-07-2010, 06:13 AM

I put 305/75/16 on both my reg cab 250 and my cc 250 (both OBS) but my speedo was only knocked off about 2 MPH

**terryknight** · #4 (**permalink**) 07-07-2010, 06:16 AM

RPM = (MPH * gear ratio * 336 (constant)) / tire size (tire diameter)

This is for the gear that is 1:1 which I'm assuming is fourth or you can multiply it by your overdrive ratio to figure it out in overdrive

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