Speed difference - Ford Powerstroke Diesel Forum

Suspension & Steering Discuss OEM & aftermarket suspension, lifts, air ride suspension, shocks, steering components, etc.

 
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post #1 of 4 Old 07-05-2010, 11:49 AM Thread Starter
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Speed difference

When I put 305/70/16 on my 2001 f350 how far off will my speedo be off?
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post #2 of 4 Old 07-07-2010, 05:42 AM
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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.

2004 F350 6.0L Power Stroke Diesel
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post #3 of 4 Old 07-07-2010, 06:13 AM
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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

1997 CC SB. Stage 1s, 17*hpop, S&B CAI. 4" straight pipe, TW tunes, zf5 swap
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post #4 of 4 Old 07-07-2010, 06:16 AM
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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

94.5 F250 Reg Cab 4x4 5 speed 4.10 276000 plus miles

97 F350 Crew Cab LB 4x4 5 speed 3.55 320000 plus miles (parts truck)



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