Hey everyone, I am hoping someone can help me figure out what gearing my truck has. I have an 01 f250 V10/auto. I have 35" tires. My RPM's at 70 (GPS not speedometer) are about 2250 or so. I am pretty sure the gearing is not stock. Anyone with a similar setup have any idea? Thanks!

 

Using a calculator:

2250 / .7 / 4.88 * (35 * 3.1415946) * 60 / 12 / 5280 = 68.58MPH

2220 RPM / OD ratio / gear * (tire diameter * PI) * (minutes per hour) / (12 inches to convert to feet) / (feet in a mile to convert to MPH)

 

😮😮 well done sir! Thanks for the help! I will double check my speed and rpms to confirm but this helps a lot!

 

Happy to help

 

Something else I am trying to figure out- my tach rpm in the truck reads higher than my sct x4 tuner by 80-100 rpms.. which is more accurate?

 

The tuner would be more accurate, but may not update as fast as the gauge.

 

One more question- I calculated the rpms at 70 with the tuner at 2170 rpms. I hand measured the tires and they are actually 33.5" talll.. thanks!

 

Measure them side-to-side not top-to-bottom - the bottom of the tire does compress a bit unless they're aired up to the max (and even then).

Otherwise, it makes more sense that you'd have 4.55's or even 4.30's.