Speedometer off?

How did you go about calculating revolutions per mile? A simple calculation of (63360)/((Tire Diameter)(Pi)) is not the correct way to do this. Read some of the manufacturer numbers and you'll see it is different due to side wall flex and loading.

 

Not enough to make a 5 mph difference....

Actual diameters of both tire installed for the dyno run and the OEM are 1/2 inch difference when measured both in the air (unloaded) and mounted abd on the ground with the same tire pressure cold.

You guys are arguing just for the sake of arguing.

 

I gave you the actual measurements of the OEM tires delivered with my truck and the aftermarket tires tested to compare so we have actual values, 1/2 inch difference.

 

does this account for deviation based on the weight of the truck?

 

In the air and on the ground with the same tire pressure, same difference in measurements, 1/2 inch overall so sidewall flex is the same.

 

My speedometer reads 3-5 mph high with stock size tires. It was very troubling to find I was going too slow.

 

Go by the digital,and same with temp, one on speedometer is outside, the one on display is weathet channel generic

 

I heard if you change your blinker fluid and then reset the flux capasitor bearing, the speedo will be dead on.

Just stay with the flow of traffic. You'll be fine.

 

I had the opposite of the OP. My digital reads slower than my analog by about 2mph