I have noticed that the faster I go the more difference there is between how fast i really am going and what the speedo registers
according to my speedo I am going 35 but actually going 34
when registering 45 actual is 43.
When registering 75 my actual speed is 72

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2009 Liberty Sport, Black, Polished Aluminum Nerf Bars, Popular Equipment Group, K&N Cold Air Intake, Stage 1 Jet Chip, Magniflow Muffler

That's because your Speedometer - Actual speed is not a linear relationship, but an exponential one.

Short answer; the rolling diameter of your tires is smaller than your vehicle is programed to think it is. Your wheels are not traveling 3x faster, but rather 3% faster.

Long Answer;
The Revolutions/mile on my stock tires (235/60R18) = 693
The Revolutions/mile on my winter tires (235/65R17) = 695

My Liberty thinks that the tires revolve 693 times for every mile traveled, but when my winter tires are on, they are revolving 695 times.

This is a difference of 2.8%. For every MPH, the difference will be 2.8% speed.

30MPH SPEEDO READING = 30mph x (1 - 2.8%) = 29.91mph ACTUAL speed. Difference of 0.09 mph
70MPH SPEEDO READING = 70mph x (1 - 2.8%) = 69.79mph ACTUAL speed. Difference of 0.21 mph
500MPH SPEEDO READING = 500mph x (1 - 2.8%) = 498.561mph ACTUAL speed. Difference of 1.44 mph

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2008 Jeep Liberty (KK) Ltd