How far is my speedometer off after putting 33x12.5x17 tires on my truck. before i had the stok chrome 17" wheels. i can tell there is a difference, but the only real way to find out would cost me about $200, that would need to be paid to the County. not how i want to know. is there some sort of calculation to use?

 

What size were your tires originally?

 

I don't think it's enough to have to worry about but I could be wrong. Sorry not much help

 

It would probably be a 2 MPH difference fo to discount tires website and use the calculator it should say how off it will be.

 

Figure the circumference of your stock tires, then the circumference of your new tires. After you get those two numbers take the circumference of the New tires/circumference of the stock tires. This number should be over 1.0 after that mulitply this number times your old cruising speed to find out what the new cruising speed is.

 

You can also do diameter of new tires/diameter of old tires. It'll give you the same ratio and the diameter is a bit easier to find than the circumference.

 

^You can also multiply the found number by the your calculated miles per gallon to get the corrected MPGs

 

Wow... All the science here... Why don't you just plug in a portable GPS unit and look at how fast your going ?..... GPS is actual speed....TOO EASY !

 

If you had the 255/70/17s (like I did on my 06 2WD) and switch to a 33" tire, its about an 8.5% difference. Your speedo when you're doing 60 is in reality about 65mph, at least that's how mine was from the stocker 30s to 33s

 

It's like 4-5mph off...