I have an '05 F150 that came with P255/65/R17. I just put Goodyear P265/70/R17s on today and was wondering if anyone could tell me about how much off that's gonna put my speedometer and if there are any adverse effects it might cause.

 

Well your new set of tires are 1.5 inches larger in diameter now. When you speedometer reads 65mph your actually traveling at approximately 68.5mph. And your revolutions per second will be less than before so you'll actually have more miles on your truck than what its showing you. But that difference is minimal, I think its like half a revolution a second at 65mph.

You can get the speedometer reflashed at the dealer to accomodate the new tires or you can get a tuner/programmer that will do the same.

 

for your answer.

 

Go to this Link and plug in your "before" and "after" Tire Info.. all your questions wwill be answered. A handy Site to bookmark..

http://www.discounttiredirect.com/di...foTireMath.jsp

 

I've got the same s/u on my 05'. I personally wouldn't worry about the speedo being slightly off, esp paying to reflash the pcm.

 

1buddyc....I tried the website...that's pretty neat, and no, I don't think I'm going to bother with reflashing. I ain't a fast driver anyway.

thanks, y'all

 

What do you think is a reasonable charge to reflash the PCM? I can't imagine it is hard for the dealer to do, but they do like to charge for everything.

 

Check the website link that 1buddyc referenced.
It will tell what your actual speed is relative to what your speedometer reads and you can figure what your actual mileage reading should be from the difference in the circumference of the two tires.
I don't have any idea what a dealership would charge but I'm sure it's too much so I'll just adjust my driving habits.