So if I go from a 255/65/17 to a 265/70/17 how much of a difference do you think there would be from the speedo to actual speed?

 

5.2% - when your speedo shows 60 your actual speed will be 63.1

Here's a handy calculator for these calculations http://www.rimsntires.com/rt_specs.jsp

 

255/65/r17 revs/mile 671....265/70r17 638 revs/mile

 

Wow! That's more of a difference than I thought. Let me guess, the only way to correct this would be a programmer?

 

Actually a dealer may be able to reprogram your ECM for the new tire size. I've heard they have some limits but definitely worth looking into. Probably an hours labor at most - a lot less than a programmer would cost you.

 

It's a lot less, yes, usually about $100, but that is money that could be put on a programmer that makes the truck run and shift like it should. plus, next time you change the tire size, you have it.

 

actually you're speedo might be correct now. the stock speedos are about 1-2mph fast, i wouldn't waste the money to fix it. unless of course you want to use this as an excuse to get a programmer lol

 

Well I must admit If there is a significant difference in speed than I may definitely want it corrected. If it's only a mile an hour than I could live with that. Plus, I'm not sure A programmer would be worth the money. I have heard of others with the V6 getting one but, I'm not sure I'd benefit as much having the man tran.