2005+ gt wheels/tires speedo reading

[ncth282]

I have a 2005 mustang v6 and I just ordered the 2005+ mustang gt takeoff wheels and tires (the stock 17" bullit wheels and the pirelli 235/55/17 tires). I have the stock 16" wheels and tires that came on the car and I was wondering if the speedometer reading will be off with the new wheels and tires. I found an online calculator that says itll be off by 6% reading 60mph when I'm doing 60.4mph which doesnt seem like much at all but will I need to recalibrate it or not? And does it effect the odometer too by adding less miles than I really went.

I realise this question has probably been asked many times so just link the thread if you know of one. I searched and couldnt find a thread specific to this problem. Thank you

 

[glewis29]

Yes, it will tell you that you're going slower than you actually are.
Yes, it will add less miles on the odometer than you've actually gone.
I believe it can be fixed by using a reflashing computer like a Predator or SCT. (But I've never done it myself)

P.S. 6% would be closer to 3.6 MPH off at 60.

 

[ncth282]

Thanks, my friend said it really doesnt make a big difference, idk if the 6% is accurate. Anyone do this mod to their v6 and recalibrate their speedo? Is it necessary, and would I be better off bringing the car to ford to have the recailibrate it or to just buy a tunner/flash chip because I'm probably going to end up buying a tuner soon anyway.

 

[ncth282]

using this calculator http://www.miata.net/garage/tirecalc.html I put in the stock v6 tire size 215/65/16 and the tire size of stock gt tires im getting 235/55/17 and it says the reading will be .6% too slow not 6% sorry. This seems so small but it also means for every 50,000 miles I go the odometer will register 49,700 miles. or 6 less miles for every 1000 miles I really treveled. This seems so small still but I'd like to fix it anyway if it can be done reletively inexpensivly or if ford would do it for free (my car is still under warantee)