Tire ?

If you keep the stock GT tire size(245/45R17) then your speedometer will be fine. You can always check what the overall diameter of the wheel and tire is using the numbers from the tire with the following formula:

[width(1st #) x profile(2nd #)/100 x 2] / 25.4mm/inch + wheel size(3rd #) = overall diameter in inches

So,
GT overall diameter:
(245 x .45 x 2)/25.4 + 17 = 8.68 + 17 = 25.68

v6 overall diameter:
(225 x .55 x 2)/25.4 + 16 = 9.74 + 16 = 25.74

So, the difference is only 0.06 inches which is not enough to make a significant difference in your speedo.

it makes a .07% difference! thats huge!

mreric:

I recommend you take a look at tirerack.com. They have some good deals. If you cannot afford those and want used ones check out ebay and stangnet partshopper/trader. Good luck

Doc

I just put a set of Steeda Ultra Lite II wheels on my girlfriends 2001 Mustang V6. The wheels are 18 x 9.5 all the way around. I put 245/40/18's on the front and 275/35/18's on the rear. In the front i installed a set of steering limiters that cost less than $3 from steeda. They clip onto your inner tie rod ends inside the rack and pinion and keep the front wheels from turning to much and causing the wheels to scrub suspension parts. There is alot of clearence in both the front and rear and give the car an awesome appearence. Other than exhaust sound it looks just like a GT since I also put GT bumper covers on the car. To be honest now that I have the tires on the car I wish I went with a 255/40/18 in the front to give alittle more squarness look seeing the wheels are very wide and with 245's the tires seem to round over if you know what i mean. Still looks bad ass.

You can also find great tire prices at GEF Racing at www.gefracing.com THey are local for me and are the best price wise on all rims!