Buying Rear Tires Tomorrow Need help 99 GT

Traction is not just about tire width. Getting a quality summer tire and suspension are important too.

Nitto 555’s are popular for your power level. Offers an affordable high performance summer tire at a good price point. I upgraded to 17x9” rims and put 275/40/17 nittos on with great results when I was NA at 290rwhp. I had excellent traction on the street in all gears. The wheel height is still stock so you don’t have to adjust your spedometer.

For your suspension at a minimum check that your shocks are not worn, your rear lower control arms are upgraded, and that your rear differential is in good shape (spinning both wheels rather than single wheel burnouts).

For your last comment about not upgrading rim width...
The rim has to be wider to fit these bigger sizes so that they have the contact patch they were designed to have. Not upgrading the rim width is a poor choice. There is a huge used and replica wheel market for our year mustangs - it is not that expensive to do it right. American muscle ships 17x9 rims with nitto 555’s already mounted. You can skip the tire shop all together!

Stock rims are 8” wide. Makes zero sense to widen your tire by 1” (275s are about 1 inch wider) and not widen the rim to a 9” inch rim to support that additional tire width. I would get a 9” rim if you want 275’s, 10 inch rim or 10.5” rim if you want 305-315 width. Either size is mote than enough for your power level if you pick some sticky summer rubber.

Does this car have ABS breaks or traction control? IF so, expect problems when there is an imbalance between the size (outside radius Not rim size) of the front verses rear tires.

Tires for 17” rims are generally much cheaper. Unless you really like the look of 18” rims I would save on the weight and cost by staying 17”. Good to hear that your have 17x9’s. I have found that a 275 wide tire is a good fit and that a better rubber will get what you want until you go to much higher power levels.

I had stock gears (soon after my hi tech stage 2 cams I started saving up for a blower). I had excellent traction (no slippage in 1st or 2nd) with 275’s on dry / good streets in 50 degree or warmer weather. My wife had a 2010 GT that had upgraded rims (275 wide Nitto 555’s) with the 3.55 rear end with excellent traction as well in first and second.

I still daily drive my car. My drive to work is short (10 mins) and I change my Nitto NT05’s every 2 years. Even at my power level I still hook decently in 1st (on good roads I have excellent traction) and have excellent traction in 2nd. I had no problem keeping just ahead the other day of a 440awhp Subaru and a 450awhp evo (we all went around a rediculously slow person coming down an on-ramp at about 20mph to suddenly having to merge with traffic going full 70mph highway speeds). Makes a big difference when you have traction (we all turned it off at the speed limit so that we could be safe - we had to get around the unsafe 20mph person that nearly caused an accident).

Overall the 555’s should work perfect for your setup. If you want the best traction bang for buck for your 17x9’s and don’t mind changing tires more frequently I would look at the NT05’s.