DTMR

I have my stock wheels that i want to put ultra high performance A/s tires in for the colder months (Yay jersey) and get aftermarket wheels with summer tires for spring nd summer i have the 17in wheels and the recommend size is 235/55/r17 but i want them to have as much grip as possible and i heard going up in size helps a lot. Should i go with a 245 or a 255? or should i just sick with 235? what will give me the best grip and traction the stupid pirellis i have on there now are crap and constantly slide when i launch or shift into second

notsofast

All-season tires are definitely a compromise between performance and all-weather traction. I've had good luck with Michelin A/S Sport Pilots and they get good reviews on the Tire Rack web site. Going up to 18-inch wheels (18 X 9 inch) will let you easily go to a 255/45/18 tire which is another 20 mm in tread patch width for better (dry) traction.
If it was me and I had the misfortune of living in the frigid northern regions I'd stay with the 17's for dedicated winter tires and use 18's for higher performance summer tires. Also remember that you'll get better traction on snow with a more narrow dedicated snow tire.

DTMR

i want to know whats the best size to prevent wheel spin like what will give me the best grip

Nuke

With the stock 17" wheels, which I recall are 8" wide, I think you can't go wider than 255's. But tire compound is more important than width when it comes to grip. If you plan on 2 sets of tires, then use the search to see what other folks are running for summer performance for that set. The 2nd should be a dedicated winter tire if you must drive the car in winter. The Stang is about the most useless winter car in all my 40 years and dozen + vehicles in PA and Illinois winters.

mayo

THIS!
Nuke is correct, on a 17x8 rim you will max out with a 255 series tire. If you intend for these to be a winter only set, why care about performance dude? Planning on drag racing in the snow are ya?lol
It's all about getting her through this crap in one piece for spring...when the real fun starts
Stick with the 235's imo, narrow is better in bad elements!

DTMR

I dont want to race in sno haha i just want to know the best sIze for the most traction so i dont slide anywhere haha

Nuke

Size won't determine traction but more rubber on the pavement improves traction but also introduces more drag. It's a trade-off but usually traction wins. I'd take a good compound tire in a 235 over some crap 255 for traction anyday.

As we stated earlier, you're pretty much limited to a 255 on those OE 17" wheels.