Help choosing tire size

[Curtis]

Hey everyone I need some help picking out tire sizes for my new rims, this is my first sports car and first set of aftermarket rims so I will admit I am lost.

Front 18x8.5 +44
Rear 18x9.5 +38

Im looking for tires that will not affect my final drive or mess with my speedometer, probably go with a slightly more sticky tire in the front than the rear. Im not sure what numbers i need. I tired to use the fitment calculator but im lost.

Any help would be greatly appreciated!

[wparsons]

I wouldn't suggest you mix tire compounds/tread front/rear unless you really know what you're after and how the different compounds/tread are going to react.

Why the staggered fitment? These cars handle best with square wheel/tire sizing.

To answer your original question, look on tirerack.com for any tire in the stock size, then look for other sizes that match the overall diameter of the originals (24.7"), and will fit the rim size(s) you want.

You're going to want a 225 or 235 on an 8.5" wheel and a 245 or 255 on a 9.5" wheel.

[gramicci101]

Do a 225/40 in the front and a 255/35 in the rear. The outside diameter of these tires is nearly identical to each other and very close to the OEM tires' diameter, which will keep your speedo and whatnot happy. Or you could do 235/40 and 265/35. OD is still virtually identical, but they are just a hair taller than OEM.

[Curtis]

Originally Posted by wparsons

I wouldn't suggest you mix tire compounds/tread front/rear unless you really know what you're after and how the different compounds/tread are going to react.

Why the staggered fitment? These cars handle best with square wheel/tire sizing.

To answer your original question, look on tirerack.com for any tire in the stock size, then look for other sizes that match the overall diameter of the originals (24.7"), and will fit the rim size(s) you want.

You're going to want a 225 or 235 on an 8.5" wheel and a 245 or 255 on a 9.5" wheel.

Staggered fitment because the car will not be on the track and I had seen some other staggered set ups and I really liked them.

As for the compound, you're probably right and ill start with the same on both wheels.

Thanks for the help!

[churchx]

Square setup and good handling is not just for track. I don't see why making daily driving ride less safe should be more acceptable just because of driving less at limit & with higher safety margins. Changing brake bias, make ABS/TSC and alikes play tricks or errors, make rear more susceptible for aquaplaning, readjust driving to compensate grip differences, ignore that suspension is designed with specific setup in mind, loose ability to rotate tires?
And just because some had made mistake, imho is not sufficient reasoning to justify repeating it.
I bought car because i liked how it handled in test drive. I wouldn't wish to pay out of my wallet for something killing it.

[Curtis]

Originally Posted by churchx

Square setup and good handling is not just for track. I don't see why making daily driving ride less safe should be more acceptable just because of driving less at limit & with higher safety margins. Changing brake bias, make ABS/TSC and alikes play tricks or errors, make rear more susceptible for aquaplaning, readjust driving to compensate grip differences, ignore that suspension is designed with specific setup in mind, loose ability to rotate tires?
And just because some had made mistake, imho is not sufficient reasoning to justify repeating it.

Thanks for your input, the rims are on their way already.

Ill keep that in mind for my next set

[wparsons]

If it's not for the track, then why would you ever consider running different tires front/rear?

[Curtis]

Originally Posted by wparsons

If it's not for the track, then why would you ever consider running different tires front/rear?

Just listening to some advice from my brother in law. He was explaining to me his street and track sets ups and what he was explaining made sense to me.

[Curtis]

Originally Posted by wparsons

If it's not for the track, then why would you ever consider running different tires front/rear?

I'll probably start with the same tire front and back, rims should be in next week.

I'll definitely let you know how it turns out, I'm not nearly as concerned as you are, but I may have gotten some bad advice. Either way the car isn't ruined... I could easily afford another 2 wheels to make it a square set up again

[churchx]

Was your brother in law also driving one of twins or some other cars? Are your daily driving style and track driving style same as his? Yes, there are sport/sporty and even common passenger cars with staggered setup out of factory. But they also have their brake bias/suspension/engine power designed to match/use it. On twins - all of those bits are designed around square setup. Hence experience on staggered tyre setup cars from factory (or with almost everything custom from aftermarket but still assembled to work together as a whole even with used staggered setup) shouldn't be blindly applied to different car designed in different way. Most of daily drivers on this forum prefer way car handles with square tires, most of track racers prefer and advise it that way, engineers designing aftermarket suspension parts for this car advise it. Of course there still is minority around that for example hellaflush lowers it, run too wide and too grippy and staggered tire setup (with most common reasoning imho being - "because some very expensive exotics have staggered setup", hence them should do that on these twins too (it's different car!), also "it looks better" (to whom? who will look under car from front and back and compare tyre width?! Someone overtaking for that purpose this car? )) and do other expensive things with which they make car worse or that require lot more extra investments to compensate/fix using other parts, when that shouldn't be done in first place. They are free to. You are free to. Just that most advise against it.

[jshadeck]

Eliminate all the concerns above^ as well as save yourself the hassle of getting the same tires in 2 different widths but trying to maintain the same overall diameter, just run 255 on all 4. 255 is perfect on an 8.5 and barely has a stretch on a 9.5. You keep all the benefits of the square setup, while gaining the benefit of the staggered fitment (front cant be 9.5 w springs w out either hitting the suspension or poking out of the fender 3/4"). I have the exact wheel specs as OP




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[Curtis]

Originally Posted by jshadeck

Eliminate all the concerns above^ as well as save yourself the hassle of getting the same tires in 2 different widths but trying to maintain the same overall diameter, just run 255 on all 4. 255 is perfect on an 8.5 and barely has a stretch on a 9.5. You keep all the benefits of the square setup, while gaining the benefit of the staggered fitment (front cant be 9.5 w springs w out either hitting the suspension or poking out of the fender 3/4"). I have the exact wheel specs as OP

Attachment 110520


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Running a 255/35 on front and back? Do the front and back end up being a different height?

[wparsons]

Originally Posted by Curtis

Just listening to some advice from my brother in law. He was explaining to me his street and track sets ups and what he was explaining made sense to me.

If he's suggesting running different tread/compound front/rear, I would stop listening to him. Not trying to be an ass, but that's terrible advice. I know a couple people that run different tires front/rear to experiment, but they're VERY accomplished racers looking for ways to change the balance of the car in subtle ways. They're also backing it up with a ton of testing so they have real data to analyze.

Originally Posted by jshadeck

Eliminate all the concerns above^ as well as save yourself the hassle of getting the same tires in 2 different widths but trying to maintain the same overall diameter, just run 255 on all 4. 255 is perfect on an 8.5 and barely has a stretch on a 9.5. You keep all the benefits of the square setup, while gaining the benefit of the staggered fitment (front cant be 9.5 w springs w out either hitting the suspension or poking out of the fender 3/4"). I have the exact wheel specs as OP

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I think you mean 225's? A 255 will be pretty squished on an 8.5, and definitely not stretched on a 9.5.

What tires are you running? Different tires also run at different widths, despite being marked as a given width. My 205 snows are wider than the stock 215 Primacies.

[jshadeck]

255 fifty five. Ventus evo2s. They are flush on the 8.5 and slight stretch on the 9.5


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