[Tbirdmike97]

I have a 97 with 4.6. Getting ready to select wheels and tires. I'm planning to keep suspension close to stock and want to know if:
A: I'm better of choosing 15s or 16s with wider grip and lighter wheels resulting in softer sidewalls to absorb the force of turning.
Or
B: Select 17s or 18s with stiffer sidewalls because option A might be too soft all around.


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[Creighton]

Welcome to the forum!
Researching this myself. Seems to come down to what you are going to do with the Bird. With a 4.6 think 15" too small. For a DD 16" should be ok. If going to the track 17" gets you clearance for a brake upgrade. Hope some others chime in.
Creighton

 

[Tbirdmike97]

DD. I can get good grip from 245 60r 15 on some 15lb rims maybe lighter.
On 16s I can do 235 60zr16 and go up about 3lbs.

I'm thinking cornering though. With a stiff body + soft suspension.


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[MadMikeyL]

Given the same tire compound and tread width, a shorter sidewall will handle better and grip more, because the sidewall won't deflect as much under load, keeping more of the tread flat on the ground. The trade-off is that the shorter sidewall will also create a rougher ride. If you want a shorter sidewall, your options are either run a much shorter tire (which will look goofy and will throw your speedometer reading off), or run a larger diameter wheel, however larger wheels will be heavier, which is not beneficial for cornering, accelerating, or braking, so finding the right size is really a balancing act, and you have to choose what works best based on your priorities. My personal preference for a street car is 17s, as they still have enough sidewall to absorb the potholes, but will handle significantly better than stock 15s or 16s.

 

[Tbirdmike97]

I was afraid that this might come down to a balancing act.
I almost had my decision made until I read that the larger side wall saves the suspension some work in cornering as it balances the load before sending the force into the struts.
That's what has me scratching my head.


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[MadMikeyL]

No, that's not right. A larger sidewall will make for a smoother ride, and save the suspension some work over bumps, but for cornering, the shorter sidewall is far better.

 

[Tbirdmike97]

So the only thing I sacrifice with the larger rim is weight and possibly a bit of grip. Not sure how wide I can go on 17s or 18s with a rather stock suspension.


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[MadMikeyL]

To a point, you will gain grip with a larger diameter wheel because the shorter sidewall will not deflect as much. Obviously going for blingy 22"s will hurt grip, but 17s or 18s will help grip. As for how wide you can go, I have run 275/40/17s on 17x9 wheels.

 

[Tbirdmike97]

You run that in just the rear?


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[MadMikeyL]

No, at all 4 corners.

 

[Tbirdmike97]

Wow! Never thought that would be possible without rubbing


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[Tbirdmike97]

No, at all 4 corners.

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[Tbirdmike97]

Hey what offset are your 17s and who makes them?


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[MadMikeyL]

They are stock SN95 Mustang Cobra 17x9's. I don't know the offset off the top of my head.

 

[Woodman]

Tire selection is a huge factor too, as well as braking ability.

On a 15 or 16" wheel, the biggest brakes you can go are the Mustang GT PBR calipers, which are a HUGE improvement over the stock calipers, but still a limiting factor as you are stuck with stock sized rotors. Also, tire selection in 15 to 16 is very limited. You can get 'stock sized" tires (225/60/16) all day long because they are a very common, pedestrian tire, but getting wider, better performing tires on 15 to 16 inch wheels, you have limited selection. Add to it the tall sidewalls, and you can get much better cornering without much decrease in ride quality with 17 and 18" wheels.

I'd honestly go with 18's for a "fun" street car. On my car, with 255/40/18 on 18x9" wheels with 35mm offset, I don't rub, I have 89SC sway bars, Eibach lowering springs (which are softer than the Vogtland springs), Shock Connectors and my car still rides very well. Yes, it's marginally stiffer than stock, but it corners much better, has much better overall traction, and there is a HUGE selection of tires to choose from. 17 and 18" wheels also allow for the relatively inexpensive upgrade to 13" "Cobra" brakes, you can get rotors/pads/calipers all day long from Rock Auto, which offer yet again a big braking improvement over the PBR calipers. Or if you want to go big, you can get some nice Brembo or Wilwood calipers and rotors.