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Widest tire on 18x9.5 wheel


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I think that's a function of what your goal is.

 

For responsive handling and safety you generally don't want the actual tread width to exceed the rim width -- the nominal size will vary by manufacturer and profile/series tire.

 

The lower the profile the more critical air pressure becomes and the stiffer the suspension needs to be, which trades of some handling/compliance since low profile tires have a higher frequency resonance than most live axle suspension can track (high unsprung weight). Lowering the pressure on low-profile 20s will help but put you at risk of rim damage.

 

Notice that the KR went with 18" Alcoas in lieu of the 20s of the prototype ...that was purely for tuning the wheels-tires to the suspension for maximum handling and traction -- not as cool looking as low-20s but far more effective on the mustang.

 

For just straight line traction, you can probably stuff 305/40 18s (just a ballpark -- will vary by brand). If 20s, likely 295s are the widest but the 18s will be more forgiving and actually hook up much better, imo. The 18s will also be more comfortable especially with lowered suspension and/or stiffer springs. I'd avoid going too wide on the front -- it will make the handling feel imprecise (delayed response), especially as the tread-width approaches the rim width -- less of a concern on the rear because the rears can generally be wider than the fronts (on the same size rims) and still be as responsive due to the lighter loading.

 

In short, there's no simple answer -- depends on what you like and what your goal is: handling, looks, road-comfort, straight-line, etc.

 

Btw, your car looks awesome!!! :happy feet:

 

Dan

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I think that's a function of what your goal is.

 

For responsive handling and safety you generally don't want the actual tread width to exceed the rim width -- the nominal size will vary by manufacturer and profile/series tire.

 

The lower the profile the more critical air pressure becomes and the stiffer the suspension needs to be, which trades of some handling/compliance since low profile tires have a higher frequency resonance than most live axle suspension can track (high unsprung weight). Lowering the pressure on low-profile 20s will help but put you at risk of rim damage.

 

Notice that the KR went with 18" Alcoas in lieu of the 20s of the prototype ...that was purely for tuning the wheels-tires to the suspension for maximum handling and traction -- not as cool looking as low-20s but far more effective on the mustang.

 

For just straight line traction, you can probably stuff 305/40 18s (just a ballpark -- will vary by brand). If 20s, likely 295s are the widest but the 18s will be more forgiving and actually hook up much better, imo. The 18s will also be more comfortable especially with lowered suspension and/or stiffer springs. I'd avoid going too wide on the front -- it will make the handling feel imprecise (delayed response), especially as the tread-width approaches the rim width -- less of a concern on the rear because the rears can generally be wider than the fronts (on the same size rims) and still be as responsive due to the lighter loading.

 

In short, there's no simple answer -- depends on what you like and what your goal is: handling, looks, road-comfort, straight-line, etc.

 

Btw, your car looks awesome!!! :happy feet:

 

Dan

 

 

So... 285/40/18 on 9.5" rim and 255/45/18 on 8.5" is good, right?

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So... 285/40/18 on 9.5" rim and 255/45/18 on 8.5" is good, right?

 

It will depend on the actual tread of the individual tire (they vary even for the same nominal profile), but yes, that's a good match for a fairly balanced car. If more weight is on the front (like most) you might want to use the same size rim on the front as on the back, but use the smaller 255s on the wider rim to tighten-up the responsiveness in the front (to better match the weight). Notice that on the GT500 Ford uses the same width rims but with wider rubber (pushed clsoe to the limit of rim width) on the rear, but smaller rubber on the front -- likely because they wanted to keep the front as responsive as possible (given the GT500's front weight) and the rear more compliant ...to 'track/follow' the front better. So you might try 9.5s up front too with the 255s. It's hard to give a specific answer without getting a feel for the car on a track first -- possibly others who have tried the GT500 wheels/tires on the S-GT may have some insight on that combo. Shock/strut rates, valving and anti-roll bar stiffness can also be used to tune the overall handling response.

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It will depend on the actual tread of the individual tire (they vary even for the same nominal profile), but yes, that's a good match for a fairly balanced car. If more weight is on the front (like most) you might want to use the same size rim on the front as on the back, but use the smaller 255s on the wider rim to tighten-up the responsiveness in the front (to better match the weight). Notice that on the GT500 Ford uses the same width rims but with wider rubber (pushed clsoe to the limit of rim width) on the rear, but smaller rubber on the front -- likely because they wanted to keep the front as responsive as possible (given the GT500's front weight) and the rear more compliant ...to 'track/follow' the front better. So you might try 9.5s up front too with the 255s. It's hard to give a specific answer without getting a feel for the car on a track first -- possibly others who have tried the GT500 wheels/tires on the S-GT may have some insight on that combo. Shock/strut rates, valving and anti-roll bar stiffness can also be used to tune the overall handling response.

 

Actually, that's perfect! I'm going with the CS56 rims that only come in 18x 9.5. :)

Thanks

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