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Discussion Starter #1
My Mustang came with the 17 inch machined aluminum wheels with a weight (I understand) of around 22 or 23 lbs and a total wheel and tire weight of about 50 lbs. I'm considering forged aluminum wheels to replace them, but I'm not sure if I should go with 17 inch or 18 inch wheels.

Here the options I'm considering...

1) 17X8 inch forged wheels weighing 15.5 lbs per wheel with a combined wheel and tire weight of about 43.5 lbs. That will save me about 6.5 lbs of rotating weight. That's like losing 80 to 100 lbs of static weight! (rotating weight reduction times 3 or 4 = static weight reduction) Not bad. If I went this route, then I'd stay with the 235/55R17 tires.

2) 18X9 inch forged aluminum wheels weighing 18 lbs per wheel with a combined wheel and tire weight of about 47 lbs. That saves me 3 lbs per wheel or the equivalent of about 36 to 48 lbs of static weight. However, the car would now have 255/45R18 tires.

I have a feeling the 17 inch wheels would be better for the 1/4 mile and the 18 inch wheels would be better for handling. True?

Or would the increased traction from the wider 18 inch wheels be more beneficial than the reduced weight of the 17's?

Surprisingly, the cost for each package is very close. So, which would you prefer? Looks aside, of course. If I'm spending $500 to $600 per wheel, then I want to get the best performance for my money.
 

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Discussion Starter #3
go 17 up front, and 18 in the back.. best of both worlds
Now that's a good thought. Would the difference in widths contribute to understeer? (Although, I am planning to add a stiffer rear sway bar in the future.)
 

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You are trying to set your car up to do two completely different things, go around corners and launch hard at the strip. When you try and make a car do two totally different things with the same setup you get a setup that "kinda" works in both situations and not great in either.

First off, lighter rims are always better. Being able to get accurate data in regards to if a lighter narrower rim/tire combo would be better/worse than a heavier rim/tire combo will be nearly impossible without some very complex data collection equipment. And then you still have a billion other variables that will come into play.

Your best bet would be to get a good set of properly sized "performance" tires on light rims for daily/backroad twisty driving. Then get yourself two wide rims with tires for the strip for when you go there.

You will never get a car to handle well with good drag tires. It will always be a big compromise.

As far as rim diameter and performance goes for the most part you want them to be as small as possible and still clear your brakes. Take a look at F1 cars, they have tiny wheels, but the brakes are tiny too. Tall sidewalls are a good thing. The flex that they offer gives you a bigger contact patch in comparison to short sidewall tires (as long as they are designed correctly and not pinched on to a rim that is too narrow). Smaller rims are lighter too. And less expensive.
 

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I agree with Sqidd. Shorter sidewalls feel more responsive, but in the real world taller sidewalls have better grip. To me, low-profile tires on huge rims is just a marketing gimmick.
 

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Discussion Starter #6
Thanks for the comments so far. I think I'm leaning heavily towards 17 inch forged aluminum wheels with General Exclaim UHP tires. Tire Rack has several forged 17X8 wheels that will fit our Mustangs for around $500 per wheel.

The total weight of each wheel and tire will be 40.5 lbs, that's 25 lbs per tire and 15.5 lbs per wheel. I'm going to save about 10 lbs per wheel/tire! I should notice a huge difference in performance by switching to summer tires while eliminating almost 40 lbs of rotating weight.

I am a little tired of the gangster wheel look that's popular right now. I entered my Mustang in a car show a few weeks ago and lost to an '07 GT that had no mods other than 20 inch Foose Nitrous wheels. Those weigh in around 30 lbs per wheel! All that time I spent wiring my nitrous kit and picking tasteful mods and I lose to guy that bolted on huge wheels...
 

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The height of the rim isnt going to give you better handling, width is what your looking for, 17's can be ordered just as wide, performance wise lighter is better as its less strain for the drivetrain to turn. Less stress Less mess.
 

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I know you didn't throw this out there as an option, but have you looked into a 17x9 wheel? That way, you can get the width without having to go with a larger diameter wheel.
 

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Discussion Starter #9
I could definitely go wider. The best option in a 17 inch wheel would be the 255/50R17, since it's pretty much the same diameter as the 235/55R17.

If I do go with a 17X9, then I'm pretty much settling on a 255/50R17, which isn't a very popular size, since a 235/55R17 won't fit on a 17X9 wheel. On the other hand I could get a 17X8.5 wheel, which will fit both 255/50R17 tires or 235/55R17 tires.

The only 255/50R17 summer tire I found on tire rack was the Kumho Ecsta weighing 31 lbs, compared to 235/55R17 tires that weigh between 25 and 28 lbs. 17X8.5 forged wheels are about 16.5lbs, that's 1 lbs heavier than 17X8 wheels.

Here's the list of tire and wheel weights I've come up with...

Stock Tire/Wheel Weight, 17 inch machined = 50.2 lbs (information from another Mustang Board)
17X8.5 Forged Wheel and 255/50R17 = 47.5 lbs
17X8 Forged Wheel and a "typical" 235/55R17 tire = 42.5 lbs
17X8 Forged Wheel and 235/55R17 General Exclaim UHP tire = 40.5 lbs
 

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Wider tires don't give you better handling, they give you more grip. Grip does relate to better handling, but it is not necessarily better handling by itself.

If I understand it right, the extra grip of wider tires positively affects your skidpad performance, but the extra unsprung weight of wider wheels and tires negatively affects slalom speed.
 

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Slaloms require a balance. Tires should not be wider than the rims. Tires wider than the rim reduces the handling. If you want wider tires you have to go to wider rims. Competition cars are also know to have the tread cut (take the outside half of the tread off). This reduces the amount of flex from the tread. This was in prior times. The new competition tires are designed to reduce this problem.
 
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