advantages or disadvantages of going from 17 to 18 rim? - Ford Mustang Forum
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post #1 of 11 (permalink) Old 07-05-2018 Thread Starter
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advantages or disadvantages of going from 17 to 18 rim?

found some 18s with new tires OEM wheels . I Have 17 now. wondered the pros and cons of switching up. tires are new and the cost is basically just tires so why not have the free wheels with almost new tires

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post #2 of 11 (permalink) Old 07-05-2018
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1st, you need to make sure the overall diameter is the same, otherwise, you'll have to "re-tune" or adjust the ECM.....a basic tuner will do this but, that's starting at $300+. Go to a dealer, probably about the same price as well.


2nd....wheel off set has to be correct otherwise say hello to fender or wheelwell rub & yes, damage to both the car and tires.


3rd..... depending on the profile on the new tires, shorter profile does not make for better handling always....while they may look good, sidewall stiffness is good to a point where it then starts to work against you....absence of give means less ability to "absorb" to deviations on the road...Ö ie less traction


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post #3 of 11 (permalink) Old 07-05-2018 Thread Starter
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I have a 2005 gt with 17s. The other wheels are off 2010 gt. 18 inch.

I have a tuner.
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post #4 of 11 (permalink) Old 07-05-2018
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In addition, going to 18 inch generally means a heavier wheel which hurts acceleration and adds unsprung weight. It means using a shorter sidewall tire which means harsher ride.
It can mean better handling and many times will allow more offset by clearing bigger brakes if you have them.
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post #5 of 11 (permalink) Old 07-05-2018 Thread Starter
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offset is the same.


why do people run 18 and up if its all negative?


I know te profile will drop from 55 to 50 ..I dont think that will be too bad


using the good ole tire calculator I find these specs somparing the two tire sizes:


Specification Sidewall Radius Diameter Circumference Revs/Mile Difference 235/55-17 5.1in 13.6in 27.2in 85.4in 742 0.0% 235/50-18 4.6in 13.6in 27.3in 85.6in 740 0.3%
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post #6 of 11 (permalink) Old 07-05-2018
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Quote:
Originally Posted by Michaelanthony2 View Post
offset is the same.


why do people run 18 and up if its all negative?
Not all negative. Most 18" wheels inside diameter clear upgraded brake kits depending on spoke configuration, like Brembo mid level, and a bigger rotor by an inch. The drop from 55 to 50 percent cross section will help handling a tiny little bit, and they look good, according to some. 18" is my limit aesthetically. I saw an early 70's Chevy Caprice yesterday with 28" copper plated donks on it. I almost threw up in my mouth a little. Unfortunately, looks is everything to a lot of people.

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Originally Posted by Michaelanthony2 View Post
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference 235/55-17 5.1in 13.6in 27.2in 85.4in 742 0.0% 235/50-18 4.6in 13.6in 27.3in 85.6in 740 0.3%
Staying around 27 1/4 inches +- a couple tenths (27.2 to 27.3 inches) diameter will not affect your computer or speedometer at all, because the differences amount to 4 decimal places less than one mile an hour. Besides, the factory equipment tires vary brand to brand more than a couple hundredths of an inch anyway. The car can't even see a difference that small.

The thing with skinny sidewalls is, the smaller the stiffer. The stiffer, the more sudden and violent it will be when they reach the traction limit, and they bring on the limit just a bit sooner with every increase in wheel diameter, while keeping the overall diameter the same.

There's a reason F1 cars don't run 30" wheels with rubber band tires.
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post #7 of 11 (permalink) Old 07-05-2018
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Quote:
Originally Posted by Michaelanthony2 View Post
offset is the same.


why do people run 18 and up if its all negative?
%
In a word..."Looks"...if you look at the speeds and dynamics that both Formula 1 & Indy cars run....look at the tires (size)Ö.. as compared to the size on "America's sport cars"...Ö they are running much faster speeds with taller tires (yes, they are a track/weather specific higher traction tire) but they are not dealing with typical road surfaces either...ie their suspension/tire assembly requires less give by comparison.


Take 2 identical cars...one running 50 series tires and one running 30 series tires....take them through a corner at speed.....elevated or otherwise..... the taller sidewall will absorb greater deviation, ultimately maintaining a higher level of traction, ie, going through the corner faster.

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post #8 of 11 (permalink) Old 07-06-2018
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In addition, going to 18 inch generally means a heavier wheel which hurts acceleration and adds unsprung weight.
Just read an article where the tested the same car 0 to 60 and around an autocross course with a set of very light wheels, with a set of the heaviest wheels they could find & with a couple of different drives. The difference in both venues was we'll under an second and in most cases .2 to .3 seconds. Unless you are a competitive driver on the track not worth considering in my book.

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post #9 of 11 (permalink) Old 07-06-2018
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F1 as of 2017 was using 13" rims but the tire manufacturers have been campaigning to go to 18".

Another thing to consider all the tire development is happing with the bigger rim sizes.

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Just read an article where the tested the same car 0 to 60 and around an autocross course with a set of very light wheels, with a set of the heaviest wheels they could find & with a couple of different drives. The difference in both venues was we'll under an second and in most cases .2 to .3 seconds. Unless you are a competitive driver on the track not worth considering in my book.

Dave
If you are referencing the article I think you are, the difference between 17 and 18 was pretty small, .1 in the quarter. Although a lot of guys spend a lot of money just for a 10th.
Going from 15 to 18 opened up a bit more, .3 seconds and 2 mph in the quarter. That is beating someone by a couple car lengths and pulling away from them.

If you look at Car and Driver's comparison between the GT350s carbon fiber wheels and aluminum, weight REALLY figured in. 30-50, 50-70 and 30-130 mph were all over a second difference.
https://www.caranddriver.com/news/te...n-fiber-wheels
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No, the article I am referring to is just in relation to weight. The tires and wheels were the same size, just that one set of wheels were much heavier.

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