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Pros and cons of 18" wheels...

Hey everyone,

I've been looking up info on wheels for some time. And I'd like to start a thread to take the FAQ's of 18" wheels. I'll list a few of my questions below and any answers or additional questions are welcome. Thanks!

How much will 18" wheels affect your speedo, MPG gauge, and odo?

Will 18" wheels affect our AWD system in any way?

Will 18" wheels affect our ABS?

What is a good performance weight for an 18" wheel?

Can TPMS be added to aftermarket wheels?

Do you receive any "performance" gains from 18" wheels over 17" wheels?
 

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Re: Pros and cons of 18" wheels...

Here are all the answers I can give...

How much will 18" wheels affect your speedo, MPG gauge, and odo? If you gou to a smaller aspect ratio(ex. 205/50/17 to a 225/40/18) it will not affect any of these.

Will 18" wheels affect our AWD system in any way? No

Will 18" wheels affect our ABS? No

What is a good performance weight for an 18" wheel? Lighter is usually better

Can TPMS be added to aftermarket wheels? I believe so

Do you receive any "performance" gains from 18" wheels over 17" wheels?I don't believe so
 

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Re: Pros and cons of 18" wheels...

How much will 18" wheels affect your speedo, MPG gauge, and odo?

18s will not affect your speedo or odo if you choose a tire that makes the overall wheel/tire combo the same diameter as stock, or very close to it.

18s tend to be heavier than 17s or 16s, so you will get gas mileage that is slightly less with them, although your MPG gauge will continue to function correctly.


Will 18" wheels affect our AWD system in any way?

Nope, not at all.

Will 18" wheels affect our ABS?

Nope, although depending on their weight, they could increase stopping distance if they are significantly heavier.

What is a good performance weight for an 18" wheel?

"Lighter is better" Ditto..20 lbs per wheel or less is decent, 15 or so lbs is fantastic, but the lighter you go, the more expensive usually .

Can TPMS be added to aftermarket wheels?

It depends on the wheel I think, but usually, yes.

Do you receive any "performance" gains from 18" wheels over 17" wheels?

All things being equal, a 17" wheel that weighs 20 lbs versus an 18" wheel that weights 20 lbs, they have the same performance specs.
 

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Re: Pros and cons of 18" wheels...

the only performance benefits of an 18" wheel over a 17" wheel are that you can run a lower profile tire (meaning slightly reduced sidewall flex giving you a bit better response) and that you can run larger brakes.
 

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Re: Pros and cons of 18" wheels...

Do you receive any "performance" gains from 18" wheels over 17" wheels?

All things being equal, a 17" wheel that weighs 20 lbs versus an 18" wheel that weights 20 lbs, they have the same performance specs.
I agree with everything you said above except for this ^^

Weight of the wheel is only the beginning. By going to a larger diameter wheel and lower profile tire, you are shortening the sidewall. This means the tire has less flex in it (shorter, stiffer sidewall), translating into sharper turn-in and response, and better feel. Also if you go to a larger wheel width you can also go to a wider tire (better).

Another thing to consider: take a 18" wheel weighing, let's say, 20 lbs. and a 17" wheel weighing the same 20 lbs. The 18" wheel will take more energy to start it moving, and to stop it moving, since its mass is further away from the center (look up moment of inertia).
 

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Re: Pros and cons of 18" wheels...

you can fit a wider tire on a 18'' wheel as well, giving you more traction due to more surface area contact with the pavement. ;D
Not necessarily - you can definitely fit a wider tire on a 9" wide, 17" rim than a 7.5" wide 18" rim.

Also, it is a common misconception that a wider tire = more grip/traction.

The reality is that the advantage to running wide tires is to utilize a softer (grippier) material, because the force exerted on the tire is now more dispersed (over a larger area) and the material won't wear down as fast. The tire compound is what improves traction.

Ie, if you were to (for whatever reason) use a 205mm wide RE92 (stock tires - ughh) and then get some shiny new 18x9 rims and put 255mm wide RE92's on it (I don't think they make it in that size - just an example - i hope no one would ever do that :( ) expecting more grip, you wouldn't get any.
 

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Re: Pros and cons of 18" wheels...

you can fit a wider tire on a 18'' wheel as well, giving you more traction due to more surface area contact with the pavement. ;D
Not necessarily - you can definitely fit a wider tire on a 9" wide, 17" rim than a 7.5" wide 18" rim.

Also, it is a common misconception that a wider tire = more grip/traction.

The reality is that the advantage to running wide tires is to utilize a softer (grippier) material, because the force exerted on the tire is now more dispersed (over a larger area) and the material won't wear down as fast. The tire compound is what improves traction.

Ie, if you were to (for whatever reason) use a 205mm wide RE92 (stock tires - ughh) and then get some shiny new 18x9 rims and put 255mm wide RE92's on it (I don't think they make it in that size - just an example - i hope no one would ever do that :( ) expecting more grip, you wouldn't get any.
I do believe the contact patch will have some effect on grip.
 

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Re: Pros and cons of 18" wheels...

you can fit a wider tire on a 18'' wheel as well, giving you more traction due to more surface area contact with the pavement. ;D
Not necessarily - you can definitely fit a wider tire on a 9" wide, 17" rim than a 7.5" wide 18" rim.

Also, it is a common misconception that a wider tire = more grip/traction.

The reality is that the advantage to running wide tires is to utilize a softer (grippier) material, because the force exerted on the tire is now more dispersed (over a larger area) and the material won't wear down as fast. The tire compound is what improves traction.

Ie, if you were to (for whatever reason) use a 205mm wide RE92 (stock tires - ughh) and then get some shiny new 18x9 rims and put 255mm wide RE92's on it (I don't think they make it in that size - just an example - i hope no one would ever do that :( ) expecting more grip, you wouldn't get any.
I do believe the contact patch will have some effect on grip.
me too :)
 

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Re: Pros and cons of 18" wheels...

Do you receive any "performance" gains from 18" wheels over 17" wheels?

All things being equal, a 17" wheel that weighs 20 lbs versus an 18" wheel that weights 20 lbs, they have the same performance specs.
I agree with everything you said above except for this ^^

Weight of the wheel is only the beginning. By going to a larger diameter wheel and lower profile tire, you are shortening the sidewall. This means the tire has less flex in it (shorter, stiffer sidewall), translating into sharper turn-in and response, and better feel. Also if you go to a larger wheel width you can also go to a wider tire (better).

Another thing to consider: take a 18" wheel weighing, let's say, 20 lbs. and a 17" wheel weighing the same 20 lbs. The 18" wheel will take more energy to start it moving, and to stop it moving, since its mass is further away from the center (look up moment of inertia).
I agree with the tire profile thing, but the "All things being equal" clause kinda acknowledges that.

True, you are correct, the 18" 20lbs wheel will accelerate slightly slower than the 17" 20lbs one, but practically speaking you won't notice the difference.

And contact patch is a huge deal...tire compound helps, but a small contact patch on a good compound will yield results that aren't all that impressive.
 

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Re: Pros and cons of 18" wheels...

Do you receive any "performance" gains from 18" wheels over 17" wheels?

All things being equal, a 17" wheel that weighs 20 lbs versus an 18" wheel that weights 20 lbs, they have the same performance specs.
I agree with everything you said above except for this ^^

Weight of the wheel is only the beginning. By going to a larger diameter wheel and lower profile tire, you are shortening the sidewall. This means the tire has less flex in it (shorter, stiffer sidewall), translating into sharper turn-in and response, and better feel. Also if you go to a larger wheel width you can also go to a wider tire (better).

Another thing to consider: take a 18" wheel weighing, let's say, 20 lbs. and a 17" wheel weighing the same 20 lbs. The 18" wheel will take more energy to start it moving, and to stop it moving, since its mass is further away from the center (look up moment of inertia).
I agree with the tire profile thing, but the "All things being equal" clause kinda acknowledges that.

True, you are correct, the 18" 20lbs wheel will accelerate slightly slower than the 17" 20lbs one, but practically speaking you won't notice the difference.

And contact patch is a huge deal...tire compound helps, but a small contact patch on a good compound will yield results that aren't all that impressive.
I'm no tire engineer so I might have been wrong. I think you are right in saying that lateral grip is better with a wider tire. However I beg to differ about the short contact patch on good compound - I'm willing to bet that a WRX, for instance, on 205/55R16 Potenza RE-01R's will pull more G's on the skidpad than with 225/45R17 RE92's.



Anyway, we're kinda getting away from the OP's initial post - good and bad about larger diameter wheels.

One thing I'll say is tires for 18" wheels are more expensive! And you might have a slightly higher chance of bending your wheel if you hit a pothole vs. a 17" wheel (you'll have a smaller sidewall to absorb impacts).

Too many nested quotes! lol
 

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Re: Pros and cons of 18" wheels...

tire compound is definitely more important than the contact patch. and the contact patch does improve grip, but not for the reasons most people think. more area touching the ground doesn't immediately equate to more grip. friction is just a consequence of force multiplied by the coefficient of friction for a material (typically a constant value), so a 1000 lb object will have the same amount of friction (i.e. traction) no matter how much of it is touching the ground given that the coefficient of friction is the same between contact areas. when talking about tires, the reason a bigger contact patch gives you better grip is because a larger force (weight) on a tire causes the efficiency of the tire (the coefficient of friction) to decrease (part of the reason why heavy cars handle worse than light cars). sooo, with a bigger contact patch, you're creating a bigger area of tire supporting the weight of the car, effectively reducing the weight each square inch of the tire is supporting making the tire more efficient and raising the coefficient of friction which in the end equals more grip.

i suppose i could've just said that sports cars/race cars run really wide tires for a good reason and been done with it ;)
 

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Re: Pros and cons of 18" wheels...

lol, yeah, there are way too many nested quotes for sure.

I agree that compound is a big deal, and I agree with your analogy of the different bridgestone tires.

I guess I was thinking about the difference between like a ferrari-wide tire on an RE92 versus a WRX on 225 wide r-comps...but not really a fair comparison even if only comparing grip...so nevermind :)
 

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Re: Pros and cons of 18" wheels...

18's for style/looks....17's for performance/functionality/cost. Style is not to be overlooked though. That said, I just ordered a set of matte graphite silver OZ Ultraleggeras in 17x8. I wish they made them in a 17x7.5, but 0.5" isn't the biggest deal in the world.
 
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