Car's Performance on bigger wheels

[Seiryuu]

I know what you are thinking... this has been discussed and trust me, as always, I have been doing my homework and browsing old topics. I still haven't found a solid answer though.


To my understanding, the general consensus here is that 17" is the best size for performance (or generally, the smaller the better... she will never say that). Less rotational mass, less moment of inertia, smaller diameter, less weight, etc.



It is said that even a lighter 18" wheel might not be as good as a heavier 17" on the same tire.


So first question, I know it is difficult to compare two wheel designs, but how assuming that you go for a performance-oriented design (mass closer to center), what is a good starting weight for an 18" wheel to be better than the stock 17" (~21 lbs)?


My second question is concerning the tS, Series.Blue, STi Sports and all those other models that come with 18"... so did Subaru compromise a bit of "performance" for the sake of style? If the general consensus is that 17" are usually better.



As always, inputs are much appreciated. Thank you all for teaching this newbie about cars.

[Ernest72]

This is a slow car and needs all the help it can get. So get a nice lightweight wheel and you will feel it. Unsprung weight gives the best bang for the buck. So stick with 17s. Only 18s for looks or maybe track only. On the street, no need for more than light 17 wheels and a good tire. Sometimes I actually enjoy my winter all season tires more because the oversteer is so much fun.

[Grady]

Rim diameter has nothing to do with it. it is the combined weight of wheel/tire combo that you need keep from gaining weight. AKA wide rims and tires will slow you down! Your stock car will do well on good sticky 225's.

[soundman98]

yep. it's about the total mass that make a difference, the car doesn't know what size wheel you're running as long as the outside circumference of the tire doesn't drastically change.

for people that live with rougher roads, 16's are best, because they offer the most amount of tire to be ran.

[Seiryuu]

Originally Posted by Ernest72

This is a slow car and needs all the help it can get. So get a nice lightweight wheel and you will feel it. Unsprung weight gives the best bang for the buck. So stick with 17s. Only 18s for looks or maybe track only. On the street, no need for more than light 17 wheels and a good tire. Sometimes I actually enjoy my winter all season tires more because the oversteer is so much fun.

But sometimes you run into the problem where that ONE wheel you want... only comes in 18. And you wanna make the best out of it and get the right size that is the least detrimental.

Originally Posted by Grady

Rim diameter has nothing to do with it. it is the combined weight of wheel/tire combo that you need keep from gaining weight. AKA wide rims and tires will slow you down! Your stock car will do well on good sticky 225's.

This is... enlightening! I think that solves a good chunk of my questioning.

Originally Posted by soundman98

yep. it's about the total mass that make a difference, the car doesn't know what size wheel you're running as long as the outside circumference of the tire doesn't drastically change.

for people that live with rougher roads, 16's are best, because they offer the most amount of tire to be ran.

I didn't think about wheel options when I got the BRZ PP... those brakes actually limited a few wheel options for me.

___


Anyways, this topic started from me coming across this old article : https://www.roadandtrack.com/car-cul...ransformation/


So I called into question Subaru/STi's choice to swap to 18" wheels on their more "hardcore" models.



But only after pondering for awhile, I originally thought maybe 235 is too much tire for this car at 18" so it was slowed down. Then after the comments here, yea... I think the diameter also has something to do with it.

[why?]

it depends what you are doing. For daily driving you don't need 18's. 17's have really been the performance size choice for a long time, and at this point going smaller can limit tire choice unless you make sure you pick that before you pick wheel size.


18's outside of the track are all about looks. And for me they look like crap.



I wish this idiotic massive wheel craze never happened. 14x5.5 Volk ce28n weigh about 6 pounds each. That would be awesome on this car, but because of the silliness it would never ever happen.

[Ernest72]

Originally Posted by Seiryuu

But sometimes you run into the problem where that ONE wheel you want... only comes in 18. And you wanna make the best out of it and get the right size that is the least detrimental.

I totally agree. There are some awesome rally wheels from OZ, team dynamics, braid and method that I would love to run on my 04 WRX. But they are all 22-25lbs or more and strong as hell. Why run that heavy wheel when there are wheels I like in the 17-19 lb range. It’s not like I am rallying, it’s just driven on the streets.

So it’s a choice looks or performance. For a DD losing some performance for looks is fine. The second reason I won’t go 18s is the roads suck in NY. So comfort helps. Don’t need to lose fillings because of a stiff suspension, small side wall and crap roads.

[nikitopo]

Originally Posted by Seiryuu

So first question, I know it is difficult to compare two wheel designs, but how assuming that you go for a performance-oriented design (mass closer to center), what is a good starting weight for an 18" wheel to be better than the stock 17" (~21 lbs)?

Yes. Brembo brakes could be fitted even on 17" wheels, but consumers prefer bigger wheels.

You can check the Rays 17" wheels that were used in the GRMN 86 and the GR 86 cars.

[ichitaka05]

Like Grady stated, wheel size or weight doesn’t matter too much. It’s all about tires & brakes balanced with the car setup.

As for the weight, I wouldn’t worry too much... unless you’re racing your car and need to shave every oz. I’ve seen FR-S that had 3 piece wheels and it was AT and ran faster lap around the track AND autox than 80% of ppl that was there. So at first, don’t worry too much about the weight of the wheels. As long as each wheel doesn’t weight 35lbs and stay around 20’s should be good enough.

As for tS and TRD model running 18’s vs other running 17’s. There are few reason for it. First is marketing. Second is performance. There’s nothing wrong with running 18’s. Having 18’s doesn’t mean it loses performance. If you look at Drift King’s GT86, he’s running 18x8.5 wheels w 235/40 tires. Iirc he ran 1min 11secs around the Tsukuba stock vs his GT86 ran 1min 7secs. Of course that’s a lot to do with tires and suspension setup, but the point is, it varies. You gotta find the right setup for you. I’m currently on 3rd wheels (soon 4th) and still figuring out what’s the ideal setup for my driving style.

TLDR: Drive and figure things out.

[Grady]

Originally Posted by Seiryuu

But sometimes you run into the problem where that ONE wheel you want... only comes in 18. And you wanna make the best out of it and get the right size that is the least detrimental.

I guess I am backwards. I always found the tire I wanted then had to find a wheel that would fit it.

[soundman98]

Originally Posted by Seiryuu

I didn't think about wheel options when I got the BRZ PP... those brakes actually limited a few wheel options for me.

check the wheel fitment stickies-- there are a number of 17's that fit with the PP calipers yet. by no means are you condemned to 18's.

but overall, wheel size alone is a red herring. everyone loves to look at just wheel size, but the complete wheel and tire package is what should be compared.

that particular article you linked specifically addresses the oem 86's tires characteristics, while happening to change out the wheels at the same time.


personally, i like big tires for that stock car look!

[Stephen W.]

Originally Posted by Seiryuu

< snip >
My second question is concerning the tS, Series.Blue, STi Sports and all those other models that come with 18"... so did Subaru compromise a bit of "performance" for the sake of style? If the general consensus is that 17" are usually better.
< snip >

Not all the editions with Brembo brakes come/came with 18" wheels. The Series Yellow (Inazuma) Series Gray (Raiu) as well as the Performance Package (RS) are actually 17x7.5 (see images)

[nikitopo]

As it was mentioned already, it doesn't make any real noticeable performance difference. However, I always go with the smaller wheel that can clear the brake kit. For me it is more of sticking to a retro look and keeping the overall car weightas low as possible. A bigger wheel with same manufacturing process will always be heavier.

[DarkPira7e]

One thing to keep in mind, is that the more weight you try to save by downsizing in diameter, the more weight you're adding in rubber on the outside of the rotating mass. That said, I ran a 17x7.5 Sparco AssettoGara (I think it weighs in around 18lbs?) with a Falken Azenis RT-615k+ in the 215/40 size and saw a nice difference in acceleration, but it looked stupid because I am stock ride height and the wheel well gap was horrendous.

I reference https://tiresize.com/ to see weight and effective width. I don't know how accurate it is, but I've been using it for a while on different tires I've ran and enjoy having one centralized location to reference.