Optimal Wheel Size for Stock Power

[ill86]

Originally Posted by Flow

So, what is your impression of the performance impact of the the different sizes?

It is the typical trade off between nimble and extra grip. For a street application it really doesn't matter much. Probably impacting buyers more in the pocket book than noticeable improvement for a street car.

In a track environment it is different. Personal preference on what the driver likes will take precedence.

It just depends on if you're needing (in most cases wanting) more grip with wider rubber. Which will in most cases take longer to get up to operating temps.

Also, in regard to small changes in sidewall profile, you're not really going to notice a shorter tire giving you more accel, or a taller giving more top end. It is negligible.

I don't believe you will "ruin" the handling between 215mm and 255mm on a street vehicle. You will certainly feel a difference though. Perhaps a heavy steering feeling and longer transitions from grip to skid. Less predictability and more weight transfer from lateral grip being increased.

If this was a 100hp car with lower c/r it would be a different story. But the FR-S makes adequate power.

[Vonsamhain]

Originally Posted by Tanuki

^Thanks. My thought was maybe a 17x8 for a daily, then save these work 18x9's for track rubber, or something along those lines.

IT would be the opposite. You want the lighter wheels for the track. ITs less important street driving to have extra weight

[Tanuki]

Originally Posted by Vonsamhain

IT would be the opposite. You want the lighter wheels for the track. ITs less important street driving to have extra weight

I didnt realize how heavy the works were back when I made that comment. The more rubber you can fit on the wheel the better was the thought, though. Honestly though it is completely proportionate to the amount of power, weight, and wheelbase though. I sold the Works months ago.

[industrial]

Originally Posted by soodxn

reviving an old topic here, just wondering if popular opinion has changed or not 5 months later. For a car staying on stock power, is 17x8, on 225/45 tires the best bet? I see a lot of 17x9 on 245/40 nowadays, even on stock power.

I think a lightweight 17x7 or 7.5 with a solid 215/45 tire will be the best functional choice. I'm going to try a 215/40 (advan ad08) on my 17x7.5 oz rims. Should be 35lbs a corner, change the gear ratio to around 4.33:1 and be much wider than stock. I'll have results in 6 months.

[Ganthrithor]

I'm gonna spend some time playing with the stock setup first obviously, but I was thinking 17x7.5 RPF1's + a set of star spec IIs?

I already have a thing for the Dunlops after running star specs on my GTI for the last few years. They're great tyres.

If there's anyone running this combo (with Z1s, of course) I'd be really interested to hear their impressions vs stock.

The only thing I don't like about the RPF1's are the looks. I'd really prefer a nice mesh design, but I can't find any that I like and that are light. TSW Nurburgrings aren't bad but don't come in a flat silver, Enkei Raijins are heavy and only come in 18"+, and BBS CH-Rs are not that light and incredibly expensive. I wish Apex made BRZ wheels. Something like this http://www.apexraceparts.com/ARC-8-1...ies_p_132.html but smaller (and lighter) and in the right bolt pattern would be amazing...

[Smudgeous]

Originally Posted by Ganthrithor

I'm gonna spend some time playing with the stock setup first obviously, but I was thinking 17x7.5 RPF1's + a set of star spec IIs?

I already have a thing for the Dunlops after running star specs on my GTI for the last few years. They're great tyres.

If there's anyone running this combo (with Z1s, of course) I'd be really interested to hear their impressions vs stock.

The only thing I don't like about the RPF1's are the looks. I'd really prefer a nice mesh design, but I can't find any that I like and that are light. TSW Nurburgrings aren't bad but don't come in a flat silver, Enkei Raijins are heavy and only come in 18"+, and BBS CH-Rs are not that light and incredibly expensive. I wish Apex made BRZ wheels. Something like this http://www.apexraceparts.com/ARC-8-1...ies_p_132.html but smaller (and lighter) and in the right bolt pattern would be amazing...

Why not get some powdercoating quotes for the TSW Nurburgrings? Get the color and design you want, in a wheel that already exists in 5x100 bolt pattern.

[Ganthrithor]

Originally Posted by Smudgeous

Why not get some powdercoating quotes for the TSW Nurburgrings? Get the color and design you want, in a wheel that already exists in 5x100 bolt pattern.

I suppose I could. I'm just not crazy about their looks and they're on the heavy side of light (almost 18 pounds). the RPF1's at 15lbs are pretty hard to beat-- I just wish there was something that light that wasn't so boring to look at.

[Joxer]

Originally Posted by denverizzles

so after reading the many posts of this thread, i'm beginning to wonder whether it's the diameter of the rims that slow down the car or the weight?

If we have an 18x9 weighing 19lbs and a 17x7.5 weighing 22lbs, will you notice the power difference? and which one will have a better response?

I think Tenuki sort of responds to this, but the answer is in where the weight is. I think a large portion of the weight of the wheel is in the rim - the farther you put weight from the hub the more power/torque required to accelerate it (like a spinning figure skater - arms out slow, arms in fast). So likely the 17" would have the mass closer to the center. The corresponding weights of the two tires would also come into play.

[jam0o0]

fastest will be the smallest diameter with the most width up to a point. so 15x9 with 255's would be quickest IMO. it's not just the weight of the wheel that matters but where the weight is. a lot of the weight of a wheel is in the barrel. the barrel of an 18 is farther from the center of the wheel than the barrel of a 15. the farther from the center the weight is, the harder it is to accelerate it. in a straight line this is basic physics.

corners are more complex. if the tire side wall is too big you get a squishy, wallowy tire. this makes the car slower in transitions. and the contact patch is less consistent when the tire is loaded.

diameter change will change the over all gear ratio. smaller diameter will shorten 0-60 times and 60-0 times.

[Carlsbad]

I like the logic of sticking with manufacturer tested set up, and here is the rub.
Subaru and toyota both have either 17X7.5 or 18X7.5 in us and japan.
In germany Subaru offers an upgarde to 18X8 (nice gold wheels). BTW if anyone has info on this wheel, please let me know
I like PRF1 gold, but I can only get them in 8 wide and 235/40/18 tires (my preference)
I read somewher on this site that toyota engineers recommend staying with 215 upfront. Does going to 235 take away too much from handling?
I guess if I could get PRF1 18X7.5 in gold, I would have been golden

[jam0o0]

Originally Posted by Carlsbad

I like the logic of sticking with manufacturer tested set up, and here is the rub.
I read somewher on this site that toyota engineers recommend staying with 215 upfront. Does going to 235 take away too much from handling?
I guess if I could get PRF1 18X7.5 in gold, I would have been golden

staying with manufacturer ratings is fine if you don't want to go faster.

235's will HELP front grip. 255's will fit with stock springs/struts, but the wheel has to be exactly right. this would leave you with less than 10mm clearance on both sides.

manufacturers have to have their set ups work for a lot of situations most of us don't care about. having a tire touch the fender with a car slightly out of spec would be a lawsuit for a manufacturer. but for us we just roll the fender a bit.

[Shankenstein]

I have 17x7 Enkei RPF1 with 215/45-17 Dunlop Direzza ZII's for autocrossing. The combo is very light, and more than enough grip for the street. 37 psi front, 32 psi rear.

Braking under ABS is incredibly strong, even with stock pads/rotors. Traction control doesn't kick on unnecessarily, and when the rear end breaks loose, it's quite smooth.

You can run 16's with the right wheel, but that won't necessarily be lighter.

If you're looking to maximize grip, get wide 17 wheels and 245-255 tires. The extra 1.5" of contact patch doesn't make as much difference as these guys are suggesting. Even at 215 with good rubber, your road feel will start to go numb and it feels like you're dragging the tires around. 255 may be grippy, but it won't give you minimalist Jeremy Clarkson grins anymore.

[rainmonkey]

wait... if smaller wheel = better for speed and tracking and stuff, why do cars like in this video have big ones??
http://www.ft86club.com/forums/showthread.php?t=33361
Still trying to understand this stuff.

Thanks!

[ST185RC]

Originally Posted by rainmonkey

wait... if smaller wheel = better for speed and tracking and stuff, why do cars like in this video have big ones??
http://www.ft86club.com/forums/showthread.php?t=33361
Still trying to understand this stuff.

Thanks!

It's not as simple as that. When it comes to wheels and tires, it depends on what you want. If you want more road feel, you will want a shorter sidewall while increasing the rim diameter. This will give an overall more rigid wheel. Then you have people that want larger wheels just for looks.

Smaller wheel does not necessarily mean it's better for speed. A smaller wheel usually means lighter and less unsprung weight that the engine and brakes need to accelerate or decelerate. It could mean that it's quicker getting in and out of turns as it takes less effort for the engine to rotate the smaller mass. The lighter the wheel, the later you can brake (generally speaking) and carry more speed through a corner.

For rolling speed, a larger diameter wheel vs smaller diameter wheel, holding the sidewall height and total weight the same, the larger diameter wheel is faster based on the angular displacement for every revolution that the wheels turn, it's angular velocity. That is, for the same number of times the wheels rotate, the larger wheel will cover more distance in the same amount of time. This is assuming that the engine is doing the same output to move the wheel masses.