brigade24

For some reason i'm struggling with this question...

I do lots of autox and lapping and i was wondering what your opinions are on running a 17 inch wheel vs. an 18 inch wheel and why? i currently run the stock ZR1s 17x9 50 offset for autox and replica 17x9.5 z06 alcoa style wheels from oe wheels for lapping which are serving their purpose for a 25lbs wheel.

I could go 17x11 but they are heavy and given the tire option not sure if i should stay in the 17s or go to 18s...the latter certainly opens up the tire options but of course, at a premium.

perhaps i have answered my own question...or i am making it more complicated than it is.

thoughts?

Rise of the Phoenix

iTrader: (27)

Both will perform well for what you do, so I'd go with which one looks better, and in my opinion, 18" wheels look better.

1981TA

iTrader: (7)

If your focus is on weight and / or cost of operation, I'd stick with 17x9.5. On a lark, I went around the paddock at the June Sprints and looked at what all the competitive pony cars were running. Nearly all of them had 275-40 17s on all four corners. I'm guessing this was for a combination of reasons:

Little benefit in going with a wider tire
Larger hoops weigh more - increased unsprung weight
Huge selection of tires in this size
SCCA Class restrictions.
On tires of the same diameter, larger wheels equal shorter sidewall (harsher ride, potentially smaller contact patch)

brigade24

Thank you for your feedback gentlemen.

weight is def. a factor in my decision...for what i'm doing, it's important to keep the weight down.

The motivation for looking at 18" setup is because the BfG Rival, StarSpec, and RS-3 are all only available in a max width of 255mm in the 17"...to get to 275mm you would need to go to 18".

orthopod

iTrader: (1)

What did you end up deciding on? I am also debating what tire/size to go with for HPDE/getting started w/ RR. Will have to do double duty for a while until I can get a second set. Considering sticking with my 17 x 9 WS6 rims and getting something like a RS3/RE11/AD08/NT01/RA1/AD48 or going with 18x 9.5 OE wheels C6 Z06 style to open up the door for a BBK in the future. Doing the research now and any opinions from people that have actually tried any of the above would be helpful.

FASTFATBOY

iTrader: (23)

Only use the wheel you NEED to cover the brakes you NEED.

Bigger wheels are heavier.

The only advantage to bigger wheels is buying race scrub tires, as they are more available in 18 inch sizes.


And to the guy who says "buy the ones that LOOk better" LMAO!

FASTFATBOY

iTrader: (23)

If you are a novice you need to be on cheap street tires for the first 3-4 events.

hbgben

With going with an 18" wheel there are many more options regarding tire sizes/wheel fitments.

1981TA

iTrader: (7)

One thing that may help you decide is looking at tirerack and seeing what tire options are available for the wheel sizes you are looking at. With your given width (9.5) you are probably looking at either 275/40-17 or 275/35-18. While I based my decision on price, quality and weight, you may have different motivations (like appearance).

My wheels were 100 a set (3rd gen corvette saw blades, 4th gen camaro SS), and the tires were 100 each for continental RR slicks and 140 for continental DW extreme summer tires. I have a total of 1300 or so into TWO sets of very good new tires and good wheels. Granted, the wheels won't win any beauty contests, but I don't care. 17x9.5 OE wheels are plenty light and cheap.

Another set of wheels that can be had cheap are 18" corvette "wagon wheels." They ain't purty, but they are VERY light.

FASTFATBOY

iTrader: (23)

Yep, you can also buy cosmetically challenged wheels and rattle can them black. Track is going to be hard on them anyway.

I bought a set of Zr1's like this and they have held up very well.

MOTO SCOOB RR

Wrong, I couldn't disagree more with this.

18 inch wheels do weigh a LITTLE more but not by much and actually i'll be making a thread for some enlightment in this subject.

18's you see a lot in autox and time attack. Why? Because of less tire flex along with more stability, less body roll, and more planted to the ground. 17's a lot of the time you will need more extensive alignment to achieve 100% contact patch out of your wheels and tires. And wider is not always better there are certain extents based on your suspension to be able to get a full consistant contact patch throughout your tires tread.

So... That is all.

FASTFATBOY

iTrader: (23)

So, you think 2-3 lbs of rotational weight means nothing? It's is without a doubt significant. 2-3 lbs less rotational weight is like taking 20-25 lbs of static weight out of the car. There is a rule of thumb or formula somewhere.

The inertia in the bigger wheel is higher, therefore it takes longer/more power to accelerate it and longer/harder to slow it down.


Smaller wheels and less rotational weight are proven faster, in every facet of any type of racing. What tire aspect ratio you put on said wheel is up to you.

How does the tire on a different wheel have ANYTHING to do with body roll ?? More grip makes body roll worse, tire flex is a function of the tire carcass, not so much the wheel itself.

A wider tire is always better on a higher powered car, Miata not so much. On a low powered car there is a point of diminishing returns.

Take a 275/40/18 against a 315/35/17 and I will outrun you on my car with the 315/35/17. More grip means more cornering speed, period.

Contact patch is a function of MANY things, mostly wheel width vs tire size and pressure. Once you start driving the car harder, camber angles come into play.

If you look at a racecar, they only have wheels large enough to get over the brakes on the car.

MOTO SCOOB RR

I agree with a lot of what you said but weight of the wheels comes into play to I think in terms of this a 20lb 17 inch wheel is the equivalent as a 18lb 18 inch wheel.

I may still be thinking in terms of motorcycles but overall generally are similar in terms of less side wall + softer tire = more grip. So your 315/35 compared to 275/40 true. But what about a 295/35 or 305/35 compared to a 315/35?

I was throwing out a general statement but in terms of tire and wheel size compared to suspension components they can be balanced out fairly well correct?

FASTFATBOY

iTrader: (23)

Its WHERE the weight is in the wheel, the further out the worse it is as far as Inertia goes. In a wheel most of the weight is in the barrel.


You did not address the 18 inch wheel being lighter, you said heavier.

Suspension components have nothing to do with inertia and how it works with brake rotors and wheels/tires.

You take weight away that the shock and spring don't have to control it makes their lives easier.

A front C5 Z06(17) wheel is lighter than a rear C5 Z06 wheel(18).

Same size tire dimensionally on say a set of front C5 Zo6 wheels 17x9.5 vs a set of C5 Z06 rears . The 17 will be faster.

MOTO SCOOB RR

Thank you for giving me that information. I do appreciate it.

brigade24

for this year i plan on staying with the stock 17x9's for autox...i'm having an awful time finding robust wheels at an acceptable price point. The stock wheels are relatively light and robust...the GM engineers did their homework.

I'm still interested in going with an 18x9, 10 or 10.5 because it opens up some interesting tire options. so my thinking is that if i get better tires i wouldn't need a BBK since the tires i'm looking at have better grip meaning reduced stopping distances and coincidentally, more cornering speed...

i found a set of 18x10 OZ wheels which i plan on checking out but they are not cheap.

brigade24

totally agree.