Carl Byck

Hello all, I have seen the light, I was headed for some 18" SSR 3 piece wheels for my track car, but I have found a hook-up on 16" GoodYear radial slicks. So, I can by Circle wheels 16x10, and 16x12(25lbs) for ~90.00 a piece, and have a set of rains, a regular set, and a soft set for autocross, or I can buy Real Racing same sizes but ~16lbs each for ~265.00 a piece. Question is can somebody quantify the superior acceleration(or other performance) of the lighter rims? have seen some statements about this before, but I have never seen good data from a reputable source. Thanks, Carl.
Also anybody have a "hook-up" on either of these?

Carl Byck

What is 10lbs of unsprung weight a corner worth?
Hello all, I have seen the light, I was headed for some 18" SSR 3 piece wheels for my track car, but I have found a hook-up on 16" GoodYear radial slicks. So, I can by Circle wheels 16x10, and 16x12(25lbs) for ~90.00 a piece, and have a set of rains, a regular set, and a soft set for autocross, or I can buy Real Racing same sizes but ~16lbs each for ~265.00 a piece. Question is can somebody quantify the superior acceleration(or other performance) of the lighter rims? have seen some statements about this before, but I have never seen good data from a reputable source. Thanks, Carl.
Also anybody have a "hook-up" on either of these?

1RedR1and1RedPEP

I think aluminium is going for .65/pound. if it is iron, you may have to pay to dispose of it. So $28.00
1R1

Carl Byck

You sir are a dork! So says my 5 year old...

REFLUX

isn't 1lb or unsprung weight = 4lbs of "sprung" weight?

turbojeff

iTrader: (30)

I remember an old statement in Hot Rod, saving 50lbs off the wheels is the same as 500lbs off the car. Now I'm sure that depends on how fast the car is and how much it weighs.

Carl Byck

Well, if somebody could expand on these tales from days of old.................. The car weighs ~2500lbs, it will be around 450hp, but I don't see how the speed of the car makes a difference, i suppose the weight of the car might be r5elevant if there are some percentages that get played with. So far we have 1:4, and 1:10 vs the cars overall mass, anyone else

christaylor

The 1:4 is sprung:unsprung weight. The generally accepted rule of thumb is that any time you can reduce sprung/unsprung weight you're going to benefit. I'll do some looking and see if I can't find some good tech, but I'd bet a dollar it's in a Carroll Smith book.

OC_

i dont have any numbers, but just adding a couple of pounds to a wheel does decrease stright line performance significantly. That includes acceleration and braking. What happens is the heavy wheels have more inertia, thus taking more force to stop/start them.
Just a few pounds makes a world of difference...
go with the light wheels, its that big of a difference.

i would go with the 18" wheels though, cuz you can corner so much better! even at the cost of stright line performance. you better be getting those tires at a deal!

maxcooper

Unsprung weight affects handling as the tire spends less time on the road with heavier wheels when the surface is rough = less grip. Your ride comfort (which is partially determined by the ratio of sprung to unsprung weight) will be worse with heavy wheels/tires as well. The rotational inertia affects both acceleration and braking performance (if your brakes are marginal for your usage).

Tires typically weigh more than wheels, and have a bigger diameter meaning they are even more significant in determining rotational inertia. Keep that in mind as you are evaluating various wheel/tire combinations. Many of us are crazy for light wheels here, but sometimes we forget how important the tires are (me included).

-Max

rockshox

iTrader: (3)

titanium brake rotors can easily save you over 5lbs per wheel too.

SleepR1

Off-Topic--Max, have you had a chance to test fit your 9.5 x 17, 40-mm offset SE37Ks up front? I know your 265/40-17s are taller than the tires I plan to run (255/40-17), but I'm looking for ballpark whether the 9.5 wide SE37Ks will rub up front? There's only a 2-mm difference between SSR Comps in 9.5 x 17, and I've test fitted 42-mm offset, 9.5 wide Comps with 275/40-17 R3S03s up front before with no rubbing problems?

in2twins

Thanks Max, the Bias ply tires are 18, and 21lbs, and the Radials are 18, and 24.5lbs. So as compared to stock(~50lbs a corner) the bias ply set-up would be 34/37, and the radials 34/40.5. The radials which I am tending towards are 390.00/450.00 new. I have a deal for guaranteed 80% or better tread for 75.00 each for the radials. These are ALMS takeoffs.
OC, I do not think there is much advantage with the 18s, most of the Trans Am/GT cars run 16s, and I doubt that I will be taxing these tires to the extent the Trans Am guys are Also the Tires are the same sidewall height or more in the 18s. The 16s are a 23.5" tire on a 16" rim vs a 26" on an 18. So as I see it that's a wash if not a disadvantage with my car. if I am wrong, I do want to know however. With the 23.5" tire I have alot more latitude with my suspension set-uop as the 25.5-27" tires that they use on the 18" rims are a challenge to fit properly even on my widebody. I'd still love to see some hard numbers on the unsprung weight though. Thanks for the feedback, Carl Eitherway, I plan to hit the track by early february when it starts to get warm again(haha mani)

Str8Down

Stock is only 39 lbs per corner. I have the FedEX shipping receipt to prove it.

in2twins

Is that an FD in your avatar? I am talking FC. 25/wheel, ~25/tire(I was running 17x8 with a 235-40-17) I should have said compared to what I was running. Be that as it may, we are talking about 12" wide rims, so even keeping it close to stock is a challenge. Carl

gambone

iTrader: (3)

I think we are talking of "sprung weight" and the rule of thum is for each lb less there is a 10lb better feel as to how it handls. At the dealer ship the stock alu where 15lb lighter X 4 = 600lb,then the steel, and yes it felt like and did handle as if there where not carrying that weight. And a few fokes had theme realy good after market wheels and if I where blind folded getting in I could tell.

SleepR1

There was an old Sport Compact Car article that did a quantitative comparison between, 16, 17, 18-inch wheels/tires, while maintaining the same overall tire diameter. The tests were conducted on strip and road course. Bottom line, the conclusion was that 17s offered the best compromise for road course work, while 16s offered the best setup for strip work. 18s were the worse. The additional unsprung weight slowed the car down to the point of having 100 lbs of dead weight in the car...

I don't recall the month or year of this article.

in2twins

Do you happen to remember the wheel weight differnce that was equal to a 100lb weight penalty? What was it about the 17s they liked? Thanks

OC_

" I do not think there is much advantage with the 18s, most of the Trans Am/GT cars run 16s"

dont the trans am guys run 16" wheels by rule?
if you look at all the touring car racing, like that german super touring on speed channel, you will notice that they all run 18"s.
its all about sidewall. If the 16"s your using has the same or less sidewall then 18"s then your tire is going to be too small, and smaller tires have less contact patch.

There is huge gains in cornering with taller wheels and tires. I run with the Midwestern Council and do a lot of high speed autoX events with them. We have a points based system of classing cars. The more mods you do to your car, the more points you get. You dont want point as you can see...
but what im getting at is that if you change your wheel hight 1", they give you 2 poitns. 2 points is really significant. someone had to know how much of a cornring increase there was with taller wheels to merit such a heavy poitns price.. so did Jim Hall of chaparral back in the late 60's and he had special tall tires and wheels made for the chaparral race cars.

SleepR1

Sorry I don't recall the details (I think this was a 2000 or 2001 article). It's like the "3 bears" story. 18s were too heavy, 17s were just right for road course work; while 16s were just right for strip work, but not enough cornering potential like the 17s, even though the 16s were the lightest...

Carl Byck

OC, if the sidewall was taller, or the tread wider, I could see what you are saying, but the differences are small, due to the 16s being available in much a shorter tire. I will give you a link to the Goodyear site, and you will see what i mean, but in the front, i will have a 23.5" tall tire with 10.6" of tread width, vs a 25.1 tall x10.2 tread width in the 18. In the rear it is even worse, 16 would be 25.5 tall, with a 12.2 tread width, while the 18 would be, 26.5 tall, with a tread width of 10.7. To get equal tread width in the back on an 18, I would have to go to a 27.7" tall tire on a 13" rim. When you read the chart, keep in mind these tires are in groups which are designed to work together, you cannot "mix and match"
http://www.rogerkrausracing.com/GYRoad.html I am using the R210 5875/5880 tires, under IMSA Radial Slicks. These are the only paired set that will work with the 10"/12" combo in a radial. Check it out, and tell me what you see.

redrotorR1

I've always heard SP & SM guys saying that saving 1 lb of unsprung weight is like saving 10lbs of sprung weight. Given the acceleration benefits as well, I'd say save on the unsprung weight and figure out how to dial in enough camber to balance out your contact patch issues.

in2twins

Thanks, with over 12" of goodyear slick on the ground I don't think I have contact patch issues

3isacharm

which leg do you like more?

j/k. i know it's a hookup, but are you sure there aren't any other wheels for less that are a similar weight?

fe1rx

With respect to acceleration, one pound of wheel an tire is equivalent to a bit less than two pounds of sprung weight.

If you add 1 pound to the tread of a tire, that pound is moving forward at the cars speed and also rotating in a circle at the same speed (since it is rolling on the ground the two speeds must be the same). Thus it has twice the momentum as a pound of sprung weight. This implies it takes twice the energy to accelerate this pound and means that it is equivalent to 2 pounds that are just moving forward but not rotating.

When you add a pound to the wheels it is not all concentrated at the tread. Thus its rotational speed is less than the forward speed of the car and that additional weight will be equivalent to a bit less than two pounds of non-rotating weight.