OC_

ok, what i was saying was that you should try to stick with the OEM tire hight and put as big as a wheel as you can in that OEM overall hight tire. This is so you minimize sidewall hight. as im sure you know, tall sidewalls flex in hard cornering and 'fold' under the wheel. Tall sidewalls are also not as responsive.
goodyear doesnt have a very good size selection do they
you could check out Avon and see what they have, they have a lot of sizes but cost a big $$$.

i think youll be ok with the goodyears, as these are hardcore racing tires with really stiff sidewalls.

AMRX7

Don't forget it will affect braking as well acceleration. If you want an actual observation, I autoxed a Boxster with about 17lb wheels and 26lbs wheels the same day. The car was noticeably quicker with the lighter wheels, especially under braking.

As far as the rule of thumb, it really depends on where the weight is located. The effect of the weight is greater the farther you get from the center axis of the wheel. So, saving 10lbs in tire would be better than 10lbs in the wheel center.

In any case, you are looking at paying about $170x4 = $680 more for the lighter wheels, right? To save 36lbs rotating weight. If the weight differences are accurate, I'd do it but that's me. I'd do everything I could to verify the weight claims, though.

-Andy

RX-Heven

iTrader: (1)

What you all are refering to is rotational inertia. Unsprung weight alone is primarilay concerned with the shocks ability to control that unsprung weight which includes the brakes, and relative suspension components including the mass of the wheel when static. It is not necasarilly concerned with the rotational inertia of the wheel and the forces involved when accelerating or decelerating the weight of the tire. That is an entirely different problem. The best I've been told was by Carrol Smith himself when I asked the same question. Force = (Mass x (Velocity)(Velocity)) / Radius of curvature. There are two unknowns, Force and Velocity. You would have to find the velocity at the point along the radius of the tire of where you assume the weight that is in question is located before finding the force required. This still would only be an estimate and would show there is not one 'holy' ratio to account for this, hence wide margin of estimates previously stated. General rule of thumb is lighter and smaller is better

Carl Byck

Tell that to my wife

Carl Byck

Thank you everyone, in the long term I will own both as I wll use a steel set for rains. The one other rub on real racing is they only come in full inch increments, but I think iI can go 5 in 5 out, and 6 in 6 out,

Carl Byck

Thanks, your rfight Goodyears selection is strictly tailored to the most active series. This is why I find myself working backwards. The carcass is their latest, and is used by the LMP cars in ALMS. Infact most of my tires for next year will come from the 24 hours at Daytona. I'll be running GT sizes that were Porsch before they went to 18s. I should have a set in a couple days, we shall see, but I'm sure I won't be anywhere near the potential of these tires. I am looking for Avons primarily for autocrosss, I will use a Bias ply so I can get them up to temp more quickly. Probably Rain tires prior to them being grooved. Kind of like when Rod Millen used TAR1 custom grooved Autocross tires to win Pikes Peak a while back. I will be able to get 80-90% Avons for ~75.00 a piece so it will be worth the experience. Honestly, combination of the difference between state of the art ~13"Goodyear Slicks vs 235-40-17RA1s, and Koni yellows vs Advanced design, and speedway bars vs RB, I think it will take a bit if seat time to approach the potential of the new set-up. Not to mention a cage to stiffen it all up, ~250lbs less weight, and ~150 more rwhp I have ALOT to Learn, hopefully my partner can keep it off the wall, and not **** the seat

DamonB

I would give anything to save 10 pounds per corner. That's HUGE!

The complete problem gets fairly complex as RX-Heven explains. It's not just the total mass, but where it is located within the system. Mass on the chassis or suspension is merely dragged around by the engine. Mass in the rotating assemblies must not only be dragged around, but it's inertia must be countered everytime the acceleration (in physics a decel is still an acceleration, it's just negative) is to be changed. Any rotating assembly not only contributes mass to the system, it's inertia must also be overcome; it's a doublehit so to speak. For a car this means everytime you press the gas, press the brakes or turn the steering wheel you must overcome the wheel/tire inertia. Tire weight is often overlooked and actually pays quicker dividends since it's the outer most part of the wheel assembly, but no matter how much we simplify the problem 10 pounds per corner is nearly an exponential savings.

SpeedKing

iTrader: (4)

There is a similar (online) article done by Grassroots Motorsports.