Rotary Titus

Hi, I'm kinda a noob so bear with me.
I hear that the lighter the wheels, the better it is for performance, how does this work?
Does anyone know a website or something that shows wheels weights? All the ads I see only show diameter/width but not many show the weight. Any recommendations on light wheels? Are BBS wheels or other expensive brands expensive because they're light?
Does too light a wheel mean it's not as durable in pot holes?
Performance wise, would a lighter 17in wheel be better than a wide 18 or 19in?
And finally, how much does the OEM wheels weigh?
Thanks

wakeech

hey RT, i see we're of the same area, so i'ma do my best to answer all your questions so that i can get a ride in your RX-8 sometime!!!!! :D

(no, serious...)

anyhoo, lighter wheels are better for performance in many ways, the largest one would be handling.

in theory, the way a suspension ought to work is that your vehicle (carrying people and stuff) should stay perfectly undesturbed whilst your wheels bob up and down suspending it above the undulating road beneath it. but because it takes force to accelerate the wheel up and down, and the suspension can dampen so much of that force before it begins to affect the vehicle it's suspending, the less force you need to actuate that wheel up and down the less force gets to your car; end result, lighter wheels let the suspension do its work faster and more easily, resulting in better handling and a better ride down the country road all in one.

sure, there are lots of websites that list the masses of the wheels. i believe www.tirerack.com does (and for that i suppose i can forgive the misspelling of "tyre")... you can click here to see the wheels they have for the RX-8 (look in the white column on the left for all the information, including weight).

yes, most expensive wheels are expensive for a reason (lighter, stronger, fancier, big brand name). it's not always the case that wheels are unbelievably expensive because they're super strong and light, but super strong and light wheels are usually expensive.
why are some stronger and lighter than others?? well, it depends on many things, one being the alloy they're made of. almost universally aluminum is the base metal of choice in any wheel you're likely to buy, as only economy car wheels and spares are still made with stamped steel (the fugly doughnuts with the holes punched in them).
magnesium ("mag" wheels) is really the height of the technology, and has been for a while, but are unbelievably expensive, and not exactly very durable (they'd spark up like tinder on a gravel road).

the method of construction also plays a very major role in the strength, weight, and cost of a wheel. cast wheels, as you could imagine, are rather cheap to produce, and allow maximum stylistic creativity, but create relatively heavy and weak wheels. the super-style one peice wheels are always cast (from what i've seen). forging, on the other hand is a process of taking a very warm (though not liquid) ring of metal and squashing it into the shape the centre of the wheel is going to take. these wheels are far more expensive to produce, and are limited in the shapes they can take, but are far far stronger (although more brittle) and far far lighter than cast wheels. often they're made without a rim attached (which has its advantages), that being made with a different process (spinning, which is also a more desireable process to make the rim itself).

...i can't really say whether lighter wheels are necessarily easier to ruin, but i know for sure that larger wheels (with smaller side-walled tyres) sure are. performance-wise, there is no reason to have a wheel which is any larger than it has to be to clear the brakes you have. the ones on the RX-8 are rather huge, so big wheels (at least 17", 18" for most designs) are necessary. smaller wheels are lighter, stronger, and cheaper for the same design of a wheel, always.
getting into the debate over how big the wheel should be is always a sticky one, because so much is dependant upon the design of the tyre itself (big bad black art, and no two tyres are very much alike), so i'm going to assume you just want some nice street performing tyres.

sticking with stock sizing on everything (maybe going -5mm on the offset and having a wheel that's +1" on width or something) i don't see why you'd run into trouble.

if i remember correctly, the stock wheels weigh ~40lbs all together, wheel and tyre all. the wheels themselves were something like 22 or 25 lbs?? i can't really remember, i'll search and find out once i'm done this post.

as for a wheel to recommend, i'd suggest you compare Mr. Paul Yaw's RX-8 specific wheel to whathever else you're interested in.

Paul Yaw's RX-8 Specific Wheel

More Pics of Paul's Wheel

they're light, terribly terribly strong, reasonably priced, in my opinion very stylish (i'm a big fan of the Y spoke wheel centre style), and was even designed to house the Tyre Pressure Monitor sensors... yeah, you're a Canadian and i know that our cars don't have these, but i'm pretty sure he offers a non-counter weighted model too now.
he's a super-cool guy, and the same wheels will be on the Speed Channel World Challenge RX-8 Race Car too!!

anyhow, there you go. lemme have just a teensy ride, please!!!!

Rotary Titus

LOL WOW thanks for all the info man, I am still trying to absorb all that information.
You mean our cars don't have the tire pressure monitor???? ok that's strike 2 for Morrey Mazda where I got my first test drive from.... the sales told me it has RUN FLAT tires (and I go home and look for the Bridgestone Potenzas and find out they're not) and that it has tire pressure monitors when the tire are flat >=(
good thing I didn't end up buying from them in the end =p
Well, as for a ride, sure, when I get my car, I've been delaying in my deal to not trade in my disco until the current "snowstorm" (watch all the east coaster laugh at us) passes.

wakeech

as a former east coaster, i laugh at all the incompetant drivers when i'm standing in the parking lot, then yelling manaically at them when they're holding me up wherever i go

eccles

A lightweight wheel will also marginally improve acceleration because there's less rotational inertia to be overcome. This effect increases with wheel diameter, too, though the difference is truly marginal and unlikely to manifest itself as more than a tenth of a second on the strip.

Sputnik

The lightweight wheel means the suspension will be able to keep a more optimal tire contact patch on the road surface. Which will have more of an impact than the rotational weight, which means that braking will be more than marginally improved.

---jps

Gord96BRG

Final point - yes, a light 17" wheel with equivalent max performance tires will result in better performance than a 18" or 19" wheel. The only reason to go with 18' or 19" wheels is for appearance/style!

My 17" winter wheels (with 17' winter tires, of course) are 6 pounds lighter than the OEM Mazda 18" wheels and tires. That's a huge difference, and I could immediately notice the improvement in ride quality with the lighter wheels. Of course, the winter tires handle relatively poorly on dry pavement, so there's no improvement in handling in this case!

Regards,
Gordon

Rotary Titus

I see..... thanks guys for the info!
wow, looking at tirerack, the SSR competitions, only 15lbs!!! and half the price of the 20lb BBS seems like a GREAT deal

AlexJ

Does anyone know what the weight of the stock RX-8 18" wheel is? I need the weight of the wheel without the tire.

Thanks Alex

mdw33333

Wakeech,
Lots of good info in your thread. Now I'm no grammar school teacher, but the word "TIRE," is really spelled T-I-R-E, not T-Y-R-E.
We'll forgive you for the mispelling.

Pk14

I've seen posts stating the stock wheels at 26 lbs each. The biggest payoff for reducing unsprung weight is improved handling, resulting in quicker lap times with a secondary benefit of quicker acceleration.

The general rule of thumb is every 1 lb of unsprung weight reduction is equivilent to 10 lbs of weight reduction from anywhere else on the vehicle. In addition to lightweight wheels, the weight of a given tire might be a couple of lbs in variance, plus the stock rotors can be replaced with two-piece aluminum rotor hats - 80 lbs of unsprung weight being removed will have a noticable impact on a 3000 lb car (equivlent of removing 800 lbs of weight elsewhere!)

In as far as the 17" vs 18" decision, the handling impact of the difference in sidewall height is noticable (assuming you are keeping the outer diameter constant) when you are pushing the car beyond 7/10ths. My friend has the exact same car I do (Audi A8) except he has 18" wheels and I have the 17's (same tire brand and same outside diameter). I do notice crisper turn-in and a slightly firmer ride with his car.

The good news is that you can find 18" wheels at ~15.5 lbs each and preserve some of the real world benefits of having some sidewall to cushion the potholes which are cropping up around D.C. at an alarming rate. No question about forged versus cast with lightweight wheels - you need all the strength a forged wheel will give.

Gord96BRG

I estimated around 23 lbs, but Canzoomer took his off and had them precisely weighed at 21 lbs each for the OEM 18" wheel. Still pretty porky!

Regards,
Gordon

Sputnik

How do you figure that?

---jps

AlexJ

21 lbs. for the OEM wheel is not bad. I think I am going with the SSR competition in a 18x8. At 16 pounds for $400 it is the lightest wheel I can find for the money. They really stand up to abuse as I used them for 4 seasons on my World challange BMW without bending a single one. I will keep the oem wheels for rain tires.

Thanks.
Alex

Rotary Titus

that's the wheel I was looking at too! that's exactly what I wanted to know... if lighter wheels = less durable
thanks!
on a sad note.... I scratched my rear curbside wheel last week... was about to put a jackhammer to that curb but guess my neighbour wouldn't appreciate it

Genom

I just feel myself being called by those 15 pound 17" SSR's

Must put away CC. Must not blow money on wheel's (yet).

Pk14

This is a general rule of thumb from Formula Continental and Porsche Cup car racing buddies.

Gordon - thanks for clearing up the stock wheel weights - a 21 lb 18 x 8" wheel is pretty good for a stock wheel. That 15.5 lb SSR Competition wheel is still awesome!

Anyone look at the OZ Superleggra III?

Pk

Sputnik

Then you either misunderstood them, or they're blowing it all out of proportion. There still is some dissention in the car world as to what that number actually is, but when people actually do some valid math on the subject, they get between 1 1/2 to 4 times as much. Never 10.

---jps

Pk14

Could that be variance be vehicle dependent - aka normal street vehcile versus purpose built machines? 2 piece aluminum rotor hats are pretty expensive, but they cut the weight in half and on the track cars I get to play around with, the unsprung weight is the biggest area of attention, hands down. Where in the car world do your numbers come from?

Thanks, Pk

Sputnik

No, there aren't different laws of physics for race cars. The priorities, requirements, and budgets do change. It is much more important on a race car to decrease overall and unsprung weight than it would be for a street car.

But don't forget, 20 lbs is a savings of 0.4% on a 5,000 lb SUV, 0.8% on a 2500 lb Miata, and 1.7% on a 1200 lb spec racer. The lighter the car, the bigger difference a pound makes. So what would make a 4% difference in weight change on your 3,000 lb. RX8, will make a 10% difference in weight change on a 1200 lb spec racer.

---jps

Pk14

Hi Sputnik -

Agree that the % of unsprung weight versus suspended weight is probably greater to start with on a spec 1200 lb race car (thus a decrease in unsprung weight has a potentially more dramatic impact to the lap times than a corresponding decrease in weight from anywhere else on the vehicle. Seems that Mazda has tried to emphasize lightweight from the get-go (21 lbs is pretty good for a stock 18" wheel).

Given a switch to a 16 lb wheel (SSR Competition), plus 2-piece rotors (9 lbs per corner removed), is 52 lbs of unsprung weight significant in a 2950 lb car?

For my 2001 911 Porsche Cup car, it is pretty apparent that they didn't ignore weight reduction from anywhere in the vehicle - however, we have noticed a difference with the lightweight rotors and carefully watching tire / wheel package weights.

I'll try to dig up a little more info on the performance impact from the rest of the off-season buddies. One of my cousins owns AWE in Philadelphia and crews for several Daytona cars - he's involved extensively in suspension development.

Good discussion! Pk

Sputnik

At 13 lbs per corner, very much so. Even on a street car for someone who never does any serious performance driving. The car will basically feel "lighter on it's feet" when you are driving it.

The thing we have to remember is that there are two aspects to wheel, tire, and brake rotor weight. And admittedly, that might be a matter of confusion in we are talking about here. We could be talking about apples and oranges.

The first is rotational weight, which pertains to the hub, wheels, tires, and brake rotors. For every pound of weight in either of those items, you not only have to expend energy moving that pound forward (or stopping it from moving forward, as in braking), you have to spin it too (and stop it from spinning). So a pound of weight in the wheels, tires, and brake rotors has more of an effect than say a pound of weight in the battery. This is something that you can actually put numbers to, although there is some dissention as to how to do the math. The problem is that the further out from the center the weight is, the more effect it has. How accurately you determine that makes a big difference in the final numbers. Like I said before, depending on the formula used, the numbers normally come out to one pound of rotational weight equals 1 1/2 to 4 pounds of weight elsewhere on the car. Due to the fact that the weight savings of a two-piece rotor with aluminum hats is closer to the center, the effect of a two-piece rotor on rotational weight is minimal.

The other aspect is unsprung weight, which also includes some of the suspension pieces, and the effect mostly intangible, in that it's very very hard to put numbers to it. Decreasing unsprung weight increases the suspension's capabilities to keep the optimal contact patch more consistently. This improves handling, braking, accelerating, and ride. In unsprung weight, it doesn't matter where the weight is located compared to the center of rotation, so two-piece rotors do make a difference in this aspect. To what extent depends on sooo many variables (chassis, car weight, initial unsprung weight, suspension, tire air pressure, weight distribution in three dimensions, etc.) that the effect is different for different cars, even for different option and modification levels. So there is no general "1 lb. in the wheel is the same as 3 lbs. in the chassis" type of comparison that one can make.

An exception would be a racing team that has enough funding that they do such extensive testing that they have found that say using wheels that were 5 lbs lighter gave them as much improvement in lap times as 50 lbs in the chassis (of course, where in the chassis makes a huge difference in that, too). But even that depends not only on the car, but on the car's setup. It will be different for different cars, and only consistent, controlled tests would tell the actual difference. In this case, because even production based race cars are that much more sensitive to suspension changes than their street equivalents, the effect may very well be greater than a similar change on the street version.

Quote:

For my 2001 911 Porsche Cup car, it is pretty apparent that they didn't ignore weight reduction from anywhere in the vehicle - however, we have noticed a difference with the lightweight rotors and carefully watching tire / wheel package weights.

Certainly. I wasn't saying that there isn't a significant improvement, it's that one hears alot of people blowing the benefits out of proportion on the Internet. Not only are there tangible performance benefits, but feel and feedback benefits too. These result in more confidence and more consistent driving, which in turn result in minor lap time improvements (tangible), improved lap time consistency (tangible), and less tendency to lose control, or just lose optimum line and momentum (not too tangible, unless you've got one o 'dem F1/CART style telemetry setups that monitors 100s of variables).

There is a small aftermarket company in California who recently offered a complete 4-wheel braking kit for the Miata, including two-piece rotors, and lighter calipers. Even though the package offered much better braking abilities, it was significantly lighter up front. Practically every customer immediately noticed the improved ride and feel in the steering just driving down the street.

---jps

Rotary Titus

what are 2 piece rotors? (like dual rotors on a sportsbike???)
are they... expensive??

Pk14

If you look at a standard brake rotor, the hub (which slips onto the wheel studs) and the rotor (area where the calipers press the brake pads onto the disc surface) are a single piece. With 2 piece rotors, the hats are typically a different type of material from the rotor itself (Porsche uses ceramic rotors to dissapate the heat and provide a more consistent surface for the brake pads to bite into over extended use (as in during a heavy track session), while the hats (the part that mates to the hub) are aluminum. The rotor bolts onto the rotor hat which slips over the wheel studs. The typical weight savings (not talking about the ceramic brakes - those are a $4-6000 option on the 911s) going from an iron 1 piece rotor to an aluminum hat / iron rotor is around 10 lbs. These are in the premium brake kits and are approximately $2000 and up for typical applications (also included are 4-piston calipers for the fronts). Baer and Brembo are two fairly well known manufacturers. Stop-Tech makes a set for a few different applications. There was someone on this website that advertised a 9 lb savings going to a 2 piece rotor set-up. Try a search on two piece rotors. (Not the same as the superbikes - cars are working into the 4 and 6 piston caliper/ single rotors of various materials to improve braking performance. From what I've seen and read on the RX-8 the stock brakes are above average for a street application.


Pk

Sputnik

To illustrate what Pk14 said, take a look at the picture below:


The two rotors on the right are one-piece steel rotors, while the two rotors on the left are two-piece rotors (the black are the aluminum pieces, and the silver are the steel pieces).

---jps