brillo

I want to first start off by thanking Brian at MazMax for his help with this project, he put it best, “There is a fine line between hobby and insanity”

As I am still on my Rx8 weight analysis kick, I decided to go weigh the stock 18’’ wheels sans tpms and tires to see once and for all what the wheels weigh so I could decide on getting lighter weight wheels or just lighter tires. Like the weight of the car, I’m not happy with someone just telling me the weight, so I not only weighed them with a digital scale used for hunting/fishing, I took pictures of the weighing so others could see it for themselves. (I will post these later today, once I get the downloaded off the camera in my vbgarage.) I did test the scale with a 2.5gal bottle of water to test the accuracy, and it appears to be accurate to within 1-1.5 ounces.

So after weighing one 18inch wheel, with 14 of the little ˝ ounce weights attached, the wheel weighed in at 22lb 4 ounces. Subtracting the weights gets us down to 21lb 13ounces which is 21.8125lb +/- and ounce.

I also took off a wheel when I was rotating my tires to see what the full wheel / tire / tpms / balancing weight combo weighed in at. The weight I got was 48lb 2 ounces or 48.125lb. Now our tires weigh in at 26lb, so that would imply sans tires a wheel weight of 21.125lb. Anyone notice a issue here? I’m not even taking out the wheel balancing weights or tpms or the air that’s in the tire. Now, my tires are also somewhat worn but in great shape for 6,300miles. So maybe they are lighter than 26lb now.

All of this has left me somewhat confused, but I think that its pretty evident that the wheels weigh about 21.5lb +/- and ounce or two, which sucks one, because I can’t say the exact amount for sure, and two, its to F@&!%ing heavy.

So the moral of the story is, our wheels are heavy and you can get nice 18” wheels for 400-500 that weigh about 16.8lb in a 18x8. Are they worth it? Well, you can take 4lb off the just the tires, with better tires. So I’m not sure yet. Feel free to chime in with your thoughts.

*UPDATE* - Pics are in my vb garage. I have more if people would like me to email them.

Spin9k

Hey brillo, I too think about this all the time, and the idea of less unprung weight, with different wheels and tires. Couple of things I've finally concluded, at least theoretically:

1) After researching wheels all over - Our wheels are not the heaviest, nor the lightest. Mazda must at least think they are strong enough to be safe, and I also think they tried to keep weight down the best they could for the money they allocated to the wheel cost in manufacturing. Sure they could have put 16lb wheels on, but why make everyone pay for that if they really don't care?

2) So of course for a pretty $ we can save 4-8lbs on wheels. Is that a good move re:safety (say on the track). That's a question I've been unable to answer as I don't know how often wheels fail and at what point too light is also too fragile! . Obviously wheel manuf don't advertize if their wheels are crap and just look pretty and weigh next to nothing.

3) It's damn hard to get reliable wheel weight data. Tirerack gives it on some (maybe only the lighter ones?) but not others. Manufactures don't generally seem to think it's important to tell us, other then the word 'lightweight' which means almost anything. This makes this whole endeavor a bitch.

4) Apply (2 ) and (3 ) to tires again making it esp hard to actually plan for what you want to end up with weight-wise. Also (racing rubber aside) it does appear that the strongest sidewalled tires handle best and they are the heaviest, or so I'm beginning to conclude. If anyone disagrees with this please chime in here, I would love to get the best handling tires that weigh in lighter than stock - if they exist.

Bottom line I've concluded something like this is the winning combo:

- 17x8" Kosei K1 TS wheels @ 15.4 lbs {tirerack}
- with 245/40-17 tires - wider, but lighter than stock due to 17" size

to accomplish these good things:

- light weight approx combined 10 lbs lighter than stock ~38 vs. ~48 lbs
- lower rotational weight beyond pure unsprung weight due to 17" vs. 18"
- while the smaller diameter tire gives a 5% boost to performance (sure ok the speedometer is off, big deal) so as to go faster.. faster :D
- also the smaller diameter lowers the car approx 1/2" in the process for zero cost !

What do you think? :D

BaronVonBigmeat

Does anyone have pictures of an RX-8 w/ 17's with the same or maybe even smaller sidewall tires than stock? I don't mean "smaller wheels, bigger sidewalled tires to compensate" I mean like an overall smaller rotating assembly (yeah, it would throw off your speedo).

Losing 10 lbs. of rotating unsprung mass per corner, reducing the inertia via the smaller diameter, having shorter gearing, being 1/2" lower, cheaper tires...these are all cool, but if it looks as silly as I imagine, I think I'd have to pass. Too bad the car is styled so it looks best with 19's.

brillo

some of the winter wheel pics are kinda close, I'm not sure how 17''s would look with say a 225/45/17, which would be the same visual proportions

GeorgeH

iTrader: (2)

Yes, I suspect lowering springs would be required to avoid the raised 4x4 look. But then that might perfect the package. Just don't lower the car too far - 1/2 drop should keep things looking kosher.

If you want to avoid all that, according to this website:

http://www.wheelweights.net/

SSR Comps in an 18x8 weigh in at 15 lbs. $419 at Tirerack. That's 6 lbs right there. So, with 4 lb lighter tires (which tires are those?) your at 10 lbs, like brillo said.

So, is it worth it? I think it depends on what other suspension mods you have done. 10 lbs is allot, and even on a stock suspension you should see an improved ride and better grip over rough surfaces. But the stock car does so well already, it may not be as significant as you would hope for. I'm not saying it will be imperceptible, far from it. Just that I don't see the RX-8 suffering from any of the handling maladies I saw in my Miata when it had a few lbs too many in the wheels.

However, drawing on other experiences with my Miata, where I have had a whole range of wheel/tire packages and suspension upgrades, I can say this. The more sway bar you have on the car, the more you are likely to perceive benefits from lowering unsprung weight. So, if you are running RB sways, or the MS suspension package, etc., shaving those precious 10 lbs off the wheels will help mitigate the downside of those stiff sways (i.e., the coupling action). Also, with stiff springs, lowering the unsprung weight can help eliminate some of that body shudder you pick up with the springs.

This is all just hypothetical for me with the RX-8. But in the Miata I have found that with a super light wheel/tire combo, you can do more to the suspension without having to resort to aftermarket chassis stiffeners, which add weight. So, save the money you were going to spend on chassis stiffeners and get some nice light wheels.

brillo

you can get perelli p zero nero's that are 22lb for a 235/40/18, close to stock

Fanman

Well, you can get the Mazda Speed rims that weigh 17 lbs. each (16.9 lbs. actually). Saving almost 5 lbs. per wheel, and you won't have to worry about them being too weak. They are $516 per wheel over at Rosenthal. If you really want to get crazy, they have magnesium MS rims that are only 16 lbs., but they are a jaw dropping $1,416 per wheel !!!

I would never get 17" tires. I guess I value the appearance of the 18", over the slight weight penalty.

GeorgeH

iTrader: (2)

Hmmm, reduced sidewall + super light rims = pot-hole damage. Do you know what the lighted OEM sized tire is?

rotarenvy

your right for point one mazda wheels are light for cast wheels but not for forged and thats due to manufacturing cost.

as for point 2 wheels have a load rating on them you shouldn't fit a whell with a lower rating than standard. if a wheel complies with your countries standards you should be getting a wheel that is about the same strength. also when you talk good quality light weight you automaticaly switch to forged wheels which in turn implies strength. have a look at the rays engineering site in japan. they have a section on testing and standards and they are quite extrem (use bable fish and you will get an idea for translation). most jap wheel companies manufacture to these stds. as for other countries you will have to do some research to see if the maufacturing stds are as good or better.

in other words I reckon you should be safe in buying light weight wheels and wont compromise safety if you buy a good brand.

Spin9k

THESE guys are MY heros and THEY run 17" wheels w/225-45s.

I think they look hot! Hot! HOT!! :D . Why be ashamed (like this --> :o ) of something that is inherently GOOD (like this--> !

They didn't win by looks, they won on skill, performance, some luck, and great moding within the rules.

IOW if the difference on track between faster, and fastest is helped by 17" wheels and tires I mean -->WTH??!!

Hang out there a little

brillo

those racing heart wheels are awesome, and about $1,500 a piece must be fun to have a racing budget

GeorgeH

iTrader: (2)

Another issue to consider is the subjective nature of the lightweight tire. The Toyo T1-S is a light, good performing tire, but has soft sidewalls that affect turn-in. Some people shrug their shoulders at this, and say "you can get used to it." I had a set on Miata and will never go back, because they kill one of the fun aspects of the car (turn-in). The RX-8 is no different. I would never give up turn-in to save a few lbs at the wheel. Yes, the Toyos probably handle better over rough pavement, but I could care less - why compromise the fun, playful nature of the car 100% of the time so you can go faster 20% of the time?

This is all subjective of course but I have yet to hear of a light tire that turns in like the Bridgestones do.

And again, this is an argument that goes on indefinitely in the Miata world.

brillo

interesting point. all though I know alot of autox folks that love them, I wasn't aware of the tires being soft in the sidewall.

I'm actually leaning more towards the Perelli's as they seem t have a longer tread life, lighter weight, uni-directional, and get awesome reviews.

mazda used them on the FD as stock tires back in the mid 90's.

GeorgeH

iTrader: (2)

I've heard good things about the Pirellies as well. If you do it, please let us know what you think. I'm curious how the ride quality works out - you are loosing four lbs (assuming stock rims), but also a few mm of sidewall height. I wonder which will prove to be more significant.

crossbow

Just a note...the Kosei's are CAST wheels. They are extremely light, and very very very vulnerable to potholes. One dip is enough to bend the rim. They do make excellent track/autox wheels due to their cost, but if you live in an area (or drive on roads) with a good # of potholes, I'd definitely skip them for street use.

I'd say the best combo would probably be some 17x8 +48 Forged SSR Comp's, with some 245/40/17's. Remember that by downsizing and running a lower profile tire, you'll change your final gearing to be more aggressive, which can really help your acceleration out. (Its like a slight rear diffy gear change).

(A 235/40/17 + SSR Comp is around 34-35 lbs (combined)). Yes the SSR's will bend if you hit a big enough pothole, but they're far more durable then the Kosei's overall.

Toyo's coming out with the T1-R's next year (already avail overseas), and the new Falken Azenis's are looking hot as well.

brillo

wish I could tell how much the t1-r is going to weigh, its not listed on the U.K. or Aussi site.

MrWigggles

My typical word of caution is this.

Use Tire Rack's side-by-side track tests lap times to determine overall tire performance not weight.

They use a 330ci as their test vehicle (RWD and similar weight to RX-8) and in the tests, the lightest tire doesn't always win by a long shot. Bridgestone has some of the heaviest tires out there and yet they do well in the comparison tests (and user evaluations). Maybe it is the flimsy sidewalls of lighter tires that keep them from higher scores, but weight is obviously not the key to lap times, slalom, comfort etc. Weight is one of the factors.

Weight of the wheel is different matter. Given that the RX-8 is going to well within the load rating of virtually any aftermarket wheel, lighter is basically categorically better. The question is how much better? In straight line performance, every pound you save in wheel weight is worth 1.5 lbs of normal weight* That's something but not a whole lot. Simply switching to 16 lb wheels is going to save you about 4 lbs per corner over stock which is 24 lbs of equivalent savings overall (24 lb reduction means the 3000lb car will accelerate a little less than 1% faster - i.e.you might shave a tenth on your 0-60 time). Now handling is a different matter and totally subjective - YMMV on that. Some swear to a remarkable difference, how this translates into lap times I am not sure - haven't seen any double blind type testing to be sure.

One of my favorite light weight wheels is the Centerline Rotary Forged series. www.centerlinewheels.com. Not a whole lot of size options but the wheels are very strong and light. My friend drove through a devestating pothole with 18" RPMs with no damage.

-Mr. Wigggles

*Other forum members and myself have worked out the exact same "1.5 lb" number using different methods. The typical "every pound of wheel weight will save you 2lbs (or more) of actual weight" are not accurate for the RX-8 or are not refering to straight line performance.

crossbow

Wiggles,

Using your formula, if you swapped to 17x8 SSR's with T1-S's, you'd drop an equiv of 90 lbs curb weight. Thats a damn good amount .

Honestly having swapped around with heavier and lighter rims myself, I'd say its far more effective then 1.5, but you can't really explain that to someone till they've tried it, themselves. Till then, nobody believes you, and they'll keep putting on 19's and spending 600 bucks on underdrive lightened pulley's...not realizing the bigger heavier wheels are roughly equivilant to putting on really heavy pulley's .

GeorgeH

iTrader: (2)

Techincally, it depends on how far from the center of the wheel the "missing" weight is. If you remove all the weight from the OD of the tire (not physically possible, other than shaving the tread), I do believe it is exactly 2. An average of 1.5 sounds about right for a lighter wheel, where the weight reduction is futher inboard.

Now, a wheel/tire combo with a smaller OD overall will show a multipliction factor greater than 1.5, since the MOI is proportional to the radius squared. How much more is left to the reader as an excersize.

George

Spin9k

From all the above, I think we all believe this is a good route to follow, at least theoretically. Bottom line is we have to start doing it. Heresay isn't enough, real stuff on RX-8s with us driving is.

I liked my stock car on the track this year, I'm hoping I know what needs changing... Coilovers, sways, and new wheels/tires are on the list.

The lightweight route makes sense to me for the suspension. We need a list of say 17x8" or 17x8.5" lightweights, w/pros and cons. There can't be so many 'lightest' good wheels in our sizes of interest. I esp. appreciate those here that have experience w/wheel brands.

My end-winter goal is to lower my baby about 1" - a free 1/2" w/17s tire's smaller diameter w/245/40x17 & 1/2" by gentle lowering w/coilovers, plus taking ~10lbs off each corner in the process.

With some new sticky rubber under me, 1" or so further hunkered down on lightest suspension possible, maybe a few add'l HP for spice.... that's what my winter dreams are made of.

EZZY

is that correct that equates to about 22kg, for factory 18" wheel/tyre combo.
my first set of CHROMED 20" with 245/35 tyre weighs 26kg each so thats 16kg extra for the 20"s

Spin9k

Just for fun, find some hand weights. Heft and swing some 4lbs/6lb or maybe some 10 lb weights. Doesn't sound like much but then swing it around in a circle and imagine it then spinning 10-15 times a second(!) on each corner of your 8. Now go the other way and think of REDUCING stock weight by that much. That would be some pretty amazing rotational weight reduction on a car!

In your case it would be 8.8lbs/corner more.

Zaku-8

thats sort of apples and oranges there. Me /= car.

On the other hand I wholeheartedly agree with your point, and also suggest that a 17"/18" ligthweight wheel weight index thread should be started.

Is there any way to empirically measure moment of inertia, as opposed to guessing or trying to calculate? I was wondering if wrapping the tire in light "frictionless" rope, mounting the wheel vertically on a stand, and then attaching a standard weight to the other end of the rope would yield any type of figure by tracking the acceleration of either the tire or weight w/ a high speed camera. At the very least it would put a year of undergrad physics to good use.

mdmaclean

I have been looking at new tires, and weight is a factor between them. The tires at the top are

1) Pirelli PZero Nero M+S 245/40R18 - 25.6 pounds
2) Toyo Proxes 4 245/40R18 - 24.0 pounds
3) Potenza RE040 225/45R18 - 26 pounds (just included for reference)

From what I am understanding from this thread, given the weight approximately at the outside of the wheel, it's effect would be double it's curb weight equivalent. That would mean that the most difference this would be 2 pounds x 4 wheels x 2 = 16 pounds.

That does not sound like it would make any significant performance difference, and a modest diet for the driver would be another easy way to save 16 pounds from the car :p.

mdmaclean

What I forgot to add was that it looks like the Nero M+S is the best choice, with all the positive reviews here, and the 1.6 pound weight savings for the Proxes 4 is probably insignificant.