mitchfried

OK, so no significant hp increases with available mods. Anyone have any actual data for the RX-8 for acceleration improvement for 0-60 and 1/4 mile times by going to lighter wheels? Not theory, or experiences with other cars, but actual RX-8 times? Assume that you stay with the same size wheels (18x8).

crossbow

What would make the gains any different between the 8 and other cars? If anything, because of the rx8's awesome curb weight, these effects would be multiplied...(especially considering the deficit of low end torque)

There have been a good deal of recent articles on unsprung weight and wheel sizes...pick up some mags .

Articles

Size Matters
http://www.wam.umd.edu/~greghess/sizematters.pdf

Finding Free Power
http://www.nerocam.com/SCC_TAPnew.asp

Bicycles and Unsprung Weight
http://www.softride.com/bike/cornering.pdf

Threads

How much does wheel weight really matter?
http://corner-carvers.com/forums/sho...ung+and+weight


Are 18" wheels and tires bling bling or a performance advantage?
http://corner-carvers.com/forums/sho...eel+and+weight


How much will 17" wheels slow you down
http://www.sccaforums.com/cgi-bin/ul...i/topic/7/303?


Effect of Lighter Wheels?
http://www.sccaforums.com/cgi-bin/ul...i/topic/7/301?


Rotational Advice
http://forum.miata.net/ubb/ultimateb...3;t=002795;p=1


If larger wheels are bad...why do sports cars have them?...
http://forum.miata.net/cgi-bin/ultim...c;f=3;t=005169


Wheel Weight, Who Cares?
http://forum.miata.net/cgi-bin/ultim...c;f=3;t=007412


1 Lb of unsprung weight =?? Static weight
http://forum.miata.net/cgi-bin/ultim...=3;t=006390;p=


0-60 simplified wheel physics and garfield's wheel test
http://www.mini2.com/forum/showthrea...730#post279748


Spreadsheet blows lid off lightweight wheel debate!!!
http://www.mini2.com/forum/showthrea...threadid=14738


6tech Article
http://www.mazda6tech.com/index.php?...d=16&Itemid=32


Wheel Weight and Performance
http://forum.mazda6tech.com/viewtopi...er=asc&start=0


Some Wheel Weight Sites
http://www.wheelweights.net
http://www.wheelspecs.com
http://www.miata.net/garage/garagetires.html

That should keep you extremely busy for awhile. Honestly though, pile all the articles and facts in front of someone...and they'll still deny it. Let them drive the same car, with lighter wheels/tires then theirs, and they'll swap sides instantly. Its that big a difference. Do realize that starting a debate on this subject will result in a massive firestorm of flaming and yelling, as large diameter wheels carry a heavy financial and emotional burden for their owners, who will defend them to the last man.

BaronVonBigmeat

Well he's not saying that smaller diameter/lighter isn't better (which it is, provided you have room for adequate brakes; that's just scientific fact), he's asking for track numbers before/after. If he's like me, he's probably trying to decide what delivers the most gains per dollar spent.

mitchfried

You got it, Mr. BigMeat. I want to know how much better my times will be with lighter wheels. Then figure if it's worth the bucks. Anyone out there with first hand experience?

crossbow

Good job ignoring the first link...which specifically compared before and after track times. (size matters.pdf) It kinda of sucks when you take the time to thoughly answer a question...and everyone just ignores it...cause it might take them actual effort to click.

IZoomZoomI

lol, thats is funny he provided you with all those links and you didn't try clicking the first one that would have ended this discussion. I would tell you the answer after reading those links, but I think you should read it yourself instead of getting the quick and easy answer. It's pretty obvious. Great links and thanks for the info crossbow.

mitchfried

I asked about 0-60 and 1/4 miles times, and the Rx-8 in particular. Want some hard numbers for MY car, so I can decide if it's worth the money to buy light wheels for MY car. Maybe you should re-read my first posting, so you'll know what I'm asking. Thanks for the links and your unnecessary rudeness. Anyone out there who went lighter, and can give some actual 0-60 and 1/4 mile data?

As an example, I wouldn't spend $400 a wheel for a one tenth 0-60 improvement, but I would spend the money for a half-second improvement. Understand the question now?

Richard Paul

iTrader: (5)

I love that Finding Free Power artical.
Anyone out there with an Rx 8 want to try this???
I'll come with my Sawzall.

globi

Ok mitchfried. I think we can calculate whether a 0.5 seconds shorter time on a 1/4 mile would be feasible with just lighter wheels.
0.5 seconds is 3.6% of 14 seconds. So your car needs to be at least 3.6% lighter assuming power to weight ratio is proportional to the 1/4 mile time. Which it's not, it might be more like 5% or even more. This would mean that you have to get rid of 153 lbs. which relates to about 95 lbs. on your wheels, which in turn is 24 lbs. per wheel. Can you get wheels that are 24 lbs. lighter, assuming you have the same rim and tire size? Probably not.
Now if you find smaller wheels it might be different. Smaller wheels are lighter and will increase torque and reduce speed of a particular gear which might or might not be beneficial to run the 1/4 mile in less time.

mitchfried

Maybe if you filled the tires with helium :D

brillo

Something to think about, while I can't say weather or not light weight wheels are worth the money from a $/performance view, wheels are one of the few parts you can sell later on if you wish and recoup quite a bit of money, especially if they are quality like Volk, SSR, RH, Centerline etc....., most other go fast parted don't get you much used, so just something to noodle on

Gord96BRG

Faulty assumption - to calculate the affect of wheels on acceleration, you need to consider the rotating inertia effects, not just gross weight.

Mitchfried, I'm sure there is some slight benefit - but the major benefits of reducing unsprung weight (and rotating weight) aren't in acceleration (or braking, but that benefit is there as well), but in the improved ride, responsiveness, agility, and maneuverability.

Regards,
Gordon

mitchfried

Brillo raises a good point about resale value of quality wheels. My son bought a nice set of used light weight wheels for his old Protege5 for about 50% of the cost of new, so figure you can get back half if you sell. A $400 wheel ultimately costs $200. Even a one tenth improvement in the quarter mile would make economic sense, if you factor in the handling improvement. I assume that there are no members of this board who did pre and post wheel swap acceleration tests on the RX-8.

Now if they only made 15 pound wheels that look stock so the wife won't notice......

mitchfried

And let's not forget about tire weight, which can vary greatly from company to company, even in the same size. According to Bridgestone, the Potenza RE40's weigh 26 pounds. Not too many tires come in 225/45/18, and not all companies list tire weight. Anyone weigh the Nitto NT555, or other same size tires??

crossbow

The first article takes a car thats "similar" in weight to the rx8 on a road course, and compares tire sizes, weights, and wheel diameter. Lap times are averaged and the change is plainly shown.

I'm sorry, but your just not going to get a better "answer" to your question then that. G-tech #'s can be easily falsed. This is an actual "published" article, with actual laptimes.

The other links go in-depth into 0-60 times, 1/4 mile times, autox times, and track times. From RWD, FWD, and AWD vehicle applications.

The rx8 is unique because of its rotary engine...its not unique with its 50/50 weight distribution or its RWD drivetrain...many other vehicles share those same characteristics with similar vehicle weights...many of which are covered in the links I gave you. Being an rx8 doesn't make the car have "magical" physics which don't apply to "normal" cars. The information applies to the 8 regardless of whether or not the other cars have rotary engines.

I've spent more time trying to spoon fed you information then if you just started clicking and sitting back with a cup o jo.

Toyo's T1-S 225/40/18 weights 22 lbs btw. Thier 235/40/18 (if you wanted to plus size from the stock diameter) weighs 22.9 lbs. (Tires used in first link)

http://www.toyo.com/tires/tire_specsheet.cfm?id=2

mitchfried

Give it up Crossbow. I just wanted to know about RX-8 owners (are you one?) who have done the switch, and the difference in their times. I know the theory, read the articles, and expect similar results for my "magical" RX-8. I've had my cup of coffee. Put away the spoon and take your cup of chill.

globi

You didn't read it correctly, that's why I wrote:
If I wouldn't have considered the rotating inertia effect, it would have been almost 40 lbs. per wheel.

Omicron

Way back when, CanZoomer ran a 13.78 s (GTech timed) 1/4 mile with a CZ unit adding ~ 25 WHP and lighter weight 17" wheels.

IZoomZoomI

i haven't timed my car, but like gord mention the most noticeable difference is the responsiveness of the car, feels like the car a two passengers. I think if you got with smaller diameter you would get better quarter mile times just because it would increase your final gear ratio but this would ultimately decrease your top speed.

GeorgeH

iTrader: (2)

Yes, tire diameter will have a greater affect than rotating weight.

However, lighter is better and it's a legitamate approach to making the car faster. Add a light flyheel, purchase some 17" SSR comps with, say, 225-45-17 Toyos, and I'm sure you'd get measurable increases in straight line performance. But it would be the combination of the reduction in rotating MOI & the lower gearing that makes it all work. And I think those big gaps in the fenders would look funny.

BaronVonBigmeat

Yeah, that's what sucks...the car performs best with 17's but really looks like it was styled with 19's in mind. Maybe you could go with black wheels and it wouldn't be as noticeable.

mitchfried

OK, let's try this. Automatic RX-8's come with 16 inch wheels, with optional 18's. If the overall tire diameter for both is the same, the gearing should be the same. If the 16's with tires are lighter than the 18's with tires, and if we know the difference in weight, then do acceleration times for each, we may have an answer to my question (albeit for the automatic version).

Anyone have the diameters, weights and the times?

Richard Paul

iTrader: (5)

Think about it this way. We hear all the praise for the effects of the light flywheels. The wheels have the same effect, after all they are attached to the crankshaft also.
BUT only when in high gear. In lower gears you have the mechanical advantage equal to the lever that is your gear ratio. Multiply your trans ratio by the rear end ratio and that is quite a lever.

My bet is that there is little to be had in acceleration. There are large gains to performance in all the other areas. Ride, handling, braking, traction (in all places other than draging)shock performance and more.

r0tor

iTrader: (1)

theres not a lot of horsepower to free up by getting lighter wheels because of the fact that the wheels aren't chaning speed that fast - so inertial losses are quite low. In third gear it looks like the stock wheels are only sucking up about 1 hp, so reducing the wheel weight by 20% with the same diameter would give you about a .2hp gain per wheel... you'd be better off just downsizing the diameter and raising the final drive gea ratio.


lightweight wheels are good for handling benefits, not acceleration benefits.

crossbow

Except when sportscar compact dyno'd 19's vs 15's and found a 8 whp gain on a civic.... Which turned out to be 0.3 seconds in its 0-60. (They were cast 19's...so obviously rather heavy as most 19's are)

In the "free power" article they dropped 0.3 off their 1/4 mile time, and 0.5 from their 0-60 time JUST from putting on lighter wheels and tires.

http://www.nerocam.com/SCC_TAPnew.asp

Step 1: Baseline (19 inch rims)
Curb Weight: 2,762 lbs
1/4 Mile:16.3 @ 84.0 mph
60-foot:2.9 sec.
0-60 mph:8.6 sec.

vs

Step 2: 15-inch Wheels
Curb Weight:2,707 lbs (55 lbs less unsprung weight)
1/4 Mile:16.0 @ 85.5 mph (Even the trap speed improved!)
60-foot:2.8 sec.
0-60 mph: 8.1 sec.

Lightweight wheels/tires have a drastic effect on a vehicles performance...in all catagories. Every link and article posted uses actual track evidence to prove that point...though for some reason people can't seem to click unless its to reply.

Once again...in the articles/links I posted.
https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/light-weight-wheel-performance-42185/

Using the most basic of math formula's, if you just multiply your unsprung weight loss by 2, thats the roughest calculation of the static weight loss (so if you shaved 50 lbs of unsprung off...thats 0.1 seconds or 15 hp added in the 1/4). Some people argue for the 3x or 4x multiplier, as many studies have shown depending on the sizing involved, the actual benefit can be larger then just 2x.

There is a complicated set of formula's which can be used to calculate your equivilant static weight loss, which can then be used to figure out your 1/4 mile times. (Based on the old formula of 100 lbs less or 15 hp more = 0.1 seconds less in the 1/4).
http://www.mazda6tech.com/files/rotational.xls

In the first set of articles (track times, 1/4 mile times, and 0-60 times) you can easily see where this formula works. One wouldn't think you'd shave 3/10th's off your 1/4 mile time just with 55 lbs less weight...because rotational mass is not considered the same as sprung mass. Basically those 55 lbs less unsprung weight was roughly equivilant to shaving almost 200-300 lbs off the car. Thats something you can feel just pulling out of your driveway. Physics are physics...it doesn't matter if your driving a bicycle, a cart, a motorcar, a van, a truck, a red wagon, a horizontally challenged land yaht, or a nice 50/50 sports car crying for a supercharger.

This just in...another study was performed at "track attack" this past weekend. Where two 6i ATX's with the same mods, sans wheels/tires, raced at the dragstip. One vehicle's overall wheel/tire diameter was 1.5 inches less then the other, and proportionally lighter, and he beat the larger diameter 6i ATX by 0.5 seconds in the 1/4, even with similar reaction times.

Once again...was posted on the front page @
https://www.rx8club.com/showthread.php?t=42185&page=1

Maybe if I spam it a few more times....
https://www.rx8club.com/showthread.php?t=42185&page=1

Or Maybe
https://www.rx8club.com/showthread.php?t=42185&page=1

Underneath?
https://www.rx8club.com/showthread.php?t=42185&page=1

Around the circle?
https://www.rx8club.com/showthread.php?t=42185&page=1

Maybe somebody will accidently click on one of the links. Then of course its far easier to just hit reply and argue.