d00df00d

iTrader: (4)

I guess this is a question for the autocrossers around here, but any input would be appreciated.

I have some random no-name aftermarket rims that my car's previous owner put on before I got it. Those rims with my 205/65/15 Continental tires weigh 42lbs total. I can get Kazera 16" wheels with 225/55/16 Pirelli P-Zero Nero tires, which will weigh about 36 lbs total per wheel/tire.

So, 6 lbs less per corner, 24lbs less unsprung rolling mass in total. Anyone think that'll be noticeable?

MDeezy

iTrader: (27)

yes, you will feel it, acceleration shold feel much better 6lbs per corner is a lot and you should feel it, plus save some on gas as well.

renatonetmail

an expensive version of a UDP mod.... of course it will be very noticeable !!! any unsprung mass will... my $0.02

mzmtg

iTrader: (11)

No only will the reduction in unsprung mass help your suspension respond better, the redutcion in rotational weight will improve both acceleration and braking.

d00df00d

iTrader: (4)

Yeah, I figured it'd help.... everything, really. Just wanted to make sure 6 lbs per corner was a significant number, because I wasn't sure.

PTownMax

iTrader: (5)

on the same topic is there any way to reduce the unsprung weight and keep heavy wheels my rims weigh 21lbs and the i'm not sure on the tires, when i put my 3rd gen wheels on the diff is night and day, do they make lightweight axles or something along those lines

d00df00d

iTrader: (4)

Hit TireRack.com, find your favorite tire, and hit the "specs" link. There will be weights in there.

Unsprung weight is anything that isn't sitting on the suspension. This includes:

The suspension itself:
- Control arms
- Springs
- Struts
Brakes:
- Rotors
- Pads
- Calipers
Wheel hubs
Wheels:
- Rims
- Tires

I probably missed some things but you get the idea.

There isn't really very much variation in brake rotor and tire weights, although for tires that depends on the size. Other than that, no one makes lightweight versions of any of the other components above for our cars, so if you're not replacing your wheels then you're pretty much stuck.

Wilwood's big brake kits come with calipers that are lightweight for their size, but they're bigger than stock so they're not actually lighter.

Lightweight axles would help rotating mass but not rolling or unsprung mass; lightweight wheels and tires help all three.

Frank Fontaine

In theory, what you say is 100% accurate. But 6 lbs. per corner, I would be willing to bet with a stopwatch, there will be absolutely no difference. But Road & Track already did such a test, 15,16,17,18" rims on a 528i. The 17's performed the best.

d00df00d

iTrader: (4)

Well, I'm not just looking for speed. I'm looking to get new springs and shocks, so I want to maximize (no pun intended) what I get out of them by adding underbody bracing and new wheels and tires. I'm trying to find out whether 6 lbs less unsprung weight will make a difference. That's the only reason I'm after the Pirelli P-Zero Nero M+S, which are all-season: they're the lightest good tire in their size that I can find. Otherwise, I will just go with an all-out performance summer tire.

Ceasars Chariot

iTrader: (16)

car will be around .240 faster in the 1/4 mile ! my next tires will be Pirelli as well, at least i plan on trying some, found that they are 1.7 lbs lighter per tire than my toyos. cost a little more though

d00df00d

iTrader: (4)

Wow, how'd you figure that, Ceaser?

Spaniard

iTrader: (1)

Can you point me toward that? Sounds like an interesting read.


Also, from reading the FAQs, they say that rotational weight savings can be approximated by multiplying by 8. I think that would be considering you don't reduce the diameter. If you really want to go for a set of performance- not looks- wheels/tires get some 12lb 15" wheels and the lightest, lowest profile tires you can find. My setup is currently 32/corner so that would be like 10lbs times 4 times 8 (actually probably more since you are reducing the size of the rotational mass) so probably would feel like dropping 350-400 lbs from the car. That would be like my friend's girlfriend not riding shotgun! HUGE difference!!

Loe max

iTrader: (6)

1lb rotational unsprung weight=8lbs of curb weight. Since he trimmed off a total of 24lbs, multiply that by 8 and get 192lbs. A general rule of thumb for a 3,000lbs car is every 100lbs=.1 of the 1/4mile right?

It gets a bit trickier if you plus size your rims. Now even though you shaved off weight with a lighter rim, you're also effectively putting that weight closer to the outer edge so it cancels out some of its effectiveness.

I do know that when I went from a 40lbs wheel/tire combo on my 3rd gen to a 50lbs wheel/tire combo, my brakes didn't like it as much during high speed runs. Acceleration didn't deteorate a whole lot, but it was noticable, especially at lower rpms where inertia has a bigger effect.

Loe max

iTrader: (6)

you beat me to it

Zack342

iTrader: (89)

this thread has some good info

and not to hijack it or anything but my stock SE 5 spoke wheels with (215/55/R16)Sumitomo Srixon4 weighs 42lbs my 1996 BBS wheel/tire weigh 30lbs how much reduction can i expect in acceleration?
i am only using 2 tires on the front

Loe max

iTrader: (6)

Those BBS are 15"s right? Thats more than 192lbs. The reason I say more than, is because not only did you reduce the weight, you brought the weight closer to the center.

Spaniard

iTrader: (1)

Heh, not really- only because I just asked about the article that said 17's were the best (??) and then went back that added the other stuff later in an edit. Lets call it a tie

d00df00d

iTrader: (4)

Thanks for the help, guys!

I think it's important to note though, for anyone who didn't know, that all these weight savings calculations only apply to straight-line acceleration. In other words, dropping 24lbs in unsprung rolling mass will make the car accelerate like it's 192lbs lighter, but it'll only corner like it's 24lbs lighter.

d00df00d

iTrader: (4)

Did you notice any difference in ride harshness between the two sets?

Loe max

iTrader: (6)

Suprisingly no, although you could hear the extra unsprung weight clomping over bumps, ride harshness was similar to the stock 15's. It might have more to do with my tire selection though.

The main thing that I noticed was high speed braking. It seemed taxed with the stock brakes.

Spaniard

iTrader: (1)

Im not any expert, but I would think that there might be less of a gyroscopic effect with lighter corners? Could this help with making the car rotate?

d00df00d

iTrader: (4)

Good point. You're probably right as far as quick and tight maneuvers are concerned. Having light wheels would probably help turn-in and transient response. Because of the car's weight and high center of gravity, though, you'd proabaly have to have really good tires and suspension tuning for that to make a significant difference. Either way, sustained grip and high-speed cornering probably wouldn't be affected.

Bobo

Not to hijack the thread, but I'm facing a tire dilemma. I plan on keeping the OEM 15" sawblades on my 95SE (5-speed). I still have the OEM Goodyear Eagle RSAs on the car (21 lb. each). I have come down to a virtual coin toss between the BF Goodrich Traction TA (25 lb.) and Yokohama Avid H4S (21 lb., same as RSAs). So this is a case of potentially adding 16 lb. total at the corners with the Traction TAs.

I take it that the 1/4 mile performance may be down 0.1 seconds and change with the Traction TAs.

Would I notice much of a difference in fuel economy with the 4 lb. heavier tire?

The Traction TAs are superior to the Avids in grip in all conditions and cornering, whereas the Avids outperform in noise levels and comfort. If fuel economy in the heavier tire is compromised, I may opt for the Avids.

Thanks

d00df00d

iTrader: (4)

This has pretty much become an educational thread anyway, so why not.

Heavier wheels would really only hurt your fuel economy under acceleration. If you tend to keep your speed stable a lot (i.e. lots of highway driving), you won't really notice much of a difference.

I got a bubble in one tire and had to replace my front Continental ContiExtremeContacts with Bridgestone Potenza G 009s, which are about 4lbs heavier in that size, and I can tell you it definitely feels slightly different. I drive very aggressively though, and the difference isn't exactly night-and-day.

In short, the difference in fuel economy probably won't be noticed.

Spaniard

iTrader: (1)

-total agreement..

Bobo

Thanks. I'm mulling my decision over a cold beer, lol!

BEJAY1

iTrader: (19)

I believe the calc for springs, struts, and those connected pieces for unspring->spring is 50% savings not 100% like wheels & tires.

My daily setup weighs 49lbs, autox is 37lbs, and my drag is 28lbs. Accel, braking, steering response, are all night and day between em.

Erjan, what combo are you running again to get 32lbs? I'm 5lbs heavier running 16" SSR Comps.

Spaniard

iTrader: (1)

Ive got them thar rota slipstream 15" pups with Toyo proxes T1-S 225/50/15.
12 lbs and 20.3 respectively. (per machiii.net and edgeracing.com)

I figured I can get away with dropping the .3 since they get eaten up pretty quick heeh... funny tho- there is a nice difference from the first track event to the next.. There is something to shaving the tires, but I definately cant afford to shave em anywhere but on the actual asphalt

edit: 15" by 6.5" - it would be worth the extra weight to get 7 or 7.5 width wheels right? but I had to stay stock at the time...

Ceasars Chariot

iTrader: (16)

well i have heard 8 and 10 lbs, back when i swapped my tires/wheels i cut out 32 lbs and did the math, lol ! using 10 i got 320 lbs. i thought, no way will this cut .3 off my times at the track, but sure enough, i blasted down the 1/4 mile and was exactly .3 faster. so i took a guess a .240 using every 100 lbs is .1 in the 1/4. i think .192 is safe to say will be knocked off. and like spaniard said making sure you stay with the same size rim.

d00df00d

iTrader: (4)

BEJAY1... How the heck did you get 28lbs per corner??

Spaniard

iTrader: (1)

Oh, and props to Ceasar, if it wasnt for him I would still be paying $160 per 25 lb tire... (translation: he told me about the T1-esses)
Hail!

BEJAY1

iTrader: (19)

Those were my front weights only that was the drag slick. I think Jime's and others got down to 23lbs or so.

PTownMax

iTrader: (5)

bump for any more good input or info

d00df00d

iTrader: (4)

Right then.... here's some.

Besides the dead weight of your car, there are two kinds of mass to consider: Unsprung mass and Rotating mass.

Unsprung mass, as mentioned earlier, is anything not sitting on the suspension. You can also think of it as everything that moves when a wheel goes over a bump. These are things like the suspension components, rims and tires, and brake components.

Rotating mass is anything that spins as the car moves. This is stuff like the crankshaft, pulleys, flywheel, axles, brake rotors, and rims and tires -- as well as the entire transmission.

So, why do we want to reduce either of these kinds of masses?

Well, here's the simple analogy. Imagine picking up 30 lbs of weights and putting them in a backpack on your back. Imagine running with this weight -- it's a bit harder than running normally, but you can do it. That's what it's like to have extra weight inside your car. Now, take those weights out of the bag and tie them around your ankles. Suddenly the same weight is slowing you down a lot more. That's what it's like when your car has a lot of unsprung and rolling mass.

Reducing unsprung mass helps the suspension work better. When you go over a bump, the suspension is supposed to absorb it by allowing the unsprung bits to move up and down. If you have a lot of unsprung mass, though, it's not going to want to move because... well, it's heavy. This means that the suspension will not be able to absorb as much of the bump, and more of it will be transmitted to the rest of the car. At best, this means you feel more of a jolt in the cabin when you hit the bump. At worst, your car can get thrown off in the middle of a fast or sharp corner, and you can lose grip and spin out. Minimizing unsprung mass lets you be sure that your suspension will be able to track the road properly and keep your tires in proper contact at all times: when you hit a bump, your wheels will move up freely and come back down immediately. Combining low unsprung mass with a stiff chassis, which will make the chassis less willing to absorb bumps, allows the use of stiffer springs and shocks without worrying as much about ride harshness.

Reducing rotating mass helps the engine put power to the ground more efficiently. It won't make your engine more powerful, but it will help the transfer of that power into acceleration. Basically, it comes down to this: if your rotating parts are light, then they don't take much power to move, so more of your engine's power will go to the wheels. Here's how it works. Let's say your car is accelerating in first gear from point A to point B. Let's say that as you travel from point A to point B, your wheels spin 10 times. If your car is a 5-speed Maxima with stock rims, that means that your flywheel would spin more than 130 times. If you take some mass off of either of these parts, that mass will count every time it turns -- and it will turn a lot. If you reduce the mass of the rims/tires and/or brake rotors, that will make your braking better too for similar reasons because brakes basically do the same thing as your engine -- i.e. they apply force to change the speed at which your wheels rotate -- they just do it in reverse. Braking with wheels that are a few pounds lighter is like braking with a car that is at least a few dozen pounds lighter.

Rotating mass is also one reason why some people prefer a 5-speed transmission to a 6-speed -- the 5-speed just has fewer moving parts, which will make for more efficient power transfer. My favorite case in point is the next Mitsubishi Lancer Evolution (the Evo 9). It will come in three versions, and only one of the three comes with a 6-speed (it's the plush, civilized, well-behaved GT model). The other two have 5-speeds, and you know it's not because they had to cut corners to save costs.

In short:

Reduce unsprung mass for a smoother ride and much better handling over rough pavement. You can do this by getting lightweight rims and tires, and by making sure that if you do get a big-brake kit, it comes with lightweight calipers and rotors (e.g. the Wilwood kits). Honda owners have lightweight control arms availabe, but we're not so lucky.

Reduce rotating mass for better straight-line acceleration, braking, and fuel economy. You can do this by getting lightweight rims and tires, lighter brake rotors (hard to find!), a lightweight flywheel, and a 5-speed instead of a 6-speed (for all you VQ35 swappers out there... ).

Lightweight wheels and tires are really cool because they reduce both unsprung AND rotating masses, so you get the benefits of both. Conversely, if you see a crazy SUV on giant 20" chrome spinners (read: HEAVY as hell!), point and laugh -- the driver has just traded fuel economy, ride quality, acceleration, and handling, all for some shiny bits that will self-destruct the first time he hits a pothole.

EDIT: I got this info in little bits and pieces from various sources around the Internet and a little from the forums here, but I can't find them any more. I just did a quick Google search and most of what I found either is really silly or has an entire page's worth of info with only one or two relevant lines. If anyone can find good articles, please post them. I'd like to give credit to people who wrote about this before me.

Bobo

Good work, dogfood!

d00df00d

iTrader: (4)

And here's rmurdoch calling me dogfood after one of my essays. The last one was on spark plugs. He didn't seem to like that one as much....

Bobo

Good memory, you're not just an ordinary dOOdfOOd, lol!

d00df00d

iTrader: (4)

It was pretty memorable. I was just about to flame you for your FLAGRANT INSULT OF MY HONOR, and the thread was locked right as I was writing my response!

It's cool. We're all friends here. I get pretty verbose sometimes, so it's not a bad thing to be taken down a notch here and there.

Bobo

At least you're literate and have a grasp of the English language, so you can't be all that bad, lol!

PTownMax

iTrader: (5)

good info, but i love how my car looks with my 18"s, do you think a flywheel and performance axles would make that much of a diff?