unsprung weight

brucelidat

If it makes a difference I can feel in terms of accel, braking nimbleness, then the heavier wheels aren't happening. That is what I am trying to learn here. I've heard some really big and hard to believe weight equivalencies thrown around so I am trying to figure out what si actually more accurate. Just want to know as much info as possible before making decisions.

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critical

I dropped around 11lbs in the wheels over all and the difference was huge in terms of feeling. Totally worth it. It probably feels about 165lbs lighter to me.

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DEpointfive0

DETRIMENTAL is a bit strong, and that contradicted itself IMO. Isn't it a little hard to drive a car you don't enjoy 100%.
You put spacers on because it LOOKS nicer, it "technically" lowered the performance of your car. How much do you care?

If you're going from 28lbs to 45lbs a piece, ok, sure. I see a valid complaint, or reason to think about it. But from 28 to 30? I don't see any concern.

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kenchan

the hell, you started modding cars this week?

never mind that i posted. GL to you guys. lol

DEpointfive0

I'm checking out from this thread, good luck

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brucelidat

I didn't know anything about unsprung weight or anything when I installed the spacers. I did it purely for looks, yes. Wheels are a bigger investment than spacers though. Also, some people are saying it makes a big difference which is why I am asking, to find out if it really does. So like I said, I am trying to figure out if there is a significant enough difference that I would feel it. According to Critical, he felt a difference from 11lbs. If I get slightly lighter wheels and drop the spacers, that'll be more like 15lbs or more. And if I switch to PSS on my next set of tires, it would be even more, like 30+ lbs overall. So I am just trying to get info.

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Chuck33079

You'll definitely feel 30+lbs. You'll feel it in the acceleration, braking, steering and handling. The car will feel livelier.

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Amuse370z

I can't seem to find the weight for the 2013 18" base wheels.

But I bought 19" TE37SLs and I'm expecting quite a difference performance wise when I put them on.

Read T

I dropped my car's rotating weight by drilling holes in my tires. Like you guys have said, it does detract from ride quality though.

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Masterbeatty

Or get these by HRE. $2.5k-4.5k a wheel but carbon fiber and magnesium. The 20's weigh only 21lbs

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totopo

Unsprung weight is SUPER important.

Basically, bumps apply an acceleration to the unsprung weight, not a force. So lighter unsprung weight means less acceleration, and less perturbation of the chassis on the other end.

The major way of measuring the end effect of springs on a suspension is the wheel frequency. Basically, you have 2 weights separated by a spring, so the wheel frequency is dependent on the weight of both, but more so on the lighter weight (the unsprung weight). The wheel frequency is almost linearly proportional to the minor unsprung weight. So a decrease of weight of 10% iirc is basically like having a 10% stiffer spring. This is where you get where people say xx lbs unsprung weight = xx lbs sprung weight. like shaving 15 or 20 lbs or whatever off a corner weight has the same effects on wheel frequency that shaving 1lb off unsprung weight will have.

but it isn't like exactly true, since shaving off unsprung or sprung weight has the same effect on the normal force on the tire and the lateral force needed to turn the car.

Other benefits of lessening unsprung weight is you usually decrease rotational mass as you do it, since most of the unsprung weight is wheels and rapidly rotating components. decreasing rotational mass effectively improves your braking and acceleration.

spacers are kind of interesting from a vehicle dynamics standpoint. They increase the wheelbase, which is super great for decreasing weight shift, but it changes your scrub angles in the front, and changes your overall suspension geometry (and i think kills bushings). I think the motoiq people actually like running modest spacers for cheap wheelbase increases for more lightly modded projects.

jz321

F = M * A

The acceleration of a mass is a force.

Riptide67

In my case I'll be dropping 8lbs from switching out OEM Rays and Spacers to ForgeStar F14 wheels.

I doubt the difference will be noticed. But when I upgrade the front rotors to Z1's 2 piece, I'm sure that will be much more noticeable.

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totopo

what I meant was that if you vary the mass (unsprung weight), it's the acceleration that stays more constant and the force that varies. so less unsprung weight means less force for same acceleration, and less momentum and less energy, and less perturbation of chassis.

Slartibartfas

Change wheelbase to track and that's right. Track is lateral width while wheelbase is longitudinal length.

Most of you are beating around the bush. The unsprung weight works exactly like totopo wrote for handling and is a linear relationship. 1 lb reduction in unsprung weight is 1 lb in regards to handling and wheel frequency.

However, the rotational inertia is very much a non-linear effect. 1 lb of rotational inertia is the equivalent to 10 lbs (or your favorite number from your favorite source) in regards to vehicle acceleration, whether it be forward (mash the gas), backwards (slam the brakes), or turning. Take ten pounds off each corner and it feels as if you've removed 400 pounds out of the car when you measure at the drag strip or race track.

Lighter wheels and brakes will make the car feel livlier but, from direct experience, the ride isn't as good. The heavier wheels force the tires to absorb small imperfections so the imperfections aren't as strongly transferred into the springs. Also, if you have a wheelspin problem, heavier wheels can help.

Like everything else in life, there are compromises to wrangle.

Sorry to practice necromancy but felt it worthwhile.

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