Unsprung Weight: What Drifters Should Know

[GRiDRaceTech]

Unsprung weight should be ranked highly in the motorsports enthusiast's mind.

Unsprung weight is "that portion of the total weight of the vehicle which is not supported by the suspension springs." (A big thanks to Carroll Smith for that.) That is, unsprung weight is, on a fully independently suspended vehicle, the mass of the tires, wheels, lug nuts/bolts, hubs, brake discs, calipers, pads, dust shields, and arms. (i.e. everything that droops when one jacks up the car) For solid-rear-axle-equipped vehicles, the entire rear axle assembly is unsprung weight. Lower unsprung weight has several benefits: better suspension motion characteristics due to less taxed shocks and springs, better steering feel, and, with lighter wheels, (and tires, if possible) better braking and acceleration. Thus, bling wheels and too-big brake conversions are just stupid.

Have any questions on unsprung weight? Ask 'em here, and I'll try to answer them to the best of my ability.

[180sx2nr8u]

yeah, umm. could you explain that in lamen's terms (you know for those people out there outside of our technical knowhow, um, circle)? just the part about HOW all these things are made better.

[Emagdnim]

Unsprung weight is worth more then sprung weight. I don't know the exact ratios but just for an example lets say removing 5 pounds of unsprung weight would be equal to removing 10 pounds of sprung weight.

I would also like to add that not only weight matters but mass does as well, For example larger brake rotors even if lighter then stock will take more energy to move.

[180sx2nr8u]

so wait, let me get this straight. How would you go about lightening this, i mean other than like smaller brakes. do they make carbon fiber nuts/bolts?

[Emagdnim]

well you wouldn't want to go with smaller brakes because the loss in weight and mass wouldn't be worth the loss in braking power. Larger brakes are worth the weight increse as long as its reasonable. Lighter wheels and tires are one way to lower unsprung weight.

Everything has its advantages and disadvantages.

[Craftsman]

Originally posted by Emagdnim
well you wouldn't want to go with smaller brakes because the loss in weight and mass wouldn't be worth the loss in braking power. Larger brakes are worth the weight increse as long as its reasonable. Lighter wheels and tires are one way to lower unsprung weight.

Everything has its advantages and disadvantages.

Or suspension pieces made from exotic materials. i.e. A-arm that is made from Carbon Fiber.

Matt.

[Emagdnim]

I'd rather have titanium for something like an A-arm, It has a good balance of weight and strenght. I don't think I could trust carbon fiber to take that kind of abuse.

[05m0515]

super light weight lug nuts like these
http://www.revolutionsmotorsports.co.../dept_297.html

as you can see the lightest weigh half the weight of the other lightweight lug nuts, so you can imagine how much lighter they'd be than stock. little things like this will add up...

[mercutio]

If you want to drop unsprung weight, find a good set of light wheels, since they're not only unsprung mass but rotating mass as well. Two-piece brake rotors shave weight without reducing stopping ability. Vogtland advertises their springs as being 30% lighter than competing designs, so they might be worth checking out, too. I'd highly advise against using anything other than high-quality steel bolts in a suspension. Titanium is better in some respects but if you want to pay $50 for a single bolt and drop MAYBE an ounce, have fun.

[svtxchinoy]

What rims would you guys recommend?? I have my eyes on a set of BBS rims right now. I drive a Mustang, so I want a lighter rim that will still kinda match the style of the car. I'd like to use titanium bolts too, but I don't have a shop and money like Takahiro does =P

[05m0515]

those zenki brand lugnuts save you around 36 oz of unsprung weight for $55 bucks. that is for a set of 20, not just 1.

[mranlet]

Ueno's red SC uses aluminum and titanium bolts to save weight - it can be pretty substantial.

Stock sized rotors that have been lightened and cross-driled or vented are often the best route. For example, the HKS EVO track car has pretty mild-sized rotors but just uses 6-piston calipers up front and 4 in the rear. Bigger brakes give the calipers more mechanical advantage in stopping, but carry more rotatinoal momentum.

If you want good light wheels, check out the Volk TE37's - they come in a plethora of sizes and bold patterns and weigh in at something like 13lbs each for 18".

BTW - I've always seen that suspension arms are considered to be 75% unsprung weight.

-MR

[Deluxe_247]

Coilovers also decrease the unsprung weight, but they have to be the complete aluminum assembly like Tein, not just a stock/sleeve assembly that some make for the 86.

[mercutio]

The Zenki lugnuts are aluminum, which is much lighter and cheaper than titanium, but not nearly as strong. I don't know if I'd want AL lugnuts, especially on a heavy car. If you're taking your wheels off and on a lot, that aluminum is likely to get pretty chewed up. For a fastener that important, I'll stick with steel.

[180sx2nr8u]

as a general rule of thumb, are 2- and 3-piece wheels lighter than 1-piece? it was said that 2 piece brake rotors are lighter, but does the same apply with wheels?

[GRiDRaceTech]

Well, I'm back from my trip, so I'll try to address everything that I can.

180sx2nr8u- Yes. The vast majority of multi-piece wheels are lightweight simply because they were borne of necessity. They are easily repaired by just taking off the damaged part and bolting a replacement on. The lightest wheels in the world are a one-piece design, if I'm not mistaken.

Don't forget that wheels and tires are not only static unsprung weight, but also rolling mass... if you reduce their weight, you reduce their mass and make the car easier to accelerate and brake.

The simplest and most effective way to drop unsprung weight is in fact wheels and tires. There is no such thing as a too-light wheel unless it bends like butter.

Although prices get quite high for lightweight wheels, I've found a 15x7, 10.2lb wheel for $179, including custom bolt pattern. That would lower the unsprung weight of a 240SX by 24lbs, assuming it has the stock SE teardrop ('89-90) wheels and by 31.2lbs if it has the '91-'94 alloys. Either is a very worthwhile deduction.

Now, tire carcass weight is quite important as well... because it can completely offset any advantages of a lighter wheel. (which, although not the best, is better than having a heavier wheel/tire combination) Any street tire with an extremely stiff sidewall (i.e. the Falken Azenis Sport or any run-flat) will be heavy. Compare the carcass weight to grip and sidewall stiffness and if it's a tradeoff you're willing to make... then go for it. Just make sure it's lighter than stock... or you just spent around a grand just to look purdy. Most tires used by drifters aren't all that stiff and thus are not extremely heavy.

Now, another way to drop unsprung weight is with aftermarket arms. The factory arms are usually very heavy steel bits and when replaced with aluminum bits significant savings can be had.

Springs are not unsprung weight, because they do not support themselves. However, they do have weight which will effect the sprung weight of the car, so a lighter spring has its own benefits.

Lighter lugs are a great idea and are relatively cheap.

Cross-drilled rotors drop very little weight from the rotor's weight. I'd recommend slotted rotors anyway due to their better pad wear characteristics and better resistance to cracking.

Did I miss anything? Any more questions?

[Emagdnim]

I'm still not sure about how much more unsprung weight is worth then sprung weight. I think there is a ratio for it but I would think it would vary depending on the car.

[GRiDRaceTech]

Well, unsprung weight is much more valuable than sprung weight; that's all I can say because I don't think there is really a ratio for it. To shave pounds off the unsprung weight is to increase response and suspension efficiency through reduced suspension inertia. Also, the car responds better to sharp and/or repeated bumps in the road. One just can't go wrong with decreased unsprung weight.

[mercutio]

As for only part of the lower suspension arms being unsprung weight, that is correct. The portion of the lower arm (we'll assume a single piece A-arm type design) between the point at which it mounts to the frame and the centerline of the spring is sprung weight. The portion of the arm outboard of the spring's centerline is unsprung weight. So the farther outboard your spring/shock combo mounts, the less of the arm that's unsprung weight.

[Craftsman]

Originally posted by GRiDRaceTech
Well, unsprung weight is much more valuable than sprung weight; that's all I can say because I don't think there is really a ratio for it. To shave pounds off the unsprung weight is to increase response and suspension efficiency through reduced suspension inertia. Also, the car responds better to sharp and/or repeated bumps in the road. One just can't go wrong with decreased unsprung weight.

There really isn't a ratio for it...

Because of the radial nature of the suspension, the tire and wheel are going to be the most important and significant part compared to a part that bolts on to the chasis. An arm or some other rod isn't going to be as significant as the tire/wheel and brakes because of the distance from the chasis. R X F. Radius Times Force = Torque. We're trying to reduce torque/momentum here so less force(weight) is wanted.

Cliff Notes : A high weight close to the pivot point isn't significant to unsprung weight.

I'm not argueing here. I'm just adding my knoledge of physics here...

Matt.

[180sx2nr8u]

are u saying that replacing the A-arm with lighter meterial is not going to yield any noticeable results? or are u saying that the results won't be as significant as a lighter wheel/tire/brake combo?

[GRiDRaceTech]

They'll only be slightly noticeable to a driver very attuned to what his car does. No, the results are nowhere near as significant as wheel/tire combo.

[J-BloodAE86]

Originally posted by mercutio
As for only part of the lower suspension arms being unsprung weight, that is correct. The portion of the lower arm (we'll assume a single piece A-arm type design) between the point at which it mounts to the frame and the centerline of the spring is sprung weight. The portion of the arm outboard of the spring's centerline is unsprung weight. So the farther outboard your spring/shock combo mounts, the less of the arm that's unsprung weight.

that changes during the movement of the suspension also, so its hard to get a accurate messure. and about the "ratio", it would change drastically from car to car as well.

[LucidStrife]

I think the Volk Racing TE-37's are a good choice. They are light and very strong, the styling is just right in my opinion. They are just a little pricy, but I think they are worth it.

Lucidstrife

[Craftsman]

Originally posted by GRiDRaceTech
They'll only be slightly noticeable to a driver very attuned to what his car does. No, the results are nowhere near as significant as wheel/tire combo.

Exactly... I'd do a photoshop diagram, but you can try this on your own...

Hug a weight and spin in a circle. Now extend your arms with the weight... Do you spin slower? You just increased your inertia by doing so. Now imagine this on your car with your piviot points being all at the frame. The farther you are from the frame, the farther you are from the pivot point and now you have more inertia...

BTW, lighter wheels and brakes also help in acceleration for the same reason as decreasing the unsprung mass....

This is why using super light wheels and exotic brake materials are prefered by racing teams.

Replacing an arm with a lighter arm does help. Just not as much as you would normally think...

My question. Let's say I buy TE37 rims, 15 and 17. Which one would weight more with tires? And which one is recommended for drifting. I would imagine that the 17s would be because there would be less tire deformation.

Matt.