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?