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Unsprung Weight: What Drifters Should Know

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  • #16
    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?

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    • #17
      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.

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      • #18
        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.

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        • #19
          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.

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          • #20
            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.

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            • #21
              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?

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              • #22
                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.

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                • #23
                  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.

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                  • #24
                    TE-37

                    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

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                    • #25
                      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.
                      Last edited by Craftsman; 07-17-2004, 11:55 PM.

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                      • #26
                        Craftsman- The 17s would weigh more, obviously. (Unless we're talking 15" Falken Azenis Sports versus 17" Hoosier RS03s in 225 section width, then they might be equal) The 17s are also arguably better for professional-level drifting, but 15s/16s are cheaper to replace after you bend one and the tires are cheaper. Up front, you can get 15" tires with sidewalls that will be almost on par with the 17" tire's stiffness. In the rear, sidewall stiffness doesn't matter so much as predictability.

                        For you 240 guys, I found out another way to decrease unsprung weight cheaply:aluminum rear suspension uprights. If you upgrade to Z32 NA aluminum uprights, it shaves ~8lbs per wheel. Now, whether or not it's compatible with stock brakes is being debated/questioned as we speak. I'll get back to you with the findings. If they're compatible, this is the absolute best way to decrease unsprung weight for the money. (I've seen the uprights go for anywhere from $50-$80 shipped) However, one would have to change the shocks to a Z32-specific model, or at least buy SPL coilovers which can be special ordered with Z32-specific forks for the S13 and S14 chassis.
                        *Edit: It's compatible, but only after the addition of a conical ball joint seat. (part # 40173-33P00, about $10 at your local Nissan dealer)*
                        Last edited by GRiDRaceTech; 07-25-2004, 02:33 PM.

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                        • #27
                          or you could just turn the boost up and not worry about that little bit of extra weight from the big wheels.

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                          • #28


                            ... and boost would fix the handling downsides to running bigger wheels how?

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                            • #29
                              You don't drift much do you?

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                              • #30
                                You don't grip much, do you?

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