Sprung vs unsprung weight

[Nicks67GTO]

I know iv'e read that un-sprung weight is a big deal when it comes to auto-x. Aluminum carriers, Lighter wheel/tire combos, lighter brakes etc....

How big of a deal is this? Is un-sprung weight more important to eliminate than sprung weight? Are the un-sprung lightweight parts something that's worth the premium paid for the casual auto x/street driver guy? Is reducing un-sprung weight a race only concern? School me. Let's discuss.

[silvermonte]

Ive also wondering this alot also. Ive done alot of reading on it but Ive never found any specifics, always more of this or less of that. What Ive done the most reading on is the truck arm suspension, http://www.hotrodstohell.net/truckarm/truckarm_index.htm , then when you compare it to 3 links and 4 links everyone says the truck arm doesnt even compare with the main factor being the weight. When it comes to the brakes and wheels there really isnt that much to think about except lighter is better, but like you have mentioned where is the cutoff or what is a round about goal to aim for?

[wayward]

In very basic form as I understand, unsprung weight does not get the benefit of your suspension correcting the disruptions of the track or road.

Meaning the more unsprung weight you have the more likely you contact patch will be negatively affected by any adverse track conditions.

[IMPALA MAN]

One way to look at it is that sprung weight can be transferred from one place to another when the vehicle's suspension moves. Unsprung weight cannot.
Sprung weight: is anything that moves when the suspension moves. Example: (engine)
Unsprung weight does not move when the suspension moves. Example (wheels and tires)
So what is a control arm considered as it does not move at the point where it is connected to the spindle, but does move on the end connected to the frame? Usually this is considered 1/2 sprung and 1/2 unsprung.

[mitch_04]

Something that popped into my head when thinking about this is that the lighter the unsprung weight, the easier it would be to control. If you swing a 5lb bat or a 1 lb bat, which could you stop mid-swing? A lighter axle assembly would have less energy after hitting a bump/dip and would be more easily stabilized. That's not a fact or anything, just something I pondered...

[wayward]

I would like one of the resident experts chime in.. I would really like to understand this type of info..

[Nicks67GTO]

Something that popped into my head when thinking about this is that the lighter the unsprung weight, the easier it would be to control. If you swing a 5lb bat or a 1 lb bat, which could you stop mid-swing? A lighter axle assembly would have less energy after hitting a bump/dip and would be more easily stabilized. That's not a fact or anything, just something I pondered...

I see what you're saying but in a 3500 lb car, is it really that big of a deal when you kill off 25-75 lbs of unsprung weight with lighter wheels, aluminum center section, Aluminum driveshaft, lightweight brakes, lighter A arms, etc?

I'm asking because I was bored and looking at aluminum cases for my 9". They only kill 6-15 lbs of unsprung weight but cost a nice premium over nodular cases. Is that 6-15 lbs really making that big of a difference?? I would think something low like a 3rd member case would help your center of gravity stay lower making cornering easier?? Also some the frame mods iv'e seen guys do on here with the steel tubing arent light weight at all and that would be un-sprung. I understand it increases rigidity but to what extent is it a benifit vs the weight??

[RobNoLimit]

As to what's what, the simple answer is that 1/2 of the A-arm mass, 1/2 of the tie rod, 1/2 of the shock, and 1/2 of the spring is "unsprung", along with the spindle, brakes, wheel and tire.
Many times, it's better to think of this weight as a percentage of the total, rather than just in pounds. My red truck weighs in at 3085 lbs, no driver. The unsprung wt is close to 310 lbs, still a bit on the high side for me. Try to think about it like this. If the total weight was 3000 lbs, and the unsprung is 1500lbs (1/2) then the two masses, sprung vs. unsprung, are the same, and it would be really difficult for the spring/shock to control anything. - 200 lb man pushing a 200 lb block. But if the unsprung is 300 lbs, then the sprung wt is 2700. Like a 200 lb man pushing a 22 lb block.

In a more honest look at my truck, the unsprung wt, 310lbs, when compared to the sprung wt, 2775 (3085 total - 310 unsprung) shows the unsprung to be 11.2 % compared to sprung wt. - my goal here is 10% - I don't have 35 lbs to loose here, and I plan to put the truck on a diet soon. It's a struggle. Total weight takes more force to accelerate, straight or direction change. - F=MA. So lighter is faster, but the higher the % of unsprung wt., the harder it is to control.

[David Pozzi]

Try going jogging with ski boots on, - that's a high unsprung weight example.
A ford 9" with 14" rotors & calipers weighs 200 lbs, wheels & tires add another 90 lbs, not counting shocks or suspension weight. Thats 290 lbs the springs & shocks have to try & control. 6 lbs off that isn't going to be felt, but if you take 6 lbs off several components, it can add up to a significant amount.

[mitch_04]

I've jogged with military boots before, hurts the hip flexors after a while. Too bad Mr. Drill Sergeant didn't seem to mind.

[Taman]

It all adds up. My 75 TA started out at 4200 lbs. I am now down to 3550. I am all steel and full interior. Who cares where you lose the weight. Dropping pounds is dropping pounds. 5 ponds here and 6 pounds there starts to add up.