Forum: HoseHeads Sprint Car General Forum (go)
Moderators: dirtonly  /  dmantx  /  hosehead

The first 410 weight rule was 1200lbs without the driver. So cars must have been weighing less than that at the time. Don Droud had added weight taped under the hood to make weight when he won the 1200lb nationals.

I'll bet your driver does not weigh 300lbs!

Jump up & down on the front of the frame. What moves is riding on the bars, ie sprung weight. The axle does not move. It does not ride on the springs, they ride on it. The weight of the axle is supported only by the tires, it is not held up by the bars. Unsprung weight.

If it is so difficult to get down to 1400lbs with driver why are cars being DQed at the scales for being too light. I know 360 cars that add ballast to make weight. One trick was filling the front axle with water. Unsprung, non rotating weight. The best kind.

Oswald.  Don't get me wrong, you seem to understand the difference between sprung and unsprung weight, you just need to understand unsprung weight reduction is way more important than sprung weight reduction.  Don't trust me, research it.   You are also correct that rotating weight reduction is a huge benefit. 

Sorry Oswald.  Your perception is backwards.  The critical weight is the stuff forced up as you hit a rut, for example, and has to be controlled by the shocks and forced back down by the springs to make contact with the track and so you can steer and accelerate the car.  Jack the car up by the frame, anything that drops.better be as light as possible.  That would include, hubs, spindles, brakes, axles, wheels, tires, etc.  You would never increase the weight of an axle to make weight. Harder to control the tire contact once the tire rebounds off a bump in the track.  

Well, you better talk to some successful crew chiefs. Cause that is where I got my info. ASCS crew chief on a very successful team. Perhaps he was talking about at a good track like Knoxville and not some dump full of ruts.

Ask any decent crew chief and he will tell you if he has to add weight he wants it non rotating and unfortunately sprung.

Jump up & down on the front of the frame. What moves is riding on the bars, ie sprung weight. The axle does not move. It does not ride on the springs, they ride on it. The weight of the axle is supported only by the tires, it is not held up by the bars. Unsprung weight.

Silly theory. Now you are working your bars in a manner they are not made to encounter. Your shocks are working harder than needed because they have to support a front axle that is crazy heavy for no reason. Person ally if you want to add weight to the front axle just make it bigger stronger tubing, but I have never seen that done because it is a hinderance & not an advantage.Any weight that is ever added on a race car is between the x at the radiator and the upright at the seat in front of rear axle. Must be mounted to the frame. If your wheels come off the surface of the track which happened to be connected to the front axle. That is sprung weight, not unsprung weight.

Shocks do not support the front axle, they control the rebound of the springs. Weight that is not supported by the springs is unsprung.  Common sense.

U guys are beautiful. Someone said common sense, 1 says the tires support the front axle. If it moves up and down & has a part either bolted to it (shock) or an arm riding on it (torsion) it is most certainly a sprung weight item.

To figure that out you unhook any parts connected to it & jack it up under the frame, not pick up a tire. If it drops or moves sprung weight. Why because it moves up and down & is controlled by other parts to control how much it moves and how fast or slow it moves. This is why u try to make every corner of the car as light as possible & only add weight to the frame..  

COMMON SENSE

Definitions 

    “Unsprung weight” moves when the wheel moves. “Sprung weight” moves when the chassis moves. 
    Weight controlled by the suspension, and usually below the suspension, which forces it into contact with the road surface or other components, is unsprungweight. 
    Weight supported by the suspension, and usually above the suspension, which separates and isolates it from the road surface and other components, is sprungweight. 
    There appears to be some confusion concerning the definition and behavior of rotating weight. Many advantages that apply solely to reduction of rotating weighthave been erroneously applied to reduction of unsprung weight. Among these are the concept that there is a ratio or formula that predicts a greater effect on the acceleration of a vehicle if weight is removed than the actual weight change; there is no single accurate formula (although some rough predictions provide useful information through a combination of generalities), and it does not apply to unsprung weight in any case. There are components on all vehicles that are both rotating weight and unsprung weight, but the effects are frequently, and improperly, combined and attributed to unsprung weight.

Effects 

    Unsprung vs. sprung weight have no difference in their effect on acceleration or top speed. There is no “1-10” rule (or any other ratio) where 1 lb. removed from unsprung weight “has the same same effect as” a higher amount of sprung weight. Any benefit from weight reduction towards increased MPH or reduced ET will be exactly the same as if the weight were removed from the chassis. Weight removed from an unsprung component, such as a rear wheel or axle housing, may affect traction if the wheel is not under control during launch. 
     Lighter wheels & tires do have a very small additional benefit due to the lower amount of power required to rotate them (true of all rotating components), but this is not due to their classification as unsprung weight. 
    The unsprung vs. sprung weight percentage greatly affects wheel control, but its importance is almost entirely limited to un-even surfaces, or conditions where the attitude of the vehicle changes (such as through G forces). This is most important in off-road and pavement road racing, somewhat less important in dirt track, and has almost no value in drag racing. As the importance of suspension travel for proper wheel control diminishes, the value of reducing the unsprung proportion of the total car weight is lessened, and becomes zero if the suspension travel is zero. 
    Cars requiring precise control of wheel movement, where a low percentage of unsprung weight is an advantage, will have faster lap times and higher top speeds,not because unsprung weight reduction improves acceleration or top speed, but because traction is improved.

    The unsprung vs. sprung weight percentage also affects ride comfort, since lighter springs are needed to maintain traction and control with lighter unsprung components (alloy wheels, independent rear suspension, alloy calipers, composite springs, in-board brakes, etc.), the chassis is less disturbed by wheel movement and road surface irregularities.

Unsprung Weight 

    Here are some examples of “pure” unsprung weight on a typical front-engine rear-drive sedan: 
  » Brake rotors or drums + shoes, wheel cylinders, backing plates, calipers, pads, caliper brackets, flex hoses, return
     springs, wheel bearings, etc. 
  » Wheels, tires, tubes & valves 
  » Steering knuckles 
  » Rear axle housing, ring & pinion, differential, axles, etc. 
  » Pinion snubber 
  » Sway bar linkage (but not the arms or center beam)

Sprung Weight 

    Almost all of the remainder of the car is sprung weight, including some components that move, oscillate, reciprocate and/or rotate, including the motor and transmission, since their movement is still supported by the suspension which isolates them from the road surface.

Hybrid Weight 

    On some of the remaining components the definition is not so straight-forward. Parts that are attached to the chassis and the wheels are “hybrid” (mixed): both sprung and unsprung. It's generally considered that the weight split is 50/50, but the actual separation is based on the centerline from the pivot point (not the location of the center of gravity). For example: the outer (ball joint) end of a control arm is unsprung, but much lighter than the inner (chassis) sprung end. 
    For a more extreme example, imagine a driveshaft 60” long, with a tiny U-joint on a 30” aluminum tube in front, mated to a ½” wall thickness 30” long steel tube with a huge U-joint in back. If the 50/50 rule applied, ½ of the total weight would be sprung (on the transmission end), and ½ of the total weight would be unsprung (on the axle end), based on a separation point located at the center of gravity. 
    This is an incorrect and misleading oversimpification, because the first 1” of the weight of the transmission end moves the same amount as the chassis, the next inch moves less, etc. and the final 1” of weight just before the rear axle hardly follows chassis movement at all - it’s tracking the unsprung rear axle movement. The balance of chassis-to-axle (sprung-to-unsprung) movement percentage doesn't have anything to do with the weight - it's based on a separation point located at the geometric center (30” in this case), where a molecule follows 50% of the chassis’s motion and 50% of the axle’s. Clearly, splitting the motion based on weight will predict that this particular driveshaft is almost all unsprung weight (because the heavier components are in the back), even though ½ of it isn't. 

Obviously just another bleacher crew chief. All you are doing is making yourself look stupid.

Call me whatever you think your mentallity permits, but if all this boils down to is about INTERPRETATION of the meaning of support & or control I will still say 2 things.

1. You still make each corner of your racer as light as possible for best results

2. Never a crew chief, but my time, energy & ability on pit road for 40 years with 3 HOF drivers and over 800 combined wins certainly means more to me than a petty argument or disagreement of an interpretation of weight.

I rest my case!!      

Weight that rides on the springs is sprung weight. Weight that does not is unsprung. No different way to interpret it.

 Funny how so many here do not mention their decades of experience until they have been proven wrong by several other posters!