Unsprung vs. sprung weight equivalent ?

Does anyone know the question?

 

How about when each changes what happens to handling? One versus the other and where or how are they equal? Say larger wheels and tires are heavier than originals. This is unsprung weight. What happens to handling?

 

Mr. Stopwatch knows.

Food for thought:

By FAR the heaviest part of the "unsprung weight" is the tire and wheel assembly.

A reduced weight tire and wheel assembly will make itself known, by stopwatch, via accelerating and decelerating rotating mass rather than some simple "better handling" often attributed to "less unsprung weight"

 

Rotating versus non-rotating is about 4:1--that is taking 1 pound off the 4 rotating wheel/tire/brake assemblies is equivalent to taking 16 pounds out of the vehicle.

Sprung versus unsprung does not have a ratio, so to speak, but if one dramtically lightens the unsprung parts, you may have to adjust the ratio between compression damping and rebound damping to retain optimal damping.

 

Strange question indeed... and I think that debate has for very long been settled on the less unsprung weight, the better.

Mitch, indeed rotating mass makes a huge difference. I did not hear about that 1:4 ratio but it makes sense assuming the weight is like for like distributed. With wheels, the weight makes a big impact on the suspension - higher weight means more damping is required. For other performance factors, not only the total wheel weight makes a difference but also where the weight is located. Mass further away from the center stores more energy and affects acceleration (and deceleration) more.
Which is also why the craze for bigger rim sizes is in many ways ridiculous, as they increase weight but also move weight further from the center, making them more often than not a detriment to the ultimate performance of a car.

 

By butt dyno can't tell differences in a car but putting carbon wheels on the Ducati was the best modification I ever did. I'd swear the bike lost 80 pounds. Different dynamics at play for changing direction of course.

Has any performance magazine done laps with different wheels? Surely some of the British mags have done comparisons....

 

That made me LOL.

A motorcycle is different; two heavier wheels produce more of a gyroscope effect. It's harder to turn or lean.

Matt

 

It was meant for a chuckle, but somewhat serious too. As the others have pointed out reducing ROTATING unsprung weight gives a (slight) twin inertia benefit for acceleration/deceleration, but reducing non-rotating unsprung weight is no different than reducing sprung weight for acceleration/deceleration. The OP's post was just so vague and full of despair at the same time that I couldn't help myself

 

Equivalent to what? Reducing the unsprung weight (whether rotating or non-rotating) raises the natural frequency of the suspension vertical motion. If you are driving on a billard table smooth surface, this can be a good thing; if you are driving on a bumpy surface, this can be a bad thing.

What is the background for your question? Considering new wheels/tires or new brakes? I think huge tires and huge brakes look great, but, if absolute maximum performance is your goal, you really only want just enough of each to do the job at hand and no more.

 

Disregarding rotating weight, just unsprung weight?

I don't believe there are any ratios to sprung weight - lighter unsprung weight is always better, and there's no minimum or threshold below which lower unsprung weight is negative. The lighter you go, the less inertia of unsprung components there is for the suspension to manage, meaning the suspension can respond to road surface better - result is better ride, more responsive and agile feel (even if those don't show up on a stopwatch).

 

I've been told its about a 3-1 ratio in terms of general benefit but I also think this dialogue shows its probably best to not over simplify...

 

4:1 is incorrect, as is 3:1.

the actual number is 3.4778994 to 1 ratio.

I read it on sixspeed.com.

 

Great examples and an eventual sorting of the issue, no matter how vague the question. I think the phrase "unsprung weight" is a little misleading in the greater scheme of things. It's more the unsprung ROTATING weight.

 

I seem vaguely to remember that sprung weight actually acts as a dynamic weight--in other words its vertical accel/decel dictates how much it affects the mass of unsprung weight--its just my vague remembrance of working with load cells and calculations for the same

 

Mitch and Steve are correct. It is reducing rotational mass that is more the focus than reducing unsprung weight (rotational mass + brake calipers + dampers+ suspension arms etc). Reducing unsprung weight which does not include rotational mass (tires, wheels, lug nuts, brake rotors etc) is no different than reducing weight on a car. Ex. Reducing 1 lb on a brake caliper (non-rotating) is the same as reducing 1lb from a hood.

HOWEVER, reducing unsprung weight does improve steering response and suspension travel should be a bit quicker. If you need accurate responsive steering, reducing unsprung weight helps in additional to acceleration and deceleration benefits of reducing overall weight on a car in general.

 

The answer is it's different for each vehicle. The lighter, the better - you can always through a cricket ball further than a tennis ball, and a heavier unsprung weight will have a greater effect on the suspension for the same reason. BUT, the wheel ratio is different from car to car, and even from front to rear on the same car, which changes the effect. (How far along the arm the spring/shock is mounted, and the angle it is mounted at)

I've long been a critic of bigger diameter wheels - the ONLY reason for doing so is to fit bigger brakes. If you fit bigger wheels and not change anything else, the rotational moment at the tyre surface dramatically increases over that of the brake caliper (ie more leverage), and your braking suffers. It also lowers the effective diff ratio, and your acceleration suffers. Provided you alter the aspect ratio of the tyre such that the overall diameter of the tyre is the same, the effect is neutralised, but you will put more mass further away from the hub, and it's rare that the whole package doesn't actually weigh more.

 

Yes, but does it help the airplane take off from the treadmill?

 

Blue and black wheels are faster than gold and white ones.