[lwlam]

I need a little help with theory, please.

I understand that a reduction in unsprung weight (specifically I am thinking about wheels and tires) will result in an increase in a car's acceleration by reducing the amount of mass that the engine has to turn. The car becomes faster without any true gain in torque.

Is there a practical mathematical formula to derive the equivalent gain in torque/ horsepower from a reduction in unsrpung weight? For example, if I can reduce unsprung weight from each corner of the car by 8lbs (total reduction of 32lbs), how much more "power" would that feel like?

I am hoping that is some rule of thumb out there that someone would care to share. Otherwise, I think this could be figured through examining the delta in acceleration times for a car before and after the weight reduction. A pretty standard rule is that a 10hp gain will reduce your 1320ft time by .1sec. If a car can reduce its 1/4mi time by X seconds after the unsprung weight reduction, then we could say that the equivalent horsepower gain from the weight reduction is equal to X times 100.

Is there a better way?

Thanks

[obehave]

Read and enjoy this thread

[andyupnorth]

I started to read that thread and then woke up 2 hours later with "QWERTY" printed backwards on my forehead and dribble running out the corner of my mouth..

[obehave]

Quote: Originally Posted by andyupnorth

I started to read that thread and then woke up 2 hours later with "QWERTY" printed backwards on my forehead and dribble running out the corner of my mouth..

Whew!

Nice to know it wasn't just me

Idiots Guide to the thread:

Heavy= Bad
Lighter= Good

[Andy@Ross-Tech.com]

I'd say the only safe assumption is that removing 10 lb of rotating mass is AT LEAST as good as removing 10 lb of dead weight. There is no hard and fast rule like a multiplying factor since factors like inertia, torque arms, etc. come into play, along with the speed and acceleration at which you are doing the measurement. Imagine shedding 1 lb from an inner CV joint. Sure, it's spinning, but it's mass is located very close to the center of its rotation. So, it may be worth 1.0001 times just cutting 1 lb out of your floorpan. On the other hand, removing 1 lb of mass from the tread of your tires (burnouts, baby!) may be worth 3 times just cutting 1 lb out of your floorpan.

obehave summed it up more succinctly.

[cristo]

here's a sample number crunch from a previous thread:

http://www.mini2.com/forum/showthread.php?t=78833

results are 1# off wheel/tire = 2.2# off chassis for typical 0-60 run.
less of a difference if you accelerate more slowly.

[lwlam]

Exactly what I was looking for. Thank you.

I'm no genius in physics, so I'll have to take my time here so as to not hurt myself.

Lester

Quote: Originally Posted by obehave

Read and enjoy this thread

[pocketrocketowner]

Quote: Originally Posted by lwlam

I need a little help with theory, please.

I understand that a reduction in unsprung weight (specifically I am thinking about wheels and tires) will result in an increase in a car's acceleration by reducing the amount of mass that the engine has to turn. The car becomes faster without any true gain in torque.

Is there a practical mathematical formula to derive the equivalent gain in torque/ horsepower from a reduction in unsrpung weight? For example, if I can reduce unsprung weight from each corner of the car by 8lbs (total reduction of 32lbs), how much more "power" would that feel like?

I am hoping that is some rule of thumb out there that someone would care to share. Otherwise, I think this could be figured through examining the delta in acceleration times for a car before and after the weight reduction. A pretty standard rule is that a 10hp gain will reduce your 1320ft time by .1sec. If a car can reduce its 1/4mi time by X seconds after the unsprung weight reduction, then we could say that the equivalent horsepower gain from the weight reduction is equal to X times 100.

Is there a better way?

Thanks

Answer to question # 1: NO
Answer to question # 2: NO
Answer to question # 3: Yes, but I'd have to kill you if I told you......

[flyboy2160]

[quote=cristo]here's a sample number crunch from a previous thread:

http://www.mini2.com/forum/showthread.php?t=78833

results are 1# off wheel/tire = 2.2# off chassis........QUOTE]

this violates the laws of physics.

to summarize the equations: FOR THE PURPOSE OF ACCELERATION NOT HANDLING, the maximum multiplier effect of reducing rotating weight is 2, which is obtained by removing weight from the tire TREAD. removing weight from the center of the wheel hub has the lowest multiplier effect, 1.

real wheels and tires have a multiplier somewhere in between, say 1.6 or 1.8. that is, removing 1 lb. from the wheel rim and tire is the same as removing 1.6 or 1.8 lb. from the chassis.

"you may ignore the laws of physics, but the laws of physics never ignore you."

flyboy

[cristo]

damn, flyboy, I looked at this problem again and I think you're right.
back to physics for me.