Unsprung weight vs. Sprung weight. & HP

[NewTurboTuner]

Lately I've been removing weight from my car and now I'm looking at suspension and wheel/tire combo's to save weight.

I'm on a search to find out How much a HP, can be free'd up by removing X amount of unsrung weight .........Can anyone help with this???

I did some searching on the net, but didnt find what I was looking for.
I think part of the problem is that I don't exactly know how to ask the question.

I have read that 1lb of unspung weight equals 4lbs, 7lbs, 10lbs, 11lbs of sprung weight, BUT I can only assume those are guesses.

Maybe the HP increse, per 1lb of unsprung weight... would depend on the ratio between the vehicles sprung & unsprung weight?
........I don't know... maybe I'm becomeing more confused

My lil brain is going off, but it don't know which way to go hahah

HELP!

Can anyone verify, or produce and equation that would help figure this out?



IT WOULD BE A COOL LITTLE BIT OF INFO FOR EVERYONE TO HAVE

Thanks

 

[awdtalontsi1992]

The general equation I have always heard was 10lb sprung weight = 1 hp. Also that for every 100lb removed = .1 less ET at the strip. As for sprung versus unsprung, I have been told a number of different ratios so I really can't help you there. From what I have heard it is generally 1lb unsprung = 10lb sprung weight. If you use all this information to answer your original question then 1lb of unsprung weight = 1hp gained.

 

[D_Eclipse9916]

There is never HP gained..... Removing unpsrung weight from the drivetrain maybe reduce hte drivetrain loss, but horsepower is never gained.

These are all just ratios that your giving out that are estimates thrown out into the wide world of the internet. In fact probably the only one that could make sense is "Almost correct" but still a complete generalization. 1LB unsprung =10 lb sprung weight.

10lb sprung weight = 1 hp????? what??? How do you gain horsepower by losing weight?
100lb removed= .1 less ET???? SO a 2100 pound civic losing 100 pounds and a 4000 pound trans-am losing 100 pounds is the same effect? no.

Where people might be getting this whole HP thing is from maybe moving the wheels, it takes less horspower to move smaller and lighter wheels then a heavier one so they think they gained horsepower?? No.

Yes your car will be "quicker" with reducing weight. Who knows what effect it will have until you get on the actual strip, and that has enough variables to make your head spin. Just reduce as much weight as you can. Weight is always a bonus unless you sacrifice rigidity.

REmember
Every pound of weight your car loses, means the car has to pull less and will be quicker
Every pound of weight your car loses, means it has to pull less and will be more fuel efficient
IF your not in shape, lose the 20-30 or whatever pounds it takes, youll be healthier, lose more weight in the car and get the effects of a 500 dollar cf hood or hatch. OR spending 2 grand on wheels.

 

[NewTurboTuner]

The motor it's self will not gain horsepower by lightening the rotational mass, BUT you will free up HP that it took to rotate the heavier parts... in effect making more power available to the wheels.

Example:
A motor makes 100hp, and it takes 25hp to turn 48lbs of drive train. Leaving 75hp to the wheels, (or to the ground). If you remove weight from the drive train, then it won't take as much HP to get the drive train moving... in effect freeing HP to the wheels,(or ground)
So if a Motor makes 100hp, and takes 19HP to turn 39lbs of drive train. That gives 81HP to the wheels!

~~~~~~~~~~~~~~~~~~~~~~~~
IF you remove weight from the car chassis. That won't free up any extra HP.
All that does is make your car lighter.... allowing the HP (that you already have) to work more efficiently, because it doesn't have to push as much weight. (Power to Weight Ratio)
~~~~~~~~~~~~~~~~~~~~

I want to know more about removing weight from unsprung, and rotati

OH CRAP!!! IT JUST CLICKED!!! Duuuuhhhh
I just kinda answered it myself up there..... OK.....
Unsprung weight doesn't directly have anything to do with freeing up HP. Its a heavy Rotational Mass that will drain HP ...not heavy unsprung weight. (The term unsprung weight is used in referance to how fast suspesion parts react.) ...The tires threw me in the wrong direction, because they are considerd Rotational Mass, as well as Unsprung Weight.

OK I got that now.
But I still want to know how I can calculate it.....

How Much Force(HP) Can Be Freed Up, By Removing X Amount Of Rotational Mass?

I think that's much closer to the million dollar question.

..............Can someone come up with a equation that will figure this out???.............
Algebra 2 was a far as I went in math class

 

[Rice Over Wheat]

I can tell you for a fact that heavier wheels translate to lower whp at least on a dyno. I did several pulls when tuning my car on a dyno with the stock 16" wheels. Then I put on 18" wheels and dyno'd again several times, nothing else modified, and I lost 15 whp. This was not a heatsoaking issue as it was a different day, same ambient temps, just different humidity.

This is why I'm going to upgrade again, this time to Volk Gram Lights or something similar, ultralight forged wheels.

 

[pneumo]

I think you guys are mixing up your terms. Unsprung weight is not always the same thing as rotational weight. Wheels and tires are rotating weight, and they're also unsprung weight. A flywheel is rotating weight, but it's not unsprung. A control arm is unsprung weight, obviously it doesn't rotate. Removing a pound of tire weight counts for about 2 pounds of non-rotating weight. Rim weight matters more when it's removed at the outer edge, but not so much the hub. A flywheel counts for more because it accellerates at a faster rate than the whole car. The wheels accellerate at the same rate as the car, so wheel/tire weight only counts for 2x. Axles and driveshafts have such a small diameter that saving weight here is just slightly better than saving weight on non-rotating parts.

A 3000 pound car that has 300 HP has a 10:1 power to weight ratio. Same thing for a 2000 pound car with 200HP. If you drop 10 pounds off each car it will have the same effect on accelleration as gaining one HP. Notice I did not say 'it gained one HP' as weight savings only counts when the car is accellerating (or decellerating).

 

[asian312]

Not saying that 15whp is not a lot, but there are many other factors that can contribute to the differace in readings. One being that humidity (ran .5 sec slower than I normally do due to 45% humidity differance). Or Possibly a small boostleak, minor changes to the tune, dyno operator (human factor), etc. What I'm getting at is that unless the pulls were done on the same day in short succession to one another with both sets its really not a valid comparison.

If this is a purpose built race car, then I can see the obsession with weight, but I still wouldn't sacrifice grip. To each their own.

 

[NewTurboTuner]

Thanks for the replies guys

Here's another way to look at it too....
You can have a motor dyno'd on a motor-Dyno making 300HP, and then put that same motor in a car.... and have it dyno'd on a chassis-Dyno making 255HP. The reason the motor makes 255HP in the car and on the chassis Dyno... is because it energy(HP) is needed to rotate the driveline assembly. So if you were to lighten up the rotating mass of the driveline... in theory you should gain HP to the wheels

~~~~~~~~~~~~~~~~~~~~~~~~~~
Well for now it looks like I'll be going with 17" Centerline Ram's~15lbs, and Kumho ECSTA ASX~23lbs. A 39lb combo. That's not the lightest tire, but for the nasty weather we've been having in Seattle lately... its probably a good choice, and for only $271 for the combo, that's not bad at all.

If a stock wheel/tire combo is like 48-50lbs ...I'll drop 40lbs of driveline weight (rotational mass ) ...I'd say that would defiantly give me a improvement in power. I LOVE IT! I buy tires for traction, and I get more usable HP as a bonus! SWEET!

Hey anyone in the Seattle area have a G-Tech?
I still wanna figure out what kind of HP gain comes from removing 40lbs of rotational mass.

 

[tstkl]

take physics classes, a LOT of physics classes.

after about 10 years, you'll under stand what happens in a perfect enviorment, aka you still won't know jack shit about whats going on in your car.

 

[95blackGsTurbo]

Lightening anything that has to do with rotating with the motor will free up some power. But it usually evens out if you are going with a track car. Show on SPEED did a thing on it where they dyno'd 14 less wheel horse power when they upgraded to a Brembo Big Brake Kit and gained 8 back by putting on lighter rim/tire combo. Yo ucan only free up to much power though.

 

[jtmcinder]

HP = torque x speed

torque = lever arm x force

What extra rotating weight (better thought of as a higher rotational moment) does is use up some of the torque.

To calculate how much of a gain will be had with different parts, you need to know their rotational moments, which means you need to know the average distance from the center for all of the mass.

This does not require very much physics. Getting the raw data is often the hardest part.

- Jtoby

 

[wret]

To calculate how much of a gain will be had with different parts, you need to know their rotational moments, which means you need to know the average distance from the center for all of the mass.

Okay, any suggestions to get that? Cut a wheel in half?

 

[KeltonDSMer]

^^^What kind of a comment is that, wret? jtmcinder is right, it matters where in the wheel the weight is removed.

Power is change in energy with respect to time. The energy of a rotating object is dependant on inertia, which for any given mass and diameter of a wheel can change depending on where that weight is distributed.

This is why although of course lighter wheels won't make more engine power, less energy is being put into the rotational KE of the wheels/brakes/tires so there is more power transfered to the ground.

Think about flywheels, ACT takes out the weight in their XACT streetlight unit as far to the edge as possible to reduce inertia; that is what is important and not the mass of the unit itself.

 

[jtmcinder]

The easiest way to measure the rotational moment of an object is to see how much torque it takes to spin it (or see how fast it spins when given X torque for Y ms).

This is not only the simplest way to do the measuring, but it also makes the relationship between rotational moment and the "loss of power due to rotating mass" rather obvious. It's a heck of lot easier to spin my 245/45/16 Hoosiers on their Kosei K1s than it is to spin my 245/40/17 SPTs on their ASA IS6s.

- Jtoby

 

[talont3t4]

Measuring the effect of unsprung weight is not as simple as x=y. The further from the center of rotation the weight is the more effect it has on how much it act on the force trying to turn in. For example adding a 25 Lb weight to the hub of your wheel then dynoing would show a lot less hp loss then adding the same amount of weight to the out side of the wheel. Hope that makes some kind of sense to you. It would be like removing 10lbs from your flywheel would make more of a difference on acceleration then 10Lbs form the driveshaft

 

[jtmcinder]

You guys are not going to get anywhere if you keep jumping back and forth from rotational moment to unsprung weight.

If you want to talk about acceleration and braking, then focus on the rotational moment and forget about the (rest of the) unsprung weight.

If you want to talk about maximizing grip (and/or ride quality) when driving on surfaces that are not perfectly smooth, then talk about the unsprung weight (or, better yet, the ratio of unsprung to sprung weight at each corner) and forget about what proportion of the unsprung weight is spinning.

- Jtoby

 

[wret]

^^^What kind of a comment is that, wret? jtmcinder is right, it matters where in the wheel the weight is removed.

I wasn't trying to be flippant. In my own mind (closed), that seemed the only way to find the center of mass. I'm not ready to donate a wheel to science. Measuring the torque necessary to spin the wheel of course is non-destructive testing, but beyond the capabilities of most of us, and as mentioned, probably not the most important factor in choosing wheels and tires.

 

[Rice Over Wheat]

Put some lead wheels on and let's see anyone not lose HP on the dyno. It is obvious that lighter is better, all other variables the same. I saw this difference when I switched from 16s stock to 18s aftermarket as I already stated and I had Garry Marsh tuning my car, a fwd dsm world record holder. So in answer to someone above, yes the guy running the dyno knew what he was doing.