Let's say that you take the stock heavy flywheel off the car and replace it with a much lighter aluminum flywheel. Now your acceleration has improved due to less reciprocating mass and allows the engine to spin up faster.. Let's say that replacing the flywheel eliminated 10 lbs causing the increased acceleration. Now lets say that you replace the drive shaft with a carbon fiber unit saving another 5 lbs causing even better acceleration now due to less reciprocating weight.

Okay, so now you have removed 15 lbs of weight and the acceleration of the car is amazing.. However, you have a problem now with traction so you go out and get some wider wheels and tires. The only thing now is that your larger tires and wheels weigh 7.5 lbs each more than the stock ones which means that you have just added an additional 15 lbs.

The question is does this reduce your acceleration back to the point from before?? In other words, did you cancel out all of your weight reduction gains in acceleration by putting on the wider and heavier wheels and tires???



What do you think????

 

:confused: :withstupid: :rolleyes:

 

I think you have too much time on your hands :lol:

Just my opinion, but I think that you would not go back to the start. I would think that half the wheel would be unsprung weight and therefore not really have an effect on anything. Just thinking out loud, but also, does the weight of the road have any effect on performance? Of course not, so the weight on the wheel that is sitting on the road shouldn't make any difference in the performance either, and that would, I think, reduce the total weight effect of the wheel. Or, I could just be making no sense to anybody except myself :crazy:

 

Increasing the rotating mass of the wheels would have a negative effect. However, the rate of acelleration of the wheels is less than the rate of accelleration of the flywheel and the driveshaft because of gearing. Therefore, I don't believe that they would cancel out.

 

You're dealing strictly with rotating masses here, not reciprocating masses such as pistons and rods. The mechanical equations that deal with rotaing masses are different than those used to calculate the effects of reciprocating masses, although both affect the acceleration rate of the vehicle. You are on the right track in looking at the effect mass has on rotational acceleration. As drivetrain mass is reduced, power transmission efficiency increases to the practical limit of material properties. Also unsprung weight and how it's distributed is very important to vehicle acceleration since it relates directly to inertia.

Your question can be answered by calculating the effect each reduction and addition of mass has on the system - it's not a one-to-one relationship. One pound of wheel does not equate to one pound of drive shaft. There are diameters, masses, gear ratios and other factors to consider as well.

 

1 lb out of the wheels is like 4lbs out of the interior (or non travetrain areas).

1 lb out of the driveshaft is like 10lbs out of the interior (or non travetrain areas).

You'll come out ahead and also have more traction. :cool:

I can't speak for the stability/real world issues of changing out these driveline parts.

 

15 pounds huh... acceleration is amazing???? I dont know about you.. but I can not tell the difference in acceleration in my car [SOTP]... with or without a passenger... 170 pounds... I know the -passenger isnt hanging on to the flywheel. GM reduced the windshield thickness to save 8 pounds.. that represents a gallon and a quarter of gas... Lots a advertising hype....

 

Too much free time. Go polish your car :iagree:

 

IMHO this is a great question. Every pound of weight lost adds acceleration, increases MPG, aids cornering, braking, etc.

To the naysayers: Why do you even bother replying if the topic is a waste of time? :rolleyes:

 

He was not saying that he noticed 15lbs removed from the car but 15 lbs removed from the flywheel/driveshaft. This reduction in rotational weight makes a HUGE difference in acceleration. Excellent question about the added weight in the tires/wheels...

 

You're going to have a traction problem anyway at the strip. With or without the weight savings. Therefore the tires are required. You will have a faster car with the mods mentioned. You can throw the rest of the math out the window on this one. Now go wax your car.

Bob
:flag


[Modified by Korreck, 11:21 AM 8/25/2003]

 

You have reduced the ROTATing mass of the engine, you have not changed the reciprocating mass.

Again you reduce the rotating mass. HOWEVER, rotating mass is not computed by simple weight (i.e. on a scale). Rotating mass is weighted by the moment of inertia. Take a bar bel with 10 pounds on each end. It is hard to get it to start spinning. Now take the same barbel, but position the weight at the center of the pole. Now it is quite easy to turn. Same weight, different moment. To compute the moment of inertia, take each unit of weight and multiply it by the distance from the center of rotation and add up all the terms.

The weight reduction of the drive shaft is (essentially) negligable with respect tothe flywheel. So you get a big bang out of the flywheel and a tiny bang out fo the driveshaft IN TERMS of ROTATING inertia. This is easy to see, the drive shaft is (what?) 3" across, while the flywheel is 24" across! Stuff multiplied by 12 add up a lot faster than things multiplied by 1.5.

It is entirely possible that your larger wheels and tires dominate and reduce the acceleration potential of the flywheel and driveshaft because the wheels are larger than the fluwheel! ITs not weight, its weight times distance from center of rotation.

Could even be worse, but I doublt it. Our cars are traction limited at least up through 30 MPH. After than the differences you are talking about might be useful on a road course but less so on the strip.


[Modified by Mitch Alsup, 11:29 AM 8/25/2003]

 

Actually your right I do have way to much time on my hands....but that's not the problem....see I have so much time on my hands that I think of stuff like this and I get smarter day by day :D ....Brian thanks for making it clearer....Thanks for the answers guys :cheers:

 

:rolleyes: :nono:

 

:iagree: :iagree: :iagree: I wonder how much a carbon fibre drive shaft would cost?

 

Gary, you and I have similar minds.. ;) I come up with stuff like this all time.. As a matter of fact that is why we now have the PART Throttle Tune..

Persistance rules over EVERYTHING.. :smash:

 

I have to ask....WTF is a travetrain :confused: :lol:

 

An option that requires a 'spellcheck delete' package. :crazy: