How much of a difference is unsprung mass really going to make?

By increments of 5:
5 lbs
10lbs
etc.

The reason for this is is that I see people arguing over lighter/bigger wheels, calipers, springs, rotors, tires, etc. but will it really make that big of a difference?

 

It makes a huge difference if it's rotational mass that you are losing, but it all depends. If you lose weight by going with a light wheel, then that's cool, but don't forget the majority of the weight is on the outside due to the tire. So you are not losing as much weight as you think you are, because the closer to the center of the circle (talking rotational mass here) the less that weight affects you. The further to the outside of that cirlce, IE the tires, then the harder it is to move that circle. Yes, lighter wheels make a good difference, but not as much as say, a light flywheel etc...

NOW if we are talking about just weight reduction, then yes, it makes a difference but in big incriments. 5lbs will not make a difference that your butt dyno will notice. But if you swap an exhaust out to a lightweight titanium exhaust, the weight savings are huge and noticeable. Same as going with a cf hatch etc....

But I agree with Jason, when he says that losing weight up in the front of the car is more beneficial since the rear is alreday light in comparison.

long answer, hope it helps though.....

 

there isn't much we can remove/change out to lose the weight in the front except maybe an engine swap right?
The hood is already aluminum, I don't resume going with cf body panel/ front fender will significantly lighten the load?
any other idea?

 

optima, or even better for weight reduction, an odyssey lightweight battery. The stocker is around 40 lbs. while the optima is ~28 and the odyssey is in the teens.

 

Where can we buy the Odessy battery?

 

Also move the battery to the rear.

 

I went through two carbon fiber hoods that kept cracking because of hood pins with daily use...minimal loss of weight from the seibon and veilside hoods. Are those titanium springs really that much lighter? There's other materials as well, right?

 

heh this thread was hijacked from unspring weight to weight reduction (which is where the real power is)

move odyssey batt to rear....cf rear hatch....cf hood....cf doors...cf pillars...i saw some Axis race car that was 2700lbs with an entire cf upper body

 

seen the hood and front bumper in CF...seems like everyone's waiting on the hatch from Fiber Images..supposed to be under a grand...it would be nice if we could figure some better ways to lighten the front besides an engine swap...those titanium springs any lighter or is it all hype that they're actually partial titanium just to get us to buy them.

 

Another memeber installed the Ti springs. Unfortunately he didn't weigh them, but said he saved around 10lbs over the stock springs. So that's a little over 2 lbs a springs. 10lbs is pretty good if you ask me for such a small part.

 

Unsprung weight has a greater effect on the handling of the car than sprung weight. The basic formula is that for every One Pound of Unsprung weight, the equivalent of Sprung weight would be FOUR POUNDS!

1 Pound Unsprung weight = 4 Pounds Sprung weight

5 Pounds Unsprung weight = 20 Pounds Sprung weight

10 Pounds Unsprung weight = 40 Pounds Sprung weight

That is why putting lightweight wheels on a car effects performance so much. Testing has shown that going to a lighter wheel/tire package decreases acceleration time, shortens braking distances and improves handling.

This is why going with a wheel/tire package that increases the unsprung weight (ie: 19" or 20") actually lowers the performance of the car.

 

OK here is the real deal and it is a matter of force and momentum. How much force does it take to put an object into motion and how much force does it take to stop an object that is in motion Unsprung weight is much more critical then sprung weight.

Let's begin with suspension. As the car is going down the road the ideal situation would be for the tire contact patch to stay constant as the road surface varies (no losss of traction and tire pressure stays constant, etc.). This will never happen, but in order to get as close as possible to ideal the suspension would have to react immediatly to road surface changes. Here it where force and momentum apply. Force=mass x accelration. Momentun= mass x velocity The acceleration we are concerned with is the vertical accleration of the suspension as a road irreglarity is encountered. This is not something you have control over. What you can control is the mass of the wheel/tire combo and suspension control arms, The lighter these are the less mass there is and less force is reqired to move them and once they are in motion less force will be required to stop them. In short, less mass means that the suspension will respond quicker will track the road surface better.

Now wheels. There are two types of momentum, translational and rotaional. Translatonal momentum describes something that moves in a straight line and this is desecribed above. Rotaional momentum is described as Angular Momentun = mass x velocity x radius. (this is why, when a figure skater spins, she increases angular velocity as she pulls her arms close to her body and decreases velocity as she extends her arms). Wheels experiend both types of momentum, but the more critical is rotaional momentum. For a given wheel/tire diameter a lighter wheel/tire will require less force to begin rotating and once rotating require less force to stop. The gyroscopic acton of the wheel can also be considered. The more mass that a rotaional body (wheel/Tire) has the harder is is to turn pepedicular to the plane of rotaion.

Soooooooo, all that being said, if you are inclined to reduce weight do the unsprung weight first, but don't make the wheel so light that they can't withstand road hazards, in which case none of this matters.........time for me to take a breather and get a drink..... have fun

 

I was watching Sports Car Revolution on the Speed Channel and they dyno tested an exhaust kit on an RSX type S. They were confused why they lost power from the stock baseline and to make a long story short were able to attribute the loss to the big brake kit and +1 sized wheels they also added.

They went on to explain that even though the wheel combo was lighter, the added diameter was more difficult to spin.

 

I remember that CAr & Driver did a test of a Honda Civic several years ago. They tested the stock tires and wheels, then they did 3 different plus sizes. They lost a noticable amount of quickness with the heavier wheels (except when Wheelspin was a factor). Wish I still had the article on hand so that I could give the exact numbers.