K27w

I got to thinking about how important (or not) it is to have the weight evenly distributed, a tribute that only a few select road going cars enjoy.
If you ever watch WRC you see cars like the Ford Focus, a really front heavy car competing and beating the Evo's WRX's etc, all cars that have a much more even weight balance.
ALMS, same thing, front engine V8 cars, GT3's, mid engines, all being competetive.
How do they make these cars competetive, suspension black art?
Is it really only matter of how the car feels to the driver or is there any real performance gains in having the car balanced.

sweanders

[quote]Originally posted by K27w:
<strong>I got to thinking about how important (or not) it is to have the weight evenly distributed, a tribute that only a few select road going cars enjoy.
If you ever watch WRC you see cars like the Ford Focus, a really front heavy car competing and beating the Evo's WRX's etc, all cars that have a much more even weight balance.
ALMS, same thing, front engine V8 cars, GT3's, mid engines, all being competetive.
How do they make these cars competetive, suspension black art?
Is it really only matter of how the car feels to the driver or is there any real performance gains in having the car balanced.</strong><hr></blockquote>

I´m not sure about all the series you mention but what many don´t think about that you can have a mid-engine car with the engine in front of the driver as well as behind.
In most classes it is allowed to move the engines position closer to the center of the car. Also, since there are weight-regulations a front heavy car can be made 50/50 with extra weigths placed strategicly.

It is also important to have the weight distributed evenly over the car, basicly it (the weight) should be low and evenly spread to avoid unspringed weight, big over hangs.
On some cars it is possible to alter the brake balance between front and back axles.

This way it is possible to setup a car for maximum acceleration performance or braking performance.

The new Volvo S60R has got a very interesting suspension system developed with Öhlins that changes the suspension stiffnes 500 times/second individually over all wheels to add stability during braking. With this system (Volvo PCC) it is possible to prepare the suspension for braking or cornering while you are doing it.

Hope this info in some way answers your questions.

/Anders

sweanders

If you look at a 911 since it has something between 60/40 and 70/30 weight distribution it is good to accelerate and brake with in a straight line.

/Anders

Steve Lavigne

[quote]Originally posted by sweanders:
<strong>If you look at a 911 since it has something between 60/40 and 70/30 weight distribution it is good to accelerate and brake with in a straight line.</strong><hr></blockquote>

The basic 911 platform has UNBEATABLE grip in straighline braking and acceleration. Also, with this rearward bias, you can get on the gas very early and hard on the exit of a corner. Unfortunately, in order to get the car to the proper attitude to do this, you really have to slow the car quite a bit to get it to take a proper set.

The notion that 50/50 weight distribution is optimal is false. A rearward bias with the mass situated somewhere close to the center of the car is always preferable in a rwd racing car. Also, keep in mind that the weight tranfers under dynamic load. When you brake in our cars, our relatively smaller front tires get a large percentage of that weight, while the larger back tires aren't able to contribute much to braking.

The polar moment of intertia is also a significant factor in this. Our cars have a high moment of intertia because the transmission is at one end and the engine is at the other. This translates into relatively slow initial rotating response, coupled with a lot of intertia once it is actually rotating. This means that once the car takes a set into a corner, it is likely to maintain that. Additionally, once it is truly sliding, the high intertia makes it difficult to correct for this.

A mid engine car has a relatively low moment, with the engine, transmission and passenger all concentrated around the center of the car. This means that it will turn very quick, but be less stable through a corner. Ultimately, however, it is easier and quicker to respond to corrections when it is out of shape.

Danno

Also under cornering, the lateral weight transfer can be split any way you want between the front & rear wheels. So a 500lb weight-transfer to the outside under cornering can be split 50/50 between the outside two tires. Or it can be split 70F/30R or 30F/30R or any other combination you want. And the resultant behavior will be different as well:



Also a 944NA actually has more weight on the rear, 49F/51R and the 951 has 51F/ 49R weight distribution.

K27w

Good info all, thanks.
That is one thing for sure, when I have pushed past the limit, the car is very hard to recover, the rotational mass at either end prevents that.
Regarding the point about regulations allowing engine placement, I noticed on a few front engine pseudo production cars with the tubular frames , the engine seems to be set much further back than stock.

nib5

Watching an ice skater spinning is the best practical example in variation of the polar moment of inertia. Arms outstretched, they will rotate slowly - if they then move their arms inwards toward the body, the rate of rotation will increase dramatically.

Lightened cranks, flywheels and road wheels are beneficial in situations when rapid speed variations are needed - racing - for the same reason.