Quick question on weight transfer....

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KSaiyu

KSaiyu

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Can anyone give me a definitive answer to this, I've tried searching on forums and web pages:

What changes how much weight is transferred, the height of the CG alone (CG lower = less weight transfer) or height of CG in relation to height of roll centre (the roll couple)?

For example, if you lowered a car 3cm, but also lowered the roll centre 3cm, would there be a change in the amount of weight transferred?

Thanks
 
I can't answer that for certain. I would hazard a guess, though, that you need to change their positions relative to each other to affect the amount of weight transfer.
 
Originally posted by KSaiyu
Can anyone give me a definitive answer to this, I've tried searching on forums and web pages:

What changes how much weight is transferred, the height of the CG alone (CG lower = less weight transfer) or height of CG in relation to height of roll centre (the roll couple)?

For example, if you lowered a car 3cm, but also lowered the roll centre 3cm, would there be a change in the amount of weight transferred?

Thanks
Click to expand...

I think yes. Lower CG will result in less weight transfer during braking, cornering.....
 
This posted edited for brevity.

The amount of weight transferred is based on CG, the car's roll center (center point at which car pivots around suspension), the track (distance between center of tires on either side of the car) and wheelbase (distance between center of tire on either end of the car).

Let's say you have a car with a CG that is equal to the track. We'll call this value x. If 200 lbs of force is exerted against the CG during cornering, the same amount of download will push down against the outside tires.

Say you lower the CG of the car by half, or x/2. The same 200 lbs of laternal force will then be halved, so you'll only get 100 lbs. of download at the wheels. What this means is that by lowering the CG of a car, you will in turn allow the tires to receive greater amounts of download. If the tires can cope with additional download forces, you will in turn get faster cornering.

There's a great section about lateral load transfer in Going Faster by Carlos Lopez that explains in greater detail what I just wrote. KSaiyu, you should get this book. It answers most of the suspension dynamics questions any car nut may have.


///M-Spec
 
hmm i just finished that chapter and it seems that it's just the CGs height that affects the amount of weight transferred, but it still doesnt explain what exactly a roll centre/axis would effect :banghead:
 
Originally posted by KSaiyu
hmm i just finished that chapter and it seems that it's just the CGs height that affects the amount of weight transferred, but it still doesnt explain what exactly a roll centre/axis would effect :banghead:
Click to expand...

A roll center is a geometric line at which the unsprung portion of the car's weight rotates around the suspension. It is important to suspension engineers because it determines how lateral loads on the car will change suspension geometry. This line will vary greatly from model to model. In sports cars, it is often close to or below the axle centerline. In many race cars, the roll center is actually under the ground!

Check out How to make your car handle by Fred Puhn. He does into some detail about this.


///M-Spec
 

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