Rear Sway bar helps a lot!
02-27-2005, 11:52 PM
#46
Race Director
"Doesn't a stiffer suspension keep the CG from moving around as much, thus keeping the weight from transfering as much? It's a dynamic chicken and egg situation."
yeah, but it's a minor amount... do the math...
It's not really chicken & egg at all because everything starts on the outside of the car with the cornering-forces from the tyres. The front-tyre pulls/pushes the car into an arc, while the mass wants to continue in a straight line. The severity of the weight-transfer then only depends upon the stickiness of the tyres and how much cornering force they can exert on the car.
The amount of weight-transfer due to the leaning body is minimal. You can push on the car or sit on the fender and cause as much weight-transfer as the shift of CG, it's not that much. Remember that there are two types of weight-transfers and the one that you can control is insignificant (actually three types, but we don't need to go into that yet).
"In your experience, how close can you get the corner weights on a 944?"
I usually aim for less than 1% difference between the cross-diagonal sums. The local alignment shop here has manager that races with NASA and TCRA, so he knows what I want. The last job they did came out to:
_L__|__R
830___789
790___773
TOTAL=3182
LF+RR=1603
RF+LR=1579
cross-diagonal difference = 24 lbs or 0.8%
Note that the left side of the car will always be heavier due to the driver. You can never have even left/right distribution unless you want to jack up the entire left side of the car by 15-25".
Also disconnect the swaybars to do this job. Then you need swaybars with adjsutable end-links so you can re-install them without pre-loading the suspension.
Be sure to configure your car exactly as it would be on the track. Spare-tyre and jack removed, average 1/2 tank of gas, lead weights in the drivers seat, etc.
yeah, but it's a minor amount... do the math...
It's not really chicken & egg at all because everything starts on the outside of the car with the cornering-forces from the tyres. The front-tyre pulls/pushes the car into an arc, while the mass wants to continue in a straight line. The severity of the weight-transfer then only depends upon the stickiness of the tyres and how much cornering force they can exert on the car. The amount of weight-transfer due to the leaning body is minimal. You can push on the car or sit on the fender and cause as much weight-transfer as the shift of CG, it's not that much. Remember that there are two types of weight-transfers and the one that you can control is insignificant (actually three types, but we don't need to go into that yet).
"In your experience, how close can you get the corner weights on a 944?"
I usually aim for less than 1% difference between the cross-diagonal sums. The local alignment shop here has manager that races with NASA and TCRA, so he knows what I want. The last job they did came out to:
_L__|__R
830___789
790___773
TOTAL=3182
LF+RR=1603
RF+LR=1579
cross-diagonal difference = 24 lbs or 0.8%
Note that the left side of the car will always be heavier due to the driver. You can never have even left/right distribution unless you want to jack up the entire left side of the car by 15-25".
Also disconnect the swaybars to do this job. Then you need swaybars with adjsutable end-links so you can re-install them without pre-loading the suspension.
Be sure to configure your car exactly as it would be on the track. Spare-tyre and jack removed, average 1/2 tank of gas, lead weights in the drivers seat, etc.
Last edited by Danno; 02-28-2005 at 12:15 AM.
02-27-2005, 11:56 PM
#47
Three Wheelin'
Join Date: Jul 2001
Location: San Francisco, CA Porsche: '92 968 Blk/Cashmere
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Originally Posted by Danno
yeah, but it's a minor amount... do the math...
03-05-2005, 04:54 PM
#48
Back from page 7
Danno,
In post 41 you state that Adrial is correct. Then, in post 42 in response to Chris's question about ride height change you state
In the rest of you response you go on to explain about how the weight transfers from corner to corner under cornering loads with comments like
So, why is this weight transferring? From what I gather you are explaining that it is transferring the way it does because of dynamic ride height changes under load, is this correct? So then if you control ride height changes through suspension stiffness (again, I am referring to springs, bars and shocks here, not just springs.) does that not control how weight transfers from corner to corner?
Basically it seems to me that weight transfers, causes body lean which imparts a secondary shift in weight.
And yes I understand karts are different from passenger automobiles, but for arguments sake we could just as well be talking about any 4 wheeled vehicle, whether a Kart, 944 or cement mixer, no?
Danno,
In post 41 you state that Adrial is correct. Then, in post 42 in response to Chris's question about ride height change you state
Originally Posted by Danno
Yes, in our universe, matter cannot be created or destroyed out of thin air. If you take it away from one spot, it has to go somewhere else
Originally Posted by Danno
Note that due to the rigid body of the car, it remains flat. But the suspension is like the legs of a table. When you shorten one, it reduces the load on that leg AND the corner on a diagonal opposite. The reduced weight on that diagonal is ADDED to the opposite diagonal pair (the total mass of the table or car has to remain the same). The car basicaly teeter-totters on the heavier diagonal, like a table with a short-leg. You end up with a car that's not corner-balanced on cross-diagonals
Basically it seems to me that weight transfers, causes body lean which imparts a secondary shift in weight.
And yes I understand karts are different from passenger automobiles, but for arguments sake we could just as well be talking about any 4 wheeled vehicle, whether a Kart, 944 or cement mixer, no?