Raising Rear Roll Center

[romeen]

Based on Jtoby's advice, I've raised the rear of my 2G so that it now sits higher than the front based on the distance from the center of the wheel to the bottom edge of the fender. This supposedly improves handling. Some members have also suggested that it will help with FWD traction by placing more weight on the front tires which seems to make sense to me. Although I wonder if shifting even more weight to the front of an already front heavy car would result in even more under steer. I can't really comment on my initial impressions because I haven't had it aligned since the height change and I know that it's way off. I can't afford to use the trial and error approach of making height adjustments, alignment, test drive then repeat. So my questions are:

1) What is the theoretical benefit to having the rear roll center higher than the front? Basically, what am I trying to do?

2) Does anyone have any personal experience with doing this either with regards to handling or FWD traction?

 

[jtmcinder]

As else being equal, raising the roll center puts more of the weight transfer under the control of the suspension, instead of being instantaneous. It also reduces body-roll as the lateral force is now less of a wedging force. Raising the rear roll center will allow you to stiffen the rear without snap-spinning at turn-in. In the case of a 2G, this is usually achieved by simply not lowering the rear as much as the front. Because the CG is closer to the front than the rear, this doesn't have as many negative side effects as leaving the nose up.

Raising the rear does not put more weight on the front tires. In fact, when accelerating, it causes more weight to shift off the fronts, because raising the rear raises the CG (as mentioned above) and a higher CG means more weight transfer. Who-ever told you to raise the butt of a FWD for more traction needs to be beaten. That's what RWD drag-racers do, because they want weight transfer; you don't.

Putting the two together: raising the tail to get a higher rear roll center might not be anywhere near as useful to a FWD as it is for an AWD. You really need to keep the weight on the front tires or you won't get out of corners very well. An AWD can afford a bit more longitudinal weight transfer because the car uses the rear wheels, as well.

 

[romeen]

Raising the rear does not put more weight on the front tires. In fact, when accelerating, it causes more weight to shift off the fronts, because raising the rear raises the CG (as mentioned above) and a higher CG means more weight transfer. Who-ever told you to raise the butt of a FWD for more traction needs to be beaten. That's what RWD drag-racers do, because they want weight transfer; you don't.

When corner weighing a car, won't raising the rear shift more weight onto the front tires? Although if I'm understanding you correctly, when accelerating the weight shifts towards the rear immediately making that a moot point and a higher CG only adds to this weight transfer (?)

Will raising the rear shift the CG more towards the front of the car? If so, is this even beneficial?

Lot of questions, I know. But the info is greatly appreciated.

 

[jtmcinder]

First, I need to undo some damage. The following is complete and utter nonsense; I really hope the guy who wrote it was on one hour of sleep or something; otherwise, he's an idiot:

As else being equal, raising the roll center puts more of the weight transfer under the control of the suspension, instead of being instantaneous.

Raising the roll center actually puts LESS of the weight transfer under the control of the suspension. That's why raising the roll center decreases body-roll. (The rest of that paragraph was OK, but the above claim is nonsense.)

OK, now the new stuff: Raising the rear might shift static weight distribution a tiny bit to the front (and, yes, it does this by moving the CG a tiny bit forward), but, as you said, this is more than out-done by the increase in weight transfer under acceleration, due to the higher CG, which is why it's not at all worth it to a FWD.