Quote:
Originally Posted by Bobcat
Bob ... thanks for the input . Haven`t calculated the suspension frequency yet, but have had the car`s corner weights set . Like yours , I have more weight on the rear than the front ( 52.5% ) and cross weights are all within .3% All weights/settings were made with my weight in car and just under 3/4 tank of fuel and all other fluids in . Interesting point on the cars that he works on and I`ll ask him about that today . BTW , I have the ERA IRS rear suspension .... and most of his cars don`t .
His comment about softer front springs made sense to me as that`s how I had my dirt car set up years ago .... as soft as I could get it and still keep it under control ( most of the time ) .
Bob
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Soft springs and big bar works really well on a dirt car. The soft springs control the suspension over the irregular surface and keep the tire in contact with the racing surface.
This is not a dirt car, and you'll be driving/racing on a much smoother surface. So those concepts don't apply all that well.
I use 650# springs in the front, and a modest bar rate. That seems to work well, and we get pretty flat cornering.
I also have IRS, and that's a whole differant ball game. The IRS should be prdominantly controlled by springs. With either no bar, or a very light bar for fine tuning. If your springs are set up just right, a bar will actually degrade handeling.
But the way my IRS is built (and probably yours too) it's almost impossible to fine tune with the springs only. The motion ratio is just too high. It can be done if you move the springs as close to the tire as possible, and straight up and down.
Quote:
Originally Posted by strictlypersonl
Bobcat,
Do the frequency calculations first. You'll find that the car is initially set up with a pretty strong difference between the front and rear (by design). I recommend that the springs be changed rather than the anti-sway bar so that the lift under acceleration is reduced, and therefore reduced camber change. This will decrease the amount of power-on understeer/lift-induced oversteer you get.
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Those caster and camber changes should have very little effect on the car in the small picture. If the changes are huge they will. Otherwise they are expected and desired. It's the toe out changes on compression (bump steer) that can really get you!
I don't know the exact numbers for the ERA cars, only mine. But to make intelligent decisions you need to collect data before making changes. Find out what the unsprung weight is at each corner. Calculate motion ratios. Measure sway bar rates. Once you have all that data, it's easy to plug the numbers into a spread sheet, and see what happens when changes are made.
The spread sheet is not magic, and will not provide all the answers. But it does get you in the ball park, and help you understand what happens when changes are made. It's a very helpfull tool.
On my car, I'm using 650# front, and 750# rear. I'm considering 850# rear, and 750# front. It looks good on paper. But I'm not sure track testing bears that out. I'll consider it again when we race in a couple of weeks.
Another note on springs. There are $5 springs, and there are $50 springs. You get what you pay for. There is a noticable differance between one and the other. I use $50 Eibachs.
BTW, I am not a suspension genius nor Guru. I credit Gordon Levy, Wayne Presley, and Carroll Smith for educating me, and helping me to make intelligent decisions. So far, it is working well for my car; it keeps getting faster and smoother, without wasting a bunch of money. A bow of thanx to my friends.
