Need help tuning setup.

[Bill Howell]

We got the charger running and ran it hard at the autocross last week. Now we are trying to fine tune the suspension for the upcoming Optima challenge and running into a couple issues.
1) What is the cure for wheel hop under hard acceleration? Car has a XV Motorsports 3link setup out back. I have Avco, single adjustable coilovers. Should I lighten the dampening or stiffen it?
2) In a hard, tight turn, I am pulling the inside rear tire off the ground. I have about 4 inches total travel in the shocks in the rear. We have tightened the front shocks compression some, and it seems to help, but I am afraid we will run out of adjustment before I cure the problem.
Remember this is a 3800 pound boat, that has been stiffened from front to rear, and with 295 Toyo 888s of the front the car will absolutely turn. My fear is there is no fix at all, given the weight transfering to the front will automatically pick up the opposite rear.

Other than the above mentioned issues, the car is great, should be alot of fun on the big coarse.

Thanks guys,

[parsonsj]

Does the car have the same problem turning hard left?

Have you scaled the car? If not, do that first. Otherwise you have no baseline, and you're just shooting in the dark.

jp

[GetMore]

You may need more front rollbar to stop the tire lifting. My question to you is: Have you found a need for that tire to be on the ground during those turns? If the rear isn't sliding out then I don't see you needing the traction of that tire, so it doesn't matter, other than looking funny.
I'm guessing that once you are off the brakes the tire is back on the ground, so you've got traction when accelerating out of the turn.

I don't know if some kind of traction bar (Cal-tracs?) will work and allow full cornering, but you might want to look into that. Honestly, I thought that Super Stock springs kept that from happening.
I don't know what springs you've got in the rear, so maybe that is the issue. The Super Stocks had more leafs up front and were clamped tightly together, so it acted like a slapper bar, but the rear part of the spring was not clamped, so it was free to articulate.

[Vegas69]

I breifly looked at one photo of you on the autocross. It sure looked like you had excessive body roll to me.

[Bill Howell]

John, yes we scaled it last weekend. 3697, about equal left and right and 55/45 front/rear
I know that is bad front to rear.

vegas, we tried several things that day, with the tools we had. The one run was horrible, the rear sway was unhooked. The rest though were pretty flat for a boat.

Getmore, yes, I need the rear planted so I can get off the corner faster, right now with it up in the air, obviously it is spinning and loosing time. It is a three link now, no leafs, coil overs front and rear.

[Bill Howell]

Oh, John, same issue, left or right.

[parsonsj]

Than what Jason said: you need more front spring or front roll bar ...

Or less rear spring or roll bar. The spring approach will also change the weight balance front to rear in a positive way.

What's the easiest thing to try? Given that you lashed up the rear roll bar in a hurry at the track, look that over and make sure you don't have a bind problem with it.

As for the wheel hop, that's a tricky one. I would start by adding rebound damping, to try and reduce the dynamic load/unload couple. If your roll bar is binding, fix that first before adjusting the shocks. Let us know how it goes... I'm always up for suspension tuning.

jp

[Bill Howell]

We went from the original 350# front springs to 425#.
What would you suggest next?

[parsonsj]

What's your rear spring?

Any idea what your motion ratios are in front and brack?

[Bill Howell]

rear is 275# I think.
If by motion ratio you mean shock travel? If so, on the rear it is 5 inches, set now at two compress and three extend.

Not sure about fronts.

[Bow Tie 67]

Bill,

Motion ratio will be inches of travel at the lower ball joint vs shock travel. I hope I remember that correct.

[JRouche]

Im just shooting in the wind here. But I would reduce the valving on the shocks at the back. Let the shock come down and be a lil softer. That might help with the wheel hop and may let the tire come back down on the turn too. Wheel hop can be caused by too tight of a valving. I like more spring (spring and bar combo) and less shock. Soft shock, stiff spring.

Prolly wont cure the tire lift. You are binding somewhere. Even though the bar is removed. With the bar removed the inside wheel should drop, unless you are binding (no bar). Id lift the rear and see where the bind is. If you raise and support the car and let the rear end hang then raise one side the other should droop without the bar. If it doesnt look for the bind. JR

[parsonsj]

Motion ratio will be inches of travel at the lower ball joint vs shock travel.Close. Wheel travel vs spring mount travel (same as shock travel in coilovers). Must cars are about .600 to .700 up front, and .900+ in back. Which is why front springs are stiffer than those in back, in most cars.

So.. 425 front / 275 back. Seems a little light up front, assuming a motion ratio of .650, and given your rear wheel lift, car's weight, and front/rear ratios, I'd try something in the 500-550 range.

jp

[Damn True]

The wheel hop could be cured by adjusting out some anti-squat, less spring or less rear compression damping.

[zbugger]

Bill, I agree with John. I think your front spring is too soft in relation to the rear. Up that to about a 550 and you'll see a better effect. What size front bar are you running too?