car balance question

[dlampe]

I weighed my car yesterday and with me in it (200lbs) and some fuel the car was 540 LF, 500 RF, 680 LR, 580 RR. The left side of the car is setting slightly lower than the passenger side. If I level the car (tighten the springs on the driver side or loosen the springs on the passenger side) how will that effect the balance?

[jmarsey]

Answer: you'll make it worse.

Right now your cross weight is 51.3% / 48.7% which is not bad at all for starters. If you wanted to dial the car for you as driver only, which is how I have mine set, I would increase the right rear to 50/50 cross weight. The ideal cross weight would be 50/50 for starters.

Your front / rear is 45% / 55%

Those Kirkhams are very light!

John

[dlampe]

It would be very difficult to build a car that was naturally balanced given the driver and driver related hardware on the left side of the car. I guess I thought you could achieve balance by messing with your suspension. Is that the case. It seems that I would need to raise the light side of the car to get this balance correct. If I do that it will not be level and that will screw up the roll centers. If I am setting up a track car what should I do? Run the car unbalanced or unlevel?

[scottj]

Hi Dean,

If what you are trying to do is equalize the left to right weight distribution by adjusting the coilovers, you can't. You can, as John suggests, balance your RF-LR and LF-RR crossweights and maintain correct ride heights with the coilovers. The only way you can change Left-Right and Front-Rear weight distribution is to move or add weight. I always set ride heights while on the scales with the equivalent of my weight in the drivers seat.

[dlampe]

Is the cross weight the important one! I am just trying to get my car "set up" what ever that means. If I have my cross weights equal, is that balanced? Is that what your do with your scales? I am really new to all this suspension stuff but I am trying to learn all I can to make this car handle as good as it can. Thanks for chiming in!

[rdorman]

Dean, assuming that you are not going to move suspension pickup points, move mass around etc..... Do the following:

-make sure the floor is perfectly level, set tire pressure, keep doing this with you and the fuel load you want in the car, disconnect shock (if possible or set full soft), and anti-roll bars, bounce car often to get suspension to settle.

- Set the desires ride height

- If you end up in the situation that you have above, try lowering the LR and RF half a turn and raising the other corners the same and see what happens.

[scottj]

Dean,

Not to get caught up in semantics but a "balanced setup", to me, refers to a car having the front and rear suspension systems working in unison to maximize the traction of all 4 tires during cornering. A setup that is too soft or has too little roll resistance in the rear compared to the front will transfer too much weight across the front tires when cornering...leading to a push or a "tight" car. Likewise, too little roll resistance in the front as compared to the rear will transfer too much weight from the inside to the outside rear tire, leading to a "loose" car. A "balanced setup" transfers an equal amount of weight across the front axle as it does across the rear axle. A balanced set up will produce neutral handling in the middle of the corner and faster corner speeds.

For my baseline setup I have my crossweights equal and the leftside and rightside weights equal. That way the car corners equally left and right. Again, that is my baseline and I might change it depending on the track. If you can't move weight or add ballast you can still get the crossweights equal with the method rdorman described.

[jmarsey]

Dean,

Chassis setup is a big subject matter and we could go on for days talking about innuendoes and small aspects of it. If I were in your shoes I would do the following:

Talk with someone at Kirkham that can help you with your concerns.

Find someone local that knows something about chassis setup for road racing. There is also some good reading material available on the subject. This is a good start:
http://www.amazon.com/gp/product/087...162231?ie=UTF8 There are some others good books too.

If you want to set your car up correctly, you need to back up and check the chassis and suspension for squareness to the center of the chassis and from corner to corner. You need to check that the wheels are the same distance from the center line: RF=LF from center line and RR=LR from center line. After that is adjusted, all 4 points, need to be square with the center line of the chassis and diagonally. You want to end up with a perfectly square rectangle, if you will, with the center line of the chassis being the center line of the rectangle.

Now that you are square and the right and left sides of the chassis are in equal relationship to each other, you would set approximate ride height, castor, camber, and rough alignment.

Now your chassis is ready for corner scaling which is where you try to get the chassis cross weights as close to 50/50 as possible, with driver and a ½ tank of fuel.

What I’ve described is just scratching the surface of this subject but I hope it gives you some kind of an idea. I have not described how to do this process nor the process of setting front & rear castor/camber, alignment, or why you would set your car up any particular way. All the experts can chime in for that. This is a vast subject matter and requires expertise to accomplish anything useful.

Your car is pretty close the way it is for now, as far as cross weight. I don’t know the adjustability of your Kirkham’s suspension. My JBL is fully adjustable and I had it pretty close for starters. When I took it to our chassis guru, he had it on the rack for more than 6 hours before he was happy. Again, this is the baseline setup, a starting point for which you would base you chassis tuning at the track from.

Good times, John

[dlampe]

I am pretty sure I can get the cross weights equalled out but left to right will be a little tougher. I am going out of town, but on Saturday I will play with it again. In the mean time I will call Tom Kirkham and see what he thinks. Thanks for the help.

[jmarsey]

Good deal. You won't get a conventional car to be equal weight side to side without moving, relocating, adding, or removing weight. You can only get the balance as close as the given weight distribution of the car will allow.

Good luck and keep us posted on your progress. Looks like you have a pretty nice Kirkham there.

John

[dlampe]

I have an adjustable front swaybar. If I offset the splines on my swaybar, it would preload one side and take some weight off. Is that a smart way to equalize the weight or would that mess something else up?

[jmarsey]

Originally Posted by dlampe

I have an adjustable front swaybar. If I offset the splines on my swaybar, it would preload one side and take some weight off. Is that a smart way to equalize the weight or would that mess something else up?

No. Corner scaling, or any static setup, is done with the sway bars disconnected. When the chassis is set you want the sway bars adjusted dead neutral so there is no preload what so ever. Your anti roll bars should have no impact on static wheel weights. There is a method to this stuff that you should first understand. I would again recommend some reading material.

Order this book: “How To Make Your Car Handle” by Fred Puhn. It is pretty dated but covers the basic concepts to proper chassis setup in simple terms.
http://www.amazon.com/gp/product/091...162231?ie=UTF8

John

[dlampe]

I will order it today. Thanks for the recommendation. Thanks again for your advice.
Dean

[rdorman]

I second the swaybar recommendation.

Fred's book is a good one. I have read it several times. He also has a very good one on brakes (Carroll Smith says in one of his books there is no point for him to write a good book on brakes because Fred already did one!).

Once you read Fred's book, the definitive book on chassis is Milliken's "Race Car Vehicle Dynamics". http://www.millikenresearch.com/rcvd.html 900 pages of great bathroom reading

Dean, where is your battery?

[Jerry Clayton]

Battery location, alterator mounting, fuel tank configuration and location,fuel pump location, fuel and oil filter location, even engine offset can all be considered in setting up or building a chassis

Jerry