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Re: I have a performance issue suspension? Posted by peter [Email]  (#2804)  [Profile/Gallery]
(more from peter) on Mon, 21 Jun 2004 22:59:00
In Reply to: I have a performance issue suspension?, jak  [Profile/Gallery]
, Sat, 19 Jun 2004 20:10:28
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Jak
There are some things to check over:
* Under hard braking you say that the back end feels like it wants to pass itself.
Weight transfer will have a small effect but would not give you the instability that you seem to indicate that you are experiencing. The slip angle of the tyre will have a pronounced effect in wanting the vehicle to move around, especially if the sidewall deflection is more then normal. While you are braking is the ground surface smooth or is it bumpy?
Check the condition of the front A arms and the Panhard bar located above the rear axle.
Check the condition of the tyres, tyre pressure.
Do you know the spring rate of the springs?
What tyre psi are you running on the rear versus the front? This works with the spring rate of the springs. Are the springs mounted correct side up (if needed)?
I would look at the tyre psi first. Judging by the speeds you are running I would set them at 7 - 10 % higher about 3 psi. I imagine that you have the same type of tyres on all 4 corners. Not the same size but the exact same tyre at each corner. Mount the best tyres on the rear, this will give you the best slip angles. You want the rear slip angles to be smaller than the front. If you have a tyre which is not carrying the carrect load than you will affect the slip angle. Changing the springs has affected this. If you put the original springs back on and the problem resolves itself you will have accomplished your goal by restoring the engineering of the car. But it seem that you are going for a look and only need to re-engineer the car but adjusting the load carrying capacity of the tyres to put the equation back to 88 spring standard. Also by jacking the car in the manner that you have done has affected the camber of the front suspension, which will have an affect on the vehicle. The weight shift that is being done places more stress on the tyre/suspension package. This can also lead to more force being applied to the suspension bushings and to the tie-rod ends, thus causing more TOE problems. It would seem to me that you are actually experiencing a DOMINO affect of a small problem. I would start with a quick inspection of the tyres and suspension. This should isolate your problem
I can only assume that your vehicle is in good mechanical shape or that you are a scary chap driving at triple digits speeds with steel belts showing on 2 of your tyres, if you know what I mean.
Test your work at low speeds building your way up progressively to 115 mph. this wa the problem will not catch you unaware. I would actually try to find a large empty parking lot and drive in a 150' circle (skid pad) gradually increasing speeds until you lose adhesion. Once you have established los of adhesion/speed try to maintain this and let off the accelerator to see if the back end swings around or the front end tucks in.
I hope that this is of some assistance.
Peter
posted by 24.27.77...
, Sat, 19 Jun 2004 20:10:28, Mon, 21 Jun 2004 22:59:00 <-- Viewing This Message, Tue, 22 Jun 2004 10:01:02, Tue, 22 Jun 2004 10:06:15, Tue, 22 Jun 2004 14:31:45, Mon, 21 Jun 2004 18:22:04
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