Question about suspension

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Question about suspension

Postby redwing » Wed Jun 16, 2010 3:32 am

I have stock suspension on a 2003 Miata LX WITH 107000 miles. Also the stock alloy wheels with 205 45 16 maybe 17 tires. Stock stock stock.

Recently I was out driving a familiar road in good weather that is full of flat turns and parallels a river. I went around a turn at some unknown speed (fast) and the rear end slide out to the right. I took my foot off the gas, the car's tires caught, and the car's motion threw it to the left. The move to the left was so violent that if I were not wearing my safety belt I would have been thrown into the steering wheel or perhaps upward some ... but probably not out. A fish tail from deceleration.??? When the suspension unloads the stored energy from the gravity pushing it out in a turn the results are notable. POW! I find close S-turns produce the similar results.

My suspension is old but did it cause the problem. Afterwards I thought perhaps I should have accelerated with the move to the right. Also I turned to the right when the car moved to the right and left as the car moved to the left.
Old soft springs??? Bad shocks??? Suspension seems good.

So ... did I do something wrong or should I toughen up the suspension? A tighter suspension would transfer the shock of the road to the body and could over time cause rattles. Hope this isn't to much material.

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Re: Question about suspension

Postby Brian » Wed Jun 16, 2010 5:45 am

Car obeyed the laws of physics. When you get the rear out and lift your foot off the gas, the weight suddenly transfers violently forward and the result is the 'tank slappers' that you experienced with the weight of the unstuck rear trying to pass the gripping front. Don't lift...a quick countersteer would have caught the rear without drama. If you had lifted like that in a car with more rear bias (like an old Porsche 911), you would have looped it three times before you knew what happened. My wife started autocrossing recently and she is having a lot of fun learning to catch the rear at the takes practice to do it smoothly without the tank slappers. So, my first suggestion is find a local club autocross and start having some helpful fun in catching the rear.

Nonetheless, low speed oversteer is a common complaint in the later NB and an upgrade to the front sway bar would help keep the rear much more in check (see our Racing Beat front sways for 99-05).

Also, if the shocks are toast...that would encourage the tank slapper behavior because the shocks are no longer doing their job of damping the body motions and the springs load up in one direction and then give that energy back instantly...encouraging the tank slap behavior (you are essentially bouncing unchecked on the springs). If you have original shocks at 107k miles...they were toast long, long, ago and you can expect more of this behavior until the shocks are replaced.
Brian Goodwin
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