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Discussion Starter #1
what does a underdampened suspension feel like?

what does it feel like if i bottom out my shock body to the bumpstop to the top mount?

bc i have no clue lol. anything other symptoms of a poorly set up suspension? im trying 2 figure out what parts i'll need to add over the summer :)
 

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xn7,

I've been thinking about this and I'm not sure if I can completely answer, but I'll give it a shot.

A underdamped suspension: the extreme example is a car without dampers, only springs. Over bumps and ripples in the road, the car will bounce and pogo. We have all seen other sport compacts with lowering springs with higher rates on stock dampers. The damper doesn't have enough to control the spring movement and when the car goes over bumps it continues to bounce down the road for a few yards and a couple of oscillations before finally smoothing out. If you are used to it, you might not notice it, because it can be subtle or it can be pretty bad (as described above).

Lack of damping robs traction. In the example above, as the car is bouncing, the spring is loading and unloading the tire. Any expansion beyond the springs static height unloads / unweights the tires, any compression loads / weights the tires. As this is happening, the contact patch on the tire is oscillating in size, getting bigger during compression and smaller during expansion. Try to drive a RWD car with poor damping out of a corner close to the limit and it doesn't want to hook up, your are going to have to wait longer to get to WOT. It can be subtle or obvious. Pro teams spend a lot of effort on damping.

Bottoming out: How this feels depends a lot on the bumpstops. Rubber bumps tend to be more harsh in engagement than foam. They may feel stiff to you and me but they tend to be *relatively* progressive when used by the suspension. Think of bumps as damped springs with high rate, because they have a rate and they don't really oscillate. Realize that the bump also has travel to allow the suspension to continue to work (I think the stock rubber bumps still allow well over an inch of travel to full compression). The bump will transmit more energy into the chassis (NVH, especially rubber, foam not nearly as much). The bump has a couple of functions, first to prevent the suspension from any hard bottoming that can break components at full compression and second to add spring rate to the suspension so that the suspension can still work and the car still be drivable when the bump is compressed.

For example, if a car had a delrin bump, it could protect the suspension from bottoming the damper or contacting the upper control arm, but as soon as you hit the bump, you have no suspension movement. The probable result is instantaneous overloading of the tire contact patch and loss of traction. If this happens up front, you get noticeable, not subtle at all, understeer. If it happens in the rear, you get rapid oversteer that is probably not recoverable.

On a progressive bump, you may notice that under extreme conditions like hard braking, the car wants to understeer more than under less extreme conditions. The bump is compressed, adding more rate to the front suspension which yields more understeer. Not as much of a problem in the rear, because Miatas don't usually generate anywhere near the g loading under acceleration as under brakes. So if you are cruising through the twisties and everything feels great until you push a little too hard and get the car closer to the limit and the understeer / oversteer balance changes a little (assuming the driver is consistent), might be getting into the bumps.

Bruce
 

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Nice work Bruce.
I like to judge a car like this.

Under dampened:
Lowrider syndrome.. bouncing on the freeway.. a little is okay but head bobing isnt. Anyway is to watch the car from the outside.. It might be more bouncy that you can sense inside the car.

Bottoming out:
It's harder to detect than you think. A sure fire way is to put a zip tie on your shocks shaft and then go corner as hard as possible. That tie will be wherever the body was.. :D Might have to dig it out of the bumpstop if you're Über low.

Pretty much 85% of stuff out there will be bottoming on a miata at anything 12" or lower.
I run my racecar pretty much on the stops.. but I'm driving it on a controlled surface! :)

The best way to learn your car and susp. is to auto-x. W. the popularity of the miata there will be probably 2-5 miata guru's out there to help you learn your car and how to drive/set it up!
 

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Discussion Starter #4
this sounds like whats happening when i go over road gaps (sudden drop): "Any expansion beyond the springs static height unloads/ unweights the tires"

i guess this means my springs are too short in the rear and don't allow for sufficient expansion :( i suppose the only fix is to get longer springs or to increase perch height/preload of springs. or only drive on silky smooth roads :)

1 problem down :mrgreen: thanks for all the info
 
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