Lowering Springs Comparisons

Rusty

Question 1. Depending on how low you go. Will determine when you will hit the bump stops and how often. Everyone has hit the bump stops at one time or another. You just don't know it.

Question 2. Lowering the car has nothing the do with the driveshaft between the tranny and diff. Both are fixed in position. The driveshaft doesn't move. It's fixed at the diff. You should be concern about the halfshafts between the diff and knuckle. The diff stays in place the the knuckle moves up and down in an arc.

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ChopsZ

Q1) I ask about the bump stops because I wanted to know just how close we actually are to them once lowered. On one of the roads I normally drive on almost daily, there's two manhole covers in the middle of the lane, and for whatever reason, the road has a couple of really sharp dips (ripples) between them. While stock, it's quite an abrupt bounce through there. Now that I'm lowered, it's an actual "jolt" going through there. I'm assuming that jolt is from ramming right into the rear bump stops. It does not seem to bother the front at all.

I'm sure we do all ride the bump stops once in a while without knowing it. If our Z's are setup like Miatas, they are designed to compress the springs fully and then gradually compress the bump stops as the bump stops on Miatas are actually factored into the handling of the car. They rely on riding on the bump stops during hard cornering.


Q2) I don't know why, but for some reason, I have been thinking about it as if it were a live axle, which it's not. I wasn't even thinking about the fact that the diff is physically connected to the chassis. Sorry about that.

On that note, what concerns would there be with the half shafts? Only asking for curiosity reasons. I have no plans on ever going any lower than what the Ark GT-S springs give me.

As it is, I sometimes think I should have stuck to my guns and went with the Swifts. Not because of rubbing or bottoming out, but because the front and rear tires tuck a little now which prevents me from using spacers, and also limits me on eventually going with wider meat front and rear.

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Rusty

To get into the halfshafts is long and detailed. It deals with angles of operation, engineering POV. Had to deal with it at work. And I don't feel like getting into right now. But with the Z. You don't have to worry about them. Unless you are pushing mega HP and torque. From a strength POV.

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MaysEffect

Constantly riding on the bumpstops is NOT a good thing. Slamming the bumps can cause damage and premature failure to the damper. Also considering the low profiles tires, this will be exerting more load on the tire sidewall and ultimately the wheel rim. The miata for example had larger sidewalls, softer tires overall and softer bumpstops with more absorption.

There are however aftermarket bumpstops with tuned bump curves that will allow some further compression instead of hard stops in compression stroke.

I'm inclined to believe the jolt you are feeling is from the rear springs binding the "dead springs" Where as the fronts are already fully bound at normal ride height due to the weight bias. Next time you have car up in the air, check if you see scratches/indentations between the tightly bound coils


With regards to the halfshafts, the suspension geometry as factory is designed to keep the shafts relatively level during normal driving conditions. Increased camber, lower ride height. higher torque loads and blown out bushings can cause premature failure to the boots, the internal cages/races and the shaft itself. Ripped boots is a slower wear issue which usually leads to damaged bearings which is a noticeable failure. Damage to the cages and races would almost definitely be catastrophic failure. A snapped shaft is probably the most preferred failure, in a worse case it will bend and start playing hammer fist with the surrounding suspension pieces. This will probably fail at lowspeed.

There are plenty of details on how it all can fail like Rusty suggested.

MaysEffect

I should clarify on this, by saying tuning bump rates should be done professionally. Using original sized bumpstops as a way to tune bump compression is not ideal, certainly with progressive rate springs.