Aftermarket springs vs stock shocks. READ BEFORE POSTING
EVERYONE should be reading this post. Mod's please sticky.
This is cut and pasted from Joe Cheng in an earlier thread:
For the record, I got into open wheel cars in 1991. Prior to that, it was all production based cars beginning in the ‘70s. If I have to do it all over again, I would have switched earlier.
Now that Zoomee jumped in and asked some good questions (not to mentioned that he is also polite and doesn’t end his sentences with WTF), I will try to put in my two cents (don’t forget this is in Canadian currency now, so it might not worth that much).
First, I would like to confess that up until year and a half ago, I have never heard anyone (and I do hang out with a lot of car guys) use the phrase “…lower springs would blow your OEM shocks….”. It was one of my friend’s son who said it to me while we were discussing his car, and I replied “…what do you mean by blown….”. He then told me that’s what he read on the internet, and he doesn’t quite know what it means either. Fast forward to last November. I bought a Mazda3 for my kids and decided to join this board, hoping to pick up on some useful information on the car. Then I hear all this talk about “blown” OEM shocks caused by lower springs. I posted a message a while back asking what defines a “blown” shock and the thread went quite suddenly. Nobody replied. My message was the last post on the thread and to this day, there is no official definition of a “blown” shock by the internet crowd.
To me, a “blown” shock is a dead shock. A shock that has ZERO damping force. A shock that has been used and has less damping force compare to a new one is a “worn” shock, according to my definition. Like all components on a car, a shock will start wearing with miles. How fast it wears is called “wear rate”. I understand “accelerated wear rate”, I understand “abnormal wear rate”. However, when someone tells me that Prokit can blow my shocks, I take that as Prokit can change my shock’s damping value from some finite value to ZERO within a short instance, similar in context as we would use when we say “blown engine” for example.
For the record, I have had many sets of lower springs over the years on various cars. All of them were driven on the streets or dual-purpose cars (street and competition use). They included Hondas, BMWs, Miata, Mazda3. Some of them have different brands put on over the period I owned them. Two Porsches were lowered using the OEM springs (or torsion bars) since they come factory ride height adjustable. The longest I kept was my wife’s BMW, 17 years on Prokit and one front shock was worn out at the 15 years mark (I won’t call that blown, I call that worn out). All these vehicles have had OEM shocks with the lower springs. The Miata is the only exception, it ran on OEM shocks and lower springs for about 3 years before Tein Flex went on. The OEM shocks were not “blown” when I removed them, yes, I did check.
Now, let’s go on with the technical stuffs (disclaimer: DON’T BELIEVE EVERYTHING YOU READ ON THE INTERNET, INCLUDING THE FOLLOWING).
Zoomee is correct when he wrote “…I suspect that the stronger spring will probably work the OEM shock a little more as it was specifically valved to damp the oscillations of the OEM spring. Increasing the spring rate should create longer duration system vibrations which may generate more energy over the life of the shock….”.
In a damped vibration system, if the damping force is high enough to allow only one oscillation cycle to complete and then come to a complete stop, we call that damping force “critical damping force”. If it allows the body to complete 2 cycles before coming to a rest, then we call it 50% critical damping or 0.5 x CD. Typically, production cars can be anywhere from 0.2 to 0.5x range and there about. Since a shock’s damping forces are rarely linear relative to its speed (shock’s shaft speed, not vehicle speed), the actual damping ratio is not a constant value dynamically. Rest assures, cars like Porsches (in my opinion the only make that has proper shocks straight from the factory) and Corvettes will have a higher damping ratio than your Mazda3. Nevertheless, this design damping ratio is a consideration when springs and shocks are picked for your Mazda3 at the factory. When a stiffer spring is installed. The original damping ratio is lowered. This means the system is under-damped compare to the original set up and the system will take more cycles before coming to rest whenever an external force is applied to it. This means all things equal, the shocks will see a corresponding higher number of cycles in a given fixed time period. However, all things are rarely equal in real life applications. Consider this, while the under-damped system is going thru its extra cycles, but before completing them, another external force is applied to it and this new force is completely out of sync of the vibration. It will actually stop (or cancel out part of) the vibration that is yet to be completed. What does all this mean??? It means if the system is 20% under-damped, in real life application you might only see part of that 20% come thru as actual increase in wear.
Now, let’s look at the component that is actually causing all the fuss. Since the whole thread started on those Prokit, let’s look at them specifically. In my opinion, the Prokit is the mildest of the milds as far as lowering springs go. They usually range from just less than 10% to somewhere under 20% stiffer than OEM spring rates according to reports from other car forums when people have actually measured the rates (but hey, what did I say about information gathered from the internet). I would say they usually average around 12-15%, give and take a few percent. Therefore, if we put Prokit on, there should be a corresponding “accelerated wear rate” on the shocks, but “blowing” the shocks (see my definition earlier), I doubt it. Now, assume your OEM shocks typically have a life span of say 5 years, so what if that 5 years decrease to 4 years. Are you going to cry over it? Maybe the OEM shocks on the Mazda3 would last 10 years without Prokit and that will get shortened to 8 years if you lowered it. Are you going to cry over that? Don’t forget, my wife’s lasted 15 years. If the OEM shocks are that bad as someone here reported “blowing” them within 6 months, then I am pretty sure those shocks wouldn’t have lasted much longer with the OEM springs anyway.
So far, I have only talked about increased spring rate. Now, let’s see what happens when the ride height is lowered.
One common characteristic of all typical automotive shocks is that they are all velocity sensitive (again, I am talking about shock shaft velocity, not vehicle velocity) rather than displacement sensitive. Zoomee is correct when he wrote “…The lowered condition causes the shock piston to ride in a slightly different location proportionate to the amount of lowering which shouldn't cause any real problems with shock absorber life….”. The only exception is some of those self-leveling shocks and a recent report on a shock which is displacement sensitive, but these are different animals compare to what we are talking about here.
For some cars, there is a lot of suspension travel from the factory. For some other cars, there is minimal. The Mazda3 is not bad. I lowered mine 1.7” and there is still travel left (not much though). I can’t say the same thing about my Miata’s rear. The problem with limited travel is that some owners end up cutting down their bump stops to gain extra travel. Once the shock’s internals touch, you will get a “blown” shock (as in going to zero damping right now). Some owners don’t cut their bumpstop and over time, the bumpstop actually disintegrates due to fatigue from being squished all the time. The hard rubber ones on Japanese cars are not bad; they last longer than the European ones which are typically made out of urethane foam rubber similar to Koni’s silasto bumpstop. They give a much more progressive rate, cushioning the bottoming action. This usually fools the owners, and when the bump stops finally wear to a certain point, instant blown shock results when a big bump is hit due to internal contact. For the Mazda3, there is more than adequate travel left before bottoming on the bump rubber if we are only talking about 1.2 to 1.5 inch of drop. As I said earlier, Prokit is the mildest of the mild in terms of both rate and ride height change. Not an issue in my opinion. For other applications where extreme amount is taken out of the suspension travel, and contact with the bumpstop is a routine thing, then the only solution is to use a shortened shock or raise the shaft above its original mounting height at the chassis end.
As to ride quality, there is not much one can do about it. Stiffer springs come with a corresponding stiffer ride. However, having driven many cars with Prokit, the only comment I can say is that for all of you who complain about the Prokit ride, I hope none of you lust after cars like Porsches, Corvettes and Ferraris because they all ride noticably harsher. And for those who are concerned about having to take a steep ramp at an angle, all I can say is my stock ride height NSX and Corvette both had more trouble because of their large front overhangs than my others cars with lower springs. If you want ground clearance, buy an SUV. If you want a plush ride, I highly recommend my last mini van, the Toyota Sienna. But seriously folks, compare to a mild increase in spring rate like the Prokit, tire and wheel packages can ruin the ride much easier.
2004 Mazda3 S 5 Door // Titanium Grey // 5 Speed // ABS/SAB/SAC
K&N Filter // RX-8 Wheels // Kumho Ecsta SPT // Skunk2 Springs