Height Adjustable Springs Bad for Shock Life?

[M3SQRD]

Originally Posted by NSX2M4

A higher preload and shorter travel of the damper will increase pressure in the damper itself. So, yes shortening travel of a stock damper will significantly shorten the life of it.

This is incorrect. Spring preload has absolutely nothing to do with damping coefficient and damping force. Lowering springs and HAS kits use springs that are ~15-25% stiffer than stock springs. Their shorter length means they do not have to be compressed as much as stock springs to install the strut upper mount. Preload is equal to spring compressed length and spring rate (Fpreload = k*x) so it’s possible for the aftermarket springs to have a lower installed spring compressive preload. The spring preload is reacted by the strut upper mount and strut outer body. ZERO preload is reacted by the piston rod and no change in internal pressure (monotube dampers have an internal pressure chamber with a floating separating piston)…Remember, a damping force only exists if there’s a relative velocity between the piston valve stack and the damper body and a pressure differential must exist across the piston valve stack to produce a rebound or compression damping force (Fdamping = c*rel velocity). Zero piston rod relative velocity = ZERO damping force = zero change in internal fluid pressure. Piston valve stacks don’t care if they’ve been lowered, or raised, relative to its original static equilibrium position.

Alternating the bump and droop travel has no effect on damping force as long as there is no internal contact between the piston valve stack and the lower strut body (one reason why bump stops are used). Again, alternating the static equilibrium position of the valve stack (e.g., shortening piston rod travel) has zero effect on damping force and, therefore, having no effect on damper life. Most dampers can typically handle a +/- ~30% change in spring rate with their original damping coefficients. Stiffer springs actually require more damping to maintain the same level of control over the spring and it’s proportional to the square root of the new spring rate divided by the original spring rate (damping increase = sqrt(knew/korginal)). However, this increase in spring rate will result in the stock damper having to perform more work, or absorb more energy, per cycle and this is what shortens the life of a damper (fluid viscosity will drop off faster as a result of more energy being absorbed with each cycle).

[SteveYem]

I'm thinking about jumping to a H.A.S. setup in a couple of months. MP vs KW.....what's the scoop? Any reason to go for MP when KW exists?

[F60TRPR]

General Question. For a Strictly Street fun setup with good ride quality can you do springs on new OEM shocks and get a little lower without sacrificing the ride quality?

[NSX2M4]

Originally Posted by M3SQRD

This is incorrect. Spring preload has absolutely nothing to do with damping coefficient and damping force. Lowering springs and HAS kits use springs that are ~15-25% stiffer than stock springs. Their shorter length means they do not have to be compressed as much as stock springs to install the strut upper mount. Preload is equal to spring compressed length and spring rate (Fpreload = k*x) so it’s possible for the aftermarket springs to have a lower installed spring compressive preload. The spring preload is reacted by the strut upper mount and strut outer body. ZERO preload is reacted by the piston rod and no change in internal pressure (monotube dampers have an internal pressure chamber with a floating separating piston)…Remember, a damping force only exists if there’s a relative velocity between the piston valve stack and the damper body and a pressure differential must exist across the piston valve stack to produce a rebound or compression damping force (Fdamping = c*rel velocity). Zero piston rod relative velocity = ZERO damping force = zero change in internal fluid pressure. Piston valve stacks don’t care if they’ve been lowered, or raised, relative to its original static equilibrium position.

Alternating the bump and droop travel has no effect on damping force as long as there is no internal contact between the piston valve stack and the lower strut body (one reason why bump stops are used). Again, alternating the static equilibrium position of the valve stack (e.g., shortening piston rod travel) has zero effect on damping force and, therefore, having no effect on damper life. Most dampers can typically handle a +/- ~30% change in spring rate with their original damping coefficients. Stiffer springs actually require more damping to maintain the same level of control over the spring and it’s proportional to the square root of the new spring rate divided by the original spring rate (damping increase = sqrt(knew/korginal)). However, this increase in spring rate will result in the stock damper having to perform more work, or absorb more energy, per cycle and this is what shortens the life of a damper (fluid viscosity will drop off faster as a result of more energy being absorbed with each cycle).

First and foremost, thanks for the detailed explanation. I think most were looking for this...

"I" know enough through my own experiences with several decades of lowered vehicles that I do not want a HAS kit installed on a super expensive adaptive suspension. If you took a HAS kit car vs stock like for like, you would see nearly zero result from it on a track. You will see increased wear on a dumped car though, with all of the scraping involved on a non related track surface. Great for the, "look" though.

[M3SQRD]

Originally Posted by NSX2M4

First and foremost, thanks for the detailed explanation. I think most were looking for this...

"I" know enough through my own experiences with several decades of lowered vehicles that I do not want a HAS kit installed on a super expensive adaptive suspension. If you took a HAS kit car vs stock like for like, you would see nearly zero result from it on a track. You will see increased wear on a dumped car though, with all of the scraping involved on a non related track surface. Great for the, "look" though.

I replied to your post so I wasn’t aware of what people were looking for. However, it appears the MPHAS has been very popular with f8x and g8x owners. I think it’s due to people wanting to stick with OEM parts and warranty, especially if it is a port-installed option. I personally am not a fan of lowering springs and HAS kits, although I’d go with Ground Control’s version if a HAS kit is my only option.

There are forum members that do use HAS kits on track and they do outperform the full stock setup. It will have little impact on street ride quality if you use BMW’s recommended lowered ride heights. Probably the worst thing you can do is to significantly lower the front relative to the rear, a significant forward rake setup, so fender-tire gaps are identical. This affects the static handling balance of the car but the people with this setup are most definitely going for aesthetics, not performance. Ride manners are hugely degraded because the dampers are constantly riding on bump stops statically and dynamically. BMW uses very little bump travel before engaging bump stops at stock ride height and uses the bump stops to control & limit bump travel. The shorter bump stops that come with HAS kits have an even more progressive stiffness vs. suspension travel which results in much higher combined compressive stiffnesses and a higher bump stiffness divided by rebound stiffness ratio. When working with people on developing a suspension setup, I always strongly recommend doing it right and live by “buy once, cry once”. I learned this first hand on my NA1 NSX where I had listened to a friend that had recommended a certain suspension brand and it was absolutely horrible. I, unfortunately, had to buy a second suspension setup only a few weeks later because the first one was a giant piece of crap which meant I ended up spending $8k total vs. only spending $5k (or an even higher performing setup for $8k!).

[M3SQRD]

Originally Posted by SteveYem

I'm thinking about jumping to a H.A.S. setup in a couple of months. MP vs KW.....what's the scoop? Any reason to go for MP when KW exists?

I would recommend the Ground Control kit. It includes front camber/caster plates, fromt adjustable drop links, front spring seat & ride height adjuster, rear spring seat & ride height adjuster, and custom front & rear spring rates. They also offer an upgrade for the rear spring seat & ride height adjuster which is their rear rear weight jacker & ride height adjuster. It allows you to easily adjust the rear ride height without having to drop the rear spring arm and it eliminates all bending in the divorced rear springs.

GC Coilover Conversion Kit

Optional Rear Weight Jacker

[knightarmor]

Originally Posted by SteveYem

I'm thinking about jumping to a H.A.S. setup in a couple of months. MP vs KW.....what's the scoop? Any reason to go for MP when KW exists?

I can't speak for the KWHAS but I've been running the MPHAS for eight years now and I still love it. I paired it with some Millway street camber plates in 2022 and everything is holding up great.
From what I can gather I had 18k miles on my F80 when I installed the MPHAS and then 30K miles when I installed the Millways. I'm currently sitting at 76K miles. I went with Millway for ease of service and the MPHAS because I wanted OE BMW parts.

It's interesting to look back on for me as I put 18K miles on my F80 in one year, had COVID not hit I'd probably be beyond 100K miles on my F80!!

[Yuille36]

Logically speaking, all Height Adjustable Spring (HAS) kits share the same functional goal: providing a threaded perch that allows you to fine-tune ride height while retaining your factory electronic dampers.
Since the fundamental "job" is the same, the "best" kit is largely a matter of subjective preference.

Because every driver has a different tolerance for stiffness and a different use case (street vs. track), you will rarely find a universal consensus on which kit is superior.

[deeLow]

Anyone recommend a replacement strut/shock kit and still run a HAS?

I run a H&R HAS kit and really don’t want to lose my EDC, but a full coil setup is too much for me.

[M 4 FUN]

Originally Posted by ales

Shocks will always start to go bad as soon as the car is lowered since they arent designed for it. The lower the spring, the harder it is on the shock and faster it will wear out. Most subtle lowering springs i know about are eibach euro v1’s. Less of a drop, longer they may last.

I disagree. I explained why earlier in this thread, just like M3SQRD did.

[M3SQRD]

Originally Posted by deeLow

Anyone recommend a replacement strut/shock kit and still run a HAS?

I run a H&R HAS kit and really don’t want to lose my EDC, but a full coil setup is too much for me.

No. All aftermarket dampers, such as the Bilstein B6 or B6D, have their lower spring perch welded to the damper body. HAS kits replace the spring perch so it must be removable. I guess it’s not an absolute no because you could get a high-end damper, such as MCS, Moton, JRZ, etc., custom made without threads (no spring seats & height adjustment) and no anti-sway bar lug which would allow you to use a HAS kit; however, all it really does is increase complexity and add weight to a damper that doesn’t need a HAS kit to be height adjustable. This type of modification is typically done for autox classes that require the use of the stock spring lower perch and stock springs but the use of a HAS kit would be banned.