What I was after: a coilover kit suitable for inclement weather (dust boots, reliable adjusters), use of OEM top mounts, a moderate drop (20-30 mm), height and rebound adjustable, monotube design, ease of adjustment, improved handling, acceptable comfort, reasonable price.
What the car is used for: mostly spirited driving in the city, some medium to high speed driving on twisty&bumpy country back roads, and occasionally high speed highway; sometimes loaded (wife + 2 kids +/- bags).
Narrowed it down to Bilstein B16 PPS10, Sachs Performance Suspension Kit, Eibach Pro-Street Multi. The latter two seem to be the same kit, packaged by Sachs or Eibach.
https://www.sachsperformance.com/bil...500.000484.pdf (Sachs)
https://media.carparts-cat.com/pdf/E...E692003101.pdf (Eibach)
Monotube shocks / upside down
Front spring is progressive, rear is linear
Front axle spring rate: 48 N/mm (pretty sure both front and rear are softer than the stock)
Rear axle spring rate: 120 N/mm
Spring height and preload adjusted simultaneously
Single rebound&compression adjusters on the bottom of the shocks / 20 clicks from closed to open
OEM top mounts
Dust boots
At the moment, the car is 12 days past install, several height and rebound adjustments, and two wheel alignments. The installation was done at an indie shop per product and BMW manuals (
https://www.newtis.info/tisv2/a/en/f...pair-manuals/)
What was not done - didn't replace the original bolts and nuts (recommended) except for the front top strut mount nut which came with the coilover kit. Tried to be careful to keep the original hardware.
One difficulty we run into was the rear shock top mount nut. It has a peculiar form and access to it is somewhat difficult. We didn’t have a special tool that fit so we had to weld one from parts in the shop and had to be extra careful with that one.
Took much longer to get a workable height, rebound and wheel alignment. Both Sachs and Eibach state the expected drop between 25 and 50 mm on both axles but it is simply not possible within the range of adjustment permissible per product certificate. The actual drop possible if done within the permissible range is up to 30 mm for the front and about 20 mm for the rear.
(similar to Bilstein and Ohlins, it seems the kit was design for M3/M4, M2/M2C being an afterthought when they came out. The range of adjustments per certificate presumably reflect what’s expected of M3/M4)
Height
Turning spring perches and locking them in place is easy, front and rear, when the car is on a lift. You have to remove the front wheels to do the front, and you don’t have to remove anything in the rear.
Still, getting the right height is a tricky part because of the limitations of the coilover kit per se, and because it’s hard to judge the exact lowering immediately after adjustment. It takes a while to settle. Moving it and driving it immediately after install isn’t enough. It doesn’t settle evenly and you may be off your target a few days later. It takes multiple tries and days.
Also, there are 2 kinds of references ranges to respect per certificate:
1) front spring perch where it meets the spring to the pinch bolt on the hub (permissible range is 165 - 205 mm) / vehicle frame to the cap of the spring seat in the rear (permissible range is 10 - 40 mm)
2) wheel arch to the center of the wheel ( 330 - 360 mm in the front, 325 - 360 mm in the rear)
The measurements of the vehicle height before install (OEM method, from wheel arch to the bottom of the wheel / tank ¾ full): front left 620 mm, front right 622 mm, rear left 620 mm, rear right 620 mm.
After the initial install and some fiddling around the first day, we got 590 mm in the front and 600 mm in the rear. That’s 30 mm drop in the front and 20 mm drop in the rear and a 10 mm rake which was not intended (I thought maybe 5 mm rake but couldn’t get that). Tried raising the front half a turn further while lowering the rear half a turn… for some reason the front only got higher 1-2 mm while the rear got higher, too, a couple of mm… Strange… and it takes time to get it right.
When you are 30 mm down in the front that’s already 330 mm from the wheel arch to the center of the wheel. So, if you are to respect the certificate range you can’t go lower than 30 mm. Tried a lower front (in fact it’s 5-10 mm lower than that if you leave the factory preset spring perch height) which produced super sharp steering but in a tight speedy turn the front plowed and it felt like the front didn’t have enough travel so we backed off.
28-30 mm front drop seems like what it takes to get it right. (also, 30 mm drop is what it takes to crawl over some speed bumps near my home)
The rear: that’s we ran into another issue. The range of adjustment is supposed to be 10 - 40 mm. With 20 mm it’s about stock height, so there’s only about 10 mm of adjustment range. I would gladly disrespect that and try lower but…
Issue: when we lowered the rear 20 mm (that’s about 12 mm from the spring cup to the frame) with the car still on the lift and the wheels hanging freely the left rear spring is firmly in it’s place but the right rear spring is a bit loose: Can’t really move it in the axial direction yet but I can wiggle a little from side to side.
Can’t understand why. The car is relatively new (19,000 km), the condition of the OEM rear top and bottom spring seats, and all other suspension parts seems OK on both sides… removed both rear springs, seemed to be assembled and seated correctly, double-checked the distance from the spring cup to the frame… I am puzzled.
(may have to replace OEM rear spring seats in the rear to be sure, perhaps some other parts… don’t know…)
Afraid to turn the right rear spring any lower because I am afraid it might get loose under some (extreme) driving conditions in a situation when the right rear suspension is completely extended. I don’t know if it’s safe to try. If not for this I could maybe get another 5 mm drop in the rear (which is what I so wanted)…
At the moment, the rear is some 10 mm higher than the front. Also, for some reason after the install the whole left side was some 3 mm higher. It took several days to settle evenly in the back and 2 mm higher in the right front (same as before the install).
The rear is begging to be a bit lower to be more controlled on imperfect undulating back roads.
Wheel clearance / Rubbing
At full lock with the stock wheels and no spacers at 30 mm drop in the front there is no rub but it may rub if spacers are used in the front. At full lock with a slightly used Michelin PSS 245/35/19 tire there is only about 7 mm clearance from the front fender liner.
With the lowering of 28 mm or lower in the front the outer shoulder of the front tire may rub against a protrusion inside where the bumper is bolted to the fender. I had that happen 2 times to my right front when slamming on the brakes in a road dip before jumping out of it at high speed, a paint mark on the tire shoulder. So you have to either shave some of that off or raise the front a bit.
It’s tight and there may be problems with other tires/sizes.
Rebound&compression Adjustment / Handling
In the front you turn the wheel full lock, kneel, reach behind the wheel and turn the knob, same for the other side. In the rear it’s less convenient but you can still do the job. The turns are not too tight and the clicks are distinct.
The factory preset is 10 clicks open all around. That’s comfortable around the city but you need at least 1 click harder in the front to counter understeer and make handling more consistent. With default settings and slightly raised rear (as in my case) the rear may feel floaty if you go fast and there is a noticeable change in the brake balance toward the front.
(I drive almost always with MDM enabled, sport or sport plus, gearbox either D1 or S3 when in manual, steering set to comfort)
For the city, back roads, and for speeds up to 160 km/hr (or 100 mi/hr) I chose +3 harder in the front and +1 harder in the rear as the most appropriate setting (aka my default setting).
With these settings the handling is sublime and playful. The steering is a bit tighter, is sharp, but may be a bit sensitive at high speeds so you are more aware of the speed than with the stock suspension, the car licks tight corners and dives into tight spaces easily, rotates under throttle, there’s brake tailing when you need it. The whole process of driving is more fluid. This simply was not there with the stock suspension. I noticed that my driving became more aggressive and it’s not necessarily because I’m trying. I’m more conscious of the rear end, though.
For high speed driving (over 160 km/hr, or 100 mi/hr), or driving loaded with passengers and bags, or driving on really crappy roads, tightening the rear shocks a bit (to +2 harder). This works for speeds up to 200 km/hr (or 125 mi/hr). Tightening the rear just one click (+2 from the preset 10 open) makes the car more stable.
+4 clicks in the front and +2 clicks in the rear gives a car a good overall balance but, unfortunately, feels too tight for the city, the steering and everything.
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Comfort
At +3 harder front and +1 harder rear the suspension is perfectly comfortable (compared to the stock), compliant and balanced, and deals with minor and medium imperfections better, not nearly as jarring as the stock. At +4 harder front and +2 harder rear it’s definitely tighter than the stock and you can feel all road imperfections more, although still not too jarring, but too tight to steer even in comfort mode.
Noise: usually perfectly quiet, but there may be an occasional muted clunk coming from the front driver’s side or somewhere in the rear on particularly crappy roads and some bad bumps. (not sure what makes that sound)
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Wheel alignment
Initially, decided to go with the front toe in 0.03` symmetrically, front left camber -1.15`, front right camber -1.32`, rear toe in 0.07` symmetrically, rear camber -1.55` symmetrically.
This, especially with the preset soft rebound settings of the rear shocks didn't work well at all. On my first drive out of a gas station, and it was a cold day at 4 C (39 F), with the usual throttle application I was caught off guard going sideways. The rear felt too loose. Also, the rear was noticeably worse putting the power down and squiggly under throttle.
One week later the alignment was off as the suspension had obviously settled, and settled unevenly: the front toe in still 0.03` symmetrically, but the rear toe in was now 0.06` and camber -2.10 and -1.57.
Decided to leave the front as is at 0.03` toe in symmetrically (perhaps too optimistic for the street?) but to compensate for the unstable/soft/raised rear and to help traction the rear was set to 0.09` toe in symmetrically and camber to -1.35`.
This helped a lot. The rear became stable, not really squiggly under throttle anymore, no unintended sideways tricks, and the traction is now comparable to the stock, also available out of a turn.
Did some aggressive driving on the back roads and took note of the scrub lines on the front and rear wheels - much better. Before, the outer shoulder of the rears was hardly working. Now, it’s better but still not perfect. Measured the temperature of the thread with… my fingers: the fronts were OK, the rears’ inner blocks were noticeably warmer than the outer shoulders. Which means when I do an alignment again it’s safe and probably better to go with even less camber in the rear (thinking about -1.30` and probably 0.10` toe in) - going to be still better putting the power down and having a slightly more stable rear end.
Rear
Front
Traction
With the initial alignment it was really suboptimal (running tire pressure 2.40 bar front and rear), the stiffer the rear shocks the worse.
After my second alignment the traction is OK with the factory presets of compression/rebound 10 open, still fine if you go a bit harder (+1, +2 or +3 harder from the preset), but would probably get bad if I went yet stiffer on the rear shock settings. I want a bit better traction.
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Thoughts:
Wish the spring rates were a bit higher. I don’t take the car to the track but still... Probably wouldn’t have a front rub. Probably would benefit from slightly stiffer springs all around.
Wish there was one setup that fit all possible scenarios. It’s easy to turn a couple of knobs to get it right for a particular occasion but I still wish there was one universal setup. Perhaps, I’ll get one if I manage to lower the rear a bit more.
Going to raise the front a bit, and probably still need to shave off that inside fender bulge where there’s a rub, and see if I can get the rear any lower, and to slightly fine-tune the rear wheel alignment.
Thinking of how to lower to the rear more... Not sure it’s safe to try to lower the rear on the current installation with the current parts, say half a turn of the spring perch… just not sure.
Also, wondering if some OEM aero for the rear could possibly improve the high speed situation without having to tighten up the rear.
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If anyone has any thoughts on where I possibly messed up, or things to try, comments are welcome.