Originally Posted by Caduceus
A common question on this forum is “what is the effect of altering ride height on wheel alignment settings?” In particular, what will be the effect of installing aftermarket coilovers or lowering springs be on camber and toe settings? I haven’t been able to find a satisfactory answer but I have documented my findings for your enlightenment.
If you are not aware, the F87, like all modern BMWs uses MacPherson struts in the front suspension. Front alignment is only adjustable for toe via tie rods. Front camber and castor is fixed by nature of the MacPherson design. Aftermarket camber plates are a common modification which allow front camber adjustment and in some cases, castor adjustment.
F87 rear suspension is a multi(5) link design. It is adjustable for toe and camber via eccentric bolts. The eccentric bolt which adjusts toe acts relatively independently but the camber adjustment bolt has a profound secondary effect on toe. When aligning the rear, camber should be adjusted first and toe finalised once camber is locked in.
I installed KW V3 Street Performance coilovers in my 2016 pre-LCI M2. I have placed an order for Vorshlag camber plates but I’m still awaiting delivery. I will update this post after stage two of the installation.
Prior to commencing installation, my M2 was aligned to factory specifications. Please note I refer to decimal degrees, not degrees and minutes as you will see in some references. Front was -1.5 camber, 0.16 (2mm) toe. Rear was -1.8 camber, 0.26 (3mm) toe. I have OEM 437 wheels with 245 & 265 MPSS tyres.
Front installation proceeded uneventfully. I chose a 25mm reduction in ride height which is well within the mid-range of the KW V3s. I’m focussed on handling over looks and excessive drop is not conducive to the former and the practicality of getting into my steep driveway without scraping also needs consideration.
After setting the ride height on the front, the camber was remeasured and found to be -1.65 on both sides. This is typical behaviour of a MacPherson strut with a slight increase in camber during the first part of suspension travel. However, if lowered even further to the point where the lower control arm goes past horizontal and starts to slope upwards then the camber change will reverse. I’m actually very pleased with the .15 degree increase in negative camber that goes with the 25mm drop and for a 100% street setup, this is an excellent value. Unless you track the car, there is simply no need to try and get more negative camber on the front so the factory strut tops will serve you well. However if tracking (which I do) more negative camber is desirable and thus camber plates become necessary.
Also pleasingly, the front toe was not affected by the ride height reduction and remained at OEM value of 0.16 (2mm) total toe-in after installation. For street driving, BMW chose this setting for a reason. It gives good directional stability, avoids tram-lining and gives confident turn-in. 2mm will cause only mildly increased outer shoulder wear which most owners would not notice. However, for track driving, some owners will reduce this to close to zero toe. The effect is to increase steering response at the expense of some stability. The car will feel more agile. I reset this to 1mm and took the opportunity to really fine tune the steering wheel alignment. I’m a bit OCD with this and it was very slightly turned to the right while driving straight. Most people wouldn’t notice. By favouring the right side to reduce toe-in compared to the left (eg. half a turn on the tie-rod) corrects this and the steering wheel is now absolutely perfect.
Rear suspension installation was mechanically straightforward but quite fiddly to get just right. Firstly, there was the well documented issue with the KW spring perch bases rotating while trying to turn the adjustment rings. Fortunately, no angle-grinders and large screwdrivers were needed ;-) I found that by jacking the car up to unload the springs and tugging the c-spanner quickly, the base would stay put. Compare this with applying gentle pressure to the spanner and the whole assembly would move as one. There is also very limited room to swing the spanner before it hits the wheel arch liners or other suspension components – so one notch at a time is very time consuming. If you need a major adjustment, you might consider removing the spring completely (as per the KW instructions). Anyway, I ended up setting the rear ride height 20mm lower than OEM. This is also well within the adjustment range of the KW hardware. Personally, I think 25mm front and 20mm rear looks even and I particularly don’t like the rear being lower. I’d have bought a Merc CLA if I wanted my car to look like an arse-dragging hyena.
After setting ridge height on the rear, negative camber was found to have increased significantly. It went from -1.8 deg to -2.6 deg. The large change in camber during compression is characteristic of multi-link suspensions (and also double wishbone designs) and is considered a positive design feature which increases grip on the outside tyre as the suspension loads up during cornering. However, -2.6 degrees static rear camber is too much for a number of reasons. Firstly, it will cause increased inner shoulder wear during normal street driving and secondly, on RWD cars, having rear camber significantly greater than front camber can promote understeer which is undesirable on the track but somewhat acceptable on the street. BMW uses only 0.3 degrees more negative camber on the rear in the OEM settings so allowing 0.95 degrees difference after lowering was unacceptable.
Unfortunately, I did not check the effect of the ride height change on rear toe in isolation since I knew I was going to have to adjust camber anyway and this has a secondary effect on toe. So for now, I just reduced the rear camber to -1.8 on each side which is the OEM street setting and also perfectly acceptable, if not preferred for track driving too.
After resetting rear camber I then measured rear toe. To say I was surprised is an understatement. The relative placement of the camber and toe eccentric bolts in the rear links is such that pushing the lower part of the wheel carrier inboard (to reduce negative camber) also cause toe-in. This is because this bolt is located forward of the toe adjustment bolt but in a similar horizontal plane. It was the extent of the secondary effect which surprised me. After setting camber back to -1.8, total toe-in at the rear was 0.86 (10mm)! This is very excessive and would cause significant straight line drag and destroy the outer edge of the rear tyres in no time at all. Rear toe-in aids straight line stability under braking, especially trail braking into turns but 10mm is way over the top.
I was able to get this adjusted to bring it back to OEM spec of 0.26 (3mm) but this almost maxed out the adjustment range of the eccentric toe bolts. If you were in a situation where you lowered more than 20mm and therefore had and even bigger camber change to neutralise, you might run out of range on the toe adjuster. Also, some people (not me) prefer a bit less toe on the rear for track driving to give the car a bit more tail-happiness for power-oversteering / drifting so you too may run out of range. Aftermarket, adjustable length trailing arms are an option in that situation in lieu of the eccentric bolts to give greater range and they are also easier to set precisely compared to an eccentric bolt. At this stage, I see no need for those since I can align to my preferred specs using the OEM hardware.
To summarise, changes brought about by lowering:
Slight increase in front camber – this is beneficial. No change in toe – however, plenty of adjustment is available either way if needed using factory tie-rods.
Large increase in rear camber. If neutralised (recommended) this causes a secondary large increase in rear toe which also need to be neutralised. Eccentric bolts for camber are within limits but for toe they are close to maxed out. Aftermarket options are available if your needs are more extreme.
I hope you find this useful. Stay tuned for part two after I get the Vorshlag camber plates install
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