The ultimate front suspension geometry guide for BMW E30/E36/E46 by MRT Engineering, page 5
Chapter 2: E36 front suspension
2.2 Geometry correction
Let's start with the problem child, E36 non-M front setup, we're looking for more caster to start with. As learned in the E30 geometry correction chapter OE eccentric FCAB or our adjustable FCAB alone won't give more than 1° of extra caster alone, so we'd like to use top mount from a E36 M3 3.0 to make a noticeable difference. Of course any adjustable aftermarket top mount will do the same trick as long as it will allow offset of over 20mm.
Here's how the geometry looks like after the changes, E36 non-M front suspension with eccentric FCAB and M3 3.0 top mount:
This change brought the caster value to M3 ballpark figures at 7°, but as a downside caster trail jumped 20mm up and due to spindle inclination change in side projection tie rod end is now sitting significantly higher than we'd like to. As a rule of thumb we're looking for only 2-4mm higher position at the outer end to result in good bump steer curve.
Let's see if our rules are valid and how it acts during a 100mm suspension sweep:
Again, outcome is as usual, as height difference increases too much, bump steer will be worse. This time the change in bump steer is double what we saw with stock setup. More work needed.
As the first and cheapest option you'd probably opt for bump steer adjustable tie rods which allows fine tuning of tie rod end height.
As we know we're looking for a lower position, let's adjust the tie rods in the lowest setting and see if the range is enough to make a difference:
E36 non-M front suspension with eccentric FCAB and M3 3.0 top mount and MRT-20006-1 in lowest position, bump steer - camber chart (pdf)
Welp, change is in a better direction for sure and we're exactly at same toe change as with stock E36 non-M setup. A fraction of a degree of caster reduction from adjustable FCABs or adjustable top mounts would help to make the curve flat.
But we're not done with roll-center correction part yet, so next we will be adding our popular roll-center / bump steer / angle -kit instead, use it with the stock tie rod and see the alternative outcome.
E36 non-M front suspension geometry with MRT-20003-2 and eccentric FCAB and M3 3.0 top mount:
E36 non-M front suspension geometry with MRT-20003-2 and eccentric FCAB and M3 3.0 top mount (pdf)
Now we're definitely on the right track!
Wheel position within 1mm from stock, still remaining the good caster value. Slight reduction in all KPI, caster trail and scrub radius values for more neutral steering behavior.
But most impressive change occurred with roll-center which jumped from -23mm to +55mm, surely noticeable in cornering behavior.
We can expect a lot better camber curve and tie rod - LCA end height ratio would indicate much more neutral bump steer curve, time for a suspension sweep to generate the curves:
E36 non-M front suspension with MRT-20003-2 and eccentric FCAB and M3 3.0 top mount, bump steer - camber chart (pdf)
As the chef says, Voilà!
Bump steer curve flat as a pancake and a proper 2° camber gain.
For those who got scared of camber curve going to positive side, don't worry, with E36 struts camber adjustment is made super easy, you can fine tune camber with OE eccentric bolt or by adding spacers under the lower mounts. This style of adjustment is highly recommended since it won't change KPI as if you'd adjust top mounts for camber! Every 1mm spacer will increase camber by approximately 0.3°.
Now as we did experiment with non-M assembly and geometry correction kits, let's take a look how M3 models will respond to these parts.
E36 M3 3.0 front suspension geometry with MRT-20003-1:
E36 M3 3.0 front suspension geometry with MRT-20003-1 (pdf)
Changes follow the same concept as always, huge gain on roll-center height and slight reduction on most other parameters. As an experienced viewer tie rod to LCA height differences are alarmingly close, wonder what it does for the bump steer curve?
...you read it absolutely correct, tie rod to LCA height difference is slightly too tight and it causes descendent bump steer curve. How to improve a descendent curve? By lifting up the tail on the right which means the tie rod has to go up.
With the help of bump steer adjustable tie rods we can easily alter the position and redraw the graph:
We thought we had seen good graphs already, but no, this is close to perfection, until you see the next one.
One more model to be run with the same setup, which is the M3 3.2 EVO. If the geometry seemed acceptable in a stock form, it can't go much worse with purpose built geometry correction parts.
As a background information, we initially used E30 non-M and E36 M3 3.2 spindles to create these products back in circa 2015. Due to "universal fitment character" of parts there's minor variations on outcomes between different models as seen in the context. Following assembly was the most interesting for ourselves too since we hadn't done any simulation at this level before.
E36 M3 3.2 front suspension geometry with MRT-20003-1:
E36 M3 3.2 front suspension geometry with MRT-20003-1 (pdf)
All looking good by far, we even got to under 30mm of caster trail on this one. It is a pity that the spindle height was reduced on a EVO which results in lower roll-center height. KPI of 14° is already almost on a level of a E30 M3 Gr.A DTM strut.
Moment of truth, does this outperform the magnificent M3 3.0 setup regarding bump steer and camber curves?
We would be happy to end the article with this one!
Still couple of worthy setups to be analyzed, this time we'll be using our roll-center / bump steer correction -kit (without angle / quick steering adapter) combined in typical setups we see.
As the page already seems neverending long, we'll just leave you the pdf files listed below, for bump steer we have picked the best performing setting:
As in the previous chapters we'd probably have many more assemblies to analyze, but all this should give better perception of what works and what doesn't and how to make significant improvements.
In the next chapter we will go though some common myths and modifications made for E36 front suspensions to see their real effect.
Previous page - 2.1 Baseline