Quote:
Originally Posted by vtl
With the front control arms, have you done any investigation on how the longer M3 control arm affects the geometry vs stock? A longer lower arm must move the front wheels slightly more forward and increase caster, and also redefine the virtual pivot point location.
I believe the pickup points on the M3 knuckle are slightly different for the control arms, they are definitely different for the steering rack pickup points - the M3 tie rods on an M3 rack are around 15mm too long if you fit it on a non M knuckle, so the pickup points must be different. This might be interesting since the long proven mod for us non M guys is to fit the control arms from an M3, but does it actually have negative effects with the geometry?
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vtl and I have been discussing the M3 knuckles for a while now, we pretty much talk about suspension 24/7.
Bit of a background, the E92 M3 knuckles are different to the non-M knuckles, they're lighter, made of cast aluminium and overall have different geometry to the non-M parts.
I retrofitted an E92 M3 steering rack on my car, and as you can seen in the link below, I had to cut the ///M tie-rods shorter to make it work.
Link to ///M rack retrofit post from by build thread:
https://www.e90post.com/forums/showp...80&postcount=3
It's obvious that the tie-rods mounting points on the knuckles sit further out on the M3, and hence why they have longer tie-rods.
The only two advantages I can think of for this, are more precise steering wheel feel/direction, and the rack will have more leverage to push/pull on the knuckle to turn the wheels, because the mounting point where the force exerted by the rack acts on the knuckle sits further away from the pivot point that the knuckle spins around (strut shock body / steering axis / kingpin angle). There might be other geometry changes associated with the ///M knuckles unknown to us at this stage.
One thing you'll notice as soon as you get into a 1M/M3, their tendency to understeer is a lot lower than non-M cars (even if non-M cars are fitted with top-shelf coilovers, sway bars, same alignment, same camber and same width tyres). Potentially upon compression, the M3 knuckles might be helping with gaining more negative camber?!
Another thing you'll notice, ///M cars seem to wander significantly less on hard braking, ///M knuckles technically move the front wheels more forwards and change the castor, which reduces front-end/steering wandering under hard braking.
///M3 technical documentation on the front knuckles:
///M3 technical documentation on the difference between the front geometry/alignment between a M3 and a standard non-M 3er:
I also bought myself a complete rear ///M3 rear-end, similar to the front, the knuckles, control arms (as already know), and rear subframe are different. The rear subframe has more reinforced control arms mounting points, and it seems that there's slightly revised geometry at the rear too.
I'll installing the M3 rear-end on the car in the next couple of weeks, will use solid subframe mounts, and converting all the rubber bushings to solid ball-joints... etc. (bit of a project, I'll document it in my buildthread once it's all finished).
///M3 technical documentation on the rear-end suspension:
///M3 technical documentation on the difference between the front geometry/alignment between a M3 and a standard non-M 3er:
By the looks of it, I'll be hunting front M3 knuckles too, to complete my full M3 driveline conversion (already got front M3 arms). It's a pain, cause I'll need new coilovers to match, and M3 calipers and rotors. I already have the Ohlins Road & Track with custom springs to suit (8kg/mm front, and 12kg/mm rear), swapped spring 3 times just to settle on those rates. But it seems that there might be some gains from the M3 driveline, I already got the whole rear-end, might as well keep an eye out for cheap the front knuckles and all associated parts.