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Originally Posted by Justin(OKC)
Just from browsing this forum, it sounds like the X1 suspension is very similar to an E90 suspension. I'm curious how similar. I have AST's on my E90 M3 that were originally on my 135i. I assume I'd need M3 rear control arms like I had on the 135i, but other than that, would they bolt right up? Curious about damper lengths (droop) and spring rates for the X1. Anyone have any good knowledge on this? I'm trying to decide if it is time to sell the E90 M3 or not. Thanks!! Justin
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I have been talking to a local race shop about doing a full-fledged JRZ suspension setup, so I've been researching this for a while.
We have a lot of good options, and a couple of limitations.
You are right that the X1 suspension is very similar to the e90 suspension, and as a result of this some of the M3 parts will swap. The M3 rear guide rods and upper rods 100% swap; they are the exact same part number as the e9x on real oem. The wishbones I'm not so sure about - they visually look like they will fit, but are a different part number.
The same goes for the bushings. The X1 subframe bushings are a different part number on realOEM, but this is more likely because they are a different pliability than the e9x ones. For example, the e91 bushings are a different part number than the 335i ones, but I believe they swap. The diagrams are the same, and I have a feeling that the M3 bushings will swap - I just haven't confirmed this yet.
The front sway bar is identical to that of an e91 touring, so upgrades for that will work on the X1 as well.
The rear bar is another situation where the X1 has a unique part number; I haven't done investigation as to whether it will swap or not yet, but I will have the shop look at it the next time I am in.
I know for a fact that JRZ can make a compatible suspension with an X1 35i xdrive, which means it's likely Ohlins or AST can as well.
As for your question about whether it's time to sell the M3 - while the X1 is not as ideal of a platform to start from for track use (after all, we are spending money to upgrade to M3 parts the M3 has stock), with a few mods it is competent enough where with a good driver you can enjoy it and overtake M3's on the track (I have personally done so, and it was a hell of a lot of fun). Nobody will ever confuse it for a 911, but it has the exact same potential as a 335 x drive - same weight and can be lowered to the same height. Throw a tune, FMIC, downpipe, sticky tires, and a good suspension setup on there and you will be passing stock M3's all day long. Of course, the M3 has all this stock and is certainly more of a drivers car - but gaining AWD and the utility of the X1 is worth the tradeoff to me.
One other thing - you can make the X1 faster in a straight line for much cheaper and easier than you can a M3. I ran a 12.1 1/4 mile on street tires. To do that in a M3, you need 5K+ of of mods (drag radials, test pipes, tune, pulley, etc). But I will warn you of this - you will miss that pure throttle response of the M3. No turbo car will be able to give you that, and I intend on picking up a pure N/A sports car as a second car in a year or so to satisfy that itch.