Another BMW Performance Suspension + M3 parts review

[vantagesc]

Parts:
- BMW Performance Suspension (shocks / springs/ fsb);
- M3 front tension rod, front lower wishbone;
- M3 rear guide rod, rearlower wishbone;
- M3 rear subframe bushings.

Alignment:
- front, 0 toe and -1.3 camber
- rear, 3/16" toe and -1.5 camber (may increase to -2)

Run-flat tires retained

Why I chose the BMW PS:
I have a heavily modified track car and am always tinkering with the suspension depending on the activity (track, mountain drive, grand touring). For this car I wanted to go with something cheap that I could install and forget about forever. This car is used 95% of the time for daily driving and 5% for mountain road driving. This car will never see the track. However, as stock, the car completely falls apart in anything more than 6 or 7/10ths driving.

While you can definitely get higher quality parts for the same price as the PS or slightly more, I've had bad experiences with aftermarket valving. I trusted BMW on this one to get it right for a daily driver, even though you're not getting superior hardware like with coilovers.

Initial Impressions:

Steering:
Steering feel is wonderful. Before it was extremely smooth, but isolated. Now you can definitely feel which direction the tires are pointed and almost feel the surface of the road. Is it Lotus-like steering? No, but very nice. Steering is significantly heavier in feel.

Handling:
Less understeer for sure, particularly on corner exit. The reduction of body roll is very nice--not much roll after the car takes an initial set. I really like how the front/rear act as one on turn-in, with the rear not lagging behind or the driver wondering why nothing is happening when you turn the wheel. Can't render final judgement until I drive the car in a more appropriate environment.

Ride and NVH:
These mods have more of an impact on NVH than I was expecting based on other reviews, but it's still comfortable. Everyone says the car feels more like one solid piece and so far that's true. The back end follows the front more quickly and the car feels a lot less disjointed. The car is definitely more composed on bigger bumps in that it recovers more quickly; in that sense the car rides better. At the same time, you are going to feel smaller bumps that the stock suspension never would have alerted you to.

You are constantly getting a lot more noise / feedback in the seat of your pants at all times. I think this feel will really pay off in a performance situation. So far I have only driven on Los Angeles freeways and around downtown. Not exactly the smoothest roads, so that's probably why I feel a larger increase in NVH than most. The stock 135i sort of just glides over everything until you hit a big bump, and then it loses all composure. The BMW PS offers more consistent performance.

The spring rate itself isn't that stiff, so it's appropriate. However, I'm not sold on the BMW PS shock valving yet. The car feels a bit "jiggly" for lack of a better word at times, particularly over uneven roads. I'm not getting the huge bounce that I was getting with the stock suspension, but I feel like the shocks aren't quite reacting as fast / controlling the springs as well as I expected. Particularly in the rear. Like when you touch a piece of jello, the car shakes around too much. (I'm exaggerating a bit to make a point). Will have to get to the bottom of this...it could be the RFTs or it could be not enough high speed give in the shocks.

I spent all of last week driving my lightweight track prepped car that has rose joints everywhere (no rubber in the suspension), so I'm one that can tolerate a stiff suspension, but perhaps my frame of reference is off, since that car's shocks react immediately and the car gathers it self faster than an M3 with EDC. Might have expected too much from what is basically an OEM shock with different valving.


Impressions after some spirited driving:

(reserved)

Conclusion:

(reserved)

[dbchun]

appreciate the background perspective and thorough review, looking forward to your conclusions

[Dackelone]

Thanks for your review/thoughts. I remember reading that the BMW PS was tuned by KW. Maybe that is why it just feels right. Most everyone seems to love the PS valving/feel.

[andrey_gta]

Intrigued at the possibility that it is KW tuned
does anyone know the PS spring rates vs Eibach rates?

[Johnny_M]

The RFT's aren't helping with the NVH. I'd recommend to ditch those RFT's and get a lighter rim. I have a similar setup to you, except I'm running the Koni Sport's since I wanted the ability to adjust the dampening. Great review. I look forward to reading how it responds to you on more appropriate road conditions.