Thought the following update/review might be of interest.
Terry (Tengocity) and I met up last night so that I could try his suspension setup. We also twigged that we knew each other when working at the same company, so also had the chance to reconnect.
A quick summary of the cars :
Mine : F31 330sD, 2012, 37K miles, stock engine, stock brakes (sliding calipers and single pistons all round, 330mm discs on the front), BMW adaptive dampers, M Sport suspension, 19" rims, Bridgestone Potenza run flats (225 fronts; 255 rears).
Terry : 335xD, 2013 (I think), 42K miles, DMS remap, M Performance brakes all round (fixed callipers, 4 piston fronts, 2 piston rears, 370mm discs front), BMW adaptive dampers, ACS springs, Birds ARBs, 19" rims, Michelin Pilot Super Sports (225 fronts; 255 rears).
We RVd at a pub on a on a road that Terry knew well. Road was generally well surfaced, some scarred tarmac here and there, and some nice twisties where we could give his car a workout.
This was mainly for my benefit (cheers Terry) as improving the ride and handling of my car is my #1 objective. Here are my thoughts/conclusions :
- Ride quality : the ACS springs and MPSS make a dramatic difference. The harshness of the secondary ride is really improved, and the primary ride is nicely controlled. Comfort setting feels like Sport in mine, but more refined. I didn't notice any control problems with the BMW adaptive dampers, and for road use they felt fine to me (actually surprisingly better, working the the springs and ARBs).
- Handling : MASSIVE improvement. You can really feel the Birds ARBs keeping the car level, and understeer (a huge problem in my car) is all but gone. Terry's car feels very neutral (a tad understeer, but just enough to stop the car feeling prone to snap-oversteer) - I really liked it. At speed the car is very controlled, and moving up to Sport+ does nothing to unsettle the drivability and confidence.
- Grip : compared to the Bridgestones, which IMO are dreadful even for RFTs, the MPSS provides a great combination of grip, stability, ride quality and balance. The turn-in is crisp, and they don't wash-out - very confidence-insipiring.
Overall conclusions regarding ACS springs + Birds ARBs + adapative dampers + MPSS = a great setup, and ideally suited to those looking for a 'fast road' orientated car. My decision is made
- Braking : before I drove his car Terry asked me to assess the brakes. I've read a lot of mixed reviews/opinions regarding the BMW M Performance brake upgrade, but this was the first time I'd driven with them. In short, they were a disappointment (sorry Terry, but I think we're on the same page here). Cold bite is surprisingly poor, the brake pedal goes long (even though Terry has had braided lines fitted) and I was hoping they would stop the car dead (so to speak) but this wasn't the case. Feel through the pedal was also lacking, compared to my expectations. Maybe the brakes need heat in them, and maybe different pads would help. It doesn't explain the soft and long pedal travel though - maybe the BMW Brembos aren't ideally configured in terms of piston volumes and valving. Personally I won't be spending my money on that upgrade.
On the run home I did a couple of maximum retardation stops from speed and found the initial bite from the stock brakes was better, pedal was firmer, and outright stopping power was not far off the M Performance setup. Being able to get to full brake pressure quickly no doubt has a positive effect here.
- Power : the DMS remap on the 335D is excellent; very smooth and crisp all the way through the rev range; no sense that the engine is struggling for airflow. It works very well. Bearing in mind there is a theoretical difference of 96bhp between the cars (335xD DMS 354 bhp Vs 330sD 258 bhp official - I've not had mine on a RR) I suggested we do a 30mph rolling start in Sport+ with both cars in 3rd, then a 3-2-1 count and full-bore acceleration run (to rule out any off-the-line traction differences that would favour the xD four wheel drive). I was interested to see if I could stay with the 335. The 335 DMS does pull away, but didn't romp away, and then we headed into the twisties - this is where the power disadvantage was plainly not the problem. I didn't have the confidence in my car to hold the same level of speed through the corners : the front end was reluctant to turn-in, substantial feeling of weight and understeer, and the poor overall control (relatively speaking) made it difficult to hold a neat line. Terry's car looked like it sailed through, and although he had driven the roads before the main factor in the speed advantage was the handling.
I have two fundamental options in terms of liberating more power from the 330sD; BMW or independent :
1. The BMW PPK option for my car (stock brakes; 330x24mm discs) includes a mandatory a front axle brake upgrade : BMW Brembo fixed calipers with 4 pistons (the same as on the M Performance system), 340x30mm discs (drilled and slotted) but which might suffer from the same lack of initial bite and the long pedal that Terry's car suffers with. Total cost quoted = <£1,600, of which ~£500 is for the brake upgrade. If they're not up to the task I can replace them without a huge loss. Even though my car only has 6 months warranty remaining, the BMK PPK does at least mean that I can buy a BMW extended warranty without quibble. As the steering rack and both front adaptive dampers have failed in the 6 months that I've owned the car, this is the likely choice and it was also good to see the results of the Surrey Rolling Road test, where the 330sD cars were generating 290-299 bhp.
2. Remap/box plus BBK (I wouldn't leave the brakes as stock). A decent BBK seems to start at ~£3K fitted, and could be overkill on a road car. Total cost could be in the region of £4K. Ouch.
Changing to a 335Xd is tempting, if not just for the extra traction (you could feel Terry's car pulling itself out of tight corners under power, whereas mine will tend to break traction on the inside rear). I'm looking into it.
Terry and I are hoping to meet up with Guy soon for a more extensive road test; a back-to-back-to-back test of standard suspension Vs ACS/Birds Vs ACS RS would be very interesting - we'll report back.