Originally Posted by Racer20
Here's the next chapter:
First, some background
Stiffer and softer aren't really that meaningful when you're talking about a whole suspension system. The reason stiffer is better is that a pair of tires (left and right or front and rear) works better when the weight on them is equal. When you transfer weight between the two, as in body roll, brake dive, or squat, you ALWAYS sacrifice grip.
All else equal, a stiffer suspension resists weight transfer better than a softer one, and less weight transfer means high total traction capacity between all 4 tires.
However, "all else equal" is rarely the case. Some factors that might cause stiffer to be slower:
- Not enough compliance to maintain grip on a bumpy track
- Poor front to rear balance (poor steering response or feedback, unbalanced roll, excessive under/oversteer)
- Non linear, jerky suspension motion or jacking
- Too responsive for the driver skill, not confidence inspiring. Stiffer suspension means there is less body motion to clue the driver in as to what's going on, and also requires faster reaction times and more precise inputs.
How this relates to the E92 M3:
My understanding is that "sport mode" in an E92 M3 is a fixed steady state setting with no adaptive control. I was surprised when I read this, because you give up the main benefit of EDC when you do this, and this will almost NEVER result in an optimum solution. I can see several of the above scenarios being the case if the shocks are being used in this manner.
The competition package supposedly uses adaptive control for sport mode, which, in theory, should be much better, but I haven't really looked into lap times. The E92 is on my shopping list for my next car, and I would not buy one without ZCP because IMO, the base EDC sport mode is useless. (I haven't driven it in sport, but that's my conclusion based on what I know and the reviews I've read).
Further, keep in mind the Nurburgring is a very unique place, and typically requires quite a bit more body control than our tracks here. A car that is optimized for the 'Ring may be too much for your average driver on an average track here. Plus, tuning on the ring isn't really about lap times, it's about making sure the car handles the various individual corners, bumps, and pavement transitions well.
Thanks for more great info, @Racer20 - a great technical explanation of what many of us instinctively believe to be the case.
On the list of factors that could cause a stiffer suspension to be slower, might overly stiff tires (e.g. run flats) contribute to a lack of compliance/ jerky suspension motion? For many enthusiasts, one of the first things we do is ditch the RFTs in favor of some good rubber.
After spending some time in Sport mode in the F30 on both road and track, I haven't experienced conditions where the suspension is lacking in compliance to the point of a reduction in grip compared to Normal mode. (We only get two modes on the F30 - Normal and Sport.)
Once you've had a chance to test an F30 with adaptive dampers (optioned with "DHP", in BMW parlance), I am anxious to hear your thoughts on how well the system performs. Normal mode definitely filters out a lot of the choppy feedback over rougher roads, but there's just too much body pitch/roll for me to enjoy driving in this mode. In Sport, things do tighten up a fair amount to where the ride is much more enjoyable, but there's still a bit more body pitch/roll than I'd prefer.
As a result, like many members here, I have found the car to balance and corner very well in general, but I've been considering options to reduce pitch/roll and improve the car's overall suspension feel (and hopefully the car's ability to grip and turn fast lap time too!) It would be great to read your thoughts on the various considerations that are popular around here... some of those being:
- Changing Just Springs - Many guys go for just lower springs (e.g. H&R Sport), with a similar spring rate to OEM. I have been considering going with slightly firmer springs, only about 1/2" lower, with matching bump stops. (Dinan plans to release a spring/bump stop kit in January 2014) Seems like these would match up well with the stock adaptive dampers in Sport mode...
- New Shocks/Springs - e.g. Bilstein B8/H&R Sport springs have been popular and well-regarded
- Coilovers - KW V3, Bilstein B16, TC Kline, etc. More adjustablity than regular shocks, but maybe not necessary? I've heard that the JRZ kits are in a different league altogether in terms of both comfort and performance...
- Stiffer Anti-Roll/Sway Bars - I've seen claims that these will address the lateral body roll issue without doing much to change individual shock damping... but I've also heard that too stiff ARBs can be counter-productive.