As John mentioned, I also brought my '00 M5 to the Thunderhill event and thought I'd share my thoughts with the board. Before I start, I do have a pretty good in-car digital video of a lap at Thunderhill and would be happy to share it with the board. It's 20,000+ KB and I need some way to get it to a high bandwidth hosting site. Can anyone help?
It probably makes sense to give some background on my track experience, since that would be important to me in evaluating the feedback provided by someone else. I've driven about 15-20 days on various tracks, all in the past three years, with about six days at Thunderhill. Almost all of that time has been in a '97 Carrera S with a sport suspension, BFG G-Force tires and the brakes from the 993 Twin Turbo. I've also had some decent track time in a Ferrari 360 Modena, Porsche 993 and 996 TTs, and an E34 M5. If I had to rank my ability relative to the typical pilot at a driver education event, I'd say I'm about an 8 out of 10.
Anyway, on to the M5.
I spent most of the morning sessions messing around with the tire pressures and I kept the DSC engaged. I wanted DSC engaged because it's a nice way to allow the car to tell me in a very safe way where the limits of adhesion and traction are. While the DSC provides a nice indication of where potential danger might exist, in my opinion in it engaged too early and too severely. In many instances I would try to go back to power at the apex of a turn and got absolutely no throttle response because the DCS was shutting down all engine power until it determined that the was car was "stable".
As for tire pressure (I have the Dunlops), I started at 40/44 psi, and the car pushed hard and really squealed in turns. I twice tried lowering the pressures in 3 pound increments but the push got even more pronounced and you could tell from the tire wear that I was really "rolling over" the treads on the front tires. I then inflated the pressures to the door-jamb specs of 44/48 and the car achieved its best balance. I was never ultimately satisfied that I had the best possible pressures, but I got tired of checking and adjusting pressures, especially given the heat (95 degrees) which made getting cool pressure readings impossible. Overall I felt the grip of the Dunlop's was mediocre at best, and I ultimately discovered that (and got comfortable with) the fastest way to get the car though most turns was to push the car hard and allow it to sort of slide/drift through the turn.
The lack of grip and the obtrusiveness of the DSC throughout the morning sessions left me somewhat disappointed with the overall experience and I was beginning to think that the track was the wrong place for a 4000+ pound sedan. My thinking and my enjoyment changed when I got the tire pressures up, disengaged DSC, and just plain got more experience driving the car hard.
Disengaging DSC vastly improved the performance in hard cornering. This occurred because I was able to use the throttle to both plant the rear end and to aid in steering the car through a turn with throttle modulation. This increased my confidence that I could essentially put the car in a sort of controlled drift in the tighter turns.
The brakes on the car were very strong for three laps, good for the next three, and poor for anything after 6 laps. I'd guess that the braking capabilities diminished by 50% or more after those first 6 laps and I had to reduce straightaway speeds and brake earlier in order to both stay on the track and drive the proper line at a decent speed. While a bit frustrating on the track, the brakes are clearly designed to haul the car down in a street environment (which they do extraordinarily well) where there is not anywhere near the heat build up issues that are present on the track.
The engine and entire drive train are phenomenal and very well suited for the track. The car really pulls! With DSC disengaged, the car accelerated hard out of turns and the engine snarl sounded wonderful (though not as good as John's B&Bs). It is quite an experience to be able to spend extended time periods at full throttle in third and fourth gear -- something you can't do on the street. In the main straight of Thunderhill I hit 130+ mph before braking for the 95+ MPH left hand turn 1. I could have probably got into the high 130s if I had been more confident in the brakes. In any case, the actual top end I achieved was 10mph faster than I would hit in my Porsche and I entered the main straightway about 10-15 mph slower in the M5 because the grip through the preceding two turns prior to the main straight just wasn't there.
While the M5 is by no means perfect for the track, it is a remarkable automobile. It's a 4-5 passenger high speed touring sedan that on the track held it's own and in most instances bettered the speeds/times of the sports cars. My fastest lap times in the M5 were the same as the times I turned in my Porsche, although the experience from the driver's seat is very different.
With respect to how the car compared to others at the track, it's really difficult to make conclusive comparisons because differences in driving ability can dramatically affect results. That said, once our club publishes the official times of the club members I can give more specific comparison points. I think M5 owners will be impressed with how the car stacked up -- especially considering that it is bone stock and weighs 4000+ lbs. (My guess is that the Z8 on the track will be unreal).
Personally, I'm not sure if I'll track the M5 again. If I were going to track it on a regular basis, following is a list of mods that I would consider, probably in sequential order, and not all at once. My personal opinion is that if you aren't going to track the car there is little reason to do any mods (expect perhaps #1), because there is no safe setting in which you could really enjoy/exploit the mod and the car is such a pleasure to drive as it sits. Also, I would be concerned about how #'s 1-2 would compromise the everyday drivability of the car.
1. New tires. Not sure what brand, but would consider wider fronts (if possible) to help with the understeer and would also look into lower profile tires that would limit how much the sidewalls roll over in hard cornering.
2. Suspension mods. I know some people have reported good results with the various Dinan stages and I would like the opportunity to drive a car with these mods. As John noted, a professional instructor who drove one the M5's suggested starting with just the rear stabilizer bar, and moving up from there.
3. Brakes. I'll admit to being spoiled with Porsche brakes, and an M5 brake change could be ranked higher, but if the other two changes are made the car should be able to safely carry more speed through turns which would reduce how much you have to ask of the brakes upon entering a turn. Also, I'm not sure about the cost of the various upgrade options. Some have said that pads/fluid alone will help, and that seems like a lower cost way to begin to improve the brake fade and is a whole lot cheaper than going to a new brake application like Brembos.
A few final thoughts:
· I loved the B&B exhaust system that John has on his car. It doesn't look at all aftermarket and is a nice aesthetic improvement to the rear end. From a performance perspective the weight loss from the stock exhausts is more interesting to me than any nominal increase in HP. The sound both inside and outside is more aggressive, but not obtrusive.
· If you are planning to track your car, don't spend a bunch of money on mods until you are sure you are happy with how you sit in the car with a helmet on! I'm only 5'9'' and the top of my helmet was noticeably grazing the roof of the car and I had the seat bottom at it's lowest possible level.
· As much fun as I had on the track with DSC disabled, when I drive the car on the street I will usually keep DSC engaged, as it can be an invaluable tool in maintaining car control when something unexpected develops.
