Gustav

I will here repost Louis excellent race story of his E39 M5. Gosh, his srory is betetr than mine... But he didn't destroy any slicks

Last weekend I took my 2000 M5 to Buttonwillow Raceway. This is one of the tracks that Road & Track Magazine uses for its testing. Where Road & Track typically uses one of the shorter configurations, the track can be split and two events can be run simultaneously, we were using the combined 2.68 mile configuration. This configuration has two long straights and a couple of shorter straights. Just what the E39 M5 likes.

First, my car is completely stock and I was running the stock Dunlop 8080s that came on the car. I wanted to see what it was like right "out of the box." As expected, and as reported in various magazines, it has more than enough understeer. It seems clear that the suspension is designed for someone that doesn't know how to handle 400 hp.

Turning in to a corner the car starts to understeer immediately. This seems to be the result of both the design of the front suspension and the dual compound rear springs. When you decelerate going into a turn, either with just a slight lift off the gas or by acutal braking, the weight shift to the front induces understeer. Normally a weight shift the the front will help the car turn. Not here. In fact, because of the dual compound rear springs and the multi-link nature of the rear suspension, it seems the rear end has a mind of its own. Even with the DSC turned off and the Sport setting turned on the car acted like it wanted to help drive. Certainly something a competent driver doesn't want, the car doing things on its own.

Also, the stock brake pads don't like a lot of heat. On my first runs I used late, hard braking techniques just to see if the brakes were as weak as some have said. Intially the brakes were great. Those big rotors and the adequate calipers stop in a big hurry, thank you. But as soon as the the temperature gets to the high side the brakes just go away. I found out when I was doing a little over 130 mph at the end of the back straight and I hit the brakes hard and there was almost no response!!! (Except to the muscles around my a**hole!). Luckily the straight leads to a long right-hand sweeper and with a lot of downshifting everything was fine.

Which leads to the next point, in sweeping turns the car has amazing balance and generates tremendous cornering force. In these turns the balance can be easily controlled with the throttle. Lots of fun!

Clearly the strenght of the car is power, which equals acceleration that is hard to believe. Even though my buddies in their track prepared cars would leave me in the corners, it didn't take much of a straight to catch them. The car literally leaps out of the corner and again with every gear shift. One time I had three passengers with me and they commented how they couldn't believe how they got pushed back in their seats in each gear, including 4th! I never got to 5th or 6th.

Like the suspension, with its "safety bias" of excessive understeer, the DSC is also biased to keep unskilled drivers safe. On my first run I thought I'd leave the DSC engaged until I had a few laps under my belt. However, the first turn out of the pits is a righthand hairpin turn that goes up hill with the crest past the apex of the turn. In all but underpowered cars you have to be careful when the car gets light at the crest or it's easy to spin. In any event, I was taking it easy because the tires were cold and afterall, it was my first lap in the car on a racetrack. Nevertheless, the DSC paniced and started grabbing brakes and it felt like someone threw an anchor out the back of the car! It felt like the DSC sensed I was going around a sharp corner with a fair amount of speed and then hit the gas. It didn't think I should do this so it brought everything to a halt. I could just hear the computer saying: "oh no you're not, I'm not going to let you accelerate. I think you're already going too fast!" In reality, I was taking it very easy, nowhere near losing control. I think the computer is a chicken! Needless to say, I immediately disengaged the DSC.

Final point -- I found the best tire pressure was 37lbs front, 34lbs rear, cold (50 degree ambient temperature). As I've said before, the owner's manual/doorpost recommended pressures are for the safety of inexperienced drivers. They add more understeer. If you go into a turn too fast an understeering car will tend to slide straight off the road. An oversteering car will tend to spin. Lifting off the gas or hitting the brakes will generally make matters worse in an oversteering car.

So what's the final conclusion? First, 4,000lbs is 4,000lbs and a car of this weight will never handle like a sports car. I didn't expect it to and it didn't. Notwithstanding the weight, the car does not exhibit excessive body roll (I let a friend drive it and I followed him in my race car -- what an awesome sight!) Second, in sweeping turns this car will generate tremendous cornering forces and will stay with much ligher cars in this kind of turn. Third, the brakes aren't bad (for stock street pads). With a little brake management on the track they stop the car pretty fast. After my first run session I started braking for turns earlier and with less pressure. The brakes never faded again and did a fine job. My conclusion is that the brakes and rotors are more than up to the job, the stock street pads are not up to track conditions (surprise?) With racing compound pads I think the brakes would be just fine. Fourth, this car is a great highway/autobahn cruiser. It's made for fast, quiet, safe motoring on straight roads and gentle curves (or sweepers!) In this element, it can't be beat. Some days I miss the sensation of speed and the envolvment I felt with my old (E34) M5. Other days I really like the smoothness while blasting along at warp speed. Nevertheless, I love the car and I don't want to go back. I guess I'm just getting older.

Louis

greg

Just for yucks I went to the last page of this Forum. It appears we have just a year of history on line. (the post below is from 3/19/00) But I did find quite interesting and it should be of interest to anyone who has tracked, or plans to track their M5. I especially noted the recommended tire pressure settings, which make sense to me and are certainly NOT obvious.

EBMCS03

Thanks greg for pulling this up from the bottom... I never read that and i found it very interesting. Question: How come they dont use the cross drilled ventilated disc brakes for the M5 like the ones in the prosches? I read somewhere that someone did use the 911 brakes on the M5 and they were a lot better.

JEM

Getting rid of the rear-biased pressures does seem obvious to me, it's SOP on any understeering road car but the pressures he used seem rather low.

In pretty much every case I can think of, up to a point generally somewhere north of 40psi, street tires gain grip as you add pressure. Given the high rated maximum pressure of the M5's tires, and the weight of the car, I'd think you'd want to run at least 40psi at both ends.

I think I'm using 40psi at both ends on the street, and I'd probably start at 44psi cold at both ends on track.

Tuning really needs a couple tools: a tire pyrometer (instant-read IR pyrometers are getting cheap now) and a bottle of white shoe polish. Some would say with the pyrometer, the shoe polish is overkill, but...

You want an even temperature across the tread surface; once you've got that, you can tweak each end up/down a little to fiddle with understeer.

The shoe polish can be used (not sure how much good it does with tires as short as the M5s) to make sure the pressures are high enough to keep the tire from scrubbing on its sidewall - put a smear on the tread shoulder and about 2" up the sidewall, go do a couple laps and don't hit any curbs, pull in and if the polish is scrubbed off above the tread you need more pressure.



[This message has been edited by JEM (edited 22 March 2001).]

greg

JEM - I don't think those are low. He stated those as cold pressures. I would expect +8 lbs on the track. And I KNOW that 50lbs is too much.

UCSD - I can only guess that it is due to cost. Porsche's brakes aren't cross-drilled, they are actually cast with the holes in. I've been told this is vital to ensuring there are no stress risers near the drilled holes.

JEM

I use 42psi cold in my Mustang's Kumhos (rated for 44psi cold max pressure), and a pyrometer shows that to come out about right.

Used to run 38/28 cold in the SHO to balance the understeer, before it got the Quaife and less front anti-roll bar.

When I actually get the M5 to the track, I'll probably start with 42psi cold, and we'll see what they pyrometer says.

Italia

Greg,

Thanks for reposting that wonderful, enlightening narrative from Louis. I not only found it to be informative but probably the most honest review I've ever read of the E39 M5.

As you mentioned, the tire pressures were far from obvious, but I'm willing to give them a try at Sears Point.

greg

Well, JEM - it is certainly easier to let air out. I can tell you that on the last M5 drive I got into trouble - started at about 44lbs in the rear, got them up to 52 if memory serves. At that point they their grip (and more importantly their feedback) were definitely reduced. I have the scuffed rim to prove it. The kumhos may shed heat better than the S-02's, but I still think you're gonna come out overinflated. What the heck- easy to check, easy to adjust. We'll sure as hell have fun finding out!

HBRAMSTEDT

I found that adding a little more air
pressure to the front relative to the
rear helped. In other words, the owner's
manual shows about a 3 lb. differential
in air pressure, less in front and more in
the rear. I reduced this to 1 to 2 lbs. and the turn in was more consistent and predictable.
Also, I added about 3-4 ft.-lbs. of
torque to the wheel nuts, and this
seemed to reduce deflection.
I can turn in a whole lot faster,
and maintain a more precise line through
the turn.

KKelly

The comment about sweepers is also true of a stock suspension in an E34. It was amazingly easy to drive in high speed sweepers. Adding suspension modifications greatly improved track handling but you have to pay attention on those high speed sweepers.

I too agree that no matter what you do you notice you are driving a 2 ton sedan--especially on tracks like Sears Point.

Mark Bradford and I will be at Buttonwillow in two weeks. It will be interesting to see what kind of top speeds we can get to on the straights.

DZeckhausen

Probably because the list price of the M5 would then go up by another couple thousand dollars. And also, it would make it impossible for nuts like me to bolt on better brakes! :-)



------------------
Dave Z.