Thoughts on reducing body roll?

J'ai fait cinq jours de piste HPDE maintenant avec ma configuration actuelle - E90 M3 avec suspension Dinan Stage III et 275/35-18 Nitto NT01s tout autour. Il y a quelques jours, à Lime Rock, je remarquais vraiment le body roll. Évidemment, certains sont à prévoir dans une voiture de rue 3600lb, mais quelle serait la prochaine étape pour le réduire? Cela impliquerait-il un changement de suspension plus agressif, tel que les capotages, rendant ainsi EDC non fonctionnel? (J'ai couru avec EDC en pleine forme.) Et est-ce même souhaitable? Le manque de roulis m'empêcherait-il de sentir ce que fait la voiture - est-il plus approprié pour les pilotes plus avancés? La voiture est aussi mon chauffeur quotidien, donc je ne voudrais pas qu'elle soit brutale dans la rue. Je m'attends probablement à l'impossible...

Je ne suis pas un expert, mais je pense que de plus gros balanciers aideraient davantage qu'une suspension plus rigide. Cependant, cela aurait un impact négatif sur la streetability.
Je dois le faire aussi pour que vous tous les experts carillon dans.

Brainofjjj a écrit

Je ne suis pas un expert, mais je pense que de plus gros balanciers aideraient davantage qu'une suspension plus rigide. Cependant, cela aurait un impact négatif sur la streetability.
Je dois le faire aussi pour que vous tous les experts carillon dans.

Exactement ce que je pensais

Est-ce que Dinan Stage 3 vient avec un plus grand balancement à l'avant déjà? J'ai un E92 et installé le balancement avant de l'E93 et il semble avoir réduit un peu de roulis dans la rue, ne l'avait pas encore eu sur la piste.

La troisième étape de Dinan est un excellent compromis, tout comme la voiture, mais elle a quelques limites lorsqu’elle est appliquée à la piste. Je sentais que le roulis de la carrosserie était minime dans la rue, mais sur la piste, il recule comme le poids de cette voiture, un peu comme l’IMO inévitable. Pensez coilovers serait certainement améliorer roll, mais comme vous voulez maintenir la conduite quotidienne et pas sûr de savoir comment "vivable" coilovers sont... plus d'informations serait grandement apprécié de ceux qui sont plus expérimentés comme vraiment faire comme le confort du dinan.
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Consider the RD Sport Sways. Front and Rear bars that each have 3 adjustable settings.

Dinan are about to come out with ED compatible coilovers for the E9X M3.

I am guessing that if you are feeling it that badly, you need to smooth out driving and your weight transfer first though. Our cars are pretty well set up out of the box, especially for the intermediate 1 level/speed at Lime Rock. Next time, grab an instructor as a ride along and show him where you feel it.

I am considering the Dinan Stage 3 suspension. How much did this kit affect the ride height of the car?

Cornering grip is much more important than how much body roll you have. As mentioned above you can probably change your car to have less body roll but I'm willing to bet that you will end up with less cornering grip.

Extreme example, if you replaced all your shocks with steel rods of the same length you would have almost no body roll at all, but you'd skate off most every corner unless the pavement was glass smooth. Which would you rather have?

LiM3y wrote

Dinan are about to come out with ED compatible coilovers for the E9X M3.

I am guessing that if you are feeling it that badly, you need to smooth out driving and your weight transfer first though. Our cars are pretty well set up out of the box, especially for the intermediate 1 level/speed at Lime Rock. Next time, grab an instructor as a ride along and show him where you feel it.

Might be the case. I felt smoother and faster this time out, though, compared to the SCDA event at LRP several weeks ago. At that event, I was one of the slower cars in Intermed 1 and you were consistently quite a bit faster than me. This time, though, I felt like I was building more speed and confidence. I was one of the faster cars in the group. I was thinking, though, that the grippiness of my Nitto NT01s compared to a street tire might exacerbate body roll. They probably dig in more and create more weight transfer as opposed to a street tire that would start sliding first. Thoughts?

paradocs98 wrote

I was thinking, though, that the grippiness of my Nitto NT01s compared to a street tire might exacerbate body roll. They probably dig in more and create more weight transfer as opposed to a street tire that would start sliding first. Thoughts?

Exactly the case. You have a great street car that is capable of providing fun on track for casual use. Once you start mixing street and track equipment, you will have a car that is not fully suitable for either. A heavy car can certainly be a fast road course car. Look at the NASCAR drivers who do well on the road courses. But, it requires such dramatic changes to the suspension setup, most folks would find it wholly unsuitable for street use. On the other hand, I know folks who would daily drive a GT3 RS, so it obviously depends on your willingness to accept compromises to streetability. I've done a good bit of work on several cars over the previous eight years or so. My advice, given your current experience level, do nothing to the car right away. It is probably capable beyond your current ability. After another year of track events, if you decide you want to get into it deeper, buy a fully prepared track car from someone getting out of racing, and leave the M3 as is.

R comps will exacerbate body roll for the reason you stated. I will upgrade my suspension in my 330 with stiffer springs.

Maybe call Dinan and get their take on this?

Whether you should get coil overs really depends on your use. If you only do a handful of events per year and daily drive the car, just leave car as is. And work on how to embrace the characteristics of your car.

There are currently no EDC compatible coil over system on the market. Therefore to adjust the firmness of your damper (like what you do with EDC) you will probably need to adjust them manually. Whether a set up has decent ride quality really depends on your ride tolerance.

One would argue that with stiffer springs, you actually feel the car and the road better because less is 'dampened' by the suspension system.

Take a look here. Lots of good info: http://www.m3post.com/forums/showthread.php?t=339168

paradocs98 wrote

Might be the case. I felt smoother and faster this time out, though, compared to the SCDA event at LRP several weeks ago. At that event, I was one of the slower cars in Intermed 1 and you were consistently quite a bit faster than me. This time, though, I felt like I was building more speed and confidence. I was one of the faster cars in the group. I was thinking, though, that the grippiness of my Nitto NT01s compared to a street tire might exacerbate body roll. They probably dig in more and create more weight transfer as opposed to a street tire that would start sliding first. Thoughts?

I am thinking there is something wrong with the install of your Dinan kit at the back. I am wondering if something is loose. The last time out, you complained of a back end wiggle (which could be MDM straightening you out while trying to turn and brake hard at the same time?), now you are commenting on body roll, which sounds worse with your Dinan III than stock (or Eibachs). Maybe the rear sway bar is loose? I would go back to the installer and have them have a look, because at the level/speed you are at, you shouldn't be feeling these things so profoundly to be worried.

Changing sway bars to RD Sport's adjustable set would give you a bit more flexibility in some ways. On a given car with no changes to geometry or CG height, increasing roll stiffness can reduce compliance, which on certain courses can be a detriment to mechanical grip. Because you're always fighting to achieve a balance between as little unwanted geometry change as possible while maintaining the best possible compliance, in my view having an adjustable sway bar setup front and rear allows you to try to achieve the appropriate balance while also gaining the ability to adjust under/oversteer balance.

As Richard said, however, sometimes adding an additional point of adjustment can be a detriment rather than a help, if you are not accustomed to making the appropriate adjustment decisions. I agree that it helps to know the car as is as well as possible, prior to adding more adjustment choices like sway bars or coilovers.

LiM3y wrote

I am thinking there is something wrong with the install of your Dinan kit at the back. I am wondering if something is loose. The last time out, you complained of a back end wiggle (which could be MDM straightening you out while trying to turn and brake hard at the same time?), now you are commenting on body roll, which sounds worse with your Dinan III than stock (or Eibachs). Maybe the rear sway bar is loose? I would go back to the installer and have them have a look, because at the level/speed you are at, you shouldn't be feeling these things so profoundly to be worried.

Good thoughts--I had the car inspected at a good shop here on Long Island a couple of days ago for an upcoming PCA event at NJMP. The Dinan suspension kit changes the front anti-roll bar only; the rear is left stock. The shop checked the stock rear bar and found nothing loose. They did comment, however, that the stock front and rear anti-roll bars are pretty puny and a potential weak point performance-wise. They also speculate that in Dinan's method of upgrading the front bar without touching the rear bar, some rear-end instability on track might be brought to the surface. In any case, they've done a lot of work on E46 and E90/92 M3s, specifically for upgrades and track prep. They also mentioned that upgrading the rear bar is a real undertaking because the rear subframe has to be accessed, making it a 6-7 hour job...

paradocs98 wrote

Good thoughts--I had the car inspected at a good shop here on Long Island a couple of days ago for an upcoming PCA event at NJMP. The Dinan suspension kit changes the front anti-roll bar only; the rear is left stock. The shop checked the stock rear bar and found nothing loose. They did comment, however, that the stock front and rear anti-roll bars are pretty puny and a potential weak point performance-wise. They also speculate that in Dinan's method of upgrading the front bar without touching the rear bar, some rear-end instability on track might be brought to the surface. In any case, they've done a lot of work on E46 and E90/92 M3s, specifically for upgrades and track prep. They also mentioned that upgrading the rear bar is a real undertaking because the rear subframe has to be accessed, making it a 6-7 hour job...

I think that you have your answer right there. I don't know enough about suspension set-up to offer any advice on how to compensate with other more accessible parts. I would call Dinan to be honest and get their advice. They have to be aware of this issue with their kit, but will have made a decision that the cost to fix doesn't match the demand.

Actually...

Adding more rear bar may take away some grip to the rear thus resulting in more rear instability. It's weird, I know.

The charming part of having a MacPherson strut up front and multi-link set-up rear is that, the MacPherson struts behavior is unpredictable due to its simple design. Meaning the camber curve is not linear, and once you go past roll center you start to lose camber instead of gain it. So the old adage that adding thicker roll-bars will increase the propensity for that end to lose grip first isn't always true...Especially on a car that has the same suspension geometry as most typical BMW (the new 5 series is the first BMW to ditch the MacStrut). A stiffer front bar may work to prevent the outside front of the car from compressing past the roll center thus promoting more grip up front, especially a stiff front bar in combination with a lot of camber (i.e. Dinan's fixed camber plate) and/or stiff suspension.

In all honesty, I would suggest CHANGING DRIVING STYLE to match the weight of the car would be the quickest and best way to cure understeer. Despite BMW's best attempts to thumb their noses at Physics, there's just no way around it...Not when they have to make a 3,600+ lbs car behave the way it does and still be a comfortable street car. In order to minimize body roll on a car like this, you need to 1) look way ahead 2) be super smooth and 3) start your turn-in a little earlier and slow down the hands even more to facilitate the weight transfer. On a car like this, I would start my turn-in about 1/2 car's length earlier, but move my hand just enough (like 2 degrees) to start the weight transfer but not necessarily turn-in, this will initiate the body roll, you'll feel the outside suspension set right at where you want to turn in, then continue to feed more steering input as you negotiate the turn. The slowed down turning transition will result in a much less noticeable roll.

paradocs98 wrote

Good thoughts--I had the car inspected at a good shop here on Long Island a couple of days ago for an upcoming PCA event at NJMP. The Dinan suspension kit changes the front anti-roll bar only; the rear is left stock. The shop checked the stock rear bar and found nothing loose. They did comment, however, that the stock front and rear anti-roll bars are pretty puny and a potential weak point performance-wise. They also speculate that in Dinan's method of upgrading the front bar without touching the rear bar, some rear-end instability on track might be brought to the surface. In any case, they've done a lot of work on E46 and E90/92 M3s, specifically for upgrades and track prep. They also mentioned that upgrading the rear bar is a real undertaking because the rear subframe has to be accessed, making it a 6-7 hour job...

Where are you feeling this at LRP anyway? I am trying to think where one would feel this so much at LRP, especially compared to other 'sharper' tracks. The only thing I can think of is Big Bend on the turn in to The Esses where you pinch it a bit to get to the apex.

The HACK wrote

Actually...

Adding more rear bar may take away some grip to the rear thus resulting in more rear instability. It's weird, I know.

The charming part of having a MacPherson strut up front and multi-link set-up rear is that, the MacPherson struts behavior is unpredictable due to its simple design. Meaning the camber curve is not linear, and once you go past roll center you start to lose camber instead of gain it. So the old adage that adding thicker roll-bars will increase the propensity for that end to lose grip first isn't always true...Especially on a car that has the same suspension geometry as most typical BMW (the new 5 series is the first BMW to ditch the MacStrut). A stiffer front bar may work to prevent the outside front of the car from compressing past the roll center thus promoting more grip up front, especially a stiff front bar in combination with a lot of camber (i.e. Dinan's fixed camber plate) and/or stiff suspension.

In all honesty, I would suggest CHANGING DRIVING STYLE to match the weight of the car would be the quickest and best way to cure understeer. Despite BMW's best attempts to thumb their noses at Physics, there's just no way around it...Not when they have to make a 3,600+ lbs car behave the way it does and still be a comfortable street car. In order to minimize body roll on a car like this, you need to 1) look way ahead 2) be super smooth and 3) start your turn-in a little earlier and slow down the hands even more to facilitate the weight transfer. On a car like this, I would start my turn-in about 1/2 car's length earlier, but move my hand just enough (like 2 degrees) to start the weight transfer but not necessarily turn-in, this will initiate the body roll, you'll feel the outside suspension set right at where you want to turn in, then continue to feed more steering input as you negotiate the turn. The slowed down turning transition will result in a much less noticeable roll.

Good info. Thanks.

LiM3y wrote

Where are you feeling this at LRP anyway? I am trying to think where one would feel this so much at LRP, especially compared to other 'sharper' tracks. The only thing I can think of is Big Bend on the turn in to The Esses where you pinch it a bit to get to the apex.

I was feeling the rear-end wiggle under heavy braking at the end of the front straight coming into turn 1. But, again, this is better now that I'm gaining experience and smoothing things out a bit.

I feel the weight transfer/body roll in the transition from turn 2 to 3 as you cut across the track, and then in the transition from turn 3 to 4. I know to hold the left side of the track coming out of turn 3 to setup for turn 4, but you still feel that weight shift.

paradocs98 wrote

I was feeling the rear-end wiggle under heavy braking at the end of the front straight coming into turn 1. But, again, this is better now that I'm gaining experience and smoothing things out a bit.

I feel the weight transfer/body roll in the transition from turn 2 to 3 as you cut across the track, and then in the transition from turn 3 to 4. I know to hold the left side of the track coming out of turn 3 to setup for turn 4, but you still feel that weight shift.

I am hoping Lucid will chime in here as he has more experience.