How to adjust tire pressure and anti roll bar settings?

Car: BMW 330i 4 dr sedan E46


Weight: 3280 lbs


Distribution: 50/50 front to rear





I have modified the car as follows:





Increased diameter of front and rear anti roll bars to 27 mm front and 24 mm rear (they are adjustable and both front and rear are set to full soft settings - least stiff)


I have added front and rear strut tower connector bars


I have added Bilstein Heavy Duty Gas shocks (automatically adjustable; no user adjustments)





Tires





I use stock sizes: 225/45/17 front and 245/40/17 rear Continental Sport Contact 2s


The manufacturer recommends the following pressures: 30 psi front and 35 psi rear


I am running 32 psi front and rear





Question:





I want handling that is as close to pure neutral as possible


There are 3 settings on the rear anti roll bar. Should I adjust the rear to the medium setting? What will be the most likely affect? If it's close to neutral now, will this push the car towards oversteer?|||Before you start trying to tune the suspension, there are two questions you need to answer:





1) are you in a position to really push the car to it's limits, both as a driver and as far as having a place where you can safely do that?





If you cannot actually take the car to it's handling limits, then making a statement of "it's neutral" or "oversteers" or anything any is mostly meaningless. But assuming you are in a situation to do that...





2) what are your goals? You say you want it neutral... but keep in mind neutral isn't a constant. A car that is neutral at one speed will understeer at another and oversteer at a different speed (and different situations), so what behavior are you really trying to get from the car? What is the current problem?





When you have those two items in line... first your start with the alignment. The initial balance of the car and it's turn-in will start by being set with a correct corner balancing and an appropriate alignment (and if you are tuning for performance, that will not be factory settings).





Once you have that, then it's on to getting the tires to work (and maybe revisit that alignment too after you've had the pyrometer on the tires). But once you have the suspension setup maximized for the tires, then it's following that same setup to get your hot pressures.





Then after all of that, you get to the ARBs... take a couple laps with them both at full soft, and then a couple with them both at full hard just to get the feel. Then you start adjusting for how the car feels... and then repeat to take into account the new ARB settings if needed.





It doesn't sound like you have a lot of adjustability... in the end the only way to find out how much it will change the car is to do it and see how the balance is affected (if too much, then you can add some to the front to balance it out... assuming you have more adjustability there).|||Use the air pressure recommended by the auto menufacturer instead ot the tire manufacturer. They(the tire manufacturer) know if these tires are going on a Beemer or a Ford pickup truck hauling loads of wet bull crap, or on a MiniAustin carrying 1 skinny person. There is a difference in weight between each vehicle, and that is what the air is holding up....weight.





As for the rest of it, I do not know why you would mess around with manufacturers specs...as it was neutral.


But now you got what you got- - - the unknown|||Anti roll bars will not change your cars front to back weight proportions. They will only change the amount of body roll on corners. BMW has a great research and engineering team so I would stay with the recommended tire pressures they list in your owners manual. If you are serious about a true 50/50 distribution you will need to find a speed shop to set your car up on scales with you in it. Then you will see the actual weight at each corner and then can start moving components and or weight blocks around. Are you racing at a track?|||1. Go back to the recommended inflation pressures first of all. BMW knows more than you do about what works best. Running them under-inflated like you are now on the rear is extremely bad.





2. Are you racing this car? Because on a street-driven BMW it is extremely difficult to do better than what BMW provide right out of the factory.





3. If you go too stiff too quickly on the rear bar you will induce roll oversteer (which is bad). I probably would have not bothered replacing the rear bar at all and gone with a stiffer front bar - but not too stiff as too much roll stiffness on the front causes BMW's to lift the inside front tire.





Really you should be addressing this to a BMW forum, of which there should be at least a few hundred on the interweb.|||Wish we knew if you plan to drive the car in the Winter and if you get any snow or ice. If you drive where it snows, you want both anti-roll bars set in their softest position. If you adjust the rear bar so as it make it stiffer, the rear end of the car will get "loose" (oversteer) on snow and ice during cornering procedures..





As for your present weight distribution (50/50) front to rear or so you say, no way in heck can that be true! A front engine 4-door sedan If that were the case both of the anti-roll bars would be the same diameter.