Pedro

In my case, I´m not going to invest any more in suspension parts until at least next year or until I think I´ve reached the limit of my current parts, which I´ve just started to try, so when I ask about the height versus weight preferences, I am obviously willing to go for a compromise. About the technical talk, I can sometimes struggle a bit and have to read the same post a few times to make sense of it, even then sometimes I am unable to until a second or third explanation, mainly because I can compute a new concept surrounded by a sentence I understand the meaning of, but a sentence with 4 or 5 new concepts is pretty slow reading for me, sometimes not because of the most demanding technical terms, but also the simple concepts that I never dealt with when thinking in Portuguese. It´s a learning process, and I find this good reading because it´s challenging and I´m actually learning. Would love a simple reply with clear instructions of how that get me the perfect setup for my driving, but this is the second best thing :rolleyes_anim:

I had never heard of this Dynamic Index until I read those threads, seems it quantifies the responsiveness or handling of a car by considerating weight distribution, placement, and the actual chassis size, clever stuff, as most of what I find here is. However, appart from being able to say my car as a certain DI, and therefore being able to look into a clear number that tells me if it´s good or not, thus having a clear means of comparing different cars, I can't seem to be able to find a use for this index when tuning a car´s chassis, not if I´m not willing to alter wheel positioning and basic axle length or wheel distance. Wouldn´t it be much simpler if, for limited tuning purposes, instead of discussing DI one discussed simple weight distribution, as including this in a more complex equation will only dilute it´s importance amongst other factors that we are unable to change? What I think I got, though, is that a 50/50 weight distribution, in theory, makes for a more controlable and rewarding responsiveness, so maybe that´s the direction I should point it, regardless of the current distribution I should tweak the front and rear ride heights, within reason, to direct weight distribution into a 50/50 direction, without consideration of the current perceived handling deffects, and then assess the "damage"? My problem is that I´m having this done as a favour and don´t want to abuse my welcome by spending a few afternoons doing several adjustments after a trial and error work process, limited I know, but it almost always is. What I was asking about is if I should try and give it a front or rear bias to counteract my handling problems, instead of heading towards 50/50. Obviously teaking ride height to affect weight placement has it´s obvious limits and affects suspension work in a way other than weight balance, thus maybe the side effects of displacing weight this way might even do more harm than good, no? Another question, in theory is it better to have a slight ride height difference between two wheels of the same axle and an equal weight load on both, or the same exact ride height but a different weight load?

I have a few doubts about weight distribution. Before I changed a thing on the car it went for an MOT, a quick glance at the brake testing area screen told me the weight for each axle, 712kg on the front and 621Kg on the rear, that´s with little more than half a fuel tank, and a driver weighting about 10kg less than me. Since then I´ve replaced front seats for racing buckets, fitted a lightweight cage, moved the battery to the boot, and will remove sound stuff and rear seats before taking it to be cornerweighted, haven´t got a clue how the overall weight is now, but I'm more worried about balance than overall lightness, I could loose a good few pounds myself The guy that is doing me a favour of letting me use his garage and his skill as a favour to my brother is a racing mechanic, they race all kinds of categories, from rally to classic barchettas, he probably knows a bit about this. I will probably give him some input of how I think the car drives now and let him do his thing, but would still like to get some concepts right. We´re going to adjust ride height on each wheel to try and balance things out on the scales, will try and not lower it too much from a "stock" look though, as I don´t want this car to stand out at all from other road users. Right now, if I had to take a guess I´ld say there´s too much weight on the rear, simply because when the mass is stable and weight transfer is over, once midcorner, if I push it then, the front wheels feel like they´re not as "loaded" as the rear ones, they tend to scrub the ground while the rear ones have a lot of traction and feel very planted. My doubts are this: With a front bias weight distribution will the front be more or less planted going into corners when comparing to 50/50, will the car tend to oversteer or underteer on big roundabout with slowly increasing speed and no harsh accelerating or braking inputs? On the other hand, if I have a weight distribution weight with a rear bias, wouldn't the car tend to easily go into oversteer once lifting off? I'd have thought that a bigger mass on the rear would cause a lot of rear momentum when lifting off midcorner as well as providing more traction when under load from the engine? Sould I aim for a 50/50 weight distribution, if possible, and disregard considerations of how the car feels now or should I try and I know a lot of other variables affect this, but lets only consider weight distribution changes from ride height adjustments for now. Can´t thank you enough for your help Toni, really learning new stuff here, if you decide to visit the Nurburgring this August, or northern Portugal, I´d like to buy you a few beers.

I get it, so you´re talking about increasing castor as a means of putting the front wheels a little further from the center of gravity, lowering the pitch axle and reducing the amount of change in weight coming off the rear wheels as the weight shifts to the front? Or did I miss it completely? The front wheels in that picture, well, the outer wheel seems to be with positive camber when pushed that far, maybe when under maximum load it should stay perfectly vertical, or at least pushing the tyre surface flat on the ground instead of twisting the inner edge of the tyre off the ground, if there is no tyre flex it should have 0º camber at that moment the picture was taken if that is maximum load? When stopped, camber is almost non existing?

This is precious stuff, you´re a star Let me see if I got it. On a corner to the right, the front left wheel is the most important, so having a higher castor will make this wheel's footprint move outwards away from the car during that corner, basicly increasing that wheel´s leverage over the forces it needs to handle (same grip by the tyre itself but more leverage on the car's body), also it´ll help the opposite rear wheel, the rear right wheel, retain some weight on it. I might have gotten it completely wrong, I´ll have to digest it over the afternoon and give it some more thought tonight. In any case, my castor angle isn´t adjustable, I know I´ve now got more than when stock, but can´t increase it now. What I am having some trouble visualizing is this: "Point to remember during weight transfer "corner entry" the steering action transports the front camber values so you cannot have aggressive front static camber positions since they are affected so violently dynamically" What are you saying that the steering action does with the camber angle? And what is the problem with agressive camber angle? Sorry, this is really very interesting but I still lack a lot of understanding.

First of all, thanks, that was exactly the kind of advice I was hoping for, very cool stuff, as I´m really starting to get interested in this, I´ll need a little help processing it though, as I simply don´t know if I got the meaning right. First time I read it I simply looked like this: So a rear camber deeper than the front will provide stability on the straights, will this help eliminate some weaving, or floating, of the rear at high speed strong braking on straights? In what way does front camber provide aerodymic gains? You lost me here , is this as you´re lifting off and turning in, the first moments the car starts to change direction? You´re saying that a higher castor would increase front wheel limits at the moment the outer portion of the tyres are loaded during cornering. So by increasing castor I´d get a better steering feedback about the front axle´s limits as well as more grip?

Would you start by having the rear wheels with more camber than the front ones? How so? Is castor the same as caster? Sorry, english isn´t my first language. Thanks !

Well, after browsing through a few threads, I think I can´t find an answer for this from someone else´s question, not sure if I should post this in the project section, but anyway, here it is, my "problem" with my car´s handling! I've got a BMW Compact, it´s a 1997 318ti, with stock engine, so fairly underpowered at just 140hp, not sure how much it weights since I haven´t gotten the chance to put it on cornerweights yet, it´ll happen soon enough I hope. This car was fitted with a welded in rollcage, with no crosses or anything, just to improve structural rigidity in case of a nasty crash at speed, but also had a rear strut bar welded between the struts, and saw the front of the car reinforced with a Sparco top strut bar, as well as a BMW cross brace that fits under the engine. Here are some pics Rear strut bar: Front upper strut bar: Front lower cross brace: I replaced the normal seats with Sparco racing ones, and moved the battery to the boot, that´s how far I went with lightening it, or relocating weight. The rear seats, however, will be removed when used on track, and as such when it get on the weighting scales, those will not be in the car. That´s so that I can use the racing seatbelts, wrapped round the rear strut bar. Regarding suspension, I changed all bushings except the anti sway bar ones, for 75D urethane ones, the rear bushings have an adjusting capability that allows me to adjust both camber and toe, although not individually nor very easily. For example, if I want to increase rear camber by 0.5º I will surely affect toe. This car has got a rear trailing arm suspension and the only way to adjust angles is to fit these bushes, or fit adjustment plates, I feel I should have fit the plates, but was in a hurry and didn´t feel like welding stuff there. It´s important to have rear wheel adjustment here because it varies a lot with height adjustments, and since I´ve got height adjustment ability ... This is better explained in this article, if anyone feeling like a read: http://www.e30m3performance.com/tech_artic...sh/ecc_bush.htm Fitted a KW Clubsport coil-over kit, with front and rear adjustable shock absorbers as well as ride height, and front camber plates. I´ve got a thread over on FastClassics where I describe the entire thing, loads of crap talk and brainstorming as well, but it´s there, if you feel like going through it all: http://www.fastclassics.co.uk/phpBB3/viewt...?f=2&t=1168 After all this word being done a new set of Bridgestone RE050A tyres were fitted, and the thing was aligned, as you can imagine what chaos it was after being completely torn appart. I usually use high pressures, as I really hate feeling the tyres start to bend, so for now I´ve got 2.5 Bar pressure on all four tyres. I am trying to get it sorted without resorting to messing with tyre pressures, until I need to. I feel like it´s sort of cutting corners if I start with tyre pressures without trying to solve things by adjusting the suspension first. As an aside comment, it left me mad that the mechanic at the shop where I bought the tyres declared it a lost battle from the start when he saw the rear bushings, after an hour of going nowhere I brought the car home and have since had it adjusted twice by my local mechanic, using a used machine, with both of us contributing, things take a lot less time and go a lot better when one just feels like doing something and helping. After it´s second alignment, it´s now more or less like this: Front Wheels: Camber between 1.41º and 1.42º Toe In = 0º Caster: 3.38º on the left and 4.05º on the right Rear Wheels: Camber: 1.44º on the left and 1.42º on the right Toe In: 0.11º on each wheel The front caster is a bit wonky because it´s got excentric bushings, like the M3 ones, and I guess one might be slightly rotated in relation to the other, but I feel it´s OK, don´t you? I really don´t feel like taking the arm off to rotate the bushing. This was the second alignment, on the first one the car was set up pretty much to factory specs, with 2.00º rear camber and 1.40º on the front. I wasnt impressed with this at all, and felt that it would ruin my tyres without actually helping handling at all. Now to the question at hand, the shocks were assembled with the reccomended adjustments, meaning they´re set right at the middle of the setup, both bound and rebound on the front, and the rear at 75% stiff bound, and 12 clicks from fully closed rebound, there's 19 clicks to go. Torsion bars are stock ones. Thing is, car didn´t feel balanced, it felt like the front was not holding the road properly, you´d enter a corner, either fast or slow, bumpy or smooth, and it´d understeer, the car was never balanced even before loosing grip, the front always felt like a step ahead of the car when loosing grip. You´ld settle into a tight long corner at, say, 85kmh, like a motorway entrance, at the limit of grip the front wheels would skid, at this point if I tighten the steering wheel it´ll have no effect, same as if if I let go of the accelerator it´ll have very little effect on the overall balance. On fast bumpy motorway like situations, at 190kmh, it´ld feel the same, understeery. On low speed smooth roundabouts it felt like crap, the front would plow ahead while the rear would have supreme traction. I could throw the car sideways into a roundabout and after half a second it´d be understeering. At first I messed with tyre pressures as I imagined that since the tyres were new they might not be scrubbed in yet, lowered pressure on all 4 wheels to about 2.2bar, all that changed was that now I could feel the wheels bending, the exactly the same would happen, only delayed by tyre bending. Returned to the higher tyre pressures. Oh, forgot to say I´m using 225/50ZR16 tyres on 7.5 rims It´s important to say that before any work had been done to it, the balance on roundabouts was perfect, it had worn tyres, good ones though, and a standard m-technic suspension with mushy bushings, felt a bit wavy at high speed but slow speed and balance was very good. Decided to mess with the front shocks to see if a little more softness would help. Softened it all up, both bound and rebound were turned to 2 clicks away from full soft, this is next to as soft as possible. After a couple of frustrated attempts, because of traffic, I finaly got a moment with low traffic and was happy to see it had a positive effect. On the same corner, at the same speed, the front wheels don´t feel so loose, they will still understeer if I turn the steering in at that point, but when lifting off at that same point one can now feel the front wheels digging into the ground, and the rear livening up, as it should. Car is now overall better balanced. I got the same feeling on another corner, this one downhill, but since I didn´t have a clear memory of how it was there before, decided to discard it. Haven´t got a chance to test it at speed yet, as the weather´s been wet at night. I´m trying to make this as scientific as possible, approaching the same simple corner at the same speed at checking for changes. I still think the car should hold the road better, and should feel more meutral, but it´s a work in progress. Going to use the conerweights of a rally team, but they´re a bit busy lately, on account of races that involve a bit of logistic, so currently waiting for my chance to use their equipment, as a special favour, this kind of equipment isn´t very available for street use here. This is as it stands now, any advice, opinion or suggestion is very appreciated. EDIT: Sorry, I went on a bit, didn´t I?