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  • #16
    Steve. You must be pretty good at handling a loose car.
    Your problem is the opposite of Uwe's.
    If you bias more towards camber negative in the rear, the car tends to understeer more. If the car is too twitchy for your taste, you'll need more neg camber in the rear.
    If your hillclimb venues are tight'n'twisty your current set up may be advantageous...as long as you're comfy with it.
    At a more open venue with highspeed corners, the car may be too twitchy to maintain a high cornering speed.
    m

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    • #17
      Sorry i've just re-read this and realise i'm with Uwe - hotter inside.
      Steve
      Scottish Cecotto

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      • #18
        No problem.
        So if your temps are biased towards hotter insides 3-4 degrees F is pretty good actually.
        m

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        • #19
          3 to 4 degrees centrigrade across the tread.

          The front's are also usually hotter on the outside, but usually by only 1 to 2 degrees C.
          Steve
          Scottish Cecotto

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          • #20
            I am not talking of 3-4 F difference. I am talking about hot and COLD. Cold like not beeing driven at all.


            Goodbye M3, you served me well.

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            • #21
              Steve,
              centigrade is not as good, but trend is still normal.
              m

              Uwe.
              should not the inside (unloaded during your laps) be cooler than the outside(loaded)?
              since you do alot of trackdays a non contact infra red thermometer would be useful as an aid to adjusting tyre pressures and seeing what deficiency the suspension may or may not have at 8-10/10ths driving. You can also use it to diagnose engine problems, isolate wheel bearing failures and brake problems.
              just a suggestion.
              m

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              • #22
                Probably not a bad idea Mark.
                I have a lot of wheelspin round this tight bends. Grip isn't good either. If I can't sort it soon I will revert everything back to stock.
                Last edited by UweM3; 03-21-2005, 03:42 AM.


                Goodbye M3, you served me well.

                Comment


                • #23
                  Mark, going back a bit - you say more negative camber at the rear will tend to make the car understeer more?
                  Steve
                  Scottish Cecotto

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                  • #24
                    Steve,
                    More negative camber within reason, would mean more understeer . As the rear rolls you get some camber going towards positive which effectively enhances the contact patch of the tire which gives you more grip at the rear.
                    Toe in at the rear also adds stability as the wheels point towards each other and cancel each other out.
                    Toe out at the rear makes the car very unstable and adds rear steer.
                    The relationship between camber, caster and toe makes it difficult to adjust the car as changing one value makes the others change as well.


                    Same principle at the front but the effects of caster when you turn the front wheels adds more negative camber at the outside front and more positive camber at the inside front



                    Uwe,
                    Is the limited slip working ok?
                    m

                    Comment


                    • #25
                      yep Diff is working. I have jacked the car up with one rear wheel on the ground. Could feel the diff holding the wheel while spinning it by hand. Did both sides to be sure, but no difference.

                      Maybe my tyres are just shod. They are due to be replaced anyway because of the worn inside edge.
                      Last edited by UweM3; 03-21-2005, 08:38 AM.


                      Goodbye M3, you served me well.

                      Comment


                      • #26
                        Cheers for the info - I assume this is why Gustave is working on his fancy multi-ajustable trailing arm design.

                        Are there any simple first-steps in improving the rear geometry? I am planning fitting some uprated ARBs both fron and back (Either Eibach or Ireland Engineering) before the start of this seasons hillclmibs (17th April).
                        Steve
                        Scottish Cecotto

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                        • #27
                          Steve.
                          The anti roll bar enhancement is arguably a way to effectively raise your spring rate under lateral load, but very little under longitudinal force, plus it comes into play late in the movement of the suspension. What they really do well is combat the positive camber that the Macpherson struts adds to the suspension when it is faced with body roll.
                          What they Don't do well is they tend to negate your independent suspension, by hooking each side to the other. So with large bars, a bump affecting the right hand front suspension also affects the left hand side.
                          Swaybars may then be les effective at bumpy crowned venues.

                          Changing the rear geometry depends on:
                          1, what is out of balance with the handling.
                          2, Rules and regs for the class and sanctioning body you compete in.
                          You probably do need more user adjustability of camber at both ends. You should work with both ends so that you can keep close tabs on the handling balance(front Vs. rear grip) of the car.
                          Without redesigning the rear suspension, there are bushes with eccentric adjusters that you use in the trailing arm mounts on the subframe to adjust camber, but once the car is capable of any kind of 1G plus grip, I don't believe they maintain adjustment.
                          Next upgrade up is similar, but the mounting tabs on the subframe (usually the inner tabs) are replaced with tabs of a different dimension. There will be no slippage of the bushes this way.
                          It depends then on what your regs say, then, .


                          I would definitely start on achieving more negative camber on the the front.
                          Start with an adjustable balance of grip biased to the front suspension
                          1, Offset M3 front upper strut bushes in combination with a fixed offset camber plate which would net you 1/2 deg neg for the bush and 1/2 to 1.5 degrees depending on the choice of plate
                          2, Offset bushes and an adjustable camber plate compatible with standard dimension springs eg Ireland engineering street camber plates. same range of camber as 1, but you can dial back for street duty.
                          3, Race type camber plates with more adjustment but work with 60mm diameter springs.
                          Once you get over the initial expense of 60mm springs on threaded ajustable spring perches, then a whole new avenue of adjustment is yours...height, corner weighting, all favouring the search for lower Cof G and roll couple.

                          m

                          Comment


                          • #28
                            Mark, thanks for the lesson!

                            I already have the factory front offset mounts. I think off the top of my head, they give me around 3/4 degrees negative? It is a road car (and my everyday one at that) so I'm not really prepared to go any further here to keep tyres lasting a bit! This slight increase in neg camber did improve turn-in a bit, but nothing dramatic.
                            I'm running with Bilstein/Eibach dmapers and springs which again are an ok compromise for a road car.

                            The main reason I'm heading along the route of anti-roll bars is due to the excessive body roll I now get since fitting R compound tyres. This roll seems to have nade the understeer worse. And it's hard to break the back loose (to try and counter the understeer) with a standard power engine and R compound tyres.

                            As my long term plan for the competition is to build a road-legal M5v8 engined M3 I don't really want to get down the modding route on my Cecotto (unless it is things I can remove again for the track machine).

                            The rules we run to are very loose - pretty much anything goes so long as it's road-legal and has a current MOT test (The UK annual test for all cars over 3 years old). The engine must remain in the same place and driving the same axle(s) but can be any type you want. As I'm competing against 4x4 Scoobies and Mitsu EVOs I've got a real power deficiancy on my hands! 4 out of the 5 guys usually in front of me run 360 - 400hp 4x4 machines so I will always be struggling. The rules will be changed soon to put the 4 wheel drive cars in their own class, but only if enough of them turn up.

                            So it looks like the rear camber mods are not on the cards - With R compound tyres, I may be closing in on the 1G level (probably more like 0.8 at the moment) so the bolt-in eccentric mounts probably aren't worht the effort.
                            As I don't really want to drop my subframe at the moment, the weld-in brackets are probably also out.

                            So maybe I just have to live with it and learn to drive better! I am very tempted to find one of the race schools that will let you use your own car - that way I can get an instructor to show me other options as to how to improve my times. I just can't get the hairpins!!!
                            Steve
                            Scottish Cecotto

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                            • #29
                              As my long term plan for the competition is to build a road-legal M5v8 engined M3
                              Wow! Now that's going to be a monster!

                              Of course, no-one here on s14 will want to know about it :-P

                              Fox
                              ---
                              (except me of course)

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                              • #30
                                Fox - just think of it as two S14's squeezed in there - maybe they won't notice!
                                Steve
                                Scottish Cecotto

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