Quote:
Originally Posted by jannisa
Wow Bill, you leave us all with a load of homework.
A few points for discussion:
- Toeing out at the front under load while cornering (the reason you suggest switching to the stiffer M3 struts) is beneficial in turn in feel so I believe there must be another reason to get the m3 struts. Perhaps they give space to lower front camber however only in conjunction with strut pin removal which alone results in a decrease at -1 degree. I 'm eagerly awaiting your feedback on the struts. If they don't decrease it further I don't see the point in switching them at least on paper before listening to your feedback.
- I would refrain from maxing down rear camber as this would produce huge amount of ''static'' grip at the back thus exposing the small limit of front camber/grip and will result in understeer. Most importantly if you run -2 degrees at the back losing traction sideways is on/off and your tail will feel like a hammer. Combined with the zero toe you won't have the trend to bring the tail back on track once loose.
- A stiffer rear arb will not decrease understeer, it will increase oversteer, this is partly the same, it's the who-comes-first game. I 'm mentioning it because the h&r arb are rear adjustable.
- I was under the impression that the rear bushings/joints had mostly vertical play and role and would not affect toe when under load.
Personally I run the eibachs and h&r sways (middle position rear) on adaptive suspension with 1mm toe in each side at the front, -1.60 rear camber and 2mm toe in each side rear. Next step will be to remove the strut pins but so far I experience close to zero understeer provided I don't slam it into the corner and a very friendly/progressive behavior once the tail looses traction.
Again I 'm looking forward to your feedback through each stage you 're taking and once more thanks for pioneering this stuff.
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janissa,
sorry for the delayed response... been a bit swamped the past week.
Having the front toe deflect under load may seem beneficial to turn in but if you're tracking the car heavily the least amount of bushing deflection the better. Bushings don't always deflect in repeatable ways which makes dialing in the optimal settings just that much more difficult. Most purpose built track cars will opt for solid mounts for this very reason, but it would feel horrible on the street. The M3 tension strut upgrade is a very good compromise. There is no other reason to get the M3 tension struts as all other dimensions are exactly the same as the stock component. The M3 lower wishbones would have a slight increase in negative camber for the front, but they currently won't mount up due to the difference in the headlight leveling assembly (although I have a possible solution in the works for this). One other thing worth mentioning on the tension struts is that they will cause more road vibrations to be transferred to the steering wheel which is a nice added bonus.
Believe it or not rear camber is far from maxed... -2 degrees is actually below the factory spec (even though I'm not tuning to factory specs they're still worth keeping in mind). -2.5 didn't produce any snap over steer on the track but I think that a little more front camber is needed (somewhere in the -1 range). It's also a bit early to come to any conclusions on specific alignment settings as various components are still in the process of being upgraded. Once I have everything fully installed and tested I will then start working to optimize the alignment settings.
Good point on the rear sway bar. You are correct in that it will increase over steer (or help correct under steer) rather than decrease under steer. I'll be going with the H&R bar also at some point but want to get several other components sorted first.
The rear bushings will have deflection opposite whatever direction force is applied to them. The rear trailing arm bushings will have the biggest effect on toe as that is the toe adjustment point in the rear. This is why I chose to use the bushing limiters. The deflection reduction and impact to ride quality by going to a tie-rod end on the camber arm probably isn't noticeable, but I prefer solid mounts where possible.
The biggest overall change will come from swapping out the dampers and springs for coilovers, but that's a whole separate post that I'll have to type up later.
Bill