If I only changed the rear sway bar ....

[Topless]

Originally Posted by LAP1DOUG

Personally I think this falls under the category of "unsticking" the end that is working well in order to achieve balance, which Carroll Smith taught us is not the best approach.

To me this seems like a particularly bad approach on a McPherson strut design with an open diff. The stiffer rear bar transfers more weight in the rear, which unloads the inside rear and wastes torque coming off a turn.

The front end on any Boxster (986 or 987) clearly does not have enough camber for maximum performance even at the maximum adjustment, and the inherently poor camber curves in roll with a McStrut design makes this even worse.

I believe that a slightly stiffer front bar is the best low cost remedy in order to limit front roll which would otherwise cause positive camber in this design. This will make the front end stick better rather than unsticking the rear. Caution though: it is a delicate balance - if you go stiffer than the minimum needed to tame the camber gain in roll, then you will cause more understeer, rather than less.

Ultimately you really need camber plates or GT3 arms to make these things work right.

Doug, I did this exact mental engineering analysis in 2009 and added a GT3 front bar. Result: the car had worse understeer even at full soft and lap times were higher. I added a Tarret rear bar and took in 1 adjustment hole and now I could rotate the car and get on the gas sooner. Lap times fell. When faced with theoretical physics vs lower lap times, I always go with faster laps. GT3 arms and camber plates might be nice but not legal in BSX class cars so they were not an option.

My brother went the budget method: "If you can turn the car with your right foot you don't need a freaking steering wheel". He added a M030 rear bar, understeer went away, the car rotated easily, and turned faster laps.

You point about wheel spin in an open diff car is valid though. I think there are a lot of BSR cars running around with too much rear spring and sway, and corner exit suffers from wheel spin. When they cry for an LSD they simply need to soften the rear of the car. Everything in racing is a tradeoff but once you have solved understeer problems, getting power down early is important.

[LAP1DOUG]

Originally Posted by Topless

Doug, I did this exact mental engineering analysis in 2009 and added a GT3 front bar. Result: the car had worse understeer even at full soft and lap times were higher. I added a Tarret rear bar and took in 1 adjustment hole and now I could rotate the car and get on the gas sooner. Lap times fell. When faced with theoretical physics vs lower lap times, I always go with faster laps. GT3 arms and camber plates might be nice but not legal in BSX class cars so they were not an option.

My brother went the budget method: "If you can turn the car with your right foot you don't need a freaking steering wheel". He added a M030 rear bar, understeer went away, the car rotated easily, and turned faster laps.

You point about wheel spin in an open diff car is valid though. I think there are a lot of BSR cars running around with too much rear spring and sway, and corner exit suffers from wheel spin. When they cry for an LSD they simply need to soften the rear of the car. Everything in racing is a tradeoff but once you have solved understeer problems, getting power down early is important.

Topless: I certainly agree with you and your bro on the throttle steering thing. It is the fast way that works well when you get the balance just right.

However, I have had a very different experience with my set-up evolution, probably due to the many variables involved. It really is a rather narrow window to hit, which is why I always try to do suspension changes on an auto-x course before taking it to a race track. It is very easy to overstep a handling tweak and get bitten in the behind.

Anyway, I first started my improvements by going with wider front tires. I did coilovers with the GT3 front sway bar all at the same time, so it probably is impossible to compare set-up results. I do know that if I go too hard on the front bar, understeer comes back, but not enough front bar also yields more understeer. My M3 is also a McStrut design and acts the same way to bar changes.

At this point, I have migrated to a set-up that uses no rear bar at all, and I generally take FTD at PCA autocrosses, but can't quite beat the 'vettes in SCCA with all that tire they can fit under there.

[Topless]

When no one has ever driven a similarly equipped Boxster with a faster lap than you around nearby race tracks, the car balance sweet spot is very near.