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

Would that require an alignment?

I hope the answer is no, but since it would be an inconvenience, I bet it's yes.

Thanks in advance.

Swaybars have no effect on the position or alignment of the tires. So no

See. Life is not that bad.
Try to stay positive :D

Interesting that you only want to change the rear sway bar. Replace with the same bar or upgrade to a larger bar? Would you be willing to comment or explain?

This is the frugal track rat's hot tip. Leave the front alone and just add a M030 rear bar. Removes understeer and allows the car to rotate more easily. This is my brother's setup and he is giving me serious heat right now in the PCA TT series. My car has fully adjustable sways and our lap times are nearly identical. I have driven his car at SOW and Buttonwillow... pretty sweet!

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.

Why? We're all gonna' die in the end!
:D

First, thanks to all for your help and interesting comments.

Th, I have the M030 springs and shocks, but I've only got a couple of spare hours tomorrow, so I wanted to see if I could do the sway bar alone. And it's a larger bar, 19.6mm.
The rest maybe next weekend.

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.

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. :cheers:

Interesting comments about the rear sway bar. I recently discovered the same thing on my 987 when I fitted a slightly stiffer rear bar from the original. The rear is now more "alive" and its possible to alter the "turn in" mid corner using the throttle which was not possible previously. This may be great for track but on the road it can also make for a few hairy moments on twisty roads, particularly if pressing on and the surface becomes less grippy. Boxsters are a handfull to control if the rear does get away from you.