I am trying to decide if I should go with the spring rates that come with the PSS9 coilovers or to go with the spring rates that the Spec Racing Boxsters use. The ones that come with the PSS9 are 260 lbs front and 370 lbs rear. The Spec springs are 450 lbs front and 500 lbs rear. Keep in mind that it is a mid engine car. Any opinions will be apprreciated. I am leaning toward the higher rate springs.

Higher is better, unless the shocks can't handle the spring rate. You also have to decide whether or not you want the heavier spring rates for street driving. Me, I would go stiffer and live with it over speed bumps, through drainage culverts and all that. The CSP car was a daily driver for a while, and it did get a little annoying after a while, but worth it once you hit the course.

Thanks Dave. Yes, the shocks will handle the spring rates because the BSR spec racing Boxsters all use these shocks and these spring rates.

In that case, I would go with the stiff setup, for glory on-track!

Properly valved shocks and really stiff springs do not ride bad on the street. 500# and 1100# for me and the ride is comfortable and much better with a monotube shock.

+1 The rates you're quoting Dave M, are not that stiff, especially if you can adjust the low-speed compression for around town. Lotus "Sport Pack" Bilsteins have such nasty high-speed compression, I would rather drive around with 2X the spring rate and my Penskes than those suckers.

Spring rates as a stand alone value do not tell the whole story. The spring performance depends on the rate, motion ratio, corner weight, sway bars and shocks. A good starting point is to make the effective spring rate (taking into account motion ratio) equal to the corner weight. There are many articles on motion ratio measurement.
An important decision point is how much of the lateral motion is controlled by the springs versus the sway bar.
Its not easy to arrive at the best compromise of all the variables.
Good luck.
Alan

I'll finally have adjustable shocks with 9 adjustments but they are single adjustable style of shocks so compression and rebound will both change at the same time. The shocks are the monotube design so I guess that is good.

All of this complication is why I decided to go with the same setup the spec racer Boxsters are using including the same front and rear sway bars, same shocks and same springs. I will have strut tower braces too. That way I am not starting from nowhere and spending time and money trying to find what works and what doesn't. I have seen these BSR cars at PCA autocrosses and they will do quite well . I am ready to order the suspension now and I will sort out the wheel sizes at a later date. I have 3 sets of 18 inch wheels and a set of 18 inch R tires to use up and then I will think about buying some other wheels and probably selling1 or 2 sets of the 18 inch wheels.

How much less do "spec boxster" cars weigh?
I've seen one being built and it was totally gutted..

I tried to get into the motion ratio and such with my car, but I lost interest once other things started taking a priority. The rates I run on my coilover setup are twice that of most off-the-shelf springs and with the Konis set to full stiff, it's actually not that bad. It's much better now that the car isn't my daily driver, but I just did a 4000 mile trip to Portland, OR and back. To me, the benefits outweigh the negatives. I'm sure if I spent more time and effort measuring, etc to to the math to get the theoretical ideal setup for my car, I could see an improvement both on course and everyday, but I don't see that happening.

Good point. They strip the interior out of them which I can't do and there are other changes they make . My car will not be exactly a spec boxster because I want to stay in street prepared class with it and spec boxsters are base boxsters anyway and not the S which I have, but I still feel it it the best starting place for me to copy the suspension they use . I have seen that they do well in autoxing and okay on the track.

How about tracking down the guy in California and see what his setup is? Maybe Jason can help get you in touch with the guy?

http://www.azsolo.com/forums/index.php?s=&...st&p=106116

Or post to SCCAForums in the Street Prepared section looking for other Boxster setups?

Good suggestions Kevin. I ordered a bunch of parts today but I have not ordered the shocks/springs yet. Choices are more limited than with a Miata and more expensive too. One can never do too much research on these things really.

I've been working on deciding on what I want to do with the Miata for a few months now. Your question alone doesn't provide enough to answer it. You need to know things like motion ratios, sprung and unsprung weights. That's just the start. Good luck with what ever you choose.

This is why I just want to copy a tried a true setup. For Miata's it seems like there should be tons of setup information so why would you have to figure it out on your own? Any class you want to build for a million other people have already built a Miata for that class. Just ask them and forget the motion ratios. I am going to use the spec Boxster springs to begin with and sort it out from there. I am going to follow Kevin's advice and see if anyone who frequents SCCA Forums has built a good BSP Boxster and wants to share their setup info.

Spec Boxster 450F 500R
Spec Miata 700F 325R
Spec E30 315F 570R

Ive often wondered where they get these numbers??

For the Miata, there happens to be a great website (miata.net) with TONS of information, and members from around the world, as well as dedicated and enthusiastic autocrossers. There are sections for pretty much any topic you could think of, including a Performance/Racing section that always has great info on setups. There is a "known formula" for what works on a Miata, though some care to go their own path, at times. I would hope there is something similar for the Boxster, but I think your direction is a good one. Find something that works for someone else and copy it! No sense in trying to "reinvent the wheel," so to speak, which would cost gobs of money, and could end up in an ill-handling car.

Anti-roll / sway bars also impact effective spring rate... adjustable bar(s) would allow you to fine-tune cornering balance should your f/r wheel/tire widths or alignment change. Higher rate anti-roll bars also minimize increase to ride harshness vs their contribution to increasing spring rates.

I will have a GT3 adjustable front sway bar and a matching adjustable rear sway bar on the car. I have not solicited any helpful information at SCCA Forums , so far no answers to my post there, and Street Prepared Boxsters are not really that plentiful but I have the general idea of what I want/need to do at this point . Some trial and error on the spring rates is probably unavoidable so I will start with the spec Boxster springs and see how it does with them. I wish the parts were as cheap as they are for Miata's.

I'm not sure of the driver's name, but there was a BSP Boxter at the El Toro event that looked pretty fast (from my corner worker position anyway).

This has to be the guy Jason Isley knows. I will post in the other thread and see if Jason can give me some contact information for this person. Still nothing helpful at SCCA Forums this morning.

Per the results link the El Toro thread going on in this forum right now, it is the same guy plus a co-driver (but results list a Boxster and a Cayman )

Some Googling around with his name and the sponsorship listed in the results (Lightcubes) and I come up with some possible contact info for him I'll send you the results of my stalking

He appears to autox with the San Diego club, not sure if they have a forum but that might be a good place to try or maybe if their is a results thread for El Toro on SCCAForums.

I also remembered the is a Boxster fourm called Boxster Petes


And Geren has a Boxster, he hasn't been out in a bit, but is he running stock? Might be worth a shot to shoot him a message.

That was actually a Cayman S. Carl Vandersomething was his name. Really nice guy...its a shame he was running BSP

The best Boxster forum is " The 986 Forum" . Of course now it is also 987's ( Boxster's and Cayman's) . I will have to find out if Carl has a Boxster or a Cayman. I am attempting to contact him using your good information. Thanks again. Geren's Boxster is Stock .

That's him alright. Too bad for me that he has a Cayman and not a 986 series Boxster but I will talk to him anyway and see what he is doing with the car.

How much different are they?

Honestly, I think he still has both ! He did mention that he was supposed to bring out a boxster but brought out the Cayman S instead...

Cayman S is built on the 987 platform while mine is the 986 platform. They are not hugely different but probably enough that the optimal spring rates would be different. I still want to talk to him and it sounds like he may have both cars. I got some answers at SCCA forums but nothing that is really very helpful.