Race suspension alignment

[993innc]

For some reason my searches seem to only bring up topics about stock suspension settings for guys wanting to run stock cars on track with a more aggressive alignment.

I am waiting to install H&R RSS coilovers and am looking for alignment specs for a track only, modified suspension car. Does anyone have that info? I'm a smooth but aggressive driver who doesn't like the rear of the car to pass the front. Looking for stability.

When I ran my 993 on track, the rule was get as much neg camber out of every corner. I'm reading here that Boxsters don't like a lot of negative camber......why?

TIA

[thstone]

Boxster's need and love negative camber just like any strut-based suspension! The stock set up maxes out at around -1deg camber in front but the car really needs much, much more.

A good starting point for a track-only setup is -3.0deg camber in front (where you go from there depends on driving technique, tire selection, tire temps, tire wear, etc.), maybe 0.5deg less camber in the rear, 1/16 toe (for stability, zero toe can feel "darty" but is generally faster), then add as much caster as you can get.

Of course, you'll need height adjustable coilovers, a set of GT-3 front adjustable lower control arms, adjustable front/rear drop links, and adjustable rear toe arms to reach this setup. Might as well throw in a set of sway bars while you're at it (GT-3 front, Tarett rear).

Have a race shop do the alignment and corner balance. You'll also need to keep an eye on air pressures to keep everything in balance.

This is a very good reference page: HELPFUL HINT: Porsche Boxster Suspension Setup - Stock, BSX, BSR - GSR Autosport Community

[993innc]

Hmm, ok thanks. Sounds like the 993 then. I don't know that i'll go all the way crazy, this is a DE car, but I am running slicks like I did on the 993, so the more camber the better :-)

[Topless]

Slicks for a DE car?? Whew, that's about $1600/weekend in tire expense! Yes, they will be in the sweet spot at neg 3 degrees.

[BYprodriver]

Originally Posted by Topless

Slicks for a DE car?? Whew, that's about $1600/weekend in tire expense! Yes, they will be in the sweet spot at neg 3 degrees.

Property tax is really low over there on the right coast.

[993innc]

Originally Posted by Topless

Slicks for a DE car?? Whew, that's about $1600/weekend in tire expense! Yes, they will be in the sweet spot at neg 3 degrees.

Yes slicks.....I drive FAST! I also buy them slightly used so more like $300 a set a weekend

Originally Posted by BYprodriver

Property tax is really low over there on the right coast.

Yup that's why I'm here. trying to get back to Topless's neck of the woods! One day.....

[BYprodriver]

Yup that's why I'm here. trying to get back to Topless's neck of the woods! One day.....[/QUOTE]

I used to live by the ocean in N.C. really cheap, in Camp Lejune. I like your rental places looks nice.

[993innc]

Originally Posted by BYprodriver

Yup that's why I'm here. trying to get back to Topless's neck of the woods! One day.....

I used to live by the ocean in N.C. really cheap, in Camp Lejune. I like your rental places looks nice. [/QUOTE]

Hey thanks, appreciate that! yeah LeJeune is an hour north in Jacksonville. It's certainly cheap compared to CA ocean front living! My wife and I grew up in San Jose/Morgan Hill (NorCal) but really like SoCal and hope to be able to retire there in around 10 years.
NC has treated me pretty well so I can't complain, but we are Californians, no way out of it :-D

[LAP1DOUG]

OP, I am running pretty close to the same set-up as Stone, which looks like good advice to me. I will add a few points that I have found:

1- Ride height, camber, and toe are all highly inter-related with this supension geometry. If you are running coilovers, then you must fix ride height & corner weights first before even thinking about camber, caster, and toe.

2- If you go too low on the rear, you will have too much negative camber, and run out of toe adjustment. This is one of the reasons that some people use rear adjustable toe links on these cars. I feel it is better not to go that low, but the after market toe links are still good to eliminate rubber bushing deflection, and be able to shim the upright attachment to adjust bump steer.

3- Optimum front to rear tire stagger is a function of what you do to optimize camber. If you don't modify camber to get near -3 deg as Stone suggested, then the optimum tire stagger will be close to "square". (something like 255 F / 265 R). However, if you crank in enough negative camber to optimize the front tire, then you will need more stagger - something like 255 F / 285 R, with the appropriately correct wheel sizes of course.

4- A GT3 front bar is the best mod you can make if you do nothing else. If you get it set at just the right roll stiffness, it will help reduce understeer by reducing the amount of positive camber in roll that all McStrut designs (911 or 986) experience. However, if you you think a little is good, then a lot is better, it will understeer like a pig.

5- If you use coilovers, go with fairly high spring rates to better control dynamic camber and toe changes. If you use a significantly higher spring rate in the rear, you may not need much or any rear bar. It is a fine balance with these cars, and sometimes a relatively small change in roll stiffness at one end can result in major oversteer or understeer. I suggest testing all new set-up changes on an auto-x course before heading to a track.

Hope to see you at a Southeast track sometime this year.

[993innc]

Originally Posted by LAP1DOUG

OP, I am running pretty close to the same set-up as Stone, which looks like good advice to me. I will add a few points that I have found:

1- Ride height, camber, and toe are all highly inter-related with this supension geometry. If you are running coilovers, then you must fix ride height & corner weights first before even thinking about camber, caster, and toe.

2- If you go too low on the rear, you will have too much negative camber, and run out of toe adjustment. This is one of the reasons that some people use rear adjustable toe links on these cars. I feel it is better not to go that low, but the after market toe links are still good to eliminate rubber bushing deflection, and be able to shim the upright attachment to adjust bump steer.

3- Optimum front to rear tire stagger is a function of what you do to optimize camber. If you don't modify camber to get near -3 deg as Stone suggested, then the optimum tire stagger will be close to "square". (something like 255 F / 265 R). However, if you crank in enough negative camber to optimize the front tire, then you will need more stagger - something like 255 F / 285 R, with the appropriately correct wheel sizes of course.

4- A GT3 front bar is the best mod you can make if you do nothing else. If you get it set at just the right roll stiffness, it will help reduce understeer by reducing the amount of positive camber in roll that all McStrut designs (911 or 986) experience. However, if you you think a little is good, then a lot is better, it will understeer like a pig.

5- If you use coilovers, go with fairly high spring rates to better control dynamic camber and toe changes. If you use a significantly higher spring rate in the rear, you may not need much or any rear bar. It is a fine balance with these cars, and sometimes a relatively small change in roll stiffness at one end can result in major oversteer or understeer. I suggest testing all new set-up changes on an auto-x course before heading to a track.

Hope to see you at a Southeast track sometime this year.

Well thank you for the write up. This is what I'm looking for. I am using coilovers (H&R) but not going crazy for just DE's.
I've not run mid engine cars before on track. My race car was a water cooled GTi. Stiff as you could rear and I always ran soft front, the car was on rails.
The 993 was similar but I cooked tires without enough camber. I'm thinking this time about adjustable camber plates for the front to dial in 3 degrees (or as close as possible).
I'll be running 8" hollow 996TT 18" wheels with Yoko slicks and thinking 35-40mm spacers with studs (questions, concerns?) to get effectively 9.5 width without all the weight of 9.5" rolling weight.

Figure I'll start there. Look forward to your responses. And I will be at VIR with Zone 2 PCA mid March. If you're there, love to meet in person. You won't miss my car (more to come)

Thanks

[LAP1DOUG]

I'm not sure how well those 8" wheels will work on the rear, even if spaced out as far as possible. My guess is that the weight in the rear may overheat the rear tires after a few laps, and you may have increasing amounts of oversteer during a session. Let us know how it works out.

I've never been to VIR, but hope to some day- good luck.

[thstone]

Originally Posted by 993innc

The 993 was similar but I cooked tires without enough camber. I'm thinking this time about adjustable camber plates for the front to dial in 3 degrees (or as close as possible).

Camber plates will provide about one additional degree of camber over stock which means that you'll max out at a bit over -2 deg. This will probably not be enough to keep from cooking the tires.

[993innc]

Originally Posted by thstone

Camber plates will provide about one additional degree of camber over stock which means that you'll max out at a bit over -2 deg. This will probably not be enough to keep from cooking the tires.

So how does one achieve -3 degrees?

Originally Posted by LAP1DOUG

I'm not sure how well those 8" wheels will work on the rear, even if spaced out as far as possible. My guess is that the weight in the rear may overheat the rear tires after a few laps, and you may have increasing amounts of oversteer during a session. Let us know how it works out.

I've never been to VIR, but hope to some day- good luck.

I've got 10's and 11 hollow spokes from my 993 track days but I don't think they'll stuff under there will they? I'll try the 8's and see what happens. VIR is a low wear tire track, will probably be ok there to start learning this car.

[LAP1DOUG]

Don't know about Stone, but I use GT3 type arms with shims for camber adjustment like these:

RSS Tarmac Series Lower Control Arms - RSS

Other advantages over camber plates are increased front track width as you add shims, and caster adjustment if you buy them with the bushing centers that rotate.

These arms are mostly for the front on our cars but are also a fairly cost effective way of eliminating all the rubber bushings in the rear when you add up all the parts and hassel of changing out the rubber bushings in OEM control arms. But, you really don't need them in the rear for camber.

If you are hooked on camber plates, I beleieve there are some tricks to get more than -2 degrees of negaitve camber out of them. These tricks seem to involve either drilling a larger center hole at the strut tower, or putting shims between the camber plate and the strut tower so that the strut center bolt has more room to move without hitting the body. If you look around on planet-9.com under the 987 competition driving section, you can find more info on how to do this. (FYI, in general there are a lot more Caymans that are tracked seriously than there are Boxsters, so you can find a lot more track info there. The 986 and 987 suspension designs are identical from what I can tell)


To use your existing wheel sizes, I would put the 8's on the front and 10's on the rear. You can forget trying to fit 11's unless you want to hack up your body work. I normally use 8.5" or 9" at front, and 10" at rear with appropriate size tires.

Good luck.

[woodsman]

Originally Posted by LAP1DOUG

OP, I am running pretty close to the same set-up as Stone, which looks like good advice to me. I will add a few points that I have found:

but the after market toe links are still good to eliminate rubber bushing deflection, and be able to shim the upright attachment to adjust bump steer.

Can you explain in more detail how to shim for a reduction in bumpsteer?

[LAP1DOUG]

Originally Posted by woodsman

Can you explain in more detail how to shim for a reduction in bumpsteer?

If you read Carrol Smith or Fred Puhn's books, you will see there are multiple ways to do this, but they all involve moving a suspension through its' travel range, and measuring the change in toe. The change in toe is what is important, and not the absolute toe value, so home made devices work fine for this.

I use a home built laser device projecting onto my garage door like this:




The bump steer curves on my 986S were pretty bad with significant toe-out in bump, and toe-in in droop. It takes a bit of shim work to get a good curve.

[993innc]

So the GT3 arms are wider or should I say longer than my stock arms? Do the gt3 arms require the steering rods etc to be changed as well? Not sure I'm understanding how one gets more camber out of arms vs camber plates. I'd love to not go the plate route since they've got a tendency to move slightly but it's what I know from my water cooled Vw days.

[LAP1DOUG]

Originally Posted by 993innc

So the GT3 arms are wider or should I say longer than my stock arms? Do the gt3 arms require the steering rods etc to be changed as well? Not sure I'm understanding how one gets more camber out of arms vs camber plates. I'd love to not go the plate route since they've got a tendency to move slightly but it's what I know from my water cooled Vw days.

If you don't have any shims installed, the GT3 type arms are the same length as your stock arms. On the GT3 type arms, the inside bushing housing is a separate piece that bolts to the rest of the arm, and you add shims as needed where these two pieces bolt together to make the overall control arm length anything that you want (within reason).

The real limitation with camber plates on these cars is that the nut on top of the strut runs into the body as you slide the top in to gain negative camber. The GT3 type arms obviously don't have this issue, and you can gain caster adjustment, and eliminate or reduce the rubber bushing deflection depending on which brand you go with.

I used to be a BMW camber plate guy myself, so don't worry about making the change from being a plate guy to an arm guy.

[993innc]

Originally Posted by LAP1DOUG

If you don't have any shims installed, the GT3 type arms are the same length as your stock arms. On the GT3 type arms, the inside bushing housing is a separate piece that bolts to the rest of the arm, and you add shims as needed where these two pieces bolt together to make the overall control arm length anything that you want (within reason).

The real limitation with camber plates on these cars is that the nut on top of the strut runs into the body as you slide the top in to gain negative camber. The GT3 type arms obviously don't have this issue, and you can gain caster adjustment, and eliminate or reduce the rubber bushing deflection depending on which brand you go with.

I used to be a BMW camber plate guy myself, so don't worry about making the change from being a plate guy to an arm guy.

I don't mean to seem like a complete tard, but might you have pictures of what you are talking about as it pertains to shims etc? This is all new to me. I'm a picture and diagram kind a guy :-) my car is, at the moment, a stock box I'm slowly going to transform. But these ideas are new territory. I only got to PSS9's on my 993, it was a dual purpose car. This one is track duty only but only occasionally. How can I set it up to drive 9/10ths without going crazy. That's what I'm after. I'm ok with a set if tires an event.

[993innc]

I went back and re read your post and looked at that site again......I get it now! So the shims force the lower arm out (how you get increased camber), while allowing for the other arms to remain the same length as stock by way of that multi holed center point (and I'm assuming that center puck rotates?). Or if not, you get a couple of different dimensioned mounting holes. Great looking product. Seems rather strongly priced for an occasional car. Looks like it almost forces on to get the adjustable toe links etc......where does it end :-D
It seems the Spec racing guys can't use these parts though per the rules, so do they just get whatever they get by lowering and squeaking out whatever is allowed by the factory parts?