Does anyone know about how many shims (or what thickness more specifically) can be used front and rear without resorting to new lower control arms or other non-OEM parts? Roughly how much camber will that allow?

Just wondering how much it can be adjusted without adding $$$$ parts.

Thanks!

 

I'll let the experts chime in, but piecing it together from various threads, the answer on the rear is 0. Once you try to dial in more than 1.1-1.5 degrees in the rear, it becomes impossible to have correct toe. This necessitates a new toe link. $4-500 part.

 

In the front, the general answer I'm seeing that allows you to maintain a safe amount of thread engagement in the LCA is 10-14mm worth of shim, which should get you 1-1.5 additional degrees of negative camber. Even with more modest shim setups though (especially when using aftermarket wheels), you'll likely end up with too much caster, which pushes the wheels forward in the well and causes rubbing under cornering; caster-adjustable thrust arm bushings are available to address that. If you go pretty aggressive with shims (i.e. into that 10-14mm range) you'll probably also run out of toe adjustment for the amount of camber you'd be trying to run because you'll fall below Porsche's recommended 25mm minimum rod end penetration in your outer tie rods, which you'd need aftermarket tie rod ends to address. And if you want to go even crazier than that with shims, you might additionally need longer studs for the LCAs to maintain adequate thread engagement there, which would require different LCA ends like the Tarett Cup monoballs, which have a thick shim built-in and longer LCA threads. Anyhow, the ideal is to get as much camber as you can with shims before adding via the top mount because shims also increase track width by pushing the bottom of the wheels out, thereby improving handling, whereas the top mount adds camber by just bringing the top of the wheels in.

In the rear, I'm not sure what shim thickness is safe, but that doesn't seem to be a limit people are running up against even when going for aggressive track-only alignments. But as vantage said, in the rear you're not getting past maybe -1.6 camber (which shouldn't require any shims since -1.5 is the OEM spec) before your OEM toe links cause too much toe-in for the camber you're attempting, so shims aren't your problem. Aftermarket toe links are longer so they can maintain proper toe even with the additional camber. They also allow much easier and more precise toe adjustment than using the eccentric bolt, and if you also get the locking plate kit you can eliminate that bolt entirely, which some do because the bolt has been known to gradually cause toe to drift out of spec, though others have been fine leaving it there. I got the kit because the bolt is completely unnecessary when you've got the aftermarket toe links, so the only downside is the cost of the kit itself, but I figured that if leaving that bolt there caused me to need even one extra alignment later that could otherwise have been avoided, I'd already be behind on cost. Lastly, the rod end boots for the toe links aren't a bad idea either. They're cheap, they help keep the links free of grime, and there's no downside to them whatsoever as long as you don't accidentally seal water IN there during installation.

The bottom line is that if you want a good dual purpose alignment, you need at least the rear toe control arms (I used Tarett and as I mentioned also got the locking plate kit and rod end boots) and front caster-adjustable solid thrust arm bushings (again from Tarett, who helpfully included some spacers required to use them with the GT4), and then either get it aligned at a shop that stocks GT3 LCA shims so they can give you what you need or buy a selection of shims beforehand as well. RSS sells a shim variety pack that's a great value compared to buying them individually, and 1 such set should be enough to cover the whole car's needs given that they can be mixed and matched. With that hardware, in the rear I got my -2 camber and 10' toe-in spec no problem. And in the front, I got my desired -2.5 camber and 0 toe spec with the top mount at roughly the halfway point, presumably because getting there entirely via shim would have required aftermarket tie rod ends I didn't have or want. Front caster was set to 8.6 to center the wheel in the well -- for reference, a previous alignment I'd gotten just to see what I could get without aftermarket parts got me -1.5 camber front and rear with front caster at 10, so shims in the front without the adjustable thrust arm bushings would almost certainly have caused rubbing problems with my camber target.

All in, it was about $850 in parts, and then $630 for installation, alignment, and corner balancing, though had I skipped the corner balance that labor cost would have dropped a fair amount. Tarett was first-rate to work with, too. I figure the money I spent will be recovered just in savings from increased tire lifespan reasonably quickly given my moderate track schedule, at which point the handling improvement is just a free bonus.

Final word: You may notice the RSS rear toe links include bump steer adjustment, and Tarett also has such a product in addition to their "standard" rear toe control arm set for the GT4. The aftermarket front tie rod ends from both vendors also feature bump steer adjustment. I, um, "steered" away from those offerings based largely on this post, and since I couldn't find any aftermarket tie rod ends that DIDN'T include bump steer adjustment, I was glad that I was able to hit my front alignment spec target without replacing those, even if it meant adding some camber via the top mount. Good luck!

 

Thanks! Do you have the RSS part number for their variety-pack of shims?
Online I see only 1-pc shims in various sizes...

 

Great information here. I am about to insert 8mm shims in my front LCAs, as my car is at -1.5 with the strut tower tops fully pushed inward. I am told 10mm gives you approx 1deg, and all I want is -2d at the front, zero toe. I have -1.5 at the rear with slight toe out, so I am hoping to stay there without any modification or adjustment.
This all happens next weekend.

 

http://rss.rpmware.com/rss/rss-align...i-1890057.aspx

 

Did you mean toe in? Toe out at the rear would create, shall we say, very interesting handling!

 

Yeah, I read the same thing about 10mm shims giving an additional 1 degree, but somehow I got an extra degree without using more shim than that and without keeping the top mount maxed out. However, according to BGB and a few other places I've read, on the rear you do not EVER want even ZERO toe in the rear on a Cayman or Boxster, never mind toe-out. Some like orthojoe have actually added a bit more toe-in than spec on the rear to keep the rear stable under braking. I'd strongly recommend getting that fixed if you do in fact have toe-out (negative toe) as opposed to toe-in (positive toe).

 

Thanks for all the quick replies!

So much for being a "track-focused" car straight from Porsche.
Well, it is - if you buy other suspension parts. And other wheels to allow better tires. And. . .

Yeah, I know - shut up and drive.

 

I think the wheels and tires are fine as long as you're willing to pay for 20" Cup 2s for the track. I don't feel any particular need to upsize the fronts at this point, and you'd basically need to go full slicks to do much better than the Michelins (except Trofeo R's I guess), but Porsche explicitly says that they don't warranty against damage caused by running slicks. Yeah the alignment limitations were pretty annoying to discover on a GT car, but other than that I think it's a pretty much turnkey track-capable car that's still livable and even enjoyable on the road, and the aftermarket parts don't seem to have negatively affected road manners at all, so I'm not too bent up about it.

 

The part number for the RSS Shim Kit is #308. It includes 2 ea. of 1,2,3,7,and 10 shims. 10 mm = 1 degree. I ordered from Tarett 4 ea 1 mm, 2 ea. of the following, 4 mm, 8 mm, 10 mm. They were out of 2 mm which is why there is 4 ea 1 mm.

 

I have seen capable autocrossers dial in some rear toe-out, on a GT3
if I recall correctly, to get the expected lively turn-in. Similar to the
rear-wheel steering of the later car, except only for the low-speed
stuff. Yes, it would be unstable at high speeds.

 

If one does not intend to track this car... Is it still a good idea to follow these alignment setups and install the Tarret pieces? Or is it perfectly OK to just get a stock alignment for the street within the limits of the factory setup.

My GT4 is strictly a street car and I enjoy reading and learning from the experienced rennlisters. Thanks for all the good information.

 

Just get stock alignment. No need to add more camber for street. You will just eat up the inside edges of your tires. More camber is only needed for track.

 

Does anyone have the torque values for the bolts that must be loosened to adjust toe / camber? I have 25 ft lbs for the strut tops, but nothing else based on searching the forum.