user33

In preparing to do a track-oriented camber alignment on my GTR Pro, I've been trying to determine the number of boxes of shims that will be needed. I'll be trying for -2.65 front and -2.5 rear.

After reading all the posts I could find, it's still unclear whether 2 boxes or 4 boxes of shims will be required (because there are posts with both claims).

My dealer has supplied the following info:
A 197 357 06 00 is listed as the correct number in our catalog for the shims. It lists qty 1 each for each corner (4 total for the vehicle).

He also put through a request for sizing info and followed up with this info (I have a great dealer!):
... unfortunately they were unable to provide me info for the size of each of the shims. They understand that it is 1 kit per corner, and includes the plates listed below.
A1973570600 kit includes the following adjusting plates:
A1973570142 ADJUSTING PLATE / 1 Quantity 4
A1973570242 ADJUSTING PLATE / 2 Quantity 4
A1973570342 ADJUSTING PLATE / 3 Quantity 4
A1973570442 ADJUSTING PLATE / 4 Quantity 4
A1973570542 ADJUSTING PLATE / 5 Quantity 4
A1973570642 ADJUSTING PLATE / 6 Quantity 4
A1973570742 ADJUSTING PLATE / 7 Quantity 4
A1973570842 ADJUSTING PLATE / 8 Quantity 4
A1973570942 ADJUSTING PLATE / 9 Quantity 4

QUESTION:
For those of you who've done similar with a GTR Pro, can you confirm whether 2 or 4 boxes of shims will be required?

For those who've done similar with any other GTx model, it'd also be great to record that information for future use ... please just be sure to indicate exactly which model(s) you're posting about.

thebishman

On my GTR I needed only 2 boxes of OEM shims to get a square camber of -2.5. Not sure why the Pro would be different.

supertanch

My pro needed 2 boxes of OEM shims, I have -2.9f and -2.8r

user33

Thanks, Bish and Supertanch, that's what I was thinking and what makes sense from the fact that the shims are quantity 4 of each thickness.

Supertanch
Your camber is more aggressive than others I ran across, can you elaborate on your tire wear characteristics? Info like the following would be great:
- type of tires if not Cup 2 MO
- guesstimate on non-track vs track usage
- inside vs outside tire wear ... ideally a comparison for non-track vs track usage
- did you use the OEM settings for toe-in
- anything else you've learned that might be useful in relation to this camber setup (e.g., track performance improvement)

(slow response on my part because I was away squeaking in another end-of-season track day ... $;-))

supertanch

- type of tires if not Cup 2 MO

I normally run two types of tires depends on availability/mood , the BS sized cup2R (285/35/19f, 335/30/20r) or Nankang CR-S (stock size).

- guesstimate on non-track vs track usage
80% track usage, the non track usage are mostly driving to/from the track, the 3 tracks near me each is about 60-100 miles one way, so it definite has a bit of HW miles.

- inside vs outside tire wear ... ideally a comparison for non-track vs track usage
Given that I have almost only track usage, the inside/outside wears are pretty equal for the most of the cases - I do push on track so the camber is mostly used for that, FWIW the current setup of my car is more on the loose side (I also run 0 toe) where I tend to use the rotation to fine tune the speed of each corner.

- did you use the OEM settings for toe-in
0 toe for fronts, 0.06 total for rear.

- anything else you've learned that might be useful in relation to this camber setup (e.g., track performance improvement)
The camber has really helped me on prolonging the life of the tires, and increased mid corner stability of the car. It took me about 1 year (the car now has > 25 track days) to find out the balance of the setup and now it's kind of sitting at a sweet spot for my driving style. Like any other setup, it does require you to tune, compare and analyze after each track day to find the right balance, and also according to your local tracks' condition. The Norcal tracks have a lot of mid speed on camber corners so the extra camber definitely helped for me.

Enjoying the tuning! the key learning from me is to tweak only one thing at a time, so you can have a good baseline comparison to improve upon. Moving too many variables actually complicate the equation.

user33

Thanks very much, supertanch ... such a complete answer that is really appreciated. So I'll go a little higher and start with -2.8 front and -2.6 rear.

My main goal is to extend the life of the tires, in particular to enable me to run lower pressures without killing the outside edge immediately. I found that I need to keep the Cup2s at 35 psi or above or else the outside edge gets destroyed very quickly. Of course that means that, even with careful management, pressures will sometimes creep up to 38 or 39 psi during a 20 min session on hotter days. At about 37 psi they start to lose grip fairly rapidly. One day I targeted 34 psi and put about 3x as much wear on the outer edge so have been living with the trade-off towards longer outside-edge life (it's the Scottish blood in me, I guess).

supertanch

If you outer edge are wearing out like that you definitely will need more negative camber. the cup2s get really greasy once they go above 36psi, just for your reference I usually start with 26-27 cold in a 20 min sessions and aim for 33-34 hot where I feel the grip is at the peak. It will definitely take a few tries to find the perfect balance, might be worth to use a pyrometer to measure the temperature across the tire surface. Enjoy!

user33

BTW, supertanch, you once posted that you were changing the sway-bar settings. Can you share any wisdom on that topic as I've not seen anyone else that's done that? 2 of the 3 tracks I visit are short, twisty/technical tracks with lots of lower-speed cornering.

supertanch

I did - I played with the rear between the stock (the middle hole) vs stiff (the inner hole), which actually didn't go well - it made the rear has less travel, stiffer but actually prematurely shifted too much weight transfer to the front under load. I changed back to the middle setting and stick with it.

The grip level actually reduced on corner exit a bit (tail happy) due to the static rate increase in the rear, given your local track has more twisty/lower speed cornering I would suggest you to use the stock setting to make the weight transfer more gradual.

user33

Thanks, again. Good to know, and it makes sense.

I was more thinking of stiffening up the front, but don't want to increase understeer ... and I have a nagging feeling that, with all the suspension interdependencies, the AMG engineers/testers probably achieved a pretty optimal balance so it'd likely be better to increase both front and rear stiffness if wanting to reduce body roll. Then the question becomes "would the ride quality become too torturous running to/from the track?" ... it's already border-line with track-ready shock settings.

Did you play with the front sway-bar, at all?

supertanch

The front-swaybar only has two settings, I tried to move it to the hard setting but was not able to get the endlink go in at all, did a couple of tries and I didn't want to loose the shock just for the swaybar adjustment so just gave it up. As you mentioned, the ride quality is borderline already with the stock setup, it does get noticeably firmer when I adjust the rear to the hard setting.

user33

Oooh-Kaaaay ... then I'll definitely skip trying any sway-bar stiffening. The 4+ hr trip to Area 27 was a killer on my lower back, after 2 hours. I have been playing with slightly different seating positions and think I have improved upon that ... but it'll still likely be painful after a few hours. At least on the way to the track there's lots of twisty mountain roads that can distract. #;-))

user33

One more question ...

I've already discussed (with my dealer) the idea of loading the driver's seat with about 150 lb (I'm skinny!) when the alignment is being done and they've indicated this can be done.

My question is "is this a worthwhile/meaningful thing to do or is it of negligible (or maybe even negative) value?"

BTW, since the 2 "short 'n twisty"/lower-speed tracks I attend are opposite-turn biased (one is CW and one is CCW), I'm aiming at a same-each-side camber setting as opposed to canucklehead's track biased setup.

supertanch

The weight on seat will be helpful only when you are doing corner balancing, otherwise it does not make a tangible difference, 150lb is too less to affect on the static height of the suspension , especially on double-wishbone setup. And yes use the balanced alignment spec is the best, unless you have a very biased track. Giving you also drive on the road, it will help on the tire wears as well.

user33

Just a follow-up on my higher-camber alignment:

- I asked for about -2.7 deg front and -2.5 deg rear

- I got -2.75 deg on both front and rear (somehow things didn't get communicated correctly ... unusual, but it can happen)

- at first it seemed fine, but as I went to tracks that had higher-speed straights, I found that the car was getting increasingly "squirrely" under hard end-of-straight braking ... fine at about 180 kph, noticeable at about 200 kph and getting bothersome at about 215 kph (I suspect that it'd be dangerous at over 250 kph and might be wanting to "swap ends")

- the as-delivered front-to-rear difference on my car was about 0.47 degrees and people have reported using a front-to-rear difference of about 0.2 to 0.4 degrees

I put a new set of tires on before my most recent track day that also involved about 9 hours of driving to/from the track. Once I measure the tire wear across all the tires, I'll make a decision about how much to back off the rear camber setting (and update this posting).

supertanch

I think 2.7 is a bit too much for the rear, what's the toe you are running? That could impact the braking stability as well.

Curious to learn what's your tire wear shows, I generally experience that the rears lasts almost twice as much as the fronts under the track alignment specs..

thebishman

Agree with the above; get the Toe checked asap and then drive the car to see if the 'instability' issue has been resolved.

user33

Assuming I'm reading things correctly, the front toe is 0.1 deg and the rear is 0.0 deg (see attachment and request for comments, at end of posting).

For tire wear -- Cup 2 MO, new prior to both trips.

2022 : standard camber: On-track time (at Area 27) with low aggressive driving (1st time w/GTR at track) was about 1.25 hour and outside temps were 25-35 deg C (77-95 deg F). The in-car "air inside tire" readout showed temps hitting a max of 100 deg C but mostly I was on target at about 75-80 deg C with pressures at about 33-35 psi. Off-track driving was about 950 km (590 miles) with temps on the return drive ranging from about 22-32 deg C (72-91 deg F) with in-car "air inside tire" temp readout showing about 30-40 deg C and pressures of about 34 PSI. Temps were 2-5 deg C cooler on the drive to the track with rain for about 2 hours of the drive. The drive includes about 1.5 hours thru rocky mountain foothills/mountains with lots of (fun when dry) twisty parts ... but had rain during the drive to the track so was taking it _very_ easy (Cup 2s are dangerous in the wet!).

2023 : high camber: On-track time (at Area 27) with medium aggressive driving (still learning track) was about 1 hour and outside temps were 30-33 deg C (86-91 deg F). The in-car "air inside tire" readout showed temps hitting a max of 100 deg C but mostly I was on target at about 75-80 deg C with pressures at about 34-36 psi. Off-track driving was about 950 km (590 miles) in temps ranging from about 25-32 deg C (77-91 deg F) with in-car "air inside tire" temp readout showing about 35-40 deg C and pressures of about 34 PSI. The drive includes about 1.5 hours thru rocky mountain foothills/mountains with lots of (fun when dry, it was) twisty parts. Corners with complete visibility typically run at 2x posted corner speed with others at 1-1.5x posted speed, depending upon visibility (I'd guess nearly always under 1G lateral, so appropriately aggressive for public roads).

Here's my tire-wear data ... the two inside/outside edge measurements are at the most wear point on the outer edge then inwards on the slope of the wear block (a little subjective) the single measurement is just the inwards one. The middle numbers are across the circumferential groves.



High-camber alignment data:


I was thinking of backing off the rears to -2.5 degrees (which was my original request), going less towards -2.4 based upon the actual shims.

Does anyone have any thoughts on this rear-camber setting and/or the toe-in settings?

supertanch

Very comprehensive data - thanks for collecting and posting for reference!

Your rear toe looks fine, it's 0.11 total (front is zero toe) so it's well within good range, also your rear/front cambers are both -2.4. So the braking behavior you experienced were most likely not due to alignment.

Any wheels having slightly unbalanced weight?

thebishman

I think your hot psi are way too high on track, and perhaps that’s exacerbating wear on the inside portion of your tyres?

I always started around 26 psi and aimed for 32/33 psi hot.

user33

I've added my last-year's/standard-camber data for comparison (duh-oh!). I'm a retired software geek ... I like data.

Cambers are -2 deg 45 min ... so -2.75 deg -- no?

Nope, the local shop I get to swap always gives me a "zero feel me" balance ... and I always lay some very sticky and temp-resistant fiber tape over the weights to ensure they stay on.

user33

I've found that's too low, especially at Mission Raceway (which, admittedly, is brutal on tires and brakes). If I run hard with those tire pressures, it'd immediately destroy the outside edges. I think in its terms, but manually measure in offset/correct terms. I've found that even 1 PSI too low increases outside edge wear very significantly.

BTW, I think I've mentioned it before, but I did create this web page that can help set initial cold tire pressures when arriving at the track:
http://car.dnsalias.com/car/startingTirePressures.jsp (note this is NOT https)
It's self-contained javascript code so, once the page is loaded, it will run without any internet access (and you can easily see what it does by examining the page source).

My bad, I keep forgetting that the in-car readout is consistently 2 PSI high when compared to 3 manual-check guages (all of which agree with each other). I've corrected my posting.

After comparing to the standard-camber wear readings (which I've added to the posting), my thoughts about tire wear were the following:

- There's decreased outside edge wear ... aside from some better handling, that was a primary goal for the high-camber alignment.

- There's increased inside edge wear. That was expected and is "the worst" in this case due to the 9 hours of highway driving to get to/from the track. This track day also had minimal on-track time <grrrrr>.

- The high-camber alignment was done with my previous set of Cup 2s and what I saw after 2 VIMC and 1 Mission trackdays, where the to/from to-the-track driving is about 1 hr 20 min each way, was much less inside edge wear. It appeared that the inside and outside edge wear was very balanced with that amount of street driving (including my normal weekly "keep it lubed" runs).

So, tire wear aside, this still leaves me with the high-speed braking "squirreliness" issue.

supertanch

My bad - I missed the ' mark! - that should still be ok, I've ran that before and didnt' really experience any instability in rear end under heavy braking, the heaviest braking point for me is turn 2 at Laguna Seca, going from ~138mph to 40mph - (222kmh - 60).

canucklehead

Here are my PRO settings.
LF = -2.6 T=0.01
RF= -2.7 T=0.01
LR = -2.2 T=0.05
RR= -2.3 T=0.06

For reference this is super stable at Area 27.
End of main straight speed ~238km/h, hard late brake into turn around 75', half way between the 100 and 50 marker. Super stable. With a bit more time I could probably brake a bit later and take that turn with more speed. Best time 2:15.

user33

What are you running for tires, pressures, etc.?
Also, do you crank your wing all the way up for Area 27 (assuming you're still using the stock wing)?
Serious lap time, BTW. I'm way slower at this point (always slow at learning a track).