Too much rear camber with ERP springplates

[JohnJL]

Hi all,

This is a 1978 911 autocross car. After setting up the car and initial break-in, the rears settled in at 4.9 and 4.1 degrees rear camber. I want to get those back to 3 degrees.

I am using the stock camber bolt and can turn it all the way around without it effecting camber more than 0.1 degree. I saw on another car someone added weld to the camber bolt lobe to increase its height, is that the trick here?


Thanks!

[Mahler9th]

I have those same excellent parts-- the 935-style spring plates from Eisenlohr Racing Products. I bought mine from Ira at Tarett Engineering.

Both great people and great companies.

It looks like you used the upper level choice on the chassis end of the spring plates. That essentially raises the outer pick up point from a stock location-- if I recall correctly, the amount is one inch.

If so, you will likely have changed the range of adjustability of the spring plate/trailing arm assembly such that you can't get the numbers you want.

If you also changed the inner pick up points via camber pivot boxes, and therefore have both outer and inner pick up points raised-- there can be great handling benefits...

But if you still have a factory cross member through which the shocks are located, and you have coilovers, you may have interference.

On my car I have the spring plates AND the pivot boxes. Plus coilovers and the factory cross member.

To get the camber numbers and ride height numbers I like (about 2.25 -2.5 negative and very low height), I have to use the "center" location on the chassis end of the spring plates.

My outer pickup points are therefore at stock height My inner points are a little higher than stock by way of adjustment of the pivot boxes.

The other thing to realize is that the trailing arm end of the ERP plates have one slotted hole and one circular hole. The slotted hole location (top or bottom) can have an effect on the range of camber you can obtain.

See the excellent diagram prepared by the folks at SRP that used to sell these plates.





Feel free to send me a pm-- I do my own set up and have some experience with these parts.

[Mahler9th]

I also encourage you to consider "locking in" the camber eccentric once you get your numbers.

See, e.g., http://forums.pelicanparts.com/porsche-911-technical-forum/1092691-track-car-alignment.html

The pictures I posted in that thread are from when I had modified factory spring plates.

I use the same method with my ERP spring plates.

[JohnJL]

Hi Mike, thanks. My PM is full so will respond here...

#1 - thanks for the SRP sheet, I didnt have that before and when I went to the ERP site last night to check documentation the site is under construction. I can see right away I need to flip the plate over to have the slot on the bottom.

#2 - Yes I saw your post about the locking washers last night as I was researching my problem. Thanks for that.

#3 - I have the stock arm mounts (though gusseted) You are right I have it on the low setting and have corner balanced her.

I will flip the plates this afternoon so the slot is on the bottom and see if I still have a problem getting camber adjustability back. I checked my spare suspension parts bucked and found these....I recall I initially installed the sway bar to the spring plate but found it less easy to adjust things independently so switched back to the stock sway bar mounting points. Perhaps one of these offset nuts will come into use...





Everyone likes pics so here's one of Gretchen...

[Mahler9th]

You may need to re-adjust your corner weights as a result of flipping the plates and re-setting your camber. This would be required if you cannot keep the ride height identical when you re-adjust.

If I recall correctly, you have to switch the plates left to right and vice versa.

Those sway bar mounting parts you show may not work as well as the factory camber eccentric. In my opinion, that million-year-old design works well especially if you lock things in place properly.

Cary E. does not normally deal directly with public or provide detailed documentation. My friends at JWE/SRP created a lot of documentation for their parts and many of the parts they sold, like the ERP spring plates. The late Gary Walton was a key contributor, and I have most of the documentation as it was available on CD Rom and either Gary or El CW (founder and owner of SRP) gave me a copy years ago.

I recommend checking the chassis area where the spring plates attach for cracks-- they can be quite common.

My '75 had them. I discovered them in ~2015 during a suspension update/refresh. I have owned the car since 2001 and never noticed them before. Glad I checked.

If you prefer not to fab, Elephant Racing Products has an excellent reinforcement kit for these chassis areas. Welding required.

From Club Race event at LS in 2002... if I recall correctly this was a paid spectator event. Car has had a few changes since then... for example I now run custom carbon fiber headlight covers instead of 993 headlights when on track. I swap in the lights for street driving.

[Gianni at Pelican Parts]

Gretchen looks great! Always nice getting input from people with nearly identical setups

[Mahler9th]

Example of crack:

[JohnJL]

Thanks. No cracks on mine, Gretchen was a bare metal build. I did gusset many points around the car and suspension but didnt modify the springplate mounting area. Hopefully her light weight will help reduce any similar cracking. She's 900 kgs with me in it wet. Yes, I will re-corner balance too when done...off to the garage now!

My lights are from a Mini ;-)

[Mahler9th]

Cool.

My car weighs more than that... about 1915 pounds with modest fuel in the cell and without driver.

The cage, 3.6L engine and big wheels and tires (12 x 16 front and 14 x 16 rear slicks) likely are part of that higher weight.

[JohnJL]

I wanted to see how good I could do without the full cage. There is a thread here on the build titled something like "Torsion Rigidity Pseudoscience" that documents the measuring and gusseting I did short of adding a cage.

Garage time cut short...son's physics test on Friday and he's not going karting if he doesnt B+ it...so shortly I will also be a B+< engineer again ;-)

[Cory M]

Move the pivot bolt to the lower hole (center of torsion tube hole)

[winders]

Originally Posted by Cory M

Move the pivot bolt to the lower hole (center of torsion tube hole)

Absolutely! Unless you raised the inner pickup points you should not be raising the outer pickup points…

[JohnJL]

Originally Posted by winders

Absolutely! Unless you raised the inner pickup points you should not be raising the outer pickup points…

Really? I thought I could get some benefit even without the inner pivot raising. I understand raising the inners is ideal but I dont want to tear her apart now, I am at Mosport next week. I want her as low as possible, is there a consensus that with the stock inner pivot points (on Elephant bearings) is better on teh upper or lower pivot position when trying for min rideheight?

I flipped the spring plates tonight and again with the pivots on the upper mount the min camber I could get was 4.2 degrees. Thats with the stock eccentric bolts. The eccentric bolts spin freely around and with the lobe in the down or 6 o'clock position thats min camber. I am considering adding some weld to the lobes of the eccentric bolt and seeing if that gets me less camber.

Thanks again for all the thoughtful comments and advice.

[winders]

Really! If you want to get the car real low, you need to raise both inner and outer pickup points. Porsche actually has the geometry right. Raising the outer pickup point alone screws it up.

Of course, if you go real low, you need to figure out a way to get the CV joint angle more reasonable or you are going to have problems with them.

[Mahler9th]

"Move the pivot bolt to the lower hole (center of torsion tube hole) "

Yes, that is what I was trying to convey.

I went through all of this a few years ago.

When I set up my car, I tried a bunch of different configurations to see what camber range/ride height range I could get.

The first try was funny... when I lowered the car onto the set up pads, there was so much negative camber that the tires interfered with the chassis! No rotation of the eccentric was possible to solve that.

Based on my experience, I'd guess that you are not likely to be able to adjust rear ride height and camber to get what you want, unless you re-locate the outer pick up points to the stock location provided on the excellent ERP spring plates..

Even with the plates flipped side to side.

I have not tried to modify a camber eccentric... so I cannot comment on that approach. I imagine whether it will work will depend on the height and camber settings you are trying to achieve.

You can get 911s pretty low without moving the outer and inner pick up points.

When you do move both of them up, there can be clearance constraints if you run coilovers inside the factory cross member.

I have many ride height specs from my set ups and I have also set up Winders car several times.

Our ride heights have been very similar.

Mine has the outer pickup points at stock location choice on the ERP spring plates, and inner pickup points right near stock location as adjusted with pivot boxes. I have coilovers through the stock cross member and I had to "make some clearance" for the springs in there with a BFH.

Winders' car has both inner and outer pickup points moved up with custom spring plates and the pivot boxes on the inside. He has no factory cross member so he has more flexibility than I have. Yet his ride height is about the same.

I don't think that the raising of the pickup points is worth more than a second... but it all adds up when you are trying to optimize.

I even have specs for CV joint height... as Winders has said, when you go low it pays to be mindful of the axles.

Both my car and Winders' car were built by the same person whom has massive experience and expertise.

In Winders' case, the rear geometry is more optimized with 930 arms and outer and inner pick up points moved up. And his rear coilover angle is also more optimized... achievable because there is no factory cross member in the way.

All of those differences are likely a second a lap or perhaps less.... based on observational experience.

Our rear tires are 16 inch diameter slicks that are 14 inches wide. So far they like about 2-2.5 degrees of negative camber for trade off between performance and wear.

Also... if the ERP parts are new to you, I can suggest a set of thin "service wrenches" from Harbor Freight to help adjust toe. And I suggest keeping an eye on that spring plate toe adjustment hardware... there is a reason that SRP recommends red loctite.

I love the fact that I can easily adjust my toe while leaving the camber set.

Good luck.

[Mahler9th]

I forgot to mention...

When I first bought my car it had factory spring plates and ran bias ply slicks. The rear tires liked about 0.75 to 1 degree negative.

Again, they were bias plys.

It was really hard to get that level of camber with a low ride height. So based upon advice from the car's builder, I had the factory slot and toe hole on both plates welded up, and cut new slots and made new holes in the plates... ~10 mm offset from the center line.

Presto!

So with these plates I could easily get the modest camber I wanted at low ride height. I could also flip to get a higher amount of negative camber at a higher ride height.

The latter can be helpful in a street/track/AX car-- so many folks want more negative than they can get at street car heights with stock parts. This plate mod is ideal for that.

I have those plates sitting in a box-- I think I put an ad for them in the classifieds.

[JohnJL]

Wow, thanks so much for taking the time and responding so thoughtfully.

I flipped the plates so the slot is on top, and moved the pivot to the center bolt location. I guesed at the camber bolt orientation (the factory ones fit) and the settings were almost bang on.

LR -2.4 Camber 0 Toe
RR -2.9 Camber 6mm total toe out

This is a 90% track car, 225/50R16 Bridgestone Potenza RE-71R

I was thinking to put the good schorr washers and hardware in and shoot for -3.2 camber. Toe suggestions? Mike I see your .75 to 1.0 note but I think my tires are a lot different?

Was tinking 1/8 to 1/4 toe in rear total, 1/8 total toe out in front?

Hoping to get things buttoned up on the geometry front tonight and do some corner weighting and EFI tuning tomorrow.

[Mahler9th]

In my experience with my car (racing application), radial tires of course want more negative than bias plys. A lot more.

I am pretty sure that this is an inherent difference (see, e.g., the Puhn book-- an excellent reference).

In my experience, the amount of negative out back can be a trade off around a "sweet spot." A little more and you can go a bit faster, but the tire wear trade off might not be ideal.

So for example with the Goodyear bias plys we used for about a decade, you had more capability at about 1-2.25 negative out back, but somewhere around 0.8 was almost as fast with much better tire wear. Everything else being equal.

When a bunch of us switched to radials, we had to go up to a "radial" camber range. My comrades made the switch before I did and settled in around 2.25 out back with the Hoosier radials. Give a take.

For toe, I have pretty much always used about 1/16 total in out back for all trailing arm Porsches-- never had much reason to fiddle beyond that relatively standard spec. Street, AX or racing application.

For the front I have almost always used about a 1/8 to 1/10 of an inch out.

Again all tires and all applications.

That being said, gotta be careful on longer street drives on the soft comp tires with that much toe out. I remember learning this back in the day when I made the long drive to Buttonwillow.

Buy oh she turned in crisply in AX...

[Mahler9th]

Its all about the tires. Everything we do is really focused on them.

[JohnJL]

Thanks guys. I have a day at Mosport tomorrow, so spent many hours getting toe, camber, caster and corner weights as good as I could. A few quick trips around the block settled things in but won't know how it feels until up to speed!

For posterity...
Front
2.7 degrees camber
3.5 caster
2mm toe out each side

rear
3.5 camber
2mm toe in each side