Bill Dearborn

Have been playing around trying to find limits on the settings for both the LCAs and UCAs. Have the Hardbar/VanSteel camber plates with Pfadt studs. I installed the VanSteel Plates in the front of the LCAs with the bolt in the inner hole with that hole located toward the inside. The rear plates were installed with the bolt hole to the outside. This pushes the lower ball joint forward. On the UCAs I have the maximum amount of shims behind the front dog bone and two shims ea behind the rear dog bone. That pushes the upper ball joint rear ward and pretty much maximizes caster. I could make it larger by moving the bolts to the outer holes.

Front Camber is -.6 L and -.8 R, Caster is +11 degrees on the left and +10.7 degrees on the right. When the car is on the lift with the suspension in full droop the stock tires hit the front fascia when I turn the wheel. Sitting on the ground everything clears. However, it is obvious to the casual observer the wheel isn't centered in the wheel well.

Other than the questionable caster setting and a slight pull to the right the alignment is pretty much where I want it for street driving. However, GM doesn't recommend a Caster setting that high.

If I pull one shim ea from behind the UCAs' rear dog bones the camber changes to -.9 L and -1.1 R but the caster stays almost the same.

If I rotate the rear LCA plates so the bolt hole is located toward the inside the camber will change to 0.0 L and -.3 R and the caster will probably fall more into the range that GM recommends.

Did some searching on the net but didn't really see anything that was definitive. I can't think of any reason why I should reduce the caster to the +8 range. The car seems to drive well and I haven't noticed anything that feels unusual about it.

Bill

vette6500

i'm no expert but more caster would probably reduce steering rate and max steering angle.
reduced max steering angle is probably not a problem for track/autocross, but maybe slows down the steering rate too much to make slaloms in autocross difficult?

that's just the picture i am imagining in the max extreme case of 90 degree caster = creates negative camber and zero steering angle.

ErnieN85

Bill, too much caster will produce impact shimmy. The steering wheel will pull violently back and forth, it starts about 35mph (usually).
the next thing it does is increase steering effort at High speeds. not necessarily bad for you but it does have an impact on the rack, pump & oil.
so much for the bad stuff.
The good thing is it helps make the car track straighter.

so............. go for a drive and see how you like it.
if it doesn't shimmy and you can still turn it is good

dbratten

I've been reducing caster down from 8+ to around 6 as I don't like the high effort needed to steer at speed. I feel that the need to run really high caster is due to suspension compliance and as you reduce the slop less caster is needed. I can still release the wheel in a tight turn in autox and the car immediately returns to straight. To me, that's enough caster.

There has to be a point where you can not get enough roll or tire adhesion to need the additional camber that the caster provides in a turn. It also seems that while you are below that point where you are using all the tire patch you are giving up grip.

But, that's just how it feels to me.

I should add that I also run between 1.8 and 2.5 negative camber on the street and track.

--Dan

froggy47

I am confused.

With not much neg. camber do you have solid bushings?

z060ntrack

dbratten

I'm curious as well. With that little of static camber in a turn with little steering input and high Gs you will roll right over into positive camber fairly quickly.

--Dan

Supercharged111

I've read that too much caster causes a mid corner push. Its arch nemesis is kingpin inclination angle. Typically, you play one off the other to strike a balance.

KPI kills camber as the steering wheel is turned, but gains it as the suspension compresses.

Caster gains camber as the wheel is turned, but loses camber as the suspension compresses.

Both add weight to the steering wheel and improve the self centering effect and road feel.

I forget what too much KPI does.

0Anthony @ LGMotorsports

Something else to think about...and I don't know if anyone else has hit on this, but Supercharged did a bit.

Caster and static camber have to work hand in hand. It isn't that you can not get a lot of caster to work, but you have to take away camber, or the gain in caster when turning can be so much that you have almost no contact patch with the tire and that will give you skipping and loss of front bite.

Many would want to add in caster to add more 'weight jacking' or weight transfer with it but again...you have to watch camber, among other things listed above.

Bill Dearborn

Based on the feedback and my own concern I readjusted the front end. I reset the rear plates so they are the same as the front plates and pulled all of the shims from behind the UCAs. With that setup front left camber went to -.4 and caster went to +7.4; front right camber went to -.7 while caster went to +4.3. I added 2 mm shims behind the right side UCA front dog bone and right side camber went to -.5 with caster going to +7.3. Not quite as much camber as I would like but it should be OK for the street and a long highway trip.

Playing with the various combinations the plates provide should help me tune the front end when i go to another track event.

Bill

blkbrd69

Don't feel limited to the standard shim washers, you can use thinner washers and get caster and camber exactly where you want it.
If you get an even street setup it's easy to just add a set stack for the track, then just redial toe.

Bill Dearborn

I am using the Pfadt Shims. They come in 2 MM, 1 MM and half MM thicknesses. Those numbers are approximate as my digital caliper reads them all just a little less than that.

With the Pfadt studs I can't get enough shims stacked behind the dog bones to get reduce the camber enough for the street (I want to have it down in the .5 range not the .9 range). That is true with the Pfadt camber plates and more so with the Van Steel plates. That means the main adjustment of caster/camber is still at the LCAs just as it is with the stock cams. I do that by flipping the plates on their bolts. There are only two positions, all the way out or all the way in although the Van Steel plates give me two offset bolt holes to work with Vs one offset hole in the Pfadt Plates.

Bill

MustOBeenYellow2015Z

More caster does several things from my experience. It gives the driver more "feel" ie the steering doesn't feel light.

Caster does self center the wheel

And also the more caster you run the more weight "jacks" around in the car when you turn the wheel. At first thought this would help the car turn in & through the center of the corner but I wouldn't know for sure until I put the car on a set of scales & turned the wheel & watched where the corner weights went.

hklvette

If don't know what parts were included with the C6Z Pfadt plate kit, but the C5 kits came with a lot of plates because of the rear arm mounting setup. As a result, you can use mismatched pairs up front similar to what you are doing with the Van Steel plates but with a less extreme difference between the two. Obviously, this gives you more freedom to adjust the caster, camber, and to some degree wheel-base to your liking.

In addition, moving the front axle forward (using a smaller # plate in the front mounts) does add a little ackerman geometry into the suspension.

Painrace

Listen to THE MAN!

Jim

Dave Schotz

I would never want less than negative 1.5 degrees Camber. Regardless of the caster...

Bring your caster in the 6 degree to 8 degree range.. and probably at least 2 degrees negative camber. And I would tell you 2 degrees is nothing on the street either.

I do realize you're compensating for 'some' of this with the 10+ degrees of caster... but you may be over estimating how much you actually are turning the wheel, and what you're actually gaining.

These settings are more inline with what I've experienced with a 'track car'.
http://pfadtracing.com/pdfs/Corvette...09.12.2011.pdf

Good Luck!
Dave

Bill Dearborn

Actually, I wasn't compensating with the +10 and +11 caster readings. The caster settings just came about when I installed the Van Steel plates the first time. Previously I had Pfadt plates mounted but they didn't fit the slots in the cradle very well so permitted about 1/16 movement of the LCA mounting bolts under certain conditions. I could tell when they would move since I could feel the pop and I could definitely hear it. I decided to replace them with ones from Van Steel. The Van Steel units fit tightly in the slots but are configured differently with two different bolt holes with each hole's center line located a different distance from the edge of the plate. Both the Van Steel and Pfadt plates can be flipped over so the hole is further inward or further outward. That way each plate gives you 4 specific positions in which the bolt can be used to mount the LCA. The Pfadt plates only provide for two specific positions. Here is a diagram showing the two:


I want to switch from street to track and back to street. Since I was coming back from a track event and setting the car up for street running I installed the plates with the least camber setting. The front plate was set with the bolt hole inward but I used the hole that was further from the inboard edge of the plate. The rear plate was mounted with the hole inward but I used the hole that was closest to the edge. This way the front of the LCA was pushed out a few mms further than the rear of the LCA. This is the setup that got gave the huge caster numbers which concerned me. Since then I have changed the plate arrangement and am using more camber on the street which reduced the extreme caster to something I thought was better.

My question is still, How much positive caster is too much caster? How far can you push it before the driver doesn't like the feel of the car? Ernie says too much can cause instability in the steering but how much caster can you run before encountering that instability?

Bill

darguy

I came across this particularly in depth discussion about alignment settings and suspension geometry / modelling -> here. It's a long read, and I'm still chewing on all the details (that link sends you to about half way through a long discussion, it's getting pretty meaty by #135).

A couple things I gleaned from all that, and will try out this year on the track, are to set the caster to ~1-1.5 deg more than the SAI of your spindles and keep the static negative camber relatively small. It's more complicated than just that, obviously but If I'm following the logic correctly the dynamic camber change in the corners from that combo of SAI/caster will produce the neg camber on the outside wheel that you want, but minimize the neg camber on the inside wheel (or even make it positive, depending on the rest of the setup/geometry). With the goal of producing the most even contact patch with the least amount of tire wear.

I have the caster/camber plates and studs/shims on my C5 and initially set the camber to -3 deg and could only get 7 deg of caster on the rack. At the track, my tire temps are telling me that I've got way too much camber. I've added as many shims as I can without playing around with the plates in the paddock and it made the car feel better and more predictable. Tire temps are better, but still more uneven than I'd like (I've seen photos of my car in a hairpin and the inner front tire is barely touching the track right now).

My understanding is that the C5 and C6 stock spindles have about 8.35-8.65 deg of SAI (would love to get a firm number from somewhere), so I'll be looking to play around with the plates/shims to get 10 deg of caster with -1 deg of camber (basically, where you're at with your car). Hopefully there is enough leeway on the studs after that to play around a bit between runs at the track.

Bill Dearborn

Good info. I copied it and will study it after the game. Last time at the track I had the camber set close to -3 and I didn't like the way the car felt.

Bill

froggy47

FWIW the Pfadt suggested alignment chart recommends 6-5 - 7.5 caster for their "track" tire/bushing setups and 7.5 - 8.5 for their "street" tire/bushing setups.

I am at about 7.1. My car does NOT steer itself straight very much, driver inputs are appropriate. I would not go any lower on mine maybe a touch higher or leave it alone.