JERRYWHO

I just ran my first time attack event and was very happy with the times. What i don't like is the front tire tread wear with this setup
Camber at 2 1/4 the max for now
Caster at 5
Toe at 1/16 out
275-40-17 Kumho XS at 41 psi
9.5 wide rims
J & M camber-caster plates
Koni yellows set at 80 % stiff
36MM sway bar with end links tight
Bumpsteer kit.
10 to 1 steering box
all parts are new (ball joints, tie rods center link ) and have under 2k on them.

All the tread wear was from the outside to the center of the tires and the inside has no wear. The funny thing is the inside 3 inches of the front tires has buildup on it. (will post pictures later today)

Is it normal run more then 2 1/4 degrees camber
Is 41 psi to low
5 degrees caster to low

On the next trip to the track maybe try 4 degrees camber, 7 degrees caster and 42 psi or is this way out of the ballpark.

Jerry

Guest

Jerry, My thoughts are that if you are running the insides slightly on curbed track corners the outsides will roll over more than if the inside stay on flat surface. Adams is tight and we all run the curbs there, not all the track, but a good # of the tight corners have them.

I ran -.75 camber and 5.5 caster on my camaro in flat autocross tracks with Goodyear GS-D3's at 49 fronts and 46.5 rears and had realitively flat wear for such low camber, but of course that is also just one lap runs and not a mini road course duration.

I think the curbs play a little bit of the equation, they produce more overall chassis roll.

We do not have a good camber gain- actually with roll its a loss, do you have travel indicators to know where your articulation of the front a-arms are migrating in mid corner?

Roostmeyer

iTrader: (3)

Sounds like the XS tires have pretty soft sidewalls, but I've never ran them myself.

http://sccaforums.com/forums/thread/358541.aspx

How much street time do you put on the car? How much is the car rolling, stock springs still? I'd try more camber and go from there if your not concerned with wearing the tires on the street. If anything mark your camber plates and see what it does to toe, you may be able to just go back and forth from a street to race alignment in about the same amount of time it takes you to change tires.

JERRYWHO

Thanks for a good link on XS tires.
My 90 Camaro is for play only, like this weekend we have a 200 mile cruise (120 freeway and 80 in the canyons)
For the car setup it has Eibach pro kit springs, 36 and 24 sway bars, yellow on car adjustable Koni dampers, bumpsteer kit and all other parts are new also.
I have tested alignments on my car on a Beam electronic rack and with a base setting of 3/4 camber, 4 1/2 caster and 0 toe and then we set the camber to 2 1/4 and rechecked the toe and it was at 1/16 total in, so with a 1 1/2 degree camber change the toe only moved 1/16 in. The next test was to change the caster from 4 1/2 to 7 1/2 and when we checked the toe it was right back to 0, so with 3 degrees of caster added we had it toe out 1/16 total. I can't believe how little toe change my car has with major caster and camber changes.
On the link you posted the BMW was running 4 degrees camber, i will try 3 1/2 and bump the pressure up 2 psi to see if i can get more inside tire temp.

Jerry

JERRYWHO

My car was traveling the fronts 1.300 to 1.550 on the indicators but i am sure that was at the end of the back straight when i go from wide open throttle to max brake with a third to second down shift at the same time.
I am sure that mid corner travel will be a lot less then that.

Jerry

Roostmeyer

iTrader: (3)

Just curious how much bumpsteer were you getting before you added the bumpsteer kit? Have you had any issues with inside tire spin with that much caster?

Something to keep in mind is that the BMW probably has twice the roll stiffness of your car. My miata with the lemming spring package and same ruleset is over 2.5 hertz spring frequency...

JERRYWHO

I never got a chance to test it before the bumpsteer kit. My car has a lot of inside tire spin, but i think it's of the diff i have in car right now, it's a Moser 12 bolt with a Detroit Truetrac Helical Limited Slip. I will change to a clutch or cone type posi to try and reduce the inside tire spin. I have a Dana 44 with the same gear ratio and a Tracloc diff.
Right now i have a tuff choice to make install a Power-loc racers diff in the Dana 44 and install it or build a new 10 bolt with an Auburn autocross / racers diff.

So with more body roll (camber loss) and less camber gain do you think we need more then 4 degrees static. Testing will show how far we have to go.

Links to the diffs.

http://www.ringpinion.com/ProductDet...px?ProdID=3272

http://www.stranoparts.com/partdetai...=183&ModelID=7

Jerry

Roostmeyer

iTrader: (3)

I was planning on running around 3° on mine once I get better strut mounts and go from there. At some point you're going to start hurting the cars ability to stop with that much camber, so its going to be a compromise. Not to mention you may have to start cutting up the strut towers to get strut clearance. Be careful on copying other people's race alignments, a lot of the smaller cars still run bias plys which can't tolerate as much camber.

I'll take it your just looking at tire wear? It may be worth taking a look at tire temps. I wouldn't mess around with a IR gun, longacre makes a decent probe type thermocouple tire probe for under $100. If you've got a nice voltmeter that can measure temps with a thermocouple you can also just buy the probe from omega. For my miata on dunlop *specs they start getting greasy and slowing down any hotter than 135°, I know the XS's like the heat though.

Sounds like your experience with the true trac is spot on, sorry you have to log in to read:
http://www.frrax.com/rrforum/index.p...12453&hl=eaton

There are at least 10 other good threads on frrax about diffs...

I've heard that you need two auburn race diffs, one to run, one to send in to be rebuilt. The power loc looks like an offroader diff, but I'm sure you could make it work. Any idea what the break away torque is on the power-loc?