tb30570

I have a 2000 C5 Z51 with stock alignment. I'm wondering if I should get it set up with the C5 Z06 alignment or a custom alignment. I'd like to get a good alignment for autocross, but also be ok for drag racing and the street. This isn't my daily driver, so I don't put a lot of miles on it. The current alignment causes the inside of the rear tires to wear faster.

Current Suspension Set-up:
C6 Grand Sport shocks all around
T1 front sway bar
C6 Grand Sport rear sway bar
C5 Z51 springs all around

Street Wheels & Tires:
275/40R17 front on 9.5" wheels
295/35R18 rear on 10.5" wheels

edwardo99

I have a 2000 FRC aligned for auto-x. Everything I know about autocross alignment makes me think it has nothing in common with drag racing alignment, which I know absolutely nothing about. Auto-x optimizes for best lateral grip with lots of camber front and rear. Camber in the rear would seem to hurt longitudinal grip, which I'd think most important for Drag racing. Auto-x optimizes for great turn-in at the expense of stability, often with toe-out in front. Doesn't seem like compromising high-speed stability would be the way to go for drag racing. Auto-x optimizes for good power-down coming off slow corners, usually with higher amounts of toe-in at the rear. No apparent need for that for drag racing. It will just waste power in a straight line. So, the wish to do both types of racing with the same alignment may be a problem. Generally, the stock alignment (low camber, low toe in any direction front or rear) would seem to be a lot better for drag racing. (I'm sure it can be tweaked for drag racing.) Anything you do for autocross is going to move away from that, I think.

tb30570

Would you recommend going with a Z06 alignment then?

avizandum

Front

~1.5 neg camber
Max caster with this camber
ZERO toe

Rear

.5 neg camber
1/8 toe in per side

Should satisfy both venues and street

tb30570

why is the stock thrust angle not zero?

edwardo99

So the car will go straight down a crowned road, is my guess. Some aligners adjust for crown with unequal front caster that works because usually the driver is by himself and compresses one side more.

The Z06 alignments quoted above are very tame for autocross work. Avizandum's numbers are conservative for autocross, maybe just the right compromise you need.

tb30570

If the front has a high magnitude negative camber and the rear has a low magnitude negative camber, would it cause more oversteer?

edwardo99

Very common to have more front than rear, especially for auto-x. I run -2.5 front and -1.3 rear. Need more in the front for good turn-in, less in the rear to get power down out of slow corners. (Many people don't go over -1 in rear, with all they can get in front.) I think the road-racers try to get more in the rear for slightly better grip in long sweepers typical of road courses. (Not typical of auto-x courses.) Balance of the car (oversteer vs understeer) is mostly sensitive to rake and toe.

I had to move my front subframe to get -2.5 on each side. Limited to -2.1 before doing that.

tb30570

It seems that all the adjustements except rear toe are going to induce oversteer. Is this going to be a big enough difference that I should plan on getting a stiffer front spring?

Camber: current is balanced front-to-rear, suggested is more in front than rear - induces oversteer

Caster: current is less than suggested - induces oversteer

Front Toe: current is toe in, suggested is no toe - induces oversteer

Rear Toe: current is no toe, suggested is toe in - induces understeer

acrace

Why don't you try autocrossing it "as is" and then decide what needs to be improved?

From my perspective, I would go with what avizandum suggested. It's a good starting point for a street driven/autocross car. My semi-dedicated autocross cars have a lot more negative camber up front and a touch more negative in the rear than his suggestions. But I'm willing to live with increased tire wear for better autocross performance, and I haven't hit the drag strip with my cars in a few years.

My remarks on your above comments:
Caster - I like to go with as much positive caster as I can. It has the effect of adding negative camber at high steering angles. Autocrossing has a lot of high steering angle inputs, as compared to track session.

Front toe - You can always change toe really easily. I'd align it at zero toe and then you can always adjust one flat at a time to suit your preference.

Front camber - I personally like as much as I can get (within reason, like -2 to -2.5). Autocrossing has, as stated before, a lot of low speed, high angle corners. You need front negative camber to have the front end bite.

I doubt that anyone can give you an idealized setting on the 'net, especially given that you've got some light mods and you didn't post if you run R compounds or not. Every course is different; different clubs and different parts of the country have huge differences in course design and philosophy.

Have fun!

SouthernSon

On the front, toe out to 'turn in'. With toe out, the inside front wheel is scrubbing a bit while turning which helps the turn in with the induced yaw effect.

dtjansen

I've noticed that if you don't have the grip of a good tire, you can hurt yourself with too much negative camber. Use a pyrometer and if you are running hot only on the inside edge of the tire after a run, you may have too much neg. I think a good starting point is perhaps 2 deg neg in front. Multiply that by .75 and you have 1.5 neg in the rear. As for toe, I like a little out in front. I may toe it in a hair at the rear. All this is with my 180 lbs sitting in the car and a full tank.

I'm setting up my FRC this week. I'm gonna do some track trials and auto-x.

edwardo99

While all above is more or less theoretically correct, it lacks an appreciation of 1) relative degree, and 2) how these changes affect oversteer and understeer in the 3 phases of a corner... it seems you are thinking steady-state only. Rest assured that you will not turn your car into an un-drivable oversteering monster with the kind of changes recommended in this thread. You will increase your cornering limits and reduce the chance of quickly ruining your front edges, which is what will happen if you autocross without more negative camber in the front. For autocross, it is a great help to have a stiffer front roll bar. This is legal in stock class. (Springs will put you into a higher prep class.) Of course, we don't know what mods you already have. (And, by the way, rake in this context has nothing to do with caster. I was talking about the relative ride height front to rear.)