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Can anyone give me some insight to a decent suspension setup for autocross? I am finishing up putting coilovers(which have camber plates) on my car, and I am wondering how much camber I should run, and additionally, how does that affect the tire pressure I should use? I know there are a tone of factors which affect this, so I am not looking for the holly grail of suspension set-ups. I am just looking for some general insight and suggestions. My tires are 215 dunlop direzza z1 star specs. Before with 0 camber, I was about 37psi(cold) in the front and 35psi in the back. On my last few runs last time around, my back end seemed a little loose, but nothing too bad. I have a 25mm sway bar in the front and a 27mm in the back, both are adjustable and both are on their stiffest settings. Any tips and suggestions are greatly appreciated!
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Rear is too stiff. Soften the end that slides, tire pressure and sway bar.
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You can go really aggressive with camber up front. I usually run between -2.5 to -3.0 with as much positive caster as my plates will allow. 34 psi front. Generally, the grippier the surface, the greater the camber. The trade-off is the loss of braking traction.
The why? More grip, = more roll, more negative camber loss to the body roll.
Generally, set up the front end first (which means soften the rear end for now).
When you have the front end gripping under power as in oversteer, then play with the balance with the rear bar.
Now, I do have Koni's (1 turn from full soft) and relatively soft springs (prodrives), and a mere 20 mm FHI rear bar, and I'm still working things out (first season out of D-Stock), and 225/45-17s, so take it for what it's worth, but on grippy surfaces, the car pulled in under power thru pin turns, enough to alter my lines. You still can't carry momentum in, but that's par for the course for a rather nose heavy car.
[edit] Forgot to mention, I can loosen and tighten the rear end quite a bit using rear pressures, tight is down around 42 psi, loose around 48 psi. Since the OP runs a MUCH bigger rear bar, the initial pressure should be much lower. Use chalk/shoe polish to establish a start point, but I'd guess 35 - 38 would be a good start point.
Last edited by Scargo (2011-09-21 21:16:23)
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Ok so what I am thinking so far is to set the front caber to around -2.5 and probably 37-42 psi? and leave the sway alone. I am thinking for the back to maybe add more camber(-1.5?) and lose some tire pressure to get more grip while putting the sway on the middle setting. The next thing which I have a need to look into is dampening. I'm assuming that I should run the front more firm than the back if the back is a little loose? Ehhhh I've got a lot to learn.
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I run something similar to Scargo's setup. IMO you want the most negative camber you can get on our cars.
There is a guy locally who was having GREAT results with ~-3* camber and 28psi in his Star Specs though.
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yawnoCmai wrote:
Ok so what I am thinking so far is to set the front caber to around -2.5 and probably 37-42 psi? and leave the sway alone. I am thinking for the back to maybe add more camber(-1.5?) and lose some tire pressure to get more grip while putting the sway on the middle setting. The next thing which I have a need to look into is dampening. I'm assuming that I should run the front more firm than the back if the back is a little loose? Ehhhh I've got a lot to learn.
You're concentrating on the wrong end. Soften the rear (go stock, essentially) and forget about it until you're front is biting so hard that your turn in is throwing you into cones. Lower front pressures as much as you can go w/o tire rolling. Slowly raise front shock settings (trying to kill dive and roll, but don't over do it, that's the spring and sways job in reality). When the front is stuck, THEN tighten up the rear to taste.
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That. Exactly.
Up your front camber, and get your tire pressures set right in front. If the rear is jumping out in slaloms or fast transitions, you might need to soften it up, but focus on getting the front to do exactly what you want. I ran about -3.7* on Hoosiers last year with smaller bars and softer springs, and it was pretty good. For street tires, somewhere around -3* is probably the point of diminishing returns. I had my best results with 0 or a tiny bit of toe out, but I know people that dialed toe up and were fast. It just seemed too twitchy for me. My opinion is "a little goes a long way" when it comes to toe, I guess.
Oh, and it really helps if you can set yourself up to do your own alignments if you're playing with stuff a lot. Otherwise, you are either spending a lot or guessing at what your adjustments really were.
Last edited by Linear Man (2011-09-22 07:55:42)
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I had the event today and finished 2nd in novice(yeah I'm a n00b). I ended up running -1.5 in the front(somehow the most I could get) with my tire pressure at 40psi. I should have listened to you guys and put my rear close to stock. 
It was loose all day, causing me quite a bit of trouble. Anyhow... I recorded all of my runs in 3D and put my fastest one up on youtube for the world to pick apart my mistakes. To watch the video, cross your eyes to line up the frames, then relax your eyes and enjoy.
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WHY are you setting the front pressures so high? This will only promote understeer due to a smaller contact patch.
One of the reasons that you "feel" that the car is loose is most of the turns (not the slaloms, those are done well) you're turning in late, which upsets the car. Seems some of the faster turns you are getting the expected understeer. Not sure why the pin turn at the end seemed to have you seem to either oversteer (or turn in too early), the one turn that I can't see precisely why the effect occured, although I think your approach was too tight, which may be part of the cause.
Finally, for a runway, that surface looks pretty rough. Lowering overall stiffness will actually help there. I imagine the car is bouncing around and losing contact over a number of those pavement changes.
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My eyes are still jumping after all that camera shake, but my initial impression was that it looks like you need brake harder entering some of those turns. Enter properly, and then get out quicker, because you will then be on a better line. Don't worry, I did this a LOT myself, but that "slow in, fast out" thing works. It's just damn hard to do when you're fired-up.
And, if you didn't drop your pressures as they got hotter, 40 probably is too high, because it would be around 44-45 after 4 or 5 runs. 40 hot might be OK, but a couple pounds lower should still be better, just as Scargo said. These things might be related, too, because you might BE rolling the tires over more if you are over-driving the entries. Believe me, I did that, too. Trying to adjust the driving is better than adjusting the tire pressure in this case. This made me miss autocross, though... 
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What did you end up doing with the camera mount?
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Scargo wrote:
WHY are you setting the front pressures so high? This will only promote understeer due to a smaller contact patch.
One of the reasons that you "feel" that the car is loose is most of the turns (not the slaloms, those are done well) you're turning in late, which upsets the car. Seems some of the faster turns you are getting the expected understeer. Not sure why the pin turn at the end seemed to have you seem to either oversteer (or turn in too early), the one turn that I can't see precisely why the effect occured, although I think your approach was too tight, which may be part of the cause.
Finally, for a runway, that surface looks pretty rough. Lowering overall stiffness will actually help there. I imagine the car is bouncing around and losing contact over a number of those pavement changes.
-I originally had the tire pressure at 38, but I thought I thought I saw the the front tires rolling a bit, so I raised them up to 40. I think think Linear Man hit it on the head though....
Linear Man wrote:
... you might BE rolling the tires over more if you are over-driving the entries.
-Turn around saw both understeer when I entered the turn too fast, and oversteer when I put more power down to rotate the back end around. Both of those ended up messing me up for the exit where I got off my line and lost some time.
-For your last point, that seems to be very true. In another run on the large slalom part, as I was coming around a set of cones and hit a bump causing my back end to swing around, and for whatever reason I couldn't control it.
I still have a lot learn though, this was only my 3rd race.
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iamchris wrote:
What did you end up doing with the camera mount?
I wish I could move it forward to get a better field of view, but that causes too much vibration.
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Have you looked at the Go-Pro mounts? They seem to quell vibrations very well and are cheap. I will admit that they are intended for the very lightweight Go-Pro's however, so a heavier camera may not fare as well.
And the vibration is partially due to that rough surface you're running on, and partially too stiff a set up for said surface.
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Scargo wrote:
Have you looked at the Go-Pro mounts? They seem to quell vibrations very well and are cheap. I will admit that they are intended for the very lightweight Go-Pro's however, so a heavier camera may not fare as well.
And the vibration is partially due to that rough surface you're running on, and partially too stiff a set up for said surface.
I have a little bit. They seem overpriced, and weak for my application. I would think that my camera set up is a bit too heavy for them. The vibration is due to multiple things. The mount that I have is the best I could think of for the time being. Ideally I would like to be able to make a mount that is stuck to the sunroof using a heavy duty suction cup(s), but I haven't been able to find any that would work for me.
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Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
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iamchris wrote:
Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
I will bring you along as a passenger as long as you're willing to drive down to philly for one of the events...
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yawnoCmai wrote:
iamchris wrote:
Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
I will bring you along as a passenger as long as you're willing to drive down to philly for one of the events...
Does this mean you're okay with being my emergency driver in the event of a failure?
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iamchris wrote:
Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
Handheld cameras are illegal for SCCA events. Do not know about other sanctioning bodies, but if you think about the concept of a free flying moderate weight camera in the event of a crash, the rule makes sense.
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Scargo wrote:
iamchris wrote:
Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
Handheld cameras are illegal for SCCA events. Do not know about other sanctioning bodies, but if you think about the concept of a free flying moderate weight camera in the event of a crash, the rule makes sense.
What if I Gorilla Glue it to my forehead? As long as it's not free-flying, I should be fine, right?
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iamchris wrote:
Scargo wrote:
iamchris wrote:
Bring me along as a passenger. I'll hold the camera. While I can't promise I won't reduce the vibrations, I can assure you that I will give snarky comments aplenty, insult your pterodactyl-like features, and wonder aloud how you managed to fit your beak in the helmet.
Handheld cameras are illegal for SCCA events. Do not know about other sanctioning bodies, but if you think about the concept of a free flying moderate weight camera in the event of a crash, the rule makes sense.
What if I Gorilla Glue it to my forehead? As long as it's not free-flying, I should be fine, right?
I don't think you would be able to get your helmet on then. I suggest super gluing both your hands around the camera.
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It WOULD be legal glued to your head or hands so long as either body part is firmly Bolted (toggle clamps also okay) to a fixed part of the vehicle. If you suction cup the body parts glued to the camera, the camera and mount MUST be external to the passenger compartment...
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I can't help but think about you improving your braking and iamchris PAYING for it, but do what you like. I know if that really was what he was trying, I would "work him out". Make sure he's up to it, you know.
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yawnoCmai wrote:
I had the event today and finished 2nd in novice(yeah I'm a n00b). I ended up running -1.5 in the front(somehow the most I could get) with my tire pressure at 40psi. I should have listened to you guys and put my rear close to stock.
Sounds like your hooked 
-2.2 all day long. anything more and your really eating the tires up pretty quickly.. put a white shoe polish stripe on your sidewall to the shoulder of the tire.. bump it up to 40 psi and see what kinda marks you have touched, Be careful with not exceeding the tires recommended air psi. You also have to base this off how the course turns are incorporated with the mix in your final result. Changing camber on the fly affects your toe just remember that.
I would put the rear bar on the softest spot, allowing the suspension to move on braking and turn in. This will help tremendously in dynamic camber 
You want positive caster for improved dynamic camber. It's really not adjustable unless you have camber / caster plates and can dial accordingly.
Dynamic camber helps reel in the ability in the car doing what you want..
as far as your video.. I see two things that stick out
1. Your not looking far enough ahead, this is a big fundamental. Do this .. pretend there is big piece of cardboard over your windshield and you can't see shit! I didn't really see your head moving left to right at all, the other point was because of this your you could see you had the car cone to cone. I could be wrong but I think I saw you pretty wide on a few of those, as a result to this...
2. Are you left foot braking?
Marty 
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There's a lot to respond to here, but here we go...
-Yes. I am hooked.
-I learned that camber affects toe, since I used the camber plates to dial in the camber on both sides. For whatever reason, I needed to move the right front in a decent amount more than the left front. After this I noticed the alignment was off... Now I know. Even up the camber plates and use the camber bolts to even the camber on both sides.
-Will do on the rear bar. What do you mean by dynamic camber though? I'm guessing it's when the suspension geometry causes the wheel to gain negative camber as more force is put down on a given corner(I have no idea how to word that right but that is my best shot).
-I do not have the ability to adjust caster with my plates. 
-As for looking ahead... I know I know I know I know. It is something I have been trying to work on, but haven't been doing very well at.
-I do not left foot brake, since I am no where close to feeling comfortable doing it yet. What is the best way to learn? I have tried doing it a bit on the streets but it just feels so unnatural right now.
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