Suspension and Alignment Suggestions for Autocross
My present setup is:
Mopar STG3 frt and rear swaybars, STG3 coilovers w/o helper springs and 550#/inch aftermarket springs. Max rebound (all the way turned in) on the dampeners. Kumho 245/45/17 with about -2.0 camber front and rear. (or what ever I can get without rubbing on shocks). And finally 1/8' toe out front and rear.
Question is would it be better to remove swaybar and use softer springs on the front only ? The car seems to have pretty good rotation now but alittle twitchy.
It's been awhile for me... But if you have pretty good rotation with that setup, run with it. My alignement was/is based on a stock setup, so I have less camber in the rear. And would have toe out in the rear if i were still autoxing the car.
If these are new parts for you then I'd reduce the shock settings to midway or full soft even until you get used to the increased responsiveness. I drastically stiffened up a car once and spun it by about the third turn on my first run because I was still driving it like a softly setup car.
Other than adjusting the driver about all I can comment on is your aligment. You need to go with toe-in up front as it will improve transition response and it will put the power down better off the corners (I know, against conventional wisdom but it works, trust me). Reduce the rear camber to about -0.5, you don't need 2 degrees back there.
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Steve W.
2005 ACR SRT-4
The gods live at corner entry - Randy Pobst, June 2006 Sportscar (paraphrased)
Thanks for the comments...about how much toe in are you running ? I would guess not much because when I tried having some toe in the car got pretty twitchy in a straight line. I didn't get to try it on course though.
I get a fair bit of inside rear wheel lift also...isn't the idea to minimize this since it would only transfer more weight and therefore less traction to the frt ?
OBW this car is MUCH faster on course with the toy box set to only 9 or at most 15 lbs boost ( I have stg 3 engine and its a hand full with 25 lbs).
I see you are running Hawk brake pads...what are your comments about those compared to stock ? Also has anybody thought about trying the new BFG R1 slick for autocross vs. Kumho 710's ?
I could almost write a book on why rear wheel lift isnt horribly bad. Basicly, we can forgo a bit of traction in the back if doing so adds traction in the front. We like to do that in our front drivers cause alot of the weight is up front. Anything we can do to get more traction to the front the better however the investment often costs more than the return. For example (conceptual numbers here these are not by any means exact) if we give up 5% traction in the rear we might ... yes "might" gain 1.5-2% in the front. This is usually accomplished by decreasing the amount of roll in the back (think larger rear swaybar)
okokok that all said, with more traction up front we can go back to power sooner in the corner.
so bottom line: let it lift.
about the toe in the back, Im gonna go with Steve and his recomendations =]
oh crap i just realized now people will be putting iron pipes between their rear tires to get MORE lift.... This isnt what i was advocating. Once the wheel's load is zero there cant be any more weight transfer. SO a little lift is ok, a lot is just and takes more time for the tire to settle on transfer of the weight back to that tire AND it makes that transition harsher something we dont want. smooth is fast. so little lift ok too much isnt.
Thanks for the comments...about how much toe in are you running ? I would guess not much because when I tried having some toe in the car got pretty twitchy in a straight line. I didn't get to try it on course though.
I get a fair bit of inside rear wheel lift also...isn't the idea to minimize this since it would only transfer more weight and therefore less traction to the frt ?
OBW this car is MUCH faster on course with the toy box set to only 9 or at most 15 lbs boost ( I have stg 3 engine and its a hand full with 25 lbs).
I see you are running Hawk brake pads...what are your comments about those compared to stock ? Also has anybody thought about trying the new BFG R1 slick for autocross vs. Kumho 710's ?
Thanks again.
Mark, sorry for the delay in answering your questions. I run a total of 1/8" toe-in and for me, it made my car less twitchy in a straight line.
Some ways to reduce rear wheel lift would be to increase the front spring rates or lower the rear spring perches if you have adjustable ones. Going softer up front would actually make rear wheel lift worse. If I were you, I'd try lowering the rear ride height a little bit and see how it affects your times and the handling. An 1/8" or 1/4" change should make a noticeable difference I would think. However, like others have said, I wouldn't judge your setup solely by how much rear wheel lift there is. The stopwatch is what has the final say.
The Hawk HP+ pads are WAYYY better than the stock ones. It feels like you have a real friction material stopping the car as opposed to brute clamping force from brake pedal pressure. Speaking of that, pads with better bite save time on the course because if you can reach maximum braking quicker, you can accelerate for a longer time between braking zones. Make sense?
I haven't considered the BFG tire at this point since it does not appear faster than the Kumho or Hoosiers. I had a friend try them on his MSP 3 and he was faster on Kumhos.
I do little to no toe in on the front infact if you have stock LCA bushings then toe in up front will cause horrible torque steer under power as the tires fight to dig and the lca bushings flex and the toe in increases... And in the rear, zero toe has been recomended by the guru of autocross (steve w.) =] I personally like a hair of toed outtedness in the rear on short tracks to help get the ass around but makes for interestingly busy straight sections if you over do the rear toed out setting.
Hope this helps.
I do little to no toe in on the front infact if you have stock LCA bushings then toe in up front will cause horrible torque steer under power as the tires fight to dig and the lca bushings flex and the toe in increases... And in the rear, zero toe has been recomended by the guru of autocross (steve w.) =] I personally like a hair of toed outtedness in the rear on short tracks to help get the ass around but makes for interestingly busy straight sections if you over do the rear toed out setting.
Hope this helps.
David
David,
With all due respect, I've tested this. I've tried different toe settings on the same autocross course and been over a second faster with the toe-in setting vs. zero or out. Changing toe front or rear between runs is easy and something I try a few times a year just to make sure I'm on the right "track" with it. The car is signifigantly faster with toe-in up front than not.
I appreciate your input. Could I get each of you to tell what you are running toe in /toe out and where and also what kind of camber you feel is best ?
Mark I'm a road racer, my settings are mostly moot on an AX course. Steve is who you should listen to. The shortests course I run on is still 3-4 times longer than the longest AX course I have ever seen =] Steve I regard your experience with much respect so no worries. Setup has a lot to do with toe settings. For example if you are running the low durometer stock LCA the toe you will like may be more 'out' than with a poly bushing or even a solid LCA ( I run stock on ACR#2 w/s3 suspension and ragetek solids on ACR #1 w/stock ACR suspension ) I need less toe out on the solid bushed car than I do on the stock bushed car. There is no toe flex under accel in the solid car so its at zero. In ACR#1 when it was a stock car if you overdid the accel ( no tire spin ) the car toed in like mad and drove you all about ... its was downright scarey. I had to toe that out from zero about 0.5-1mm. All bets are off if you got bumpsteer due to over lowering your car as well.
Generally speaking ( and this is again VERY general... like from the textbook)
Too much toe-in makes the car unresponsive and spongey like a wet towel.
Too much toe-out makes the car twitchy and a bit short of straightline stability.
Just the right amount of toe out (very little mind you) is good for hiding tourquesteer and improving turn in and steering feel.
I feel that toe numbers of 3mm or more is excessive, again IMHO.
I guess bottom line the setting you have on your car is specific to how you like your car to drive. I tend to not care a bunch about stability and opt for reducing friction so I can go faster. For me, it all comes down to the end of the straight before braking. If I can squeeze out 2-3mph on the straights, and carry that at turn-in, I will be beating the guy who can't =] if we go one direction or the other we prefer to err on the side of toe out to improve turn-in. Again on a AX track you are not needing to do ANY of this. You are looking for the best setting to keep the driver happy and confident so he can concentrate on getting around the track and not on fighting a nervous car .. this is where the toe-in makes sense.
Sorry if this was confusing and for butting in, I should have left this to Steve in the first place =] lol
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Suspension and Alignment Suggestions for Autocross
and takes more time for the tire to settle on transfer of the weight back to that tire AND it makes that transition harsher something we dont want. smooth is fast. so little lift ok too much isnt.
Setup has a lot to do with toe settings. For example if you are running the low durometer stock LCA the toe you will like may be more 'out' than with a poly bushing or even a solid LCA ( I run stock on ACR#2 w/s3 suspension and ragetek solids on ACR #1 w/stock ACR suspension ) I need less toe out on the solid bushed car than I do on the stock bushed car. There is no toe flex under accel in the solid car so its at zero. In ACR#1 when it was a stock car if you overdid the accel ( no tire spin ) the car toed in like mad and drove you all about ... its was downright scarey. I had to toe that out from zero about 0.5-1mm. All bets are off if you got bumpsteer due to over lowering your car as well. 
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