First Autocross

[GTBradley]

Well, I finally got around to enrolling in an autocross event, in fact, I did the Rocky Mountain Region's Porsche Club Autocross University this last Saturday and then their regular autocross event on Sunday. Let me say first, this was the best experience I've had in a car! well...ah...you know what I mean. The training was very helpful. They had us do skid pads, which are just big circles while holding the steering wheel steady and steering with the gas; slaloms; and triangles, where you speed from one gate straight to the next - brake hard, turn hard, go hard. Then, in the afternoon we practiced an autocross course. I learned a lot and and had blast!

Sunday was the real autocross with 70 or more attendees. I ran over a few cones and got a couple of DNFs by missing gates, but in the end I think I did okay and the car is fantastic! The issue I need help with is car handling, as in, the addition of anti-sway bars, and or...suggestions appreciated.

I'm pretty sure I need the front bar to control the oversteer I'm experiencing, but I don't know that I need rear bar, and if I do, I won't install it until I can do another autocross to see the result of adding the front one. I've got a very short video of my runs and input is appreciated. I can tell already that I need to tighten up against the cones more, but beyond that I really don't know what I'm doing wrong, or right. It's pretty much all instinct right now, other than some things I can apply from the training.



Also, I see that Mike Forte has just the front anti-sway bar for $189. Is this a good one to install and where would I look for one for the rear?

Thanks

[J R Jones]

GTB, you appear to be on the right track. If you have no anti-roll bars add one to the front and evaluate. Then you may be able to add a rear bar but a rear bar can make oversteer worse. A locked differential will also make oversteer worse. Testing at different places or different days is confusing. If you add a front bar, make a run with one link disconnected. Connect the link and make another run. The difference will be apparent.

[GTBradley]

I didn't think of disconnecting the bar to evaluate, thanks, I'll do that.

What causes a locked differential, by the way?

[Jeff Kleiner]

Let’s start with the basics—what is your tire pressure? I’m not seeing steady state oversteer; I’m seeing a snap oversteer when you jump out of the throttle while it’s pushing. With the factory spring rates our cars understeer and adding a front bar without a corresponding change to the rear will exacerbate that pushing condition. These cars run on a knife edge and reward smooth. You have to go easy with the inputs; no jerking the wheel and no treating the throttle like an on/off switch. When I instruct novices they almost universally think they need to change the car but more often than not there are 3 other things that they need first 1) seat time 2) more seat time 3) still more seat time

Jeff

[mike223]

When I instruct novices they almost universally think they need to change the car but more often than not there are 3 other things that they need first 1) seat time 2) more seat time 3) still more seat time

It's going to take your average non-autocross experienced enthusiast at least two years (20+ autocrosses) to learn to manage one of these cars "pretty well" on an autocross course.

It would take a "good" fast experienced Miata driver at least a year (maybe more).

It's one of the most challenging cars you could pick to learn to autocross "well".


The tricky thing about them is all your driver inputs (can/should/will) cause a whole lot of weight transfer - real fast - with consequences.

Once you learn to manipulate that weight transfer to your advantage - it's a beautiful thing.

Until then - most chassis modifications are pointless.


On an autocross course - the driver's ability to transfer that much weight, that quickly - can make the best handling car completely unmanageable (with the wrong driver input), and a poor handling car FTD (with the right driver input).

There are few other vehicles that compare in that regard.


Looked like you got through your first autocross pretty well to me - no disasters - keep at it.

[Mike N]

As Jeff said, Smooth is fast. Smooth also feels slow. If you consciously ever so slightly slow down your throttle and brake application (weight transfer) you should find things easier to control. My first year at auto x the two biggest changes I made to the car was a seat with more lateral support and a Russ Thompson gas pedal that is far more progressive and less like a switch. If you mess with the car set up at the same time you are learning the car you will probably get frustrated. Get a good alignment and make sure your tire pressures are consistent. My car likes 21/22 front and 23/24 rear. Then practice learning the car. I had a local pro drive my car a couple of times with me as passenger. His first run he was 2 seconds faster than me having never driven the car. With him as passenger and a little instruction on unlearning bad habits I was soon much faster.

[Jeff Kleiner]

I wasn't going to go there yet with my earlier post but since Mike & Mike started talking transfer of weight I will---there is no better time than now for you to start learning left foot braking. This allows you to modulate the brake and throttle together to smooth those transitions. You'll be applying brake (sometimes a lot of it!) before you're fully off the throttle and vice-versa. It will allow you much, much more control on turn in as well as coming out than doing a busy and clumsy one footed dance with an on the gas...off the gas...on the brake...off the brake...on the gas routine. You can often feel the car start to move in an unwanted way and settle it with just a little more brake without having ever having to get out of the throttle---or the other way around.

Whatever you do though HAVE FUN!

Jeff

[CraigS]

I agree to some extent w/ the you need seat time comments. Still your car is loose. A couple of questions;
- what tires and what tire pressures?
- what alignment specs are you running? All of them please.
- what springs front an rear?
A way to get some idea of camber and tire pressures is get an old school white shoe polish w/ the sponge applicator. Put 3 inch or a little more dots at the edge of the tire tread. This will show you how much the edge of the tire is rolling over. You want the white worn away down to the tip of this triangle.
Tire triangle by craig stuard, on Flickr

[TMartinLVNV]

Bradley, this is something that I also want to try. I'm pretty nervous to do it. The training beforehand is pretty awesome too.

When watching your video, this is what came to my mind

[J R Jones]

GTB, As you can see there are suggestions beyond your anti-roll bar (ARB) question. Indeed acquired experience improves performance but also understanding of what the mechanical bits are doing. Do not underestimate yourself. Some people are naturals and develop driving skill quickly (Mark Donohue); some people just don't get it (my wife). Your SCCA event sounds like an excellent learning experience.
My locked differential comment is not malfunction related. Differentials can be open, limited slip clutch type and limited slip ratchet type. There are also "spools" that lock the axles together. As the axles are coupled together the outside (heavily loaded) tire dictates the axle/tire RPM. The inside tire (lightly loaded) on a smaller radius has to compensate by skidding. That can result in oversteer. In the seventies I set up a Shelby GT350 to run a Trans Am at Elkhart Lake. I had previously run a 289/302 with 3.89 gears on a Detroit Locker (ratchet type) differential. For this event I had a Boss 351 and was over-revving on the straights. I was out of Lockers and set-up a 3.50 gear set with a (cheap) spool. Next day the Shelby had transitioned to oversteer. We disconnected the rear anti-roll bar and the car improved dramatically. The reason? In roll, the inside ARB link is restaining the body lift and unloading the inside tire, leading to more skid.
Other things to consider is weight proportion and power application. A big block cast iron engine has weight bias forward, and a lighter rear axle. If you have adopted the huge power philosophy, that makes autocross more difficult. I was asked to run a GT40 MKIV (427 side oiler) at an Elkhart Lake vintage event. The car was hard to drive in traffic and passing was compromised by (2) 4V carburetors with all throttle plates liked together. Acceleration was explosive. Not only was oversteer an issue, I could not follow other cars closely to set-up a pass. A progressive throttle makes a car easier to drive.

[GTBradley]

Thanks for the input guys, except you, Terry, but I'll get to you later.

I understand seat time is king, I am a professional pilot and the value of chair flying is very important too. I'll keep at it.
- Tire pressures are 22 all the way around. The car weighs 2272 lbs - maybe I should go to 23 psi?
- The throttle is a problem, no doubt. It's the electronic control pedal for the Coyote and the engine responds so quickly that I know I'm causing a problem. The pedal had to be shortened and that just makes it that much more sensitive.
- What I'm getting is that the car doesn't necessarily need the ARBs (thanks for the initialism, JR...much easier!), front or rear. That was the reason I didn't add them during the build, but so many builders add both that I figured there was an obvious need for them. Not to mention, every experienced driver I talked to at the event told me to get the front one. Granted, they don't know these cars. I'll get better at this and then consider it.
- What the car does need is accurate, controlled inputs. First, I will try the right foot throttle and left foot brake technique. This will be a good time to set that habit for Autocross and is easy enough to do as I don't need to shift out of first anyway - not impossible I know, but just less to do for this novice. Second, I bought a heel stop from Breeze and will install that to give me, hopefully, more stability, reference and control on this hyper-sensitive gas pedal I have. Third, I'll slow down the inputs. That's a tough one because I'm very excited and happy driving the course. Discipline! Smooth weight transfer!

The springs are standard FFR kit springs - front: 500#, back 400#. I'm wondering about the fronts now though, the engine is only 445 pounds, but I have the battery up there too. My corner weights resulted in nearly 50/50 weight distribution front to back with just a bit of rear bias. The shocks are the Koni red single adjustable and the ride height is 4.5 inches front and back. The white dot is a nice idea Craig, I'll try that.

JR, I'm almost sorry I asked about the diff lock. I'll save that education for when my brain is bigger.

Alignment specs:

Alignment specs 10-20-2020.png

And last but least, Terry, I was way deep in this treasure trove of technical information so graciously given by these talented people that when I looked at the picture you posted my first though was: hmm...those people are looking at a monitor...ah! my video is what they are looking at and their faces seem to show they are impressed by my driving?...wait...no...there is a white bubble helmet!...yep that's me. I snort-laughed at that one. Thanks, buddy.

[J R Jones]

GTB, I am new to this group and by nature, I do not pay attention to embellishments. If I had reviewed your signature(??) I would have seen two details I questioned, rear axle type and engine.
Your comment on (not) shifting causes me pause. I have difficulty hard-driving a car in first gear. Not only does it slap-load the driveline to excess, the weight transfers are huge. Additionally it results in an excess of rear wheel braking on decell. Adding hard braking to 1st gear decell can cause the rear tires to lose traction. I suggest using second gear regardless of not being at optimum power and torque. You have plenty of power and minimal weight. The throttle inputs will be more modulated and decell brake from the rear tires reduced. I assume you do not have an automatic transmission.
I was USAF with Fighter/Interceptors and respect the capability of pilots. I predict that you are a "natural". Back in the day the Road Atlanta road course was purchased by the Porsche endurance racing Whittington Bros. They were consistent winners "out of the box". Road and Track magazine interviewed the Whittingtons and asked "Where the hell did you guys come from?" Answer: "We have been pylon racing aircraft for years, this car racing stuff is child's play". I attend the Reno races, and I get it. OTOH there was the issue of their substantial wealth, which turned out to be large scale drug commerce. They were not nearly as fast in jail.
BTW you may consider going to a cable driven throttle body that can be set-up to your preference.

[Jeff Kleiner]

I didn't catch that you ran the entire course in 1st gear when I watched the video but I agree with J R.; that's a big contributor to the extra sensitive throttle. I'd grab second between the first and second gate and stay there. Your tire pressure is a good starting point (I think you're running 555G2s right?) You could come down a bit but I wouldn't recommend going up because that will begin to lessen your contact patch. I usually run very low 20s and high teens on R-Comps depending on the temperature and surface, often times with a 1-2 psi front/rear split.

Jeff

PS to J R Jones: If you didn't happen to catch the news, Bill Whittington died when a plane he was piloting crashed in Arizona last Friday.

[GTBradley]

Embellishments!? No one has any embellishments in this forum! You are correct, it’s a five speed manual. I was so impressed by the engine’s wide rpm band it never occurred to me that the back-pressure alone would cause rear braking issues. Point taken, straighten up and fly right it is! I don’t know about “natural” but I do have the confidence to push my comfort level and that can help.

In my corporate flying days I had a couple of guys pursue me for a while to fly for them. They were fond of telling everyone how rich they were. I dodged them until they went to federal prison for campaign finance law violations and wire fraud.

Welcome to the forums, you’re an asset to us already.

Correct, Jeff, they are the triple fives. I’d read, probably from you, that starting on less sticky tires will help me learn. I’ll keep it to low 20s psi range.

[Mike N]

Before you consider a cable throttle it's worth noting that with a drive by wire throttle sensitivity is adjustable with a simple tune and customizable to almost any progression you want.

[GTBradley]

Before you consider a cable throttle it's worth noting that with a drive by wire throttle sensitivity is adjustable with a simple tune and customizable to almost any progression you want.

That’s good to know, thanks. I’m guessing that second gear is going to have a pretty pronounced affect on the “switch” like condition you mentioned, so I’m hoping to not have to spend that kind of money just for throttle application. We’ll see - I’m enrolling in the very next autocross event in May.

[Avalanche325]

If you had fun and got at least one timed run in. Good job on your first autocross! You did a nice job catching the car when it got loose.

I get out of 1st immediately. Launch (you can launch a little harder in my opinion) and short shift to 2nd. These cars a bucking broncos in 1st. What gears are you running? That was a pretty open course and I didn't hear any rev limiter.

Mark your sidewalls with sidewalk chalk ... it comes off easily. Adjust your tire pressure according to that and the triangles mentioned above.

For sway bars. Yes they definitely help these cars, and you could go ahead and do it. However, there is no need to do ANYTHING besides adjust air pressure for the first season. For the first two seasons........it ain't the car ;-) I am running VPM swaybars on a 3-link. Front is set to stiffest and I adjust with the rear.

When you do start spending money, start with tires. 555s are a good cruising tire. NT05s are a good all around tire. Tires are what make you accelerate, turn and stop. They are the single best upgrade. I also agree that less grippy tires are good for the 1st season learning curve. Well, maybe your own helmet 1st if that was a club loaner. Loaners get real nice in the summer.

Get a camera mount that will let you see what your hands are doing. Looking at the back of your helmet really doesn't help to see what you are doing.

I find that if the car is 100% hooked up, I am slow. Mine has to be dancing on the very edge. Try to never coast. You should be accelerating all the way to where you have to brake.

I haven't been for a while due to COVID, I am getting back out in a few weeks.

[GoDadGo]

Go-Dad's Input:
You Drive Better Than I Do!
Looked Like An Absolute Blast!

[GTBradley]

Thanks and, yeah, I felt like I was progressing and learning. In the morning two runs were DNF, then one cone, then a good run. In the afternoon two DNFs and then two good runs. My best time was the 7th run and it also had the most "dancing on the edge" ie. the video. That put me about two thirds the way down the list of times at the end of the day.

The gears are 3.55. I did see I recorded a top speed of 47 mph and that would put me at about 6200 rpm with a 7000 redline. The Space Balls helmet is mine - I really didn't want to stick my head in an old, sweaty helmet countless other people have worn.

Good luck getting back out there.

[J R Jones]

GTB, There are cars designed without ARBs and they do OK. Spring load limits are experienced under max braking (2) and max cornering (1). Bottoming in either case results in no suspension travel, leaving the spring rate of the tires to adsorb surface deviation. Tire hop can result. Installing an ARB adds to roll spring rate. An ARB could be combined with lighter coil springs for more suspension compliance. We ran a season of SCCA Showroom Stock "B" against Saab 900s and they had outrageous roll angles, and won the National Championship. Racing in the rain, roll compliance and (side) weight transfer is advantageous for traction. ARBs are disconnected.
An advantage you have as a pilot is operating in three dimensions, you have to see more and react more. Obviously even in IFR your senses are acute for survival. The horizon is a constant reference. Your reference on the track is similar in that you should not be monitoring the environment around the car. You should have the next cone memorized as you seek the cone(s) further down the course. Muscle memory is in the corner, your head is down-range.
In the back of my mind I seek energy conservation. The corner will adsorb some forward momentum, and the brakes supplement as necessary to make the turn. Obviously long straights require braking to set-up the turn. Eventually you will be picking apexes, a more specific conversation

[GTBradley]

And here I was thinking of buying a book on the subject. It really seems that you know this sport! Maybe you should write a book. Thanks for all the advice/education. I can see this becoming a serious pastime for me and this help early on just adds to the excitement.

I really didn’t have much trouble looking past the next cone or two once I told myself to do it, but I haven’t developed the spatial sense that would allow me to get tighter to the cones. In fact, I was impressed with my ability to avoid hitting them until I saw in my video how far I was from them. The big thing for me will be developing that “line” in my head. Gotta stay ahead of airplane, right?

keep it coming, I’m sure many other people are enjoying this too.

Bradley.

[J R Jones]

Brad, Autocross attracts a variety of cars which makes for entertaining competition. Each contestant has strengths and weaknesses. Playing on strengths means not all cars will address the course in the same manner.
You would not look to a Mini Cooper or Lotus for technique. A WWII P-38 pilot told me of dogfighting Mitsubishi Zeros over China. The Nippon Ace got on his tail and Ralph used the "energy tactic" for escape. Full Mill from two 2000hp Allisons spinning 12 foot props provided a vertical climb to safety.
Prior to running for effect, evaluate the course for your energy tactics. The best line through the corners is not necessarily the tightest radius. Some corners are just a means to optimize the straights for maximum speed.
For instance picking an early apex before a straight means you dwell through the turn before acceleration. Coming in from the outside and a late apex positions the car to accelerate straighter and earlier. On the other end of the straight, provided the turn does not lead to another significant straight, you may consider late braking over optimum corner speed.
BTW I was at Lowry AFB 12 months for training and had a part time job working near Cherry Creek for Vince Martino. Vince had full service Texaco stations and a tire store. Quite a guy.

[Avalanche325]

You will find that most of your cone strikes will be with the rear of the car. As JRJ is saying, late apex is your friend. In autocross terms, "back-siding the cone".

On the course walk. Walk where you (not the center of your car) will be. You should be right next to the cones on the left and 4 ft away from the cones on your right.
Find the fastest section or two. Then do everything you can to come out the preceding element as quickly as possible. Even if it means going in extra slow.
Find the slowest section. Then realize it is going to be slow no matter what. Don't try to make it fast. Just keep it tidy. You can lose a lot of time trying to take a 20mph turn at 21 mph..
Almost always, the shorter distance is faster than carrying speed in autocross. Unlike a road coarse.
A little bit of slip angle. Never drift.........well if you want a fast time. It sure is fun though.

You should be looking very very far down course. Way more than a couple cones. I went to an SCCA Starting Line autocross school run by two national champions. They had us walking the course. One of the instructors walked crazy far down course and then they said , "That is where you should be looking". I thought I WAS looking down course. But needed to double it. I was also looking at apex cone on a turnaround, and have since learned to look at the exit cone as I am entering.

Here is a little warm up that I do on the way to the event, if you have open road. I move over until I am just clipping the lane reflectors on one side then the other a few times. As I am moving over I try to nail exactly when I will start hitting them. That helps with refreshing my memory on where the outer edges of my car are.

[Jeff Kleiner]

A 40 year autocrosser once told me that anyone who never hits a cone thinks his car is wider than it really is! An exercise that we sometimes do during our novice schools us to send drivers out and tell them to clip some cones to help them learn where the corners of their cars are. Oh, and our cars WILL blow cones over with the exhaust if you’re close to it and hard on the throttle. I’ve been told more than once by courseworkers that they’ve seen it happen.

Jeff

[GTBradley]

Finally came up with a negative aspect off side pipes.

That's not a bad idea, I think I'll purposely try touching cones on my first runs, I was running them slower anyway.

[nucjd19]

I just wanted to chime in and say thank you to everyone that have been posting. This has been an excellent and informational thread. I can't wait to get my rig out there soon and give it a go in my roadster and some schooling as well.

[Jeff Kleiner]

My friend Ben caught me in an "Eyes up and looking ahead" moment a few years ago...



Our minds have an amazing ability to take in what's ahead and process it long before you get to it while still unconsciously maneuvering us through the previously processed part of the course we're on at that instant. Keep this in mind:The hands go where the eyes go This plays right into something that I tell the students when instructing---"If you're not focused ahead and are looking directly at the cone you're approaching you'll hit it!"

Cheers,
Jeff

[CraigS]

Yes, 2nd gear will be a much smoother run for you. A few times per year I get a course where there is one very slow turn and am tempted to go back to first. I have tried it a few times and it never works out. Too much power at first and then wasted time going back to 2nd. Looking ahead is key. The next turn almost allways determines how I will do this turn. Last weekend we had a part of a course where we had a series of 2 cone gates forming slightly curved straight and then a slalom. They were both going the same direction but the slalom was offset to the right by maybe 100ft. The first cone of the slalom was 200 ft past the last gate. The tendency was to hold the gas down as long as possible after the last gate and then make the jog over to the slalom. I was lucky enough to see that part of the course while I worked. It was immediately obvious that one needed to slow going through the last gate, actually starting the turn to jog over to the slalom a little before the last gate. That meant I was as far left as possible through the next to last gate, right on the right cone and already turning at the last gate. If that slalom had not been there I definitely would have been going through those last 2 gates differently. One other tip I have found useful is figure a way in your mind to describe the overall course. Helps me not get lost. For instance on a rectangular lot, if looking at it from a drone, it might be in landscape orientation and start is at the left lower corner heading up along the left side. A way to describe the overall shape might be this; it is a huge extra wide letter 'M' with the points rounded off, the first point of the 'M' is a big wide 180 deg turn, the center point of the 'M' is actually more of a square, finish is a slalom coming down the right leg of the 'M'.

[GTBradley]

That is a nearly identical instruction I gave my flight students, Jeff. They tend to stare at the point they want to land and end up hitting hard sooner. Looking farther down the runway gives a much broader picture of what is happening all around.

Nice action shot there, by the way.

[GTBradley]

Craig, that sounds a little like the setup for the slalom I was doing. I wasn’t sure weather to treat it like the triangle exercise - head straight at it brake hard and turn hard - or sweep wide to be in position for the slalom entrance, or just not accelerate and keep it slower. Sometimes it seems really difficult to see what is best.

PS. I bet that hardtop comes in handy when waiting your turn at the start line in July.

PSS. Did you get a chance to look at my alignment specs?

[Rdone585]

I'm sure Craig will take a look soon. As pointed out earlier, an abundance of seat time before making too many changes will be the best thing for you in the long run. Hear are my thoughts on your alignment specs, you could benefit from running more camber in the front. My front camber is -1.8 degrees. I have a solid axel rear, so that's not adjustable for me. I've been told that rear alignment can make dramatic improvements in car performance. If you have a IRS, there may be some benefit from putting more camber in the rear also. Others can provide better advise about rear setup with IRS. Running more camber (front or rear) can cause quicker wear on the inside of the tire. If you also do a lot of street driving, you may notice this sooner, so manage accordingly. Some drivers with the ability to do their own alignments may have different setups for street versus track use.

[J R Jones]

GTB, Opinions on alignment specs is a bit like debating politics. Diverse opinions!? My career has been development at and for OEMs and I understand how much time and money they spend on that. I will weigh-in but defer to your assembly manual, the FFR Tech Department and Jim Schenk. Your car is straight forward without the influence of FWD or AWD. My guide is Carroll Smith's Prepare to Win, despite it's origin in the seventies.

The castor is excessive, for the street but more so for autocross. 7+ degrees leads to high steering effort and hard self-centering. 2.5 to 4.5 will steer quicker and still be straight line stable.
The camber is OK but you might measure camber gain with suspension deflection (like bump steer) Increasing camber with jounce to -2.5 degrees is good. After a run if you measure excess heat on the inside tread, your camber may be too negative.
Toe in front is OK, could be half that as long as straight stability does not degrade.
Toe in rear is to compensate for suspension deflection under acceleration/braking. 0.12 is a little high, especially if you do not have plastic/rubber bushings.
I am surprised at the wheelbase difference. It is a challenge to alter that with (rear) adjustments and maintain alignment. Maybe half on one side and half on the other.
Craig and I have discussed bump steer. It could be helpful, but more for the street. Many like the dial indicator method, Craig and I prefer a laser.
With spring/shock, wheel/tire removed:
Place a laser (line or gun-sight dot) on the wheel hub aimed to the side. Place a target field at the tire tread radius distance. Trace the laser at ride height.
Cycle the suspension to jounce and droop to see if the laser moves off the tracing. The difference is bump steer.
jim

[Matt Ries]

I'm always amazed by by the Factory five community willingness to share there wealth of knowledge! GTBradley, I think I might be this summer 4yrs of playing this Autocross game, it really is a lot of fun! I still think of my self as a rookie I think of it like a theory that you have to prove out, examine, inspect, question, make notes, make changes and repeat. Make notes is what I would add this this thread, I keep a little black note book to log as much as I can. I can't remember numbers, and there are lots of them in this game, Temps for example; 4 tires, 3 each, temp for the day, morning, noon, evening? engine temp. Tire pressures. Heat cycles. Dates, suspension alignment settings, shock settings. Corner weights, fuel load. Plus changing the loose nut behind the wheel (Me). Start basic tire pressures and temps add as you go and as you feel comfortable. This thread has a lot of information in it I want to take a highlighter to it and keep in my book!

[mike223]

Playing on strengths means not all cars will address the course in the same manner.
You would not look to a Mini Cooper or Lotus for technique.

The "perfect" Miata / Mini Cooper line is certainly not always (or maybe even often) the same line as would be for these cars.


But I'm occasionally reminded that (in autocross) I often have to run the same line they're running because their (high) traffic is keeping their line clean and throwing all the debris (pebbles, scruff, etc) on to my (higher power / lower traffic) line.

And the cleaner line is simply faster than the ideal line.


Not to disagree - just food for thought - an observation.

[CraigS]

I think your specs are fine for the street. I run a LOT more camber because I prioritize AX, -3 front and -2 rear. I use cheap as possible street tires so I just put up w/ them wearing off the inside edge. They still last 4 years or so. I checked your build thread and see you have power steering so the 7 deg caster is exactly what I run. You may end up wanting to be able to do your own alignments. Just depends how serious you want to be about AX. If you do decide on that we can help w/ equipment thoughts. You can get everything you need for <$300 so that compares pretty well vs paying someone to do them. But for now, lets see how you do running 2nd gear. I think you will have much less oversteer so it will be a lot easier to drive. When you are judging your handling balance keep a couple things in mind;
- slaloms are generally faster w/ a little more understeer(BTW when you walk the course measure the distance between cones by counting steps of any slaloms w/ 4 or more cones. It doesn't matter the number, you just want to know if the spacing is the same all the way though)
- if you have a nice wide turn of about 180deg this is where you can judge pure mid turn balance and it's nice to have it perfect to a tiny bit loose
- balance can vary on different parts of the course due to surface type and amount of debris/sand. So, if you are always loose in a given turn, ask a couple of the guys near you in the grid how it is for them. Just be sure they are driving a rear drive car. If they are loose too, then you just have to drive around the problem.
- don't make any changes based on the first run. Wait until after the second run to make notes and/or change something.
- I always drive every run as fast as possible. I see/hear some say they do the first run slightly slow to learn the course. I don't think I have enough runs to plan on throwing one away. I feel they 'may' learn the course but they don't learn anything about how the car is doing by driving at 90%.
- we all love the sound at full throttle so the tendency is to try to hold it as long as possible. But understeer is often not the car, it's the driver charging into a turn too hard. I would much rather be 2 mph slow on entry but be able to get back on the gas sooner.

[BradCraig]

I think your specs are fine for the street. I run a LOT more camber because I prioritize AX, -3 front and -2 rear. I use cheap as possible street tires so I just put up w/ them wearing off the inside edge. They still last 4 years or so. I checked your build thread and see you have power steering so the 7 deg caster is exactly what I run. You may end up wanting to be able to do your own alignments. Just depends how serious you want to be about AX. If you do decide on that we can help w/ equipment thoughts. You can get everything you need for <$300 so that compares pretty well vs paying someone to do them. But for now, lets see how you do running 2nd gear. I think you will have much less oversteer so it will be a lot easier to drive. When you are judging your handling balance keep a couple things in mind;
- slaloms are generally faster w/ a little more understeer(BTW when you walk the course measure the distance between cones by counting steps of any slaloms w/ 4 or more cones. It doesn't matter the number, you just want to know if the spacing is the same all the way though)
- if you have a nice wide turn of about 180deg this is where you can judge pure mid turn balance and it's nice to have it perfect to a tiny bit loose
- balance can vary on different parts of the course due to surface type and amount of debris/sand. So, if you are always loose in a given turn, ask a couple of the guys near you in the grid how it is for them. Just be sure they are driving a rear drive car. If they are loose too, then you just have to drive around the problem.
- don't make any changes based on the first run. Wait until after the second run to make notes and/or change something.
- I always drive every run as fast as possible. I see/hear some say they do the first run slightly slow to learn the course. I don't think I have enough runs to plan on throwing one away. I feel they 'may' learn the course but they don't learn anything about how the car is doing by driving at 90%.
- we all love the sound at full throttle so the tendency is to try to hold it as long as possible. But understeer is often not the car, it's the driver charging into a turn too hard. I would much rather be 2 mph slow on entry but be able to get back on the gas sooner.

Please let us know that alignment equipment list! My shopping cart was ~$700 so I welcome an alternative to do my own for a cheaper price point. TIA

[J R Jones]

CraigS, GTB, I do not know what is the traction benefit of more vs less caster. It does provide more steering feel, and return to center, so perhaps with power steering there is an advantage. A collateral result is that caster increases camber when steering, more more castor = more steer-camber. Many suspensions designs incorporate camber gain with jounce, so static camber + +?
Our last SCCA National effort was a Mitsubishi EVO in T2, with the primary competition Turbo Solstice (factory supported) and BMW M cars (factory supported). We got invitations to the runoffs all three years and was the highest finishing EVO. We ran DOT tires, mostly Hoosiers but got supported BFGs for a while. Tires were significant, requiring a break in process and they lasted practice-qualifying-race. Maybe one more practice session.
Common practice was measuring tread temperature after every session with the objective of even temperature (tire factory recommendation). If we ran uneven temperature the tread blistered and we lost.
As a side, our car chassis dynoed at 260 as new. With stock parts we pushed the 2 liter with 21lb boost to 360 on race gas. Our advantage was not AWD, it was power and brakes. We aligned the car for speed in the straights, no toe-in.
Some academic questions are:
Does the tread have more traction hot? Methinks yes. If the tread is hot on the inside and cooler in the middle and outside, is the net effect more or less total traction? Maybe there is not enough time to heat the whole tire. (skinnier tires?)
What is the traction result of PSI (pounds per square inch) If the tread is heavy loaded PSI on the inside and light PSI on the outside, is the net effect more or less total traction? Does only a portion of the tread grip?
A skid pad G-force evaluation (scientific method, ABA) of camber extreems would resolve this. I wonder if Jim Schenk has done it?
Understeer or "push" tells you when the front tires are losing traction. I have trouble seeing that as beneficial. Obviously oversteer is a disadvantage too, especially snap oversteer and recovery oversteer. Sliding has been critiqued earlier in this thread, there just is not enough room on an autocross course. My theory is that driving to the threshold of traction of four tires is better than the traction threshold of two tires.
I raced a Sunbeam Tiger that was wonderful in that regard. Lap record and wins.
jim

[Jeff Kleiner]

Jim,
In the case of our FFR roadsters and Coupes more positive caster is beneficial leading to straight line stability, return to center and camber gain when turning however as you've alluded to it becomes unmanageable without power steering. They are unique animals and power steering is virtually mandatory if you want to autocross one of our roadsters fast. My buddy Joe suffered through a couple of seasons with a manual rack before changing to power and making a corresponding alignment change to more positive caster. The result was an immediate 3 second reduction over a slalom heavy 50 second course. As for front toe; toe out will get a little more bite at initial turn in but with our cars can make them a little darty at highway speed. Personally I'm willing to trade that off for better highway manners and run mine with about 1/8" toe in. That bit of toe in wearing the outside of the tires kind of evens the inside wear caused by the 1.5 to 2 degrees of negative camber...in the end neither are consequential since the 100 treadwear tires I use are used up in <5,000 miles anyway. If someone was so inclined it would be quick and easy to give a tie rod end a couple of twists at the venue to change from a street friendly toe in setting to a more track oriented toe out condition---I'm just not that ambitious

Jeff

[J R Jones]

Jeff, I understand. Looks like your alignment specs are more familiar to me. I agree with your sticky tire philosophy.
My last autocross experience was actually a BMW promotion, sent to me as a BMW owner and car magazine subscriber. They set-up a fair-park parking lot with a wet straightaway, and a dry AX course. They had a Volvo, Mercedes, Acura and the BMW 5-series. I expected the BMW would be quicker. A Pro gave us an in-car demo then we took turns. The Volvo was a yawn, the Merc was better and the Acura was spirited for a couple of turns, then the power steering pump ran out of pressure. I finished with shear muscle. The BMW was marvelous and I was flying on the pre-ultimate straight into the last hard left, then a short chute to finish. I late-braked wide with all I had and the Beemer was totally hooked-up. Crap! I underestimated the car and let-up on the brake to enter the turn harder. Wrong. The weight transfer and ABS had the front tires hooked up but when I lightened the brake the Beemer understeered through the cones. I wonder how the Backdraft with BMW suspension bits compares?

[Jeff Kleiner]

...I wonder how the Backdraft with BMW suspension bits compares?

Backdrafts are good cars! My Backdraft autocross buddy and I have swapped cars at events and have come to the same conclusion; his car with a Coyote has more power than my mildly built 325-350ish HP EFI 5.0 Windsor but mine has more grip. When we compete against each other it's a darn near even back and forth; sometimes he's faster and some times I am. Different ways of getting to the same end

Jeff