Techniques To Practice for Track / Autocross

[profbooty]

Anyone who has even had a classroom session with Dan Unkefer with NASA has probably heard the following:

If you want to practice heel/toe or rev matching go find a cloverleaf. Mastering this technique means you won't upset the car if you are somehow in the habit of downshifting mid corner, and makes it easier carry more speed vis a vis trail braking. I'm not advocating practcing trail braking on a cloverleaf at track speeds even though most people technically do, but it doesn't matter so much at the speeds the average driver is traveling at on a clover leaf.

If you have an empty parking lot figuring out how to threshold brake or where your abs engagement point is will help you maintain higher speeds for a longer period of time on track/autox. I would never practice threshold braking in daily driving as you may get rearended.

[Ferdinand]

the soft suspension transfers weight very easily.

Relative roll-stiffness, front vs rear, can be used to tune understeer/oversteer.

If you put a massive big swaybar on the front end of the car then the front will be stiffer in roll than the rear. At the limit the car will pick the inside front tire off the ground, thereby transferring 100% of the front weight of the car to the outside front tire, overloading that tire and causing understeer.

At the same time, because of the relatively softer rear roll stiffness, both rear wheels will remain on the ground, more evenly distributing the rear weight between the two rear tires, thereby generating greater overall grip at the rear end of the car relative to the front, again inducing understeer.

The opposite, oversteer, happens if you put a great big honking swaybar on the rear while leaving the front relatively soft.

Here it is obvious that the stiffer end of the car, visually lifting the inside wheel, actually transfers more weight compared to the softer end which is allowing the car to lean over further under cornering without lifting the inside wheel.

[TomSuddard]

One small, but vital, clarification required here. It is a common misconception that a soft suspension will transfer weight more easily than a stiff suspension, or because a car leans over further on its soft suspension that it is thereby transferring more weight than a stiff suspension that barely moves.

Weight is transferred because the car is experiencing an acceleration, whether that is seen as body roll from side-loading due to cornering, or pitching nose down due to braking, or squatting at the back due to acceleration.

The only thing that affects how much weight is transferred is the magnitude of the acceleration experienced and the ratio of CG height relative to trackwidth (for cornering) or CG height relative to wheelbase for accel/decel. At the same cornering speed a car that is low and wide will experience less side-to-side weight transfer than a car that is tall and narrow.

Given two identical cars, cornering at the same speed, the only difference being one has soft suspension and the other stiff suspension, they should each experience exactly the same amount of weight transferred from the inside wheels to the outside wheels. It is because that weight is being transferred that you can see the suspension moving. A soft car will lean further because soft springs compress more under that load. The stiff car will lean less because stiff springs don't compress as far under the exact same load increase.

Sorry for the error. You've explained it much better than me, as I wasn't clear before. I'll edit my post to clarify it.

[TomSuddard]

Good point on sway-bars, I forgot to even mention them in the original post. I wasn't thinking of bars when I mentioned a stiffer car.

That's why all the ricers run "mad tyte big rear bar JDM y0!" It makes their cars drift y0.

[Bishop]

I know it's probably been asked and answered, but I have a quick question about sways.... I'm running stock sways right now, GC coils w/ plates w/ M3 mounting points and GC adjustable links.... A friend of mine said that from a spectator's standpoint, my car had NO body roll at all during my several autocross runs, however... I want to maximize the suspension... Options without having to worry about ripping out the mounting point? Would stepping up to e30m3 sways offer a noticeable difference and be a solid choice?

[Ferdinand]

I'm running stock sways right now,... I want to maximize the suspension... Would stepping up to e30m3 sways offer a noticeable difference and be a solid choice?

Generally stiffer sway bars are beneficial in two ways. In some cars with poor suspension design, when the car leans over in a corner it tends to tip the wheels over so that the tires lift their contact patch and roll over onto their shoulders. My old AE86 Corolla GTS suffered from that. In hard cornering it would trip over its outside front tire and lift the inside rear tire. It chewed the crap out of the shoulders of the front tires and then had no traction, spinning the inside rear wheel when trying to accelerate out of corners. Lower and stiffer springs, with stiffer sway bars, made a world of difference because it reduced the amount of body roll in corners and hence corrected much of the adverse camber change otherwise experienced when the car leaned over.

Our E30s have a much better suspension design. It doesn't seem to matter how far the body leans over while cornering, the outside tires always seem to be squarely planted on their contact patches. Tire pressure makes a difference in how much the tire will move on its rim, but the amount of body roll doesn't seem to affect the stance of the tires much. The E30 has very good camber control through its range of travel in roll. However, a car that leans over a lot in corners does not feel as responsive compared to a car that leans very little and has a quick response like a gokart. You'll especially notice the difference in autocross in slalom sections where you need rapid transitions from side to side.

Again, it's important to remember that the body roll is caused by the lateral acceleration as the car is turning the corner. It's because the car is turning that it responds by leaning over. It is an illusion that a stiffer car turns quicker than a soft car. They're both turning, it's just that the soft springs and swaybars will deflect further before reaching a steady state position. The big difference is in the time it takes for the car to reach that steady state position. A soft car takes much longer to settle in the transitions compared to a stiff car.

But, it's not always advantageous to have a stiffer suspension. It's great if you only ever intend to use the car on billiard table smooth surfaces. But if you drive on real roads with potholes, speed bumps, railroad crossings, etc, whenever your wife rides in your car she'll be complaining about potentially losing the fillings from her teeth.

Furthermore, a stiffer suspension ultimately provides less grip than a soft suspension. Take the most extreme example where your suspension is welded solid, no movement allowed. The only suspension travel available is in how much the tire sidewalls compress over bumps. If you hit a raised bump with the left front tire, instead of compressing the suspension at just that wheel, it will instead lift the entire front of the car, and thus the right front tire gets lifted clean off the road and is hanging in the air, while both the rear tires are still on the road. Imagine this happening in mid-corner. Instant understeer. A second later both front wheels are back on the ground, and then the left rear tire hits the same bump. That raises the right rear tire off the ground. Instant oversteer.

The whole point of having a compliant and independent suspension system is to keep all four wheels on the ground at all times, ideally as close as possible with all four tires equally sharing the weight of the car. That's where the car will generate its maximum grip. The more the weight is unevenly taken off one tire and concentrated onto another tire, the less the overall grip of the car.

So, unless the road is always perfectly smooth, a soft car with long suspension travel (assuming good camber control) will have superior overall grip compared to a very stiff car with little suspension travel.

[ed94r]

All this advanced talk about shocks, springs, bars, and weight transfer is beneficial to understanding car set up...the average novice autocrosser will not benefit from it all too much. Don't get me wrong, car set up is key in any class if you want to be competitive...but the the new guys needs to focus on course management rather than car set-up.

Beginners: Do NOT focus on car set-up, weight transfer, bar settings, etc. They will not help an inch when you are getting lost on-course, or not carrying enough speed through the features to exploit your perfect corner weighing and optimized spring rates and associated shock valving and big rear bar.

Focus on managing the course and opening the wheel up on corner exit, rather than pinching corners and scrubbing momentum. Consistently manage courses over time and learn...then optimize the car for maximum no-compromise speed. Don't band-aide poor course management with grip.

Ed

[RadioRon]

Focus on managing the course and opening the wheel up on corner exit, rather than pinching corners and scrubbing momentum. Consistently manage and learn...then optimize the car for speed. Don't band-aide poor course management with grip.

Ed

+1 for autox wisdom

[Ferdinand]

Consistently manage courses over time and learn...then optimize the car for maximum no-compromise speed.

100% agree with that. Wise words.

Ultimately it's only you against the clock. It doesn't matter how you compare against others. As long as you can consistently improve your times run after run, learning to drive smoother and better, then there is no need at all to modify your car. Only after you are totally convinced that you have nothing left to learn and that you are no longer making any driving mistakes, only then consider upgrades to the car to make it faster if that's what gives you joy.

There is far more personal satisfaction to be gained knowing that nobody else could possibly have driven your car better than you, even if you don't win anything, rather than collecting meaningless trophies just because you have more money invested in your car than anyone else.

[TomSuddard]

Good points above.

Remember that smooth is fast. The more aggressive and violent you are, the slower you will be. Use gentle inputs, and don't overcook it going into a corner. Slow in - Fast out.

Oh, I know it's already been said, but walk the course. Lots. Then do it again. Then walk it again. Then get a course map and walk it in your head.

[Bishop]

Thanks all for building on this thread.

[10/10ths]

Reading through this thread made me want to post, lots of good advice here.

Not so much techniques to practice, but stuff you should focus on as a beginner autocrosser.

As a novice, I sucked. I know that sounds obvious but what I mean is compared to even the other novices I was competing against, I sucked. My biggest single problem was I didn't take course walking seriously. I would walk the course twice, and think I had it down. Then when it came to the run I would "drive fast" (cause thats what your supposed to do, right?) and every corner would take me by surprise. I would end up having to react to everything coming at me and the result: I was understeering EVERYWHERE. It must have looked pretty sad, and it is by no means fast.

My contribution to this thread would be this. If you are a first time/season autocrosser make sure you get everything sorted out and ready the day before, you want to have as little to do the morning of an autocross as possible. Get there early, get your car ready for inspection and get registered. Then you can start walking the course, over and over and over and when you think you have got it down for sure, walk it one more time. When it comes time for your first run, DRIVE SLOWLY, dont drive fast because its what you think you should do. Your biggest goal is simply to get the course right and you don't want to drive any faster than your knowledge of the course. Even though you walked it 6 times it will look and seem different when your inside the car. If you get the course right from your first run, you can now build on that and start going faster with each new run.

Forget driving techniques at first (besides maybe, looking ahead) just simply start going a little faster each run now that you got the course right. At the end of the day you will likely put up a respectable time that stacks well with the other novices. The need for certain driving techniques will present themselves as you have some events under your belt. Dont worry about looking stupid in front of everyone for driving slow at first, experianced autocrossers know it's a smart novice who's goal is getting the course right the first time. If you take a group of first-time autocrossers, I guarantee most of them will get the course wrong the first run, and some will spend the whole day just trying to get ONE right. But the driver who got it right from the very first run has a good chance at taking the novice win, or at least placing high in the results.

Anyway thats all I wanted to add, and as I'm writing this I'm kind of reminding MYSELF of these things. I have over 5 years autocross experiance but I have not competed in 2 years. I will hopefully be ready for an event this month.

Justin

[whiltebeitel]

There are a lot of really good comments in this thread. It's always better to run a less than ideal setup and just plain get track time for 99% of the people than waste your time the night before or the day of adjusting sway bars, camber, etc.

No matter what kind of event you are going to, try to make a point out of driving: What do you want to do better? tighten up on the slalom at the AX? Build up confidence to go flat-out in that 100 mph let-hander at the track? Focus on smoothing your transitions? If you have a goal, chip away at it until you've nailed it, then move on to the next goal. Run out of goals? Get a book like Carroll Smith's Drive to Win, A twist of the Wrist (very good line instruction, made for motorcyclists, but very good for all drivers)

But really, just drive as much as possible, don't go out without something to improve on in mind, and bug the hell out of faster drivers to show you how they eke out the next couple tenths. (instuctors, Evo schools, doing co-drives, ride-alongs, lead-following, etc. are all a part of this!)