Physics Of Racing

[AtomicLabMonkey]

Here's an excellent series of articles explaining how things work when driving at the limits of adhesion. It's a fairly long series and can get very technical, but you can always just gloss over the technical parts and read it for the generalizations.

http://www.miata.net/sport/Physics/0...-Transfer.html

[dknv]

Thanks for posting this link, I bookmarked it for later in-depth reading.

Some of these principles are explained in the Audi car club safety seminars I go to. But not only do I want to understand the principles, I want to try it out & feel the car's handling in these scenarios as well.

So, at Spring Mtn this past weekend, I kept trying to get the car to rotate coming out of a couple of turns -- by first a hard acceleration (weight xfer to the rear), quick lift (unweight the rear, which should help in rotation), then hard acceleration again. Never was successful. I did it at Sears Pt, but could not get it to work at Spring Mtn. However on a different turn, the rear end slipped out after coming over a crest of a hill, when I tapped the brakes to settle the car for the next turn. It was scary the first time, fun after that.

Now to work on refinements on a flat autox surface this summer....

[AtomicLabMonkey]

With your AWD cars it seems like it's usually hard to get them to rotate at all... Scott's car understeered like a mofo at autocrosses when he first got it, damn near rubbed the front tires off like erasers on sandpaper plowing around the corners, hehe.

[sperry]

Go RE-92s.

The rear bar help A LOT on my car. It's much more neutral now, and at full rear bar it can even be a little loose if you get off the gas to quick. For example... 1st lap on a pretty quick course out in Sacramento... Big slalom early on. I went in a little hot, and tried to just steer therough it. I realized I was hot and jumped off the gas... WHEEEE! Went right around in a screeee of Bridgestone dust. Austin was in the passenger seat laughing at me for the rest of the lap... punk!

Good times.

[sperry]

Hey, I've read this before! Back when I was working on the physics simulation for my driving simulator.

Austin, did you have this back then? I wonder if you pointed me to it back then too.

[AtomicLabMonkey]

Originally Posted by sperry

Go RE-92s.

The rear bar help A LOT on my car. It's much more neutral now, and at full rear bar it can even be a little loose if you get off the gas to quick. For example... 1st lap on a pretty quick course out in Sacramento... Big slalom early on. I went in a little hot, and tried to just steer therough it. I realized I was hot and jumped off the gas... WHEEEE! Went right around in a screeee of Bridgestone dust. Austin was in the passenger seat laughing at me for the rest of the lap... punk!

Good times.

Hehehe The course workers we went by were laughing a lot harder than I did, I was just like "Yeahhhhhh! That ruled!" I almost did the same thing the event I drove your car too when I went out on the first lap... I got into the gas coming out of a section and it started doing it's typical power understeer.. not thinking I lifted off and it got way out of shape and almost came around on me. I was like ohhh yeah... this car drives quite a bit different than mine.

[AtomicLabMonkey]

Originally Posted by sperry

Hey, I've read this before! Back when I was working on the physics simulation for my driving simulator.

Austin, did you have this back then? I wonder if you pointed me to it back then too.

I think I might have.. it was written in 1991 and I first found it a long time ago.

[sperry]

Originally Posted by AtomicLabMonkey

Hehehe The course workers we went by were laughing a lot harder than I did, I was just like "Yeahhhhhh! That ruled!" I almost did the same thing the event I drove your car too when I went out on the first lap... I got into the gas coming out of a section and it started doing it's typical power understeer.. not thinking I lifted off and it got way out of shape and almost came around on me. I was like ohhh yeah... this car drives quite a bit different than mine.

The better time was my 1st day of AutoX ever in the T-Bird down in Monterey. I totally missed my braking point at the end of the longest straight. Austin's screaming at me: "Brake Brake Brake Brake!!!!" So I ride the ABS to the last second, crank the wheel left and procede to go straight off the course... plow city. I ate like 7 cones on that boner. I think the specators and course workers got a kick out of that.

[ArthurS]

Your stories are starting to scare me. This will be my first year out there. I am positive I am going to have some errors. :?

[sperry]

Originally Posted by ArthurS

Your stories are starting to scare me. This will be my first year out there. I am positive I am going to have some errors. :?

Actually, that's the point! You can't find the limits of driving w/o crossing them a few times. So cross the line where it's safe.. i.e. at 30mph in a parking lot w/ saftey gear on, rather than at 90 on the freeway.

[ArthurS]

Originally Posted by sperry

So cross the line where it's safe.. i.e. at 30mph in a parking lot w/ saftey gear on, rather than at 90 on the freeway.

Damn. Forgot about gear. What will I need and were do I get it all?

[dknv]

Originally Posted by ArthurS

Damn. Forgot about gear. What will I need and were do I get it all?

Hat, sunscreen.
Comfortable clothes, comfortable shoes (no sandals or slipons, because you may need to run for cones while you're a course worker).
If the weather is cold, bring a jacket and gloves. I've been at Stead when it's been 35 degrees in the morning, and is just freezing.
Helmet (snell 90 or better, DOT is not enough)
Vehicle needs to have seatbelts for driver & passenger (if applicable)
Drivers license
Tire gauge, chalk (if you want to monitor tire rollover)
Check or cash for event entry fee

Are you changing wheels? If so, you'll want your jack, torque wrench.
There are several websites that list items to bring, I'll try to find one & post a link.

[ArthurS]

I will change my wheels before the event. Were can I get a helmet like the one you mentioned? Summit?

[dknv]

Originally Posted by sperry

...For example... 1st lap on a pretty quick course out in Sacramento... Big slalom early on. I went in a little hot, and tried to just steer therough it. I realized I was hot and jumped off the gas... WHEEEE! Went right around in a screeee of Bridgestone dust. Austin was in the passenger seat laughing at me for the rest of the lap... punk!
Good times.

I did exactly that on my 1st autoX run in my WRX last year in April. WHEEEEE!! Stalled too!

Reference point for the uninitiated: in a spin, both feet in so you don't stall. Then get the car turned back into the course & finish!

[sperry]

Originally Posted by ArthurS

I will change my wheels before the event. Were can I get a helmet like the one you mentioned? Summit?

I got mine (Bieffe Formula 1 Composite Helmet (SA2000)) here:

http://www.bellmotorsports.com/



A good, lightweight, close-faced, entry-level helmet. It's prolly overkill for AutoX, but I figure if I'm spending the money I want one I can run in an open-wheel car with... at say Skip Barber or something.

[ArthurS]

Stall? Whats that? I have Auto. I don't think thats my main concern. I am more worried about spinning out or turning to hard. Hopefully by then, ill have more suspension components to help me out.

[sperry]

Originally Posted by dknv

I did exactly that on my 1st autoX run in my WRX last year in April. WHEEEEE!! Stalled too!

Reference point for the uninitiated: in a spin, both feet in so you don't stall. Then get the car turned back into the course & finish!

Hah ha! Kept mine running

But I had a long time to find the clutch since it wasn't a snap-spin... the back end came out and I dragged it a good while trying to save the car... When I realized I was countersteered all the way, and it wasn't enought I gave it up and put 'em both in and that's when I finished the 180 and came to a stop.

It was one long SCREEEEEEEE...URP!

[ArthurS]

the whole thing sounds really fun though. Minus the laughing experienced crowd. I have never been able to push my car a little without worring about a ticket for reckless driving.

[sperry]

Originally Posted by ArthurS

Stall? Whats that? I have Auto. I don't think thats my main concern. I am more worried about spinning out or turning to hard. Hopefully by then, ill have more suspension components to help me out.

Don't stress extra suspension bits too much. They'll make the car potentially faster, but for now you're the weakest link (no offense intended). It takes a while o get fast. This is my 3rd season coming up, and I still totally suck compared to the guys in my class. Seat time is the #1 thing that makes you fast.

[ArthurS]

I just feel a little safer knowing I have put a little into my suspension. I know its not going to give me a extra edge during my frist few years, I am still gonna suck big time.

[AtomicLabMonkey]

Originally Posted by ArthurS

the whole thing sounds really fun though. Minus the laughing experienced crowd. I have never been able to push my car a little without worring about a ticket for reckless driving.

You should probably go out and ride along with a more experienced driver in their car first before you get out in your own car, that way you can get a feel for how things are done overall, from staging on grid all the way through finishing a run and lining up on grid again. Plus, with all the people around there with WRX's it'll probably feel like riding in your own car and give you an idea of what to expect from it. And Scott's right, auto-x is the perfect place to push your car to and even over the limit without worrying about anything... cause you don't really know where the car's limits are until you exceed them.

[sperry]

Originally Posted by ArthurS

the whole thing sounds really fun though. Minus the laughing experienced crowd. I have never been able to push my car a little without worring about a ticket for reckless driving.

People will laugh, but not necessarily *at* you. Everyone's been there, and usually AutoX people are a close knit kinda people. (At least with the crew I've raced with). Seeing a n00b spin is entertainment, because we've all done it. As long as you're not cocky (or really fast ), people will usually go out of their way to help you.

For example, this guy showed up with an NSX... really nice one, supercharged and everything... anyway, he'd never raced before, but he figured his $100k car should be faster than everyone else... so he stomped on it and spun like every lap. I didn't matter that people told him to slow down and he'd get a better time, he figured he should just win it all right away. The poor guy kept spinning and DNFing 'cause he didn't understand how the slalom worked . Eventually he sucked it up, and had someone ride along with him to show him how the course worked. He finally finished a run.

Don't be that guy! Consider your 1st season a learning experience. Ask questions, even the "stupid" ones... no one will knock you for trying to learn. Take it easy on course. You'll save $$ on tires, and become a better driver because of it. Smoothness, and looking ahead at the course are the keys to being fast, IMO.

[dknv]

Originally Posted by sperry

Seat time is the #1 thing that makes you fast.

I second that!

Re: helmets - we have some loaners if you don't have your own.

[dknv]

Originally Posted by dknv

...several websites that list items to bring, I'll try to find one & post a link.

I don't know how to insert a link to another forum -- so, see Reno Area forum, autocross thread.

[sperry]

Just paste it from the address bar into the message, the forum's smart enought to turn it into a link:

http://www.doink.net/forums/viewtopic.php?p=1039#1039