Title drifting pic


by Billy Johnson

Braking late, hitting apexes, and powering out of corners:  The goal of driving a car quickly requires keeping the tires at their limit at all times.  Having good car control is a crucial skill in the development of a driver to not only drive a car fast, but also to have the ability to get up to speed quickly in a new car and on new tracks.  However, without self control and discipline, having good car control can actually work against you.

For those of you who don’t know me, my name is Billy Johnson.  I have raced professionally for close to 10 years now and was an instructor at the Skip Barber Racing School before privately coaching drivers ranging from beginner HPDE students on up to drivers in the IMSA and NASCAR Sprint Cup Series.  The following article is a result of what I have learned in over a decade of racing cars ranging from spec Miatas to prototypes and stock cars, and from instructing drivers in all of these fields with various backgrounds and driving disciplines. 


Billy Pic


This is going to be a long, in-depth analysis of driver development and I may lose some folks right off the bat, however if you care to improve your driving craft and understand where you are as a driver, it may be worth hanging in there.  Whether you are a beginner or a pro, I hope the following information helps you on your quest to become an even better driver.  Now on to the article.

During the development of a driver, learning to approach - and mastering the craft of balancing the car at the limit of grip is the name of the game.  Having the comfort and confidence (or lack thereof) greatly affects the process of learning and the ability to execute driving a car fast.  To simplify things I will separate the car control abilities of drivers into three categories: Under developed, Over developed, and Refined.  However, before talking about these three types of drivers, we first need to get a crash course on understanding how tires behave.


3D Tire ModelSince speed is taken into account, a 3D tire model is a more accurate depiction of the relationship between grip and slip angle than a 2D graph.  The graph above shows when speed is increased, the slip angle of the peak coefficient of friction is reduced.  For simplicity’s sake, we will stick with 2D models.

We could talk about tire deflection, aligning torque, mechanical and pneumatic trail, tire load sensitivity and a bunch of technical details of how a tire works, but for driving purposes we will focus on themes and abstract concepts related to driving without getting too far off on a technical tangent.   


Slip AngleThe slip angle of a tire is the difference (in degrees) between where the wheel and tire is aiming, and the path the tire actually takes.  This deflection at the contact patch is very small and is a result of the actual tread twisting within the tire as it rolls over the ground.

First off we need to be aware that “SLIP ANGLE” and “YAW ANGLE” are different.  Generally speaking, SLIP ANGLE refers to the difference between the direction the tires are aiming and the path that they actually take.  For example, if a car encounters a heavy cross wind, the force pushing on the side of the car will cause its path to change even though the steering wheel is held straight.  This happens because the crosswind generates a slip angle on all four tires which is different from where the steering is pointed, causing the heading to change.  When cornering, tires will always generate a slip angle regardless if the car is pushing off the track while understeering, sliding the rear tires while oversteering, balanced through a corner, or simply turning the car in a parking lot at 5mph.


Yaw AngleThe yaw angle of a car refers to the difference (in degrees) between where the centerline of the vehicle is aiming, and the actual path the vehicle is traveling.

YAW ANGLE refers to the difference from where the front of the car is pointed and the path that the car is traveling in.  In drifting, an important judging criteria is how large of a yaw angle a car can achieve.  In some cases the car can be perpendicular (90-degree yaw angle) or even slightly past perpendicular from the direction it is traveling.  Yaw angle is somewhat of a separate but related concept from slip angle.  For example:  If a car hits a patch of ice and the driver adds full steering lock, the front tires could have significant front slip angles, zero rear slip angle, and zero yaw and the whole car would just go straight.  Likewise, a car that is drifting could have significant yaw (sideways) and rear tire slip angles, but a much lower front tire slip angle since the front tires are not sliding very much and controlling where the front of the car is heading.  When we discuss slip angles, we are talking about the deflection at the tire and not the yaw angle of a car during over or understeer.

Page 1 of 5 Next Page
Bookmark and Share
Monday, June 09, 2014 3:10 AM
Billy, keep these articles coming. Great description of driver's ability - I have no problem identifying myself in the under-developed category. Until now haven't thought of giving a session at a track day to allow for experimentation - but I have instructed my marshals to not 'black flag' certain drivers who I knew were doing exactly what you've described. And bring on the rain!
Monday, June 09, 2014 7:34 AM
The mention of rain and control reminds me of a little dip in the 65mph highway near my home. A car would go off into the grass almost every time it rained hard. (Florida summer afternoon showers.) The DOT finally repaved it and the spins have stopped.
Monday, June 09, 2014 8:13 AM
Wonderful succinct article!
Monday, June 09, 2014 9:01 AM
Good stuff. Makes me want to get out there and start learning. Unfortunately, this isn't the right time in my life (I don't have the right car, time, or money), but I get some satisfaction that I at least get to read about it!
Monday, June 09, 2014 9:12 AM
I do mostly autocrosses, but I'm pretty comfortable past the limit. I wouldn't be so arrogant to say I'm in the over developed car control category, but I do over drive my car and am past the limit most of the time. I'm not the fastest guy in the dry, but in the wet I'm usually up at the top somewhere. Loose is fast, and fun!
Monday, June 09, 2014 11:18 AM
Enjoyed reading this Billy.. Thanks. Your descriptions and examples are an easy read. I will share with my friends interested in developing their driving skills.
Tuesday, June 10, 2014 7:03 AM
Nice pic of Billy drifting the horseshoe at Daytona after his 2013 Conti win!
Tuesday, June 10, 2014 2:42 PM
One of the best article I've read about car control!
The distillation of the most useful and practical knowledge I've read anywhere.
Peter Medina
Peter Medinalink
Tuesday, June 10, 2014 11:24 PM
This makes for a really great read Billy, especially coming from a guy with seat time in all sorts of cars and formula. You should almost do a blog/chapter every time you get in a different car. My own aha moment was taking a single speed kart out in the rain on slicks, where I had to flip a switch in my brain to actively control the kart instead of being reactive.

What are your thoughts on every instructor pushing for smooth steering input at the expense of finding the limit? I feel like it always promotes timidness albeit producing fast, but underdeveloped drivers. I feel that if the car is setup fast, then you can afford to be smooth and there shouldn't be a need to overdrive to find the limit.
Wednesday, June 11, 2014 5:05 AM
good read.

I've been preaching people to come out and try our Ice-RallyX events. Safe, fun, and very easy to learn driving beyond the limit of grip.

Thursday, June 12, 2014 9:13 AM
I can't say that I agree with practicing "car control" at a regular HPDE. You will be doing something the other drivers and instructors are not expecting, and that is what causes accidents.

I've got a couple of suggestions on how to work on this in a more controlled manner:

1) Wet Skid Pads! I think this is by far the best method. A wet skid pad provides a constant turning exercise (versus just one turn on a track and then a bunch of straightaway) so you can continuously feel out the area around the edge of traction. You can also do this exercise at various speeds by adjusting the turning radius. The downside? These are hard to find with limited seat time, like the drifting events mentioned. Normally these can only be found at professional schools. The other great source is volunteering at your local Street Survival School and then getting some instructor time on the course while the students are in the classroom.

2) Snowy parking lots. While obviously only available seasonally in certain areas, hitting an empty parking lot after a fresh snow fall can get you quite a bit of uninterrupted, edge of traction seat time. Obviously, don't do this with any cars parked. The key to the snow is the exercise can happen at a VERY low speed (so no excuse to get close to those light poles) and still be useful.
Monday, June 16, 2014 9:37 AM
Great article! I think you are underestimating autox for developing car control though. After reading your ariticle, I would have to say I am an over developed driver bordering on refined, and I got here mostly by autocrossing for many years. Although you are correct that most autox organizers will frown on people who excessively over drive and spin alot, or make a habit of taking down walls of cones at a time, you are over blowing it a little. You see that is the beauty of autox, to be really fast at it you have to be right on the edge of adhesion at all times, and the entire format is designed so that you can make errors without damaging yourself, your car, property or anybody else. Unlike with pushing the limits on a road coarse, where regardless of the event type there is always walls, dirt or gravel shoulders and other drivers. I personally find hpde events relaxing to somewhat boring compared to autox. I live for the adrenaline rush gained by driving a 40 something second run at 10 tenths, with no consequences to worry about if I happen to hit 11, whereas at a lapping day I'm hesitant to exceed 8 tenths for fear of putting my pride and joy into a wall.

At an autox nobody is going to care if you take out a few cones now and then, there's 15+ workers on course for a reason. If you drift the entire course you can expect a talking to or be asked to leave (had both happen lol), as it should be, but generally people getting a little sideways and exploring the limits of their car is what autox is all about, its the only way to get really fast at it.
Saturday, June 28, 2014 10:20 AM
Great read and perspective. I guess this is a reminder not to hate 'everything' about our winters up here in Canadia.
Too bad that many TCS systems can't always be turned completely off any longer. It just makes us dumber, with less opportunity to explore/practice.

Having said that, all this is a good reminder that racing on some of the more sinous (slower) tracks is still something that I shouldn't so quickly brush off in favor of the more epic 'fast' tracks. Thanks for sharing
Tuesday, July 15, 2014 7:39 AM
Fantastic article. Great depth unlike the frustrating shallowness of articles these days. Keep them coming please
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com