HPDE - Throttle

Gas. Go pedal. Loud pedal. Happy place. Whatever you call it, it's the one control most folks already think they know how to use when they take Driver Skills or do an HPDE. How hard can it be? Mash it and go!

My very first day as an HPDE instructor, I was giving a ride to a first-timer. He asked for a ride, as his instructor was not driving that day. We had a great time in my R32 in the rain. He asked me a question that I was unprepared to answer, "I just want to know at what point I should be full throttle in my Audi S5?"

One of the early challenges of instructing HPDE is articulating things that you just "feel", putting them into words that make sense to another person. At that moment, I gave him an answer like, "That depends on many things" and I said I would get back to him on it (best not to have long involved discussions on track at speed).

I later emailed him this basic explanation: When I'm on track, I'm giving the car as much throttle as it needs / wants in any given situation. As I'm unwinding the steering wheel exiting a turn, I'm adding throttle smoothly. It's almost a 'surprise' when I get to the end of the throttle travel. He got it.

One of the visualizations that helps for applying throttle at corner exit is to imagine the edge of the steering wheel is connected to a rod that is connected to the throttle pedal. As you unwind, the throttle is being pressed down.

The throttle is an often overlooked tool to transfer weight around in a car. Add throttle, weight shifts rearward. Lift off of the throttle, and weight transfers forward, almost like applying the brakes. This can have a marked response in how the car corners. There's a couple of fancy terms for this: "Trailing Throttle Oversteer" and "Lift Throttle Oversteer". To my knowledge, they mean the same thing. If the car is at steady state at speed in the middle of the corner, with much of the weight on the outside tires, lifting the throttle will unweight the rear outside tire causing the rear to step out or even spin the car out.

The majority of new cars don't suffer much from Trailing Throttle Oversteer (TTO), particularly with stability control engaged. It's when you make modifications, like adding a stiffer Rear Sway Bar (RSB), that these effects get magnified. I have made a few modifications to my car, including a stiffer RSB (a little bit of daylight under rear inside tire in photo at right). In controlled testing on some freeway cloverleafs, I could feel the onset of TTO, but I judged it manageable. After a few high speed "departures from controlled flight" on the track, I decided it was not manageable and reverted to the stock RSB.

With experience and a good "feel" for your car, the throttle becomes a steering control. On big sweeping carousel turns like T6 at The Ridge and Portland or T2 at Pacific, you can easily tweak your line with your right foot. Running a little wide and can't get to the apex? Lift throttle very slightly and feel the front end tuck in. Still have lots of track left and car isn't tracking out? Add a touch of throttle and the front end will point a little wider, all without modifying your steering input. I enjoy demonstrating this in my R32 as the exhaust is loud enough for the student to hear what I'm doing with the throttle.

Throttle response of course varies widely between different cars. I had a student last year who had had a fair amount of prior experience at The Ridge in a relatively low powered Miata. He was an intermediate student, returning to The Ridge. The twist is that he now had an M5 with a V10. He was pretty giddy about having so much torque to play with. The problem was he now had trouble keeping the M5 anywhere near the proper student line. It was almost as though he no longer knew this track. After a couple not-so-good laps, I asked him what gear he was mostly in. He said third. I asked him to put it in fourth and leave it there. Problem solved. He now successfully hit all of his reference points and in general behaved like he knew the track well. From there, I freed him up to shift wherever he wanted, with an emphasis on smoothness and staying in contact with the line.

I sometimes find myself in a car with a student and he/she is just a little tentative in a high speed (50-60+) corner; they feel like they're tip-toeing through and ever so slightly unsettling the car by lifting throttle. I usually say (calmly, at first) "Gas, gas, gas." They often ignore me, and since (if I'm doing my job right) we're pretty far from the edge of control, I save the point for later discussion. They're usually coming from a mindset of "Instructors always try to make me drive faster than I'm comfortable with" (and many do). I explain to them that in this instance, I'm actually trying to get them to recognize that their actions are making the car unstable, and adding a little gas will bring it back to balance and control. A senior instructor once shared with us that he won't allow a student to record video with audio inside the passenger compartment while he's instructing. He was concerned about the possibility of a future court case, "Mr. Jones, can you explain to the jury why you were shouting 'Gas! Gas! Gas!' just before the accident?"

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