Speed Secrets: Finding – And Driving – The Limit

By Ross Bentley

June 27, 2016

For those of you who have built a piston engine, you know what Top Dead Center (TDC) is. For those who have not, let me explain.
Macintosh HD:Users:RossAir:.Trash:TDC.jpgAs I'm sure you're well aware of, the engine in your car has some number of cylinders, and each one has a piston that moves up and down in it (unless you have a Mazda rotary engine). Without going into great detail, the camshaft (which essentially opens and closes the valves) must be in sync or time with the movement of the pistons. To do that, during assembly of the engine the builder must start with one piston at the very top of the stroke (the up and down movement of the piston). As I suspect you also know, the piston is connected to a crankshaft by a connecting rod (I wonder how they ever came up with that name!), and when the crankshaft is turned, the piston moves up and down in the cylinder. As the engine builder turns the crankshaft the piston moves up in the cylinder, it gets to TDC, and then begins moving back down again. By turning the crankshaft back and forth in incrementally smaller movements, the engine builder can hone in on the exact point where the piston is no longer going up, but has not quite started moving back down yet. That’s TDC, when the piston is at its peak.
Driving the limit is just like finding Top Dead Center.
You work your way up towards the limit, then go over just slightly, then back up, over the other side… making each of the “over the top” excursions smaller and smaller until you’re spending all your time at Top Dead Center. Or, in this case, at the limit.
Before I get into a very specific step-by-step approach for finding the limit, let’s get clear on what “finding the limit” means.
Macintosh HD:Users:RossAir:Desktop:Tire Limit.jpgOne thing that is critical to notice when you look at a tire’s slip angle versus grip/traction curve (see the graph below - the limit is the green area; under the limit is yellow; over the limit is red) is this: You have just as much grip just over the limit as you do before the limit. For many drivers, that’s a comforting bit of knowledge. I’m sure every driver knows this at a gut level, but until they become consciously and logically aware of it, there is this fear of the unknown over the top, over the limit. The fear is that once our tires reach their limit, they give up completely and the car will immediately spin or slide off the track. Obviously, when we think logically we know this isn’t the case, but we often don’t think logically when driving at high speeds around a race track!
This is why I think it’s important that you have a good, strong mental model for what the limit is, and thinking about a piston moving up and down in the cylinder, reaching TDC, going past, back to the other side… and honing in on that exact TDC is important.It's no different from driving with your tires at their limit.
The real question is how to get closer to the limit without taking such big steps that going too far results in a crash.
Let’s look at one (there are many) step-by-step approach, or process, for honing in on driving the limit. To do that, we’ll use braking later as our target, since that's an area that many drivers consider first when trying to go faster.
Step 1: Figure out where you're braking now. That might sound simple and easy – and it is – but it’s not something that many drivers do. By this, I mean identifying where you’re currently beginning to brake for the one corner you’re wanting to brake later in. Note a brake marker, a crack in the pavement, your position compared to the some curbing, or whatever.
Step 2: Decide how much later you want to start braking. I recommend thinking in car lengths, as that's easier to picture in your mind while traveling at high speed approaching a corner than some measurement. Even if you use data acquisition analysis to determine that you could brake twenty feet later, turn that into car lengths. In that case, you'd say to yourself that you're going to brake two car lengths later. Unless you know absolutely for sure that you need to brake much, much deeper, I recommend moving your brake point in units of two car lengths for starters.
Step 3: This step is critical, so don't skip it. While standing in the paddock, look and identify what two car lengths is. Get a strong image in your mind of what that distance looks like.
Step 4: Take the "where do I brake now" image and merge it with the "two car lengths later" image. Imagine what that would look like on the track. Play it through your mind a few times - the more, the better.
Step 5: Go on track, and on your out lap - at lower speed - drive past the place where you used to start braking by two car lengths (where you imagined in your mind), and start braking. Even if it takes two or three laps at a slightly lower speed, ensure that you brake two car lengths past where you used to brake.
Step 6: Increase your speed until you're driving at your normal fast pace, ensuring that you continue to brake two car lengths later.
That's it. Notice that I didn't suggest moving your brake point ten car lengths later. You said you wanted to inch up on the limit, and that's what we're doing. Once you're comfortable with two car lengths from your original braking point, then step it up another two, then another two, until you feel you're reaching the ultimate limit or your late braking is negatively affecting your cornering. You may want to even fine-tune with one car length.
Also notice that you didn’t go on track at your normal speed, and then begin thinking about braking two car lengths later. You thought it out, you made a plan, you built a mental image/model of what you’re going to do, and then you started out doing exactly what you wanted to do at a lower speed. This last part is critical. You’re building a new mental program – one of braking two car lengths later – so getting into a habit of applying the brakes at the place you want while driving slightly slower is critical to making this work.
Of course, the entire time you’re going through this process you should be focusing your eyes in to your End-of-Braking (EoB) point, and being aware of the timing and rate of release of the brakes as you turn in. Combine all this with the mental model of honing in on the limit, just as though you’re finding TDC with a piston, and you’ll definitely move closer to braking at the limit.
And by the way, this step-by-step approach can be applied to inching up your cornering speed, applying the throttle sooner, or anything else. Use it, and enjoy consistently driving a little closer to the limit.
- Ross Bentley