Ghosting the Aliens: part 4, advanced techniques

If you’re joining this post in the middle of the series, go back a few weeks to the start and read those. There’s software and data to download.

When thinking of advanced driving techniques, two of the most common topics are rev matching and left-foot braking.

Rev Matching

The way iRacing models a manual transmission is somewhat of a joke. You can shift the car into gear seconds ahead of the shift and then quickly bounce the clutch to change gears. If you look at clutch traces, you’ll see that most upshifts are incredibly quick because of this. You can also choose to have iRacing blip the throttle for you on downshifts. Doing so gives a slight penalty to your lap times because there is a pause before the throttle is fully activated. Some drivers don’t cheat on downshifts and do their own rev matching. Let’s load up Andrew Barron’s 1:42.279 lap to see what that looks like.

In the figure above, I’ve got the brake pressure selected rather than the clutch. But what you see is incredibly ragged. If you cycle between clutch, brake, and throttle, you’ll find that his feet are pretty busy in this section. The reason that his brake trace has valleys in it is because he’s also using the clutch to slow himself down. Why? Partly because he stepped on the clutch too soon. If you do that, the revs start to fall and you’ll have to spin up the transmission again to match speeds. Gradually letting out the clutch is a sign that you didn’t match revs at all. Andrew’s lap time is actually pretty good compared to others we’ve looked at. That’s because he’s been a member of iRacing for 7 years. Unfortunately, he’s perfected a suboptimal way of driving.

LFB

There’s an old saying “in a spin, two feet in”. People who try to recover from spinning often end up crossing the track several times, taking out multiple nearby cars. The two feet in question are on the brake and the clutch. The clutch application is so you don’t stall the car when it comes to rest. This reminds me of my very first track day where I spun and stalled… Hey, we all start from somewhere, and I started at good old rock bottom.

But wait, there’s another kind of driving with two feet in. It’s called left-foot braking, which is often abbreviated LFB. It’s easy to determine if a driver brakes left-footed because the brake and throttle traces overlap for extended periods (not just when blip shifting). Most Formula 1 drivers brake with their left foot. Also lots of ass-idiots on US freeways. LFB is an advanced skill when done properly and a source of amusement when not.

Let’s load up Alex Czerny’s 1:39.681 into Lap 1 of iSpeedLapAnalyzer just like we did for the last few weeks and then add Alberto Moraes’ 1:47.265 into Lap 2.

The first thing you will notice is that Alberto’s speed trace shows really gradual deceleration in turn 1. This is highlighted in the image above. If you don’t look at the braking graph, you’ll assume it’s because he’s braking too softly, much like Bastian last week. But upon closer examination (click the brake tab) you’ll find that his initial brake pressure is actually higher than Alex. But he’s also got the throttle pedal on the floor at the same time! He eventually releases some left foot pressure but it’s synchronized with the right foot. Both feet in, both feet out. If you look across the whole lap, you’ll find that his foot is on the throttle to some degree pretty much all the time. This must be a carry-over from driving a single-speed go-kart where he’s trying to keep the revs in the power band. It has no place here. Common sources of track driving errors are skills learned elsewhere. Possibly the most insidious are street driving habits. But that’s a topic for another day.

More LFB

Now load up Joshua Homan’s 1:42.730. This is a pretty fast lap compared to the others we’ve been investigating.

If you look at the brake trace, you can see that Joshua has good technique. He hits the pedal hard and then modulates it as he steers into the corner. Switch from brake to throttle view in the highlighted region and you’ll see that he stabs the throttle a lot while braking. Not just here, but every corner. He’s late on throttle because he’s braking too late and trying to make up for it mid-corner.

As an aside, if you look at the throttle trace you’ll see that there are huge regular dips at the shift points. That’s because he’s using an automatic transmission. This slows the car a couple tenths over the entirety of the lap. It’s not a big deal until you’re trying to chase aliens.

Opinions

I don’t feel that strongly about rev matching. If you shift really late in a corner, it’s not really necessary. That said, I almost always rev match. And while I’m against using the clutch as a brake, there is one corner on one track where I do it to help rotate the car. In any case, if you’re going to rev match, learn to do it correctly. If you’re constantly feeding out the clutch gently, you’re driving poorly.

I don’t practice LFB ever. I do see the advantages though. Some of the fastest drivers set up their cars with extra rear brake bias. While a normal driver might find this hazardous, those who practice it can use the brake and throttle against each other to dynamically change the balance with great precision. Brake bias is something we normally set up in the paddock. If we’re lucky, we might have an adjustable bias control in the cockpit which we can change if it starts to rain. Advanced LFB-ers can change it mid-corner as they modulate brake and throttle. That’s pretty awesome. Having both feet on the pedals means there’s no delay between getting off the brake and on throttle. If you’re searching for every tenth of a second, there’s a good reason to learn to LFB. If you’re an endurance driver who cares a lot about wear on the car, there’s not much to gain.

Rev-mashing: part 2 of 2

Are you rev-matching or rev-mashing? Let’s repeat the question from the end of last week. Where in the corner should you downshift and what are the consequences of shifting at the wrong point.

Red Zone

Lots of people start to downshift during threshold braking. As soon as they hit the brakes, they also depress the clutch and blip the throttle. There are several problems with this.

  • The car was already at high RPM and the blip just sent it even higher.
  • The car is currently going too fast to engage the lower gear.
    • If you shift to the lower gear immediately, you may destroy the engine by revving it past redline.
    • If you wait with the clutch depressed, the engine and transmission will spin down, negating any benefit of blipping the throttle. When you do engage the clutch, you’ll have to feed it in gradually to prevent locking up the tires. Congrats, you just ruined your brake bias and made the stopping distance longer. You’re also putting wear on the clutch.

Blip-shifting in the red zone is the worst possible place to shift.

Orange Zone

This is generally the best place to downshift. For really long decreasing radius corners, it’s too early though, as you’re still aggressively bleeding speed through half the corner.

Yellow Zone

In this trail-braking zone, your concentration should be on controlling the speed and angle of the car using a combination of brake pedal and steering wheel. It’s not a good time to take your hand off the wheel or dance on pedals.

Green Zone

This is the point of maximum lateral g-force. Your foot is making the transition from brake to throttle. In longer corners with extended trail-braking zones, this is a fine time to shift.

Blue Zone

You’re balancing throttle and steering as you pass the apex and track out to the exit. The over-rotation you initiated in trail-braking has to be wound out some in here. Probably better to keep both hands on the wheel.

Purple Zone

Although it seems way too late, shifting in the Purple zone is an ok place to shift. You’re not going to break any lap records doing it this way, but you’re also not going to do any damage to the car. If you drive through a corner in a gear that’s too high, it’s not that big a deal. If you’re balancing throttle and steering, as you should be, you don’t really need full power anyway. I don’t know anyone who actually downshifts after a corner. It would be like shooting free-throws underhanded: works okay, but looks too silly to be taken seriously.

Demonstrations

Here’s a popular YouTube video instructing how to heel-toe shift. The video overlays footwork and RPMs. Watch as he starts the downshift too early. The revs drop and feeds out the clutch gradually. If you have to release the clutch gradually, you’re not rev-matching, you’re engine-braking (or engine-breaking). One wonders how such a flawed example can have so many views.

Here’s the right way to do it. Notice how quickly the clutch is released as he blips each gear. You might also notice how he changes his hand position depending on which gear he’s selecting. It’s most noticeable for 2nd gear where he rotates his hand thumb-down. He’s not doing this to look cool, but I’m guessing somewhere there’s a ricer in a stanced Honda back-handing every fucking gear…

Rev-thrashin: part 1 of 2

Check out this awesome 1980s movie poster.

I weep every time I see this poster, partly because I grew up in the 80s, a time of particularly embarrassing fashion. But now I also weep because I just learned that Pamela Gidley recently died. She’s probably most famous for “Twin Peaks: Fire Walk With Me” but I’ll always remember her as Cherry 2000. However, the real reason I’m bringing this poster poseur to your attention is that the wrist guards are on backwards. Wearing them like that would do more harm than good. Obviously nobody at the photo shoot had any idea about skateboarding. Why am I talking about skateboarding. Oh, I don’t know…

Whether you call it rev-matching, blip shifting, or heel-toe-shifting, this technique is often categorized as an advanced skill. I agree, but not because it’s difficult to do, but because it doesn’t have much effect on lap times. It only becomes really important when you’re searching for tenths of a second and not whole seconds. That said, driving enthusiasts love to display their rev-matching skill on the street or track. Like the Thrashin’ movie poster, sometimes they do it so wrong that it looks like wrist guards on backwards.

Let’s look at an idealized corner depicted as a rainbow of colors.

  • Red – Threshold braking zone. All brake no steering.
  • Orange – Initial trail-braking zone. Ideally, this zone is really small.
  • Yellow – Trail-braking zone. The car is rotating as the mixture of brake plus steering puts more weight/grip on the front of the car.
  • Green – Nadir. This is the point where the right foot is moving from brake to gas, and the point of minimum speed. Ideally, this zone is really small, but some corners do benefit from a little coasting.
  • Blue – Throttle zone. The position and angle of the car are controlled by a mixture of steering and throttle.
  • Violet – Straight. All throttle no steering.

At what point along this path should you downshift? Your perspective may be different from reality, so if you have some video of yourself driving, observe your shift points. Ask yourself “what are the consequences to the driveline and handling of the car?” Tune in next week for some discussion.

P.S. The image above is from my upcoming book, “In Slow Out Fast (and other lies of the race track)”. This long-awaited sequel (by me, not you)  to “You Suck at Racing: a crash course for the novice driver” focuses on the intermediate driver. Due out this Summer and available from Amazon.