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.
you suck at racing 
Hi, this is a great article serie, thanks for taking the time writing about it.
Incidentally, these days I have been trying to get some useful info from some sort of telemerty, displaying and comparing only speed (stracker and ptracker for AC only shows speed). I cannot give sim-driving the time I would like, but I managed to get 1sec better. It’s really hard to dismiss bad practices :-)
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If you’ve got AC, you can get all the telemetry data you need by importing the telemetry.dump file into Race Studio Analysis. It works really well. You just have to mirror the track map when you create new tracks.
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That’s great, I’ll try for sure some proper telemetry on my car.
I forgot to say that i’m comparing speed-only telemetry with other racers, that’s why it’s the only data available. It’s interesting, i think i have found a couple of later apexes than mine and a bigger curb cut.
Next session will be trying to apply what learned.
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What car and track are you driving?
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In this case i drive a Porsche 911 gt3 cup 2017 at Mugello.
The short story is the i wanted to take on an online challenge qualification, even knowing i’m not fast on gt3 cars, and while doing it i discovered ptracker add-on, showing me speed graph of other’s laptimes. So it was interesting to see why the aliens are sooo faster.
The long story, if interested: i’m not a fast sim-driver, about 105% of alien’s times (103-104% on easy cars like Miata and E30, over 105% on GT3s). Here is some ranking: http://www.radiators-champ.com/RSRLiveTiming/index.php?page=driver_profile&id=21415
So i took this challenge, given that 911 is nice to drive and Mugello is one of my favourite tracks (give it a try, it’s a flow of corners around some hills, quite technical IMHO).
My laptimes were, as expected, around 105% (best time, not recorded RSRLapTiming is about 1m53s6xx).
Ok, aliens gave ma over 5s, how did they do? It was mandatory for this challenge to activate rtracker plugin, so I discovered speed graphs of any driver :-)
In this picture i compared the best time overall and one lap of mine, before i cut another second:
https://photos.google.com/share/AF1QipOi6xMDNiVG0-yFJG_cuENIuRGdj3a1SWNaFxzxtTIjg7ar1K6_zEN7JXvSJJxz4g?key=ZnQwQXc0RjRScXJ6U0s1LXl4MlhVR01oNEI3czNR
Here are my thoughts
1) At the end of the huge straight, we start braking about at the same point, but my line is steeper than his in the very first moments. I should have started braking later
2) I tried to trail-brake entering the first corner, and i’m indeed faster in that particular corner; he continued braking straight (no change in line steepness, so i thing he is using all grip to brake in straight line) and sacrified the entrance of the first corner to optimize the following S.
3) i thing i have used less road than him, he maybe made a better line and used all track width
4) This is a right descending semi.blind corner, followed by a descending quick left turn: i still have to find good references and the consistency to follow always the same line. He is for sure more aggressive in cutting the curb. I’m more precise with Miata, this 922 is still too fast for my reflexes/muscle memory.
5) a couple of right quick turns to concatenate together, the “arrabbiate” are one of the most challenging part of this track. I found being a bit better than average people on online racing, but he still manages to be 20Kph faster than me. I cannot say how it’s achieved with a better line and how it’s a custom setup (I use default setup, i think i should first learn to drive faster, then play with setups).
6) This is a slow descending right-left, even if i try to remain at right in the entrance to optimize exit speed, it’s clear i still have to work on it :-)
7) right downhill hairpin, i just cannot find how to drive it fast. I think i entered too fast, went fighting against grip. I think i should take an even later apex.
8) this is a fast S, now i learnt to take it in ful acceleration almost like the alien
9) this is the most difficult corner for me, and very critical, having a long straight following it. I’m trying late apex, but he manages to be perfectly smooth. I’m turning in too soon and find myself fighting with grip. Again.
Maybe i will have to do more exercises, like driving in one gear only to concentrate on the line only (already made some laps, i will try again). Go to run away, 1 year old twins starting geting awake, another hard night ahead… Bye
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I just drove Mugello and the GT3 Cup for the first time. I put in about 10 laps and managed a 1:57. Clearly I don’t know the car or track very well. I will say that it’s a really good track. It has lots of connected corners requiring one to compromise the first in order to maximize the second.
I don’t think there’s anything wrong at (1) or (2).
What I see at (3) and (4) is trail-braking. He’s off brake and on throttle much earlier in the corner because the car is already rotated to the exit.
The turns at (5) are fun. I agree that you should focus more on driving than setups, but a good setup can take a second off your lap time.
In (6) I think you’re taking the first corner too fast. You have to throw away the first one to maximize the second one. He’s not tracking out as far as you, which gives him a better angle.
At (7) and (9) you’re being impatient I think. Overspeeding the middle will mean you can’t get to throttle as soon.
It sounds to me like you’re on the right path. Keep at it.
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I decided to try seeing how I would stack up against some of the faster drivers in a car and track I’m more familiar with, so I loaded up Brands Hatch Indy and the NA Miata. My best time was 1:00.832, which would put me at #24 on the leader board. I only did a few laps and I don’t tinker much with setups. I think I can knock a half second if I really worked at it but the #1 time at just under 1 minute is beyond me.
—
Improved to 1:00.637 (#18).
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Great! I only have MX5 Cup time on that track, so I cannot compare it. It’s a bit old, ad I’m at 105%, I think I could work on it some more. I will give it a try, it’s a track I like.
Meanwhile, I spent the little time I had to practice trail braking: took that 911 on Vallelunga Club, another ideal circuit to practice TB: only 180° turns and a chicane. Fun and 104%, which represents a small victory to me, considering the powerful car.
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1. I love your blog. That I go back and read and comment on years-old entries says so.
2. Left Foot Braking simply grew from karts. In a kart you have no choice: a gas tank and steering column separate your legs. Since essentially all formula drivers for the last 30 years have come straight from karting, it only makes sense to set up the modern F4321 cars like karts. This requires that both heels have braces — in karts, a bar; in formula cars, a heel cup. These give your body, and particularly your feet, a stability you can’t get with a traditional car foot pedal set-up — stability you need for left-foot braking. The clutch is operated by hand, and both use sequential transmissions, so no clutch needed after the vehicle is moving.
3. In karts, particularly single-gear karts, it is important to keep engine revs up during turns. Keeping some pressure on the gas pedal during braking helps this (as does a wider line), and separating right and left foot functions helps that.
Again, big fan of your blog.
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Thanks for the kind words
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I just wanted to say the same thing, this blog is incredible.
I’ve been involved in iRacing now for 6 months and am starting to realize it’s going to take serious conscious efforts to improve. I’ve been left foot braking the entire time and have my rig setup “formula style” with the gas and brake separated out like a kart but the majority of the time I’m driving the Miata, TCR, and the GT4. I’ve wondered if trying to right foot brake could be helpful but I’d have to make adjustments to my pedal setup to try it out. Maybe braking in a more realistic fashion is worth more than the potential benefits of LFB setup much like trying to find speed by braking later and later just to give up speed mid corner and on exit.
Thanks again for the information, it’s absolutely wonderful
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I would stay with LFB. Eventually you’ll be better off than those who exclusively RFB (like myself). Just gotta keep training and checking your data against the aliens.
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