Intermediate Topic #4: downshift timing

ATTENTION

This is the last weekly post. YSAR is moving to an event-based format. Race reports, experiments, reviews, etc. will now happen when they happen. This means YSAR will probably not be updated as frequently, but the content will hopefully be more meaty.

Back to our series in progress

This series of posts is aimed at you, the intermediate driver. Let’s identify and fix some common errors. If you’re not an intermediate driver, fake it till you make it. Last week we talked about driving a higher gear as a way to keeping momentum. Let’s get more complicated this week and actually perform a downshift.

The engine is not a brake

One of the big misconceptions I inherited from my father was that downshifting improves your braking. He told me that by feeding out the clutch gradually, I could use the friction of the drive train to slow the car down. While it is true that engine braking slows you down, it does more harm than good. Back in the old, old days when cars had drum brakes, engine-braking actually did reduce stopping distances. But today, with disc brakes, engine-braking just changes the brake bias from optimal to sub-optimal. In addition to longer braking distances, engine-braking also wears out the clutch and may kill the engine by over-revving it. There’s really no need to do it on a race track ever.

Downshitting is bad

Engine-braking in a FWD vehicle doesn’t do much harm, except as noted above, but in RWD it can make you spin. One of the terms I’ve come up with on this blog is downshitting. This is the act of downshifting, locking the rear wheels, and spinning. Although it occurs most frequently in corners, downshitting can spin a car going in a straight line. It’s a lot like grabbing the e-brake. Most downshitting is accidental. It results from putting the clutch in too soon.

The exercise: downshift later

Once you’ve pushed the clutch pedal, you’re mentally committed to the downshift, especially if you heel-toe. Your thoughts run something like this: “I don’t want the revs to fall, so I had better shift soon”. This is the source of downshitting, so we need to fix that. In this exercise, I want you to shift as late as possible. As you enter a braking zone your thoughts should be “brake, keep braking, keep braking, downshift”. Make it a game to see how late you can downshift. You can even shift after the corner. What? The video below is queued up to Tim O’Neil describing when to shift. He says “after the corner”. I’ll let his driving speak for him.

Wow, just freaking wow.

Telemetry Analysis

Let’s take a look at the difference between early and late shifting. The green line shifts much earlier than the blue. The top panel is gear. The second panel is RPMs. Here we can see some of the properties of early shifting. The highest RPMs occur when engaging the lower gear. Over-revving an engine causes excess wear if not outright destruction. It also causes the rear end of the car to drag (because the car is RWD) and re-proportioning the grip may induce a spin (and another chance at destruction). Lots of intermediate drivers, especially those using heel-toe technique, shift way too early and are consequently in danger of damaging their engine or spinning. If you have to ease the clutch out gradually, you didn’t match revs. That doesn’t mean the fix is to dump the clutch! Please don’t do that. Learn to match revs.

The blue line shows me shifting much later. In fact, later than I normally drive. This is a drill after all. I’ve gone through a surprising amount of the corner in the higher gear and then switch down after all the hard work is done. The speed and time graphs show there isn’t much difference in the outcome. The extra-late shift wins by 0.3 seconds. Shifting too late is better than too early because it’s much easier on the car. I’m still rev-matching because the engine is spinning very low by the time I want to engage the lower gear. If you’re not comfortable with heel-toe technique, you’ll have to ease out the clutch.

6 thoughts on “Intermediate Topic #4: downshift timing

  1. Agree. Would emphasize avoiding downshifting during trailbrake portion (which seems to destabilize car). Seems optimal shift time is just before turn-in.

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    1. This exercise is about shifting as late as possible. That means shifting after turn-in. So the entirety of the trail-braking is done in the higher gear and then the lower gear is engaged when moving from brake to throttle. Outside the drill, I downshift during trail-braking all the time.

      If you’ve down-shifted before turning in, what’s the engine doing while you’re trail-braking in the early part of the corner? It’s either dragging or you’ve got the clutch in (and have to ease it out later). I sometimes shift too soon and the rear does drag a bit. It’s not ideal, but then again, I’m a work in progress.

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      1. I just watched some video of myself and I have to say that in real life I shift a bit earlier than in simulation. I generally DO shift just before turn in. I think I should be shifting later. However, Ross says you should have your left foot on the dead pedal before turn in, which would mean all shifting done before turn in. Huh.

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  2. When I flub a downshift I strongly prefer to still be headed straight – seems easier to catch the resulting squirreliness. I still agree that it should be at the very end of the straight portion, but I find the drag to be less disturbing than instability caused by engaging into the lower gear.

    Not that it proves anything but I have seen this recommended several other places (Driver 61 I believe, for example).

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  3. Hi Ian,
    Enjoyed Ross Bentley’s webcast last week on Track Attack, which I noted you attended too. While it wasn’t my question to him, I noted Ross confirmed what you and I settled on: best time to downshift is as late as possible during straight deceleration, just before turn-in. I did note that your question was about best teaching techniques. I admire your dedication to teaching!

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    1. I’m definitely a teacher at heart. Which makes sense given my profession. “Those who can’t do, teach” is a famous quote. But not a lot of people know that the next line is “and those who can’t teach, teach gym”. And there is another line after that, but only people who actually watch Woody Allen films know it.

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