No, Your Engine Isn’t Slow: It’s the Concertina Effect

By Alessio Lorandi, 2013 CIK-FIA World Champion, KF-Junior. Updated on 15 October 2026.

Is your engine slow if they pull away on the exit?

I can’t tell you how many times I’ve heard this at the track:

“Alessio, I was closing up on entry, but then on the exit they just pulled away. My engine is not good. Something must be wrong.”

Truth? Most of the time, nothing is wrong. No broken engine. No magic tyres. No secret setup.

What you’re seeing is something called the concertina effect. I even like to call it the “elastic effect” or the “rubber band effect” when I explain it to kids. That’s how I understood it when I was a kid.

What is the concertina effect?

Think about an accordion, or an elastic band.

• When you brake, speed contracts, so distance shrinks.
• When you accelerate, speed expands, so distance grows.

That’s it. It’s not black magic. It’s just physics.

Say you’re behind a driver, 10 metres behind, at 100 km/h. Same speed, no slipstream. If you both go from 100 to 200 km/h, those 10 metres become 20. At 300 they become 30. Nobody pulled away. It’s just the speed expanding. More speed equals more distance, less speed equals less distance.

At slow corners especially, it feels dramatic. You brake late, close right up to the guy in front, maybe even nearly hit their bumper.

I spent years reading that as proof I was good on the brakes, when it was only physics.

Then, as both of you accelerate, it looks like they have more power because they pull away again.

But most of the time, they don’t. It’s just the concertina effect in action.

And knowing what is an illusion and what is a real gap is part of racecraft. It is one of the things I teach in my six month training program, together with the starts and the overtakes.

Is the driver behind really braking later?

It always feels like it. In a hairpin the driver behind closes the gap on the entry, so it looks like he brakes later. Most of the time it’s not true.

Think about it. The driver in front is ahead, so he goes on the throttle earlier in time. As he goes on the throttle his speed expands, so the distance expands. Then the driver behind gets on the throttle too, a little later, and the gap he closed on the brakes opens again.

I have a lesson in the course where you see it clearly. One of the drivers brakes really late, and to be honest he does a very good job. He makes the apex, he does everything right. But the gap to the kart in front goes from about four kart lengths down to one on the brakes, and then on the exit it’s back to three. That is not all late braking. A lot of it is the rubber band.

Now, of course, sometimes the driver behind really brakes later. And sometimes the driver in front really has a better engine. But it’s not always the case. Actually, 99% of the cases, it’s not.

What does the concertina effect look like in F1?

Look at Monaco, especially the famous hairpin. You’ll see cars closing up like crazy on the brakes. One driver nearly on the gearbox of the guy ahead.

Then, as soon as they get on the throttle, the gap stretches again.

How come?

That doesn’t mean one car braked way later or had a rocket engine on exit. It’s just speed contracting and expanding. Yup.

Here’s a great example to watch:

And it’s not only Formula One. Watch a KZ shifter race. Every time they close up on the brakes and drop back on the exit, it’s absolutely the concertina effect in place.

Did I fall for it too?

Yes. When I was younger, racing in juniors and seniors, I used to think I was some kind of braking genius. I’d close up so much on entry and tell myself: “Wow, I’m amazing on the brakes.”

Then I’d get dropped on exit and think: “Damn, my engine is s***. Something’s wrong with my kart.”

Looking back? I was just falling for the concertina effect, which, by the way, 99% of drivers, parents, and mechanics don’t even consider. It wasn’t my engine. It wasn’t bad luck. It was simply physics playing tricks on me.

And it still plays tricks on me today. Say I’m at Lonato, behind somebody, trying to close up on him, and I keep losing out of the last corner. Yes, a bit of it is the concertina effect, because on the exit the speed expands and you always lose a little. But if it’s the only corner where I lose and I gain everywhere else, I tell myself: listen mate, you’re going in too deep. Open it up and go for a later apex.

Do you lose ground on the exit even if you drive the same corner?

Yes. You should always lose on the exit to the driver in front. Period.

Unless he goes on the throttle super late, you go on the throttle super early, he misses the corner and you get a perfect one. I don’t believe there’s such a thing as a perfect corner, but let’s say you both drive exactly the same corner in terms of lap time. If there was a mini split there, you’d both have the same time in it.

And you’d still be gapped on the exit. Because it’s just the physics. As speed expands, distance expands. And on the brakes you’ll be closing up and you’ll feel like you’re braking later, just because of the concertina effect.

So losing a few metres on the exit, on its own, tells you nothing about your engine.

Why does it matter for your engine tuner?

Because if you don’t understand the concertina effect, you’ll:

• Give your mechanic the wrong feedback
• Think your engine tuner messed up
• Waste time chasing setup changes that don’t fix anything

Imagine you come back after a session and say: “I’m losing on the bottom, I’m struggling on the exits of the corners.” But the reality is probably the opposite. You’re probably struggling at the top, because your sprocket is already towards the bottom. If the tuner follows your feedback, you’re actually going to go slower, not better.

And if you keep asking him for more bottom while you keep losing at the top, it’s going to upset him. You’ll also lose some credibility. I’ve seen many drivers giving wrong feedback, and nowadays they still do. Unfortunately the engine tuner is going to stop listening to that kind of driver. Don’t be that driver.

Instead, once you recognise it, you’ll:

• Stay calm when rivals pull away on exits
• Give clearer, more accurate feedback to your team
• Understand when you’re actually improving, and when it’s just physics

I go through the whole driver and tuner side in how to set up your engine.

How do you tell a real gap from the concertina effect?

Here’s the test. Watch what happens after the exit.

In one of my races I closed three kart lengths on the brakes into one corner. Three down to zero. You can tell me, Alessio, that is just the concertina effect. Well, a bit. But if you’re able to then maintain that gap on the exit, it’s not the concertina effect. That was full commitment on the brakes, trail braking till the apex, and it put me in position to overtake and win that race.

It works the other way too. I have a clip of two karts at the same speed with the same gap out of a corner. The driver in front puts his head down and pushes himself out of the corner. The driver behind looks back. And the gap grows. It’s not the rubber band, because they started at the same gap and the same speed. It’s maybe one or two hundredths, half a kart length, one kart length. I’d take that every day.

And then there’s the data. Your feeling is not enough, it has to be what’s really happening. That’s why data analysis is key, and I use a lot the MyChron 6 and the Race Studio 3 software, and I work relentlessly on that. If you only have your own data you can just compare against your other laps and sessions.

That’s the power of teammates. At BabyRace we have about 17, 18 drivers on average per race between the two tents, and when one is super fast in a corner you compare him against the ones struggling there. More in analyzing race data.

What if you really are losing on the exits?

Then it’s not the illusion anymore, and you have to fix something. But first look at your driving and the chassis, not the engine.

If you feel the driver in front is getting way better exits, and it’s not just the concertina effect, or the data shows you’re getting worse exits, try a later apex. Stop the kart more on the entry, induce more rotation on the entry, so that on the exit you’re left with simply getting the power down. I explain the trade off between early and late apex in mastering the racing line.

If you’re overshooting and early apexing everywhere, it’s quite obvious your exit speeds will be worse. Sometimes it’s the chassis that’s not properly balanced and doesn’t help you out of the corners, or has too much friction or some sort of misalignment that literally drags you down.

And only when you’re already driving 10 out of 10 does it make sense to look for where the engine can be improved. If you’re still five tenths off in your driving, think about the driving first.

Why should P2 never be ahead of the leader at a rolling start?

Because at the start the elastic is not an illusion. It costs you places.

In a rolling start the driver in P2 has to be behind the leader at the yellow line. If you’re ahead when you cross it, you get a 5 second penalty. So if you find yourself ahead of him by mistake, you’re going to have to lift. And if you lift while he’s on full throttle, you get the elastic effect against you and you lose a lot of time.

The tricky part: the driver on the inside of the last corner does less distance than the driver on the outside at the same speed. So if you’re on the inside you can end up ahead without wanting it. Stay a little bit behind him before the corner.

I have a start in the course where the driver in P2 gets a little bit ahead, has to back off the gas to not get a penalty, and the leader gets a massive start with the elastic. The driver in P2 goes from P2 to P7. It’s okay to lose one position. Time it properly and get a parallel start, instead of dropping to P7 like that.

How do you use the elastic effect when you start from pole?

Now flip it. If you’re the driver in P1, you dictate the pace. Nobody else. So you choose when to go on the gas.

I learned this one from Max Verstappen. At the 2012 Lonato Winter Cup I couldn’t explain to myself how he built such a gap in the first laps. When I rewatched the videos I saw he would make the driver in P2 be a tiny bit ahead of him, so P2 had to slow down a lot.

In that very moment Max would slam the throttle and catch him by surprise. He’d even add a bit of brake before the jump. A pretty big elastic, and a gap not only to P2 but to P3 as well.

And it was a rubber band effect I used to like so much. When somebody was a little bit ahead of me, I’d get on the gas the moment he was coming off it.

Pull at least two kart lengths before turn 1 or turn 2, and you don’t have to defend. From P2 onwards they fight each other and lose time from you. Easier said than done. But when you do, the race is in your hands. More on that in pre-race start strategies.

Why does a train of karts bunch up and then spread out?

Same physics, in a group. If the speed is lower, the distance contracts between all the drivers. The gaps contract. When the speed goes up, the group spreads out.

That’s why I used to make very slow starts from P1. The earlier you go on the gas, the more spread the group is going to be. Go later and slower and the group behind you stays bunched up. Counter-intuitively, I promise you, that creates more confusion behind you, and when the gaps are contracted it’s more likely that drivers get involved in crashes. I’m not saying I was looking for that. I’m saying a bit of a mess behind you gives you a gap and breathing room.

You see the same in the middle of a race. I have a clip where the whole group is bunched up. The leader of the group brakes pretty early, the next driver brakes too late and bumps him. Now he wants to overtake but he can’t, because he has lost the momentum.

Look ten seconds later and the group has spread out. Drivers having different braking points, the concertina effect, call it what you want. The only one who benefits is the driver who kept his momentum. He extends his gap and doesn’t have to think about the driver behind for at least one more lap.

So when you’re in a train, don’t lose your momentum fighting. That’s racecraft, and I go through it in when to be patient vs when to attack.

Where does the concertina effect show up most?

• Tight hairpins, the biggest speed delta gaps in braking and on exit. You’ll feel it the most here.
• Shifter karts, even more noticeable because of front brakes and big speed changes.
• Tracks with heavy braking zones, you’ll always feel that “closing in, then dropping back” sensation.

So is it the engine or the concertina effect?

If you gain five metres on braking and then lose five on the exit, don’t panic. Don’t blame the kart. Don’t cry about your engine.

99% of the time, it’s just the concertina effect. It’s just an illusion.

Once you accept that, you stop wasting energy on excuses and start focusing on what really matters: your own driving.

So next time you feel like you’re closing up on entry and then getting “dropped” on exit, remind yourself:

“Probably it’s not the engine. It’s just the concertina effect.”

That awareness alone will make you a smarter, calmer, and better driver.

Frequently asked questions

What is the concertina effect in racing?

An illusion from physics: as speed expands, distance expands, and as speed contracts, distance contracts. Two cars or karts close up on the brakes and the gap opens again on the exit, even when neither one is faster.

Why do F1 cars close up at the Monaco hairpin and then pull away?

Because the speed drops a lot in the hairpin, so the distance between them contracts. When the car in front gets on the throttle first, its speed expands and the gap stretches again. It doesn’t mean one car braked way later or has a better engine.

Does the concertina effect mean my engine is slow?

No. 99% of the times it’s not the engine. Even if you drive exactly the same corner as the driver in front, you get gapped on the exit. Telling your tuner you’re losing on the bottom because of it can send the setup in the wrong direction.

How do I know if a gap is real?

If you close up on the brakes and you can keep that gap on the exit, it’s real. If the gap opens again on the exit, it’s the concertina effect. Check it in the data against your teammates.

What is the elastic effect at a kart start?

At a rolling start, if the driver in P2 gets ahead of the leader he has to lift to avoid a penalty. If the leader is on full throttle at that moment, the gap opens fast and P2 can lose a lot of positions.

If you want me to tell you whether you’re losing on the exits for real or it’s the rubber band, send me your onboard for an onboard review. And if you want to work on your braking, your exits and your starts for good, that is what we do in the 6 months transformation.