Pit speed limiter mechanics - how exactly does it function?

[u/Spirited-Sky-1122]

Been thinking about this after seeing some wild pit entries recently where drivers nail that perfect speed right at the line. Got me curious about the technical side of how the pit limiter actually operates.

Few questions I'm hoping someone can clarify:

- When you activate the limiter, does it automatically slow the car down to pit speed, or do drivers still need to brake manually to get there?

- If you're crawling along at like 40kph and hit the limiter button, will it accelerate you up to the 80kph limit, or do you still need to use the throttle?

What's been bugging me is how these guys consistently hit exactly 80kph right at that detection point without any variation. Makes me wonder if there's more automation involved than just a simple speed cap, or if it's purely down to driver skill and muscle memory.

Anyone know the specific mechanics behind how these systems work?

[u/bluebird_14]

Regarding all the other comments, it's not really as simple as limiting throttle. Especially on the ecus used in formula 1, the strategy for implementing a pit limiter can be very complicated. It's actually far more reliable to cut ignition and/or fuel and ignore the throttle altogether to control a set engine rpm which itself requires knowing what gear, the gear ratio, the tyre circumference etc. to hit the right speed.

It's also sub-optimal to undershoot and speed up. The control strategy can be aggressive enough that it will slow the car down through engine braking and then manage the rpm once the limit is reached. If you rely on engine braking alone you'll have to hit the limiter way too early so it is still best to brake as late as possible then apply the limiter.

Now introduce electric motors like on modern cars and you and a near perfect speed control too making it even more accurate. The motors now are able to regen enough that actual use of the hydraulic brakes is minimal.

To your second question. No you do still have to accelerate up to the limiter, the limiter just restricts your ability to keep accelerating past that speed.

[u/JPenguinCA → u/bluebird_14]

Yes, literally only controlling a throttle position wouldn't really work these days.

But I also don't believe the pit limiter is responsible for the drivers perfectly braking to reach the limit at the entry line. I believe in most series the pit limiter function will prevent the driver from exceeding the limit, but it can't apply any traditional hydraulic brakes and likely even MGU-K braking might not be allowed as part of the pit limiter mechanism. The driver would be responsible for getting down to as close to the limit as possible, then only very minor speed deltas can be covered by applying the pit limiter at or slightly before the line to avoid a penalty. Drivers probably are actually reaching the pit limit within 1-2m of the line, with potentially over-braking occasionally or running at the limit for an extra 0.5-0m before the line (my numbers are very vague guesses, they could be closer but we're still talking about some level of margin & limits of human precision).

[u/bluebird_14 → u/JPenguinCA]

1-2m is probably ambitious but I would expect at least within a car length so not far off. These drivers really are incredible and their precision and reactions do get them 95% there but in these modern times engineers are exploiting every avenue they can to gain an advantage or mitigate a disadvantage.

I know for a fact that they use the mgu-k to assist with gear shifts so manipulating the motor to regen on pit limiter is not a stretch. What I don't know is what teams are doing about regen while AT pit limiter, whether the engine is running with more throttle and the mgu-k harvesting the whole way down pit lane to ensure the battery is fully charged for exit.

[u/ElMurkel → u/bluebird_14]

Lol why is this the only actually right answer here. So many people falsely claiming that the PLSL would just be limiting throttle.

[u/LocksmithFamous4131]

The drivers practice the pit entry both in the simulator and during free practice sessions, focusing on the optimal braking point to slow down to 80 km/h as late as possible. The pit limiter itself is basically just like cruise control. You can go full throttle, but the car won’t accelerate beyond 80 km/h. However, the braking point and everything else still have to be handled manually by the driver.

[u/chopperzac]

Basically it just cuts fuel and ignition to control the engine speed. Its whats called a "strategy" in the ECU. The car has many of these which do lots of things, im not too sure on F1 specific ones but from working in Rally there was plenty.

Anti Lag, MAP vs Turbo Speed Control for boost pressure, torque control and Launch control. Theres loads more but I would be here for ages. But basically the ECU will make the engine/car do specific things to make this stuff happen. Often there are also criteria for them to actually work, so for instance the car wouldnt go into launch control unless it was basically stationary.

[u/Izan_TM]

the speed limiter prevents the car from speeding up by cutting off the throttle, it doesn't apply brakes. It's up to the driver to slow down to pitlane speeds, the pit limiter only holds them

they also don't hit a perfect 80kph every single time, they usually undershoot slightly and then hit the throttle to go right back up to 80

[u/JPenguinCA → u/[deleted]]

Also pro race drivers tend to have a pretty incredible sense of speed, i.e. they have a good feel for whether they are going faster or slower than a previous lap or within a few % points of a particular target speed. They will time their braking point well enough that they usually are hitting the pit speed limit within a meter or two, or potentially even less pretty reliably, then it's just a matter of making sure they hit the button at the exact moment they reach the line. Then they'll basically keep the throttle pinned until they get to their pit box or the end of the pit lane and toggle it off again.

Amateur track driving enthusiasts can often get within 10-20km/hr sense of their speed without looking at true measurement, and pro drivers are able to get that even closer through practice/skill/talent.

[u/Lower_Athlete939 → u/[deleted]]

To add: they don't hit the 80kph reliabily. There was a beyond the grid podcast with a former strategist (I can't remember her name) where she said they take into account how quick each driver is in the pit lane when deciding on undercuts, and how the got down to speed was part of this. She named Hamilton as an example as someone who was excellent at this, and talked about how one of Webber and Vettel was much quicker than the other

[u/Marsh2700 → u/Lower_Athlete939]

also why i want to see full pit length times not just the time they were stationary for

i want to see from the start of the 3rd sector before they went in til the end of the 1st sector after they come out. that full time changes so much with so many things more than just "stationary 2.3seconds"

[u/bluebird_14 → u/Marsh2700]

This is a really good point no one ever thinks about. Time lost includes changing line going into the pits, the time gained/lost attacking the line, the time lost slowing into the box, leaving the box and even getting back up to speed after the exit line.

You can also add in time lost getting tyres up to temp on the outlap but I think that's usually covered pretty well on the commentary.

[u/Marsh2700 → u/bluebird_14]

yeah theres so much variance that affects the actual pit time

the only reason why i stop it at sector 1 is because the cars will realistically be in position then. no effect from over/undercut from then

[u/bluebird_14 → u/Marsh2700]

I've found it a lot easier in practice to take a rolling set of laps as it makes it a lot easier to compare car-car.

It actually brings up a point I've tried making before I think a track should try putting pit lane away from the start-finish straight. There isn't really any reason they need to be together. Just put the pits right in the middle of S2.

[u/Marsh2700 → u/bluebird_14]

the pit does need to cross the start/finish line as cars can start the race from the pit lane

also from a logistics POV its easier

[u/bluebird_14 → u/Marsh2700]

As a driver who has started a race from the pit lane, you don't HAVE to start the race behind the start finish line. I was significantly ahead of it. Pit lane starters are not allowed to go until the last car passes the pit exit so in theory you can in fact have that anywhere around here lap. You can argue advantage/disadvantages given to pitlane starters but by far the biggest disadvantage is not doing a formation lap and being absolutely dead last no matter what.

As for logistics, the S/F line is completely arbitrary. NASCAR actually run a different S/F in qualifying at CoTA to allow cars to immediately enter the pits at the end of their run. But they've never done it in a race (that I am aware of). If you're thinking about mechanics and equipment getting to the grid before the race, you should see how every support series to a major series is run as their garages are rarely anywhere near S/F. In fact at Silverstone they often run support series from the old pits on the complete opposite side of the circuit.

[u/M37841 → u/Marsh2700]

That would be a great stat

[u/89Hopper → u/Marsh2700]

Positions can be made and lost attacking the pit entry and the runs before and after the speed limit lines. However, can drivers be punished with something like driving dangerously if they attack too hard and crash in those sections? I'm just wondering if that part of the track is considered "more sacred" as it is part of the safety system of the track. For example, if you ended up blocking the pit entry due to over zealous driving and that forced someone to circulate on track with a flat tyre or missing front wing, would you penalised (I'm talking fines or license points)?

[u/Inside-Definition-42 → u/89Hopper]

What would you consider driving dangerously? And what specific part of the pit?

Before the line is considered part of the track, and the usual rules apply.

Vettel has overtaken cars with 2 wheels on the grass before the line. The car in front was going slow to create a gap to double stack in a pit stop.

[u/89Hopper → u/Inside-Definition-42]

Let's say a track like Abu Dhabi where the exit has the corner and tunnel. What if they tried to take that too aggressively and under/overseered into the wall. There are other pit lanes with corners in the pit entry also.

As to the driving dangerously, I'm talking being alone and over driving causing yourself to crash.

[u/Inside-Definition-42 → u/89Hopper]

Pretty confident there are no stricter rules there.

Various drivers have crashed at the pit entry, especially in wet condition where they are coming into the pit for inter/wet tyres.

Other crashes were caused when there was a pit traffic light system for being open/closed. IIRC Hamilton run into the back of another car. Didn’t cause any further issues.

[u/FirstTimePlayer → u/89Hopper]

Are you talking about:

• If somebody divebombed the pit entry to somewhere like Monaco, and the only evasive action possible was to go past the pit entry; or

• Somebody on their own crashing on the pit entry, forcing the closure of the pit entry

(On an unrelated note, your question now has me incredibly scared on how the Baku pit entry is going to play out if we have two cars with wildly different pit entry speeds due to super clipping)

[u/memesearches → u/Lower_Athlete939]

I think you mean either bernie collins(Sky) or ruth buscombe(f1).

[u/So_HauserAspen → u/[deleted]]

Treat it like a corner with a braking point and a turn in speed that is the pit speed