McLaren Formula 1 car throwing sparks from its titanium skid blocks at the 2025 Japanese Grand Prix

Why F1 Cars Throw Sparks: The Plank Rule, Explained

August 12, 2026

Welcome to the Happy Hour Racing Formula 1 Tech Breakdown - where we take one confusing part of Formula 1 and make it make sense. No engineering degree required.

McLaren Formula 1 car throwing a shower of sparks from its titanium skid blocks at the 2025 Japanese Grand Prix at Suzuka — That shower behind the McLaren is metal, not fire. It is the skid blocks under the floor scraping the track at Suzuka. (Photo: Liauzh, CC BY-SA 4.0, via Wikimedia Commons)

The Short Version

The sparks flying off the back of a Formula 1 car are not damage and they are not a special effect. They come from metal blocks bolted into a strip of wood that runs down the middle of the floor. That strip is called the plank, and after the race the FIA measures how much of it wore away. Wear it too thin and the result gets deleted. That is exactly what happened to both McLarens in Las Vegas last November, and the rule that caught them just changed for 2026.

Meet the Plank: A Strip of Wood Under a Formula 1 Car

The plank is a flat strip fixed to the underside of the floor, running front to back down the centreline of the car. The 2026 rulebook calls the whole thing the Plank Assembly: the plank, the metal skids set into it, and the bolts that hold it all on. It must be 10mm thick when new, give or take two tenths of a millimetre, and it has to be uniform.

The material is not carbon fibre. The rules only say it must be homogeneous with a specific gravity between 1.3 and 1.45, which in plain English means a dense resin-bonded wood laminate. Teams have used a product called Jabroc for decades. It is essentially very serious plywood, sitting under the most expensive racing car on earth on purpose.

Why a Piece of Wood Polices the Entire Car

Because it is a ruler nobody can argue with. An F1 car makes a huge share of its grip from the floor, and that grip climbs sharply the closer the floor runs to the track. Lower the car, find lap time. The FIA needed a way to stop teams from dragging the floor along the ground, and a stopwatch cannot police that.

The plank does it by wearing. If the car runs too low, the plank scrapes. If it scrapes too much, the car is illegal, no debate. The rule arrived in 1994 after the San Marino weekend that killed Roland Ratzenberger and Ayrton Senna, and the first big name went down almost immediately. Michael Schumacher won that year's Belgian Grand Prix and lost the win in scrutineering for plank wear.

Downforce squashes the car toward the track. The plank runs down the centre of the floor, and the metal skids set into it take the hit when the car bottoms out.

Where the Sparks Actually Come From

The plank has three 34mm inspection holes drilled through it, and the rules let teams fit metal skids flush into the plank around those holes. For 2026 a metal skid is mandatory around the forward-most hole and optional at the middle and rear ones. The permitted metals are spelled out: Ti6Al4V titanium alloy or 17-4PH stainless steel, machined from solid, with no coating, welding or extra heat treatment allowed.

When the car bottoms out over a compression, a kerb or a bump, the metal takes the hit instead of the wood. Titanium shaves off in tiny flakes that get hot enough to burn in the air, and that is the white shower you see trailing the car on TV. It is the car telling you the floor just touched down.

Those titanium flakes stay hot after they land, which turned into a real problem when they started grass fires at Suzuka. During 2025 the FIA began specifying steel skids at selected events instead. Steel adds around 750 grams and wears much faster, so teams have to lift the car slightly to survive a race on it. The 2026 rules keep both metals legal and set which one is used at each event in a separate FIA document, so the material can change race to race.

Underside of a Formula 1 car showing the wooden plank running down the centre of the floor with round FIA inspection holes and metal skid washers — The plank from underneath, on a Honda Formula 1 car at the Honda Collection Hall. Note the wood strip down the centreline and the round inspection holes with metal set around them. (Photo: Morio, CC BY-SA 3.0, via Wikimedia Commons)

F1 technical analyst Craig Scarborough laid out the same maths on the night the McLarens were thrown out in Las Vegas:

The plank under an #F1 car is 10mm thick when new. The @FIA measure wear in the inspection holes, anything more than 1mm is a simple disqualification. Teams fit titanium skid blocks around the holes, but too much bottoming will still wear the assembly away. #F1tech
- Craig Scarborough (@ScarbsTech) November 23, 2025

How the FIA Measures It After the Race

This is where teams get caught. The skid is removed from the car and measured with a micrometer fitted with a 6.35mm anvil, and the entire rim of every inspection hole has to be within tolerance. It is not an average and there is no rounding in the team's favour. One thin spot in one hole on one corner of the car is enough.

Through 2025 the legal floor was 9mm, meaning teams had exactly 1mm of wear to play with over a full race distance. In Las Vegas the McLarens came back measuring between 8.74mm and 8.96mm. Lando Norris lost second place, Oscar Piastri lost fourth, and a championship fight that looked settled reopened overnight. McLaren told the stewards the car had bounced more than expected and that a wet Friday cost them setup time. The stewards were not moved. Keeping the car legal is the team's job.

One millimetre of wood decided a championship fight. Under the 2026 limit, those same McLaren measurements would have been legal.

What Changed for 2026

The legal floor drops from 9mm to 8mm, so teams now get 2mm of wear over a race instead of 1mm. That sounds like the FIA going soft, and it is not. It is a trade. In exchange, the metal skid at the forward-most hole became mandatory.

Here is why that matters. Under the old rules teams could let the front of the wooden plank wear away as a sacrificial part, which let them run the nose lower than the static rules really intended. Putting hard metal in that exact spot is a physical stop on the trick. The bolts are covered too: the rules require the bolt shank to be the weakest point in the assembly, so a heavy kerb strike shears the fastener and drops the skid rather than dumping that load into the survival cell around the driver.

What You Will See on Track

Now you can read the sparks. They are heaviest early in a stint, when the car is full of fuel and sitting lowest, and they fade as the fuel burns off. They cluster in the same places every lap: high-speed compressions, the bottom of a dip, the exit kerb a driver keeps clipping. If a car is lighting up more than its rivals, its team is either running lower for lap time or is about to have an uncomfortable conversation in scrutineering.

Formula 1 is on its summer break right now, and the season restarts with the Dutch Grand Prix at Zandvoort on August 23. Watch the banking there and you will see exactly this: cars compressed into the track, floors touching down, metal shaving off in the dark.

The Bottom Line

Sparks are not a light show. They are a receipt. Every one of them is a team telling you it has parked the car right on the legal limit, and the difference between a podium and a deleted result is about the thickness of two credit cards.

Watching the floor spark all season and want to rep the team doing it? Grab the McLaren F1 New Era 9Fifty camo hat, the McLaren Racing shadow beanie for the night races, or the Red Bull Racing Austin GP bucket hat. The rest of the paddock is in our Formula 1 collection. New tech breakdowns drop every week, so bookmark the blog and never get lost in the jargon again.