Car

Behind the scenes with Pirelli - how F1 tread wear is measured

by Josh Suttill

6min read

Red Bull F1 car in Hungary

There’s a hive of activity at the back of every Formula 1 garage after each session of a grand prix weekend that’s crucial to the outcome of the next event.

Aston Martin F1 car exiting garage

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Almost as soon as an F1 practice session is complete, all of the tyres used in the session are wheeled out of the garage ready for assessment by a team of Pirelli engineers. 

Those Pirelli engineers are measuring the tread wear of every slick F1 tyre using a Tread Wear Indicator (TWI) and feeding that information back to the teams. 

It’s a process that rarely has the light shone on it, but it’s absolutely fundamental to teams picking their strategy for a grand prix weekend - so with the help of F1 tyre supplier Pirelli, Raceteq went behind the scenes to understand more. 
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A close-up view of Pirelli F1 tyres showing surface tread wear and rubber pickup

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How the TWI works  

Free practice one has just finished and the Pirelli engineers are already placed at the back of Formula 1 garages, ready to test the used tyres brought to them by the teams.
 
The measurement is taken by inserting the TWI probe into six narrow holes on the surface of the tyre. There are three pairs of holes on the inside, outside and centre of the tyre, as the wear rate across a single tyre can vary depending on the stresses of the circuit characteristics. 
 
There are also different sets of holes around the tyre in case there’s a flat-spot (an area that has gone flat due to heavy braking or a lock-up) right over one set of holes, which would skew the measurement.
 
The Pirelli engineers first check the surface of the tyres and decide where it is best to take the necessary measurement.

Pirelli F1 tyres with engineers measuring tread wear

Pirelli engineers scraping away rubber residue to ready tyres for measurement

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They clean the surface of the tyre, scraping away debris and the rubber pick-up that builds up on the surface of the tyre.

“What is also important for us, when we do the measurement, is to clean the surface properly,” Pirelli F1 chief engineer Simone Berra tells Raceteq.

“Just to avoid any pick-up or any other external factors that can influence the measurement itself.”

The TWI probe - a small device that fits into the palm of your hand - is then carefully inserted into the selected holes on the tyre, and that sends data to the electronic tablet it’s connected to.

The data is displayed on the electronic tablet and shows the tread wear of each tyre (on a scale of 0-100% tread wear) and the expected remaining lifespan of that set. 

That data is then shared with the relevant F1 team, a member of whom will also be present while the Pirelli engineers take the readings to exchange any additional information on how the tyres performed. 
Pirelli F1 tyres with engineers measuring tread wear

A Pirelli engineer measuring tread wear on an F1 tyre (left)

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“Our guys are well experienced not to push too much because when you have a hot tyre and you push too much with the wear gauge, then you risk deforming the tyres in that area and you can measure completely different [skewed] values,” Berra explains.

“So we need to be precise, because this data is a vital, key factor for the teams. But also for us to collect significant information and have proper averages.”

The exact wear data is kept private from rival teams, but there are two ways teams can check their tread wear against the rest of the grid.

Pirelli issues the average wear rate of the grid across the selected slick tyre compounds for the weekend so teams can find out how they compare to the competition.

But teams are also able to choose five rivals with whom to compare tyre wear numbers. 

For example, a midfield team can select five of its closest rivals to get an average, so it knows how it compares to its direct competition, rather than the frontrunning teams that it’s unlikely to be fighting that weekend. 

Pirelli Tread Wear Indicator

The Tread Wear Indicator shows a number that can be used by F1 teams to indicate how much tyres have worn over a session on track

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In-race importance 

On a conventional grand prix weekend (without a sprint race) the tyre data is probably most important after second practice on Friday, when teams have completed their long-run simulations that help them to make crucial set-up and strategy decisions for the race. 
 
But it can also be useful in the middle of the grand prix.  
 
“During the race, after the set comes off [at the pitstop] each [Pirelli] engineer should take the wear check as soon as possible and share this information with the teams to give them live information on what is going on,” Berra says. 
 
“And because [the teams] can adjust the strategies based on what they are measuring,  sometimes they  also ask us to not clean the tyres but just take the wear [measurement] as soon as possible and have a rough idea and then take the proper measurement.
 
“Even if you don't have the exact number, at least you can understand how the profile is and how far you are from 100% wear. 
 
“It's [a measurement during a session is] already a really good indication for the next stint or session.”
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A team might choose to receive tread wear readings during a session for a quick update on tyre wear information

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Driving with 100% worn tyres 

It’s important to note that sometimes the Pirelli readings will show 100% tread wear - that’s because drivers can still use the tyres at maximum tread wear.
 
“The teams are always looking at the performance life [how long a tyre proves effective], and sometimes the performance life is higher than the wear life,” Berra said.  
 
“So, you reach 100% wear and the tyre is not really degrading. And so you can continue the stint and prolong the stint to stop later on - if you still have some performance. 
 
“This happens especially if you wear the front axle in a localised point; you don't have a big [enough] drop in performance that you must stop. 
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“While if it happens on the rear axle and you are on a rear-limited circuit [where rear tyres are the factor limiting a car's performance, rather than the front tyres] like Budapest, then you start losing performance and then you need to stop.”

Berra adds that Qatar is the opposite example because teams will run on the limit of tread wear and they must decide when to stop before risking a terminal tyre problem.

Pirelli is in constant dialogue with the F1 teams throughout a grand prix weekend - and the TWI measurements provide a small but crucial piece of the complex strategic puzzle that is tyre wear.

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