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How Pirelli’s F1 “Doggy” is helping drive tyre development

On every Formula 1 race weekend Pirelli engineer Martin Wahl logs up miles walking patiently around each circuit pushing a curious looking three-wheeled device.

Pirelli grip tester

Resembling a cross between a lawn mover and the things football groundsmen use to paint white lines, it’s actually a grip tester, and its job is to log the level of grip all the way around the lap.

Known within the company as the “Doggy” - because it has to be taken for a walk now and again – it is an innovation introduced by Pirelli this year in order to improve the company’s modelling as it develops its tyres and makes its race-by-race compound selections.

The new machine was first used prior to the British GP in July, and has been gathering data at circuits ever since.

Wahl, the Doggy’s master, had spells at Williams and the Jaguar Formula E team before joining Pirelli last year.

"Martin came with a proposal to introduce it also for Pirelli activity and to collect additional data,” says Pirelli F1 boss Mario Isola. “As you know, we measure the track roughness every circuit, on the Wednesday before the race weekend.

“We have a sort of 3D picture of the tarmac in different positions around the track. The difference here is that it is possible to measure the actual level of grip all around the circuit. So it's not just in a few points of the circuit, it's a continuous measurement. And it is giving us an idea of the level of grip of the circuit.

“And now, there is an ongoing activity in trying to correlate these measurements with other stuff, like truck roughness, like the level of grip that the cars are experiencing on track, if there is a correlation with the different types of compounds that we select for each event.”

Isola says that the new stream of information has already proved to be valuable.

"We started using a laser to measure track roughness almost the first year that we were in F1, so we have now a database on circuits from 10 -11 years period.

“And it's also useful for us to understand the ageing of the track, because even if they are not going to re-surface the track from one year to the following year, you can see a change in these parameters, micro and macro roughness, there is an ageing.

“And it depends on how much the track is used during the year, the weather condition in that area from summer to winter, the type of tarmac that is used, and this is giving us a good information. But it is not complete.

“For example, one important element that is coming from the grip tester is the difference in grip from one corner to another corner, from the braking point to the exit of the corner, from the straight line, because clearly there is an influence of the cars running on track.

“And sometime we can see that in some corners the level of grip is lower, because with the cars running they make it more flat, or less abrasive, while on the straight line we have a higher level of grip.

“But on the straight line you don't really need the grip, because you don't have any grip limited point on the straight. And that's why we want to use this information in the future to make better correlations."

Pirelli Doggy, grip measurer at work

Pirelli Doggy, grip measurer at work

Photo by: Pirelli

Pirelli has already discovered some intriguing numbers as circuits develop over a race weekend.

“To give you an example Qatar was our first time that with F1,” says Isola. “And so Martin was on track on Wednesday to measure the grip. It was quite low compared to other circuits. But then, during the free practice, we saw a lot of track evolution during the day. And the feeling was that the actual grip on track was higher than our measurement.

“And so Martin decided on Friday night to go on track again with the grip tester. And we found an increase in grip of 28%. That is quite a huge difference with only two sessions, and consider we didn't have any support events – just two hours running of the F1 cars.

“So all this information is important for us to characterise the circuit. It is not just the layout severity, it's not just the track roughness, but any other element is important also for our modelling, because in our model, we have a level of grip, and we want to correlate this level of grip with something that we can measure on track."

So how does the Doggy work? It’s all about the front tyre and how it interacts with the track surface,

"There's a slip ratio between the rear axle and the front axle of 15%,” Wahl explains. “So from that it knows how much force should be there, from the longitudinal strain gauge in the front axle. And then based on how much resistive force it has, it then gives us a grip number from that.

“Basically the front tyre rotates 15% slower than the rear tyres through a chain. So you can't just rotate one of the tyres, they're all interconnected through that chain.

"You've got to hit a target speed when pushing it. We aim for metre a second just for ease – it’s better to do the whole year at one speed then do different tracks at different speeds.

"You’ve got a gauge and you just hit that one metre per second, you've got a slight leeway. And if you are either side of that, then it beeps at you and tells you to speed up or slow down.”

So what exactly is that crucial front tyre?

"It's the stock tyre that it came with from the supplier at the moment,” says Wahl. “These were designed for use on heli pads in the North Sea so they don't get any cold cracking in the winter.

“So it's got quite a low working range, because it's not very temperature sensitive, which is quite good when you go to Interlagos and it's raining and it's cold, compared to Qatar where it was 35 degrees track temperature.”

The hope is to eventually replace to stock front tyre with a bespoke item based on a proper racing compound that Pirelli has good knowledge of. However for the moment the standard one does the job.

"We had this discussion before taking the tool,” says Isola. “We believe that for this phase of the investigation, we prefer to use the rubber that is designed by the supplier. The tool is calibrated with that compound, which is comparable in different circuits.

“We had basically two choices, one was to take this one, and the other one wants to make a small tyre with our C3 compound, for example, that is an average compound, and use that.

“But then we were losing the reference from the supplier. And so for the moment we want to use the reference compound, and we get the data, and then try to correlate it with our compounds. But this is a post processing activity."

A Pirelli technician with a grip tester

A Pirelli technician with a grip tester

Photo by: Steven Tee / Motorsport Images

One obvious issue is that racing compounds operate at high temperatures: “That's exactly the point,” says Isola. “Our compounds work at a temperature higher than 80 degrees. And if you push the machine at one metre per second, you cannot keep 80 degrees!

“And so it's much better to use something that is already tested. And then post process the data in order to make a correlation with our compounds."

As Wahl walks around the tracks it’s important that he follows the racing line as best he can.

"What we do is we take the outside tyre,” he says. “Because if there is going to be any degradation of the time, that's probably where it will be. I use pole laps on YouTube to do line analysis. I'll look at that the night before and memorise it and then work out where to go.

“Qatar was a little bit difficult because we were using F4 videos, so you have to kind of take a bit of expectation of how an F4 car will differ to an F1 car. They were taking quite a lot of kerb, while the F1 cars not taking as much on the apex. So it's just things like that where you have to be a bit pre-emptive at times.

"Kerbs, we can't deal with. You just go as close as you can to the kerb at that point because with the bumps you would just get complete useless data. We just get as close to the reference as possible."

The grip data is logged on a memory card, but Wahl can also follow it in real time as he completes a lap.

"On the screen, you can see a graph. So when you see a change in tarmac you can see either a drop or increase in grip. There was an occasion in Spa where, because of the damage to the facility with those big floods, they'd had to bring on trucks on to different parts of the circuit.

“So one corner was a bit more dirty. You could see a drop of grip there as well. A bit like Qatar with the sand, anything that's on the circuit that's not meant to be there, you can see it change the grip."

Wahl and the Doggy have had a few adventures on their walks this year.

"We did a run in Budapest on Sunday evening,” he says. “And obviously Budapest is pre-shutdown, and everyone wanted to get out. And I had lorries overtaking and it was about to chuck it down with rain. So that was interesting!

“And then on the Wednesday in Spa, I was halfway halfway up Eau Rouge and there was an old F1 car that was doing filming from La Source up to Les Combes, so I had to stop and get someone to come and pick me up.

“The next time I tried it ran out of battery, because it hadn't been charged fully after Budapest. So I got around to the end of Sector 2 and started Sector 3 and it stopped. I think I did Spa about five times, including once in the rain!”

Measuring tracks in the wet has been a particularly interesting exercise: "Spa was good because it was spitting and it was so cool in the mist that it wasn't drying very much.

“So we had a constant read all the way around the circuit, which was interesting. And then we then went for the dry run as well. So we have got that comparison which we fed back to our modelling department of how much the grip differed around the lap with that amount of water."

Where the Doggy can be particularly useful if when F1 heads to new tracks – but only if they are ready. Construction work in Jeddah was too late for an early visit, but Miami looks set to be completed well in advance of May’s inaugural race.

"That is exactly the purpose,” says Isola. “For Saudi it was too late. And also it was difficult this year because of the COVID restrictions. But Miami is a good example. We are in contact with local organisers, and when they confirm that it's done, we are planning to send the guys with the laser and the grip tester to have a picture of what we can expect, and maybe adjust the selection."

Pirelli Doggy, grip measurer at work

Pirelli Doggy, grip measurer at work

Photo by: Pirelli

Isola says that Wahl’s work is already paying dividends as the numbers are crunched back at base.

"We give all the measurement to the modelling department and they are working around that,” says Isola. “I believe that there is a good correlation between the measurement and the level of grip that is expected from calculations.

“And what is useful is to understand different conditions. We were talking about the racing line, for example, that is the most representative. But in some cases, you have the racing line with a level of grip, and outside the racing line, you have a complete different level of grip, because it's dusty, because it's less used, because of many elements.

“But it's still useful to understand for other applications, what is the difference between different parts of the circuit, or different conditions in the heat of the day, in the night, when it's damp, when it's wet.

“And this difference is affecting the performance. The performance means also the level of energy that you put into the tyres, or if the tyres are sliding or not. And when you slide, you overheat the surface.

“So when we talk about overheating, there is a part of that is due to the level of grip of the track, and knowing the level of grip and trying to make correlation with the telemetry data with a measurement from the grip tester, with the conditions on track that we know from experience, we can build a picture that is a lot more complete than just with less data.

“Ideally, it would be great to make this measurement before the race and after the race. Because clearly, we can also understand the track evolution.

“It's not always possible, because in a triple header, we rush to pack everything and obviously move to the next event. But in the future, if there is the possibility on some tracks to collect the data before and after, that would be also good information.”

Isola says there is also a bigger picture for Pirelli: "I'm happy that we started this analysis because we use motorsport as an open laboratory and then use that knowledge for other purposes.

“We have a simulator now in Milan that we use for road tyre development. And one element that is important in the model that we use is the level of grip, that is clearly due to the compound, the working range, many parameters, but also on the level of grip from the asphalt on the road is different compared to the track.

"We start getting data from the track, when we have a better idea, we can have an idea of which is the level of grip on different types of roads.

“On the highway, you have this special asphalt to avoid aquaplaning, for example, that is a lot rougher compared to what we have in other applications. It could be interesting to understand the level of grip of this tarmac compared to an asphalt that you have in a city centre or another place. It’s not just about what we do on track."

That’s all for the long term. In the mean time on Wednesday Wahl will be taking the Doggy for its regular exercise around the Jeddah Corniche track, and no doubt as usual he will get a few funny looks from drivers and team engineers.

"I often get asked what it is,” he says. “And we coyly answer to say we're measuring the distance of the track, because it does do that as well!"

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