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A different class: How LMDh and GT cars differ

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7 Mins

Porsche 963

Porsche driver Laurens Vanthoor explains the similarities and differences between LMDh and GT cars.

If you drive a Porsche 992 on the road, or you see one driving by, it’s clear that it is not a million miles away from the Porsche 911 GT3 R that’s raced in many categories around the world. However, there are plenty of differences, and that’s before you look one more level up the ladder at the 963 LMDh purpose-built prototype car, which is an alien compared to any car on the road today - even if it’s based on the 918 Spyder Hybrid sportscar. The differences don’t end with the looks, either: There are plenty of other contrasts in the machines and the way they are driven. Let’s assess what’s different between driving the GT3 R and the 963, built to fight for the win in the biggest races on the World Endurance Championship (WEC) and IMSA WeatherTech Sportscar Championship calendars. “If you look at it very basically, it's a car with a steering wheel, four tyres, an engine, two pedals,” laughs Laurens Vanthoor, who has raced both cars extensively and knows there is much more to it than that. “In the end, what it comes down to is that you need to adapt to what has been given to you. “As Porsche drivers, we got used to that. Because in the past, we used to drive the RSR and the GT3 R, the LMDh was quite a bit different. I always say a good driver can drive everything quick after a while.” The 963 is faster, has more downforce, more electronics and a hybrid unit, creating a more complicated feel as a purpose-built prototype designed to win the 24 Hours of Le Mans.

The cars

Porsche 963Porsche 911 GT3 R
4.6-litre turbocharged V8Watercooled six-cylinder naturally aspirated engine
Seven-speed gearbox
Six-speed gearbox
Qatar WEC pole position time: 1m39.347sQatar WEC best qualifying time: 1m55.611s

One of the aims of the GT3 category is that the cars look similar to road cars, remaining identifiable to fans, so there is less room for modification. That also helps another goal of the category: to operate at a lower cost than the top level of sportscars. The principles of the two categories underpin the polarity between them, even if they both compete in the same two championships.

Are you sitting comfortably?

The first big changes a driver might see between the two are inside the cockpit, and even what you see and how you sit. In the GT3, you sit much like you would in a road car, in an upright position with your hips in line with your shoulders. The 963 is more of a single-seater position, where a driver sits almost as if their legs are on a workout bench and with their torso laid back. This, combined with the different windscreen, means a different view of the track for the driver of each car. Because the prototype is custom-built, the driver is lower, so that also affects the view. The GT3 R does at least have a protruding dash set-up that makes things easier to reach.

Need some assistance?

The GT3 category only has basic driver aids, with the ABS (anti-lock brakes) and traction control as the main two. But the 963 is a totally different story. “There's a bunch of high level electronics, which you can all adjust, which you all have to manage with different compounds of tyres,” added Vanthoor. “WEC races require quite a bit of energy management as well as tyre management because it's double stints. “Your true driving pace is important, but the LMDh is a lot more complicated, and there are a lot more details which you have to pay attention to. “So therefore GT3 when we go back now, it feels like sometimes a little bit of holiday. It's not easier to go quick, not all, but it's just less things to manage.”

On the 963, Vanthoor adds: “There's a lot of electronics, which you can adjust on braking, differentials, traction control, and so on. “Everything to do with electronics in the hybrid too. There's also the roll bars, which you can adjust. “In the beginning, it's very complex. The first race is maybe a bit overloaded with it. But it's important to understand it and to make it your strength. It's part of that game.” Part of the reason for all of these electronics, and having to adjust them all the time, lap by lap, is because often in longer endurance races you have to do long periods where you don’t change tyres. The teams and drivers call this a double-stint, because they come in and pit to get fuel and make changes in between, but don’t change tyres. As well as the tyres losing grip with every lap, making the car handle differently as the race goes on, the track surface can also change the amount of grip you have each lap. And if drivers have to make an overtake and go off the usual racing line to do so, it’s very slippy. Drivers are also aiming to use a certain amount of energy through the hybrid, and can’t just run on full power and full regeneration for the whole race. Even though the 963 is designed to use more sustainable fuels, drivers are still having to save some through the race to make sure they don’t lose time by pitting too much. In the GT3 car, there are fewer driving aids, so drivers are always fighting the car to make it behave as they want, without the same level of help from the car.

Even racing has traffic

The biggest driving difference between the two is racing in traffic. Because the 963 car is so much faster, it’s only a matter of time before the top class catches the GTs, which are often side-by-side and fighting for positions themselves. On a qualifying lap, the driver can set the car up and just drive as fast as they possibly can, taking the optimum line at each corner. In a race, often on older tyres, you’re having to manoeuvre around GT cars all over the track and this takes a spectacular blend of patience and all-out risk. It’s an art form. “Being quick over one lap is nice. But especially if you look at WEC it's pretty irrelevant,” adds Vanthoor. “Because it's all about managing your tyres over a double stint, about managing your energy, about managing traffic. And that almost plays an equal role as being quick.”

What’s the drivers’ favourite car?

We asked Vanthoor which is the most satisfying car for a driver to extract the maximum out of in a perfect qualifying lap. “I think every driver will always pick the faster car,” he says. “So it would be the LMDh car. But I also enjoy driving GT3 R. Each one of them has its own parts, which I personally enjoy.”

Aerodynamics are vital

The GT3 car does have aerodynamic tweaks compared to a road car, but testing them can be very expensive, so in keeping with the category’s cost-effective nature, the teams can’t use too much resource in this area. This means that the handling of the GT3 R mainly comes from the tyres and the suspension - the mechanical grip. But the increased aerodynamic power of the 963, combined with its lower weight, means it has more grip and is therefore fundamentally easier to drive in most cases than the GT3. Where the 963 is difficult is in the management of all the above factors, while also trying to maintain driving speed. Drivers are adjusting the various electronics in the car, finding ways to choose when to overtake slower cars or not, trying to save the tyres and fuel and energy to be efficient and keep an eye on where the other cars around them are. It’s the combination of all these things that makes the 963 a tricky beast to master. Both cars really reward a smooth driving style, not too aggressive on turn-in and on the power. And thanks to Porsche’s ladder of championships and the number of drivers it promotes through those series, it has a roster of really adaptable drivers who can jump between the two cars without too much difficulty.

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Where values are indicated as ranges, they do not refer to a single, specific vehicle and are not part of the offered product range. They are only for the purposes of comparison between different vehicle types. Additional equipment and accessories (add-on parts, tyre formats etc.) can change relevant vehicle parameters such as weight, rolling resistance and aerodynamics. These factors, in addition to weather, traffic conditions and driving behaviour, can influence the fuel/electricity consumption, CO₂ emissions, range and performance values of a vehicle.