The biggest change to the 24 Hours of Le Mans grid this year is the arrival of LMGT3, which has supplanted GTE as the event’s production-based class. Aside from boosting car manufacturer numbers from four to nine, the introduction of GT3 machinery has brought some differences in how the race will likely run, as well as retaining some similarities. We look at the key battlegrounds.
To the layperson, GT3 and GTE cars may look very similar, if not the same. But the former has traction control and anti-lock braking, plus more weight and slower lap times by around four seconds at the Circuit de la Sarthe. The GT3 top speed is also 15-20km/h less than in GTE, whilst the GT3s will be doing much shorter stints. In most series, it is common for GT3 cars to do one hour before pitting, but at Le Mans they are expected to complete only around 40 minutes or 10 laps. This means that cars will be pitting more, likely in excess of 30 stops, whereas last year’s winning GTE-Am car completed 24 stops.
GT3 cars at Le Mans have a limited amount of energy (measured in MJ) they can use during a stint. This number is defined in a Balance of Performance table. Saving energy is key because it means less time spent replenishing at pit stops. Teams calculate how much energy they can use per lap and instruct the driver to reduce the consumption rate, using familiar tactics such as lift and coast. Energy can also be saved during a safety car, when the pace is reduced. Fuel and energy consumption rates typically correlate on a standard racing lap, but in safety car conditions, more fuel is used than energy. The 40-minute stint estimation is based on Le Mans being an energy-intensive circuit, due to its long straights. When a car pits to replenish its energy allocation, it will still have fuel left in the tank.
‘Everything is done on energy, not fuel,’ says Aston Martin Racing head of performance, Gustavo Beteli, who has engineered both GTE and GT3 entries at Le Mans. ‘There is mileage in the energy – getting the best lap time for the least amount of energy is key. Whereas before, you would just run to the fuel and go again. Now, the energy varies a lot. In safety car laps, you use a very small amount of energy, so you can extend your stints. You try to do that the whole race, to minimise your pit stops.’
Torque sensors are a new technology in the GT ranks at Le Mans. These devices are fitted to the driveshaft and collect torque data that determines the car’s power output and energy consumption. Sudden increases in said data are investigated and can be penalised. As is the case in Hypercar, not breaching the car’s prescribed power curve is essential in LMGT3. Most teams give themselves a margin underneath the curve to ensure they are not running exactly on the curve all the time, because that would inevitably register limit-breaking spikes through the torque sensor, which can happen in several ways. Common causes include running over kerbs or bumps, shifting gears and wheel slip. This was never a consideration in the GTE category.
‘Back in the day, we had air restrictors [whereas] the standard BoP now is a [torque sensor] power controller,’ says Manthey racing division manager, Patrick Arkenau. ‘Ambient changes will have a less significant impact on power than the air restrictors did. In the past, we had some cars which have been very powerful in some stages of the race and others have dropped a bit. All that will be gone, which takes something out of the race, but makes it more equal.’
Although most of the LMGT3 teams are experienced hands with GT3 machinery, the mandatory torque sensor is new to all of them. It has been an extensive, and costly, exercise to integrate and understand them, in cooperation with the car manufacturers.
‘It took a lot of development and testing last year,’ adds Beteli. ‘You have to be as close as possible to the power target to get the best lap time. It’s very difficult to get there… because it’s very sensitive. The engine is always changing that target power too much. You get the power from the torque meter and the engine is varying all the time, being constantly on the limit. It’s tricky to know that you’re not overshooting and getting a penalty.’
In the latter years of GTE, it became more common for teams to attempt Le Mans without changing brake discs and pads. Meanwhile, it is common for GT3 cars to do so during the other major European 24-hour contests at the Nürburgring and Spa. Beteli reckons this could continue to be a battleground in LMGT3 and is confident that the updated Aston Martin Vantage GT3 EVO can go the distance without changing brakes.
‘It will be, for sure, because a GT3 is 100kg heavier than a GTE was,’ he points out. ‘It increases the temperature of the brakes. It’s still going to be a challenge here. The target, for everyone, will be to try and do it without changing. If it will be possible or not, we will find out on Sunday.’
An adjustment to the safety car rules could open a window for GT3 teams to sneak in a brake change without substantial time loss. Le Mans uses three evenly spaced safety cars due to the long length of the track. A new rule for 2024 is that a car pitting during a safety car phase will need to wait until the next safety car train has passed it before rejoining the track.
‘If you pit under safety car, you have to [drop back] one safety car,’ explains Arkenau. ‘You open up a window where it will be, not easy, but manageable to do a brake change without significant time loss. If you have a safety car in the last three hours and we go to a sprint race, it can be an advantage to have fresher brakes and not monitor your brake wear and input on a high level, in order to make it to the end. I believe the A plan would be to change brakes.’
The important number for teams is the time lost by changing brakes under a safety car, but this can vary.
‘It will depend on which safety car you are in and where you are in the queue,’ adds Arkenau. ‘How big is the queue behind the next safety car you have to drop to? There are some options where it will be manageable to only lose the mandatory one safety car by doing a brake change.’
On the tyre side, GT3 teams only have one slick compound available from the single supplier, Goodyear. The GTE era had a tyre war until Dunlop exited after the 2017 WEC season and Michelin went on to supply all teams. In the final season of GTE-Am last year, Michelin brought three slick compounds, plus a ‘drying’ wet tyre and a full wet. The French supplier’s wet range from GTE lives on at the Nürburgring 24 Hours.
The LMGT3 allocation of 15 sets (or 60 tyres) for the 24 hours is the same as GTE-Am last year. It means double stinting will be necessary for most of the race. Goodyear is confident that its tyre could even manage four stints. This is based on it observing four-stint capabilities on some tyres during the WEC pre-season test in Qatar, and double stint race data from the early rounds of the championship and the European Le Mans Series.
‘Four stints do sound like a lot, but those stints are only 40 minutes now, instead of an hour,’ highlights Beteli. ‘So a triple is the same as a double before. It sounds bigger, but it’s not a massive challenge. It depends on where you are in the race, when you start to do triples or quadruples. It is a trade-off [between] how much time you lose in the fourth stint against the pit stop to change tyres.’
So far, teams and drivers have been complimentary of the Goodyear LMGT3 tyre for its limited degradation over multiple stints. Le Mans is a low-energy track, meaning it will produce less degradation than the previous WEC round at Spa, where teams faced the toughest test so far to maintain tyre performance over a double stint.
‘I think tyre degradation is still a question mark,’ suggests Arkenau, when asked if teams will be pushing to do four stints. ‘We will get the most accurate numbers during the race. Anything before could be an indication, but not the final number. Track evolution is a big topic at Le Mans as the track rubbers in a lot, which has a significant effect on tyre degradation.
‘Tyre pressures will definitely have an impact on how many stints you do, especially when track temperature is changing [through different parts of the day]. The tyre pressure rule is quite strict, depending on how much margin you want to take. You also have to take into consideration how the track temp evolves through a triple stint. This could have an impact on how you drive your first stint against the last stint.’
On the sporting strategy side, there is little difference between GTE and LMGT3 at Le Mans. The driver rating criteria remain unchanged, so each lineup still requires one Bronze and one Silver-rated driver. The pace of the non-professional Bronze driver is often the differentiator, considering the skill gap between drivers reduces as you get to those who race for a living. Teams will be watching for weather changes, and for long safety cars, to see how they can most efficiently burn through their Bronze’s minimum driving time of six hours. It is one of the fundamentals of GT race strategy at Le Mans, and is unlikely to change any time soon.
So whilst there are some differences to how the LMGT3 race will run, there are also some similarities. The teams that can handle the slight differences better than their opponents are poised to gain an all-important edge.
