The Limits of BoP
Much has been made of how well IMSA has managed to balance the performance of the former Daytona Prototypes (DP) with the former Le Mans Prototype 2 (LMP2) cars. I'll admit they have come closer than I had thought they would, but there are still significant differences between those two formulae that have direct impact in head to head competition. Even though on most tracks, the lap times of the two cars are similar, as has been pointed out many times, they get those lap times in different ways. Generally the DPs have the advantage in speed, while the LMP2s have the advantage in handling and braking. A bit more subtly, the DPs accelerate more quickly and bring their tires up to operating temperature more quickly than the LMP2s. This makes starts and re-starts a big problem for the LMP2s. The greater torque also helps the DPs in traffic, and makes it easier for them to defend a lead. It cost LMP2 cars wins at Sebring and at Watkins Glen this year. In both races an LMP2 car was leading the race until there was a final Full Course Yellow (FCY) near the end of the race. The advantage of quicker acceleration of the DP meant that on the re-start after the FCY doomed the LMP2 to defeat. In the case of Watkins Glen that final FCY was certainly called for, so that was the luck of the draw. The case at Sebring is less clear; in my opinion that last FCY was not called for and cost the Extreme Speed #1 the win. Those results affect the outcome of the four-round North American Endurance Cup race.
I don't know that much can be done at this stage to mitigate the "acceleration gap" between formulae without compromising the degree of lap time balance that IMSA has achieved. There are a couple of things that might be done to mitigate that other advantage (tire temps). If the pit-stop regulations were to revert to the ACO rules, where fueling and tire changes must be done separately, then there would be a greater premium placed on double-stinting tires and the lighter weight (less tire wear) of the LMP2 might be able to make up for their taking longer to come up to tire operating temperature. I don't expect to see this change, but I would welcome it.
Laguna Seca Lap Times
Another bit of information about BoP can be illustrated by looking at recent lap times around Laguna Seca. Both the Grand-Am DPs and ALMS LMP2s ran separately there in 2013 and together in 2014. The major differences in the DPs between those years was an increase of downforce and an increase in horsepower. The major differences in the LMP2s in those years were the change in tires.
In 2012, the LMP2 cars ran on bespoke Dunlop LMP2 tires. In 2013, due to a pull-out of Dunlop from ALMS the teams were forced to source different tires and went to off-the-shelf Michelin tires for 2013. In 2014 the LMP2 teams were required to use the same spec Continentals as the DPs have run in recent years. A peek at the lap times for the most recent 3 years tells a tale.
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| Fastest Race Laps |
The increased power and downforce gained 2 seconds for the DPs, while the required tire changes for the LMP2s cost them significant time in both years since the Dunlop pull-out and the switch to Continentals. This difference will show up when LMP2 cars from IMSA and the WEC are compared at the Circuit of the Americas in September.
How Do You Define "Endurance"?
This year the Laguna Seca round of the TUSCC was divided into two races: one for the "Pro-Am" classes (PC and GTD), and one for the "Pro" classes (P and GTLM). Each of these races were two hours long. In the past the shortest endurance race at Laguna Seca was two hours forty-five minutes and have been as long as six hours as recently as 2012. I understand why the street races (Detroit, Long Beach, Baltimore etc.) are shortened-up; they share a tight schedule with other organisations, but when your organisation controls the feature events as at Laguna Seca, that is disappointing. In a two hour race the GT-class cars need only one pit stop, and for all classes it is a sprint race.
New Prototype Class Announced by the ACO
A few months ago there was talk about a new prototype class to replace the aging LMPC cars. At that time the thinking was that an evolution of the FIA CN class would be the basis of a new lightweight prototype class. Now the ACO have annouced the basic specs for a proposed LMP3 class and it is not the new ligthweight class I was so excited about, but an apparent evolution of the LMPC cars. A good description of what is known about this new class can be found at RaceCar Engineering.
Instead of being a ~600KG chassis with a ~375bph V6, the ACO basically want what would be an LMPC coupe with a shark fin. Rather than a completely spec car, the chassis and bodywork will be set by regulation with a spec engine, tire, transmission, and ECU. The engine hasn't been settled upon yet, but it will be a V8 of 420bhp. That is exactly what the current LMPC runs: a 6.2L pushrod Chevrolet V8 . This is to be a cost-capped formula. As of yet no constructor has announced a product for the new class. I can't think of another V8 420bhp crate engine that would be less expensive than the Chevy, and with the cost-cap I would be surprised if another engine were chosen for this class.
In the LMP1-H regulations there was a conscious effort to appear "green" by requiring a hybrid powertrain. Why not move the new LMP3 to a lightweight formula that could also appear more "green"? I am a bit disappointed.
