Friday, 20 May 2011

ACO announces Adjustments to Performance for Le Mans

There has been a lot of chatter in recent days, following the publication by the ACO of the Performance Adjustments in advance of the Le Mans 24 hours, for which scrutineering is due to begin in just two weeks time. My sympathies lie with all concerned. First, with the ACO, who is coming under criticism for doing ‘too little, too late’. Second, with the smaller teams who now have very little time to test out different engine mappings and the impact on fuel consumption and tyre wear of running with less weight and more power. And third with the major manufacturers, whose advantage over the rest has (to an extent still to be determined) been diminished.

For the spectators and media though, it can only be good news. The media can now go into a frenzy of claim and counter-claim and the spectators have the prospect of a closer race to witness, with all kinds of possibilities now in prospect for the great race.

The detail of the adjustments can be found elsewhere on the web and if you are savvy enough to get here, then you’ll be able to read the exact changes that have been mandated. I also commend to you the interview (published both in English and French) with Vincent Beaumesnil (sporting manager of the ACO) justifying the adjustments. My purpose here is merely to comment.

First, a defence of the ACO. Article 1.3 of the 2011 Sporting Regulations (first issued in December 2010) was clear enough: the adjustments would be applied to ‘the slower technologies’ and there was no suggestion that the faster cars would be ‘reeled in’. So the idea that the ACO was going to adjust the performance of the diesels to slow them down to the ‘target lap time’ of 3 mins 30 secs was never (in my opinion) an objective for the ACO. I’ll admit that it was their stated objective when the Technical Regulations were written in the first place, but not the objective of the mid-season performance adjustment.

So suggestions that the ACO missed an opportunity to slow down the diesels are, quite simply, wrong.

It was equally obvious therefore that the impact of the performance adjustment would fall on the teams using the slower technologies. So the time to complain was in December and January (or in the many meetings that the ACO held with Le Mans entrants beforehand), not now that the actual adjustments are made known.

The regulations also made clear that only race data would be analysed, and adjustments would only be made after two races had taken place. Sebring and Spa were the first two rounds of the ILMC, but the ACO also had the chance to analyse data from Long Beach (ALMS) and Paul Ricard (LMS), but of course there were no diesel-engined cars at either of these events. Data from practice and qualifying sessions, and the Le Mans Test Day was inadmissible. From looking at the calendar, it was apparent that time would be tight between the data being available to analyse and the outcome of the organiser’s deliberations being made known.

The way I look at it - and for the moment focussing purely on LMP1 cars, the adjustments fall into two categories: firstly the diameter of the refuelling hose (or at least the orifice through which the fuel has to pass) and secondly the engine performance parameters.

The diameter of the refuelling hose obviously has no impact on lap times, but will affect the amount of time spent in the pits refuelling. Now I am no expert at fluid dynamics (I believe the term is rheology), but by reducing the size of the orifice through which the fuel must flow for the diesels by 3mm (to 25mm) and by increasing it for the petrol-powered teams by 10mm (to 38mm), the ACO has made a significant impact, without demanding the teams to make any change to the configuration of the car itself.

By my somewhat rough and ready calculation, the fuel flow rate for the diesels will be roughly half that for petrol-engined cars. In other words, petrol will flow (less viscosity, through a larger restrictor) at a rate of nearly 3 litres per second, but for the diesels at about 1½ litres per second. This will mean that a fuel-only stop will cost a petrol team 25 seconds (depending on how much fuel is left in the tank when the car stops), whereas a diesel car will be at rest for around 50 seconds.

Reassuringly, I did this calculation before reading the interview with Beaumesnil, who also suggested that the difference in refuelling time would be “over 22 seconds, the equivalent of two seconds a lap”. Over the course of 24 hours, this is like giving a diesel car around three and a half laps penalty. If that’s not “reeling in the diesels”, then what is?

The other category of change is the reduced weight / increased air restrictor combination, and this is what leads me to sympathise with the petrol-fuelled privateers. It’s now decision-time. Run at the reduced weight and risk a problem occurring in the race that hasn’t previously been encountered? Maybe the car is not at the weight limit anyway; in which case, the increased restrictor could mean additional engine development costs and changed mappings. But doing nothing is not really an option either - the extra air entering the engine should provide enough horsepower to reduce lap-times by up to a couple of seconds. But would Pescarolo or Rebellion (for example) want to come to Le Mans with a different package from the Test Day without proper testing? It is a real dilemma.

The trouble with all this performance fiddling, is that it makes comparisons difficult. Lap times obviously can’t be compared from last year to this, but nor really can pit stop times. “Time spent in pits” is one of those interesting statistics that I collect. But when I look back at the amount of time spent by cars in the pits over the years, I find myself increasingly comparing apples with pears. In the days of Group C, the fuel fill rate was one litre per second, and the tank (under the first iteration of the regulations), took two minutes to fill. More recently, the nonsense with the restrictions on the number of mechanics changing the tyres has made it meaningless to compare pit stop times with those from the early years of this decade.

This year, however, the fact that fuel is allowed to flow into some cars more quickly than others, will make "time spent in pits" even more irrelevant as a measure of a team's efficiency - although it may well have a bearing on the outcome of the race.

There are other aspects of the adjustments which also bear discussion, such as the reduced weight of the Oreca Peugeot (yes, the one that won at Sebring) and the LMP2 changes (which seem to penalise the slower cars), but I think I will leave those for another occasion.

What do you think?


  1. Great insight as always Paul, one question though about LMP2.
    Will the regulations bring the cars more in line next year? Specifically level the playing field instead of the cost capped 2011 model vs. a 2010 restricted car, vs. a non cost capped 2011 car, etc?

  2. Thanks Paul, good info there!

    Not entirely sure what I think of the fuel fill changes - we want to see the petrol cars fighting with the diesels, not being given a massive head start every 12 laps!

    If the other changes make a decent difference, then that 22 second pit advantage may make for amazing viewing, if it puts mild pressure on the Peugeot's and Audi's - having to catch back up and pass every stint!

    It all could just be wishful thinking though, either way, at least it will be closer than before!

    Can't wait - just 16 days until the first session!

  3. I am not in favour of the ACO playing with fuel nozzle sizes as a way of balancing performance. We all go to watch a race and not extended time in the pits. To me, it feels like a sticking plaster over the real problem of power advantage of one fuel over another. What the ACO really need is a target bhp for each fuel type and calculate the restrictor size required.
    Last year, I managed to talk to the Aston Martin mechanics and asked about the problems of restrictor size changes. I was told that to change the restrictor, the car would require a new exhaust system, a new/tweaked induction system, mapping etc.etc. So, seriously expensive stuff. Having said that, many teams will be customers of AER/Judd who must be set up to handle these types of rule changes.
    At the risk of falling into the conspiracy theorists, I also am struggling with the ACO’s stated target of 3.30 lap times. To give you an idea, if you check the qualifying Spa times and compare those to the F1 lap times, you’ll find that an F1 car is around 15 seconds a lap faster. Multiply that up to La Sarthe and at a guess, the F1 car would be around 25 ish seconds faster! Clearly, if it was seriously considered that a sub 3.30 lap time is unsafe, then F1 cars would also have been slowed and they race on far more dangerous circuits than La Sarthe. So, I am suggesting that perhaps, the reason for a 3.30 lap time is to maintain a clear performance gap between sports cars and F1.
    Finally, one further point to make (and one that I think Paul made on the radio last year!) is that when you look at the speed trap times, much of the faster lap times is coming about through faster cornering rather than outright grunt. Watching the Peugots through the essess in 2009 was just astonishing. They were SO fast it was like watching a scalextric. Visibly, the cornering speeds are tumbling. This leads me to think that if you HAVE to slow lap times (and based on my comments above, I fundamentally think that they should not be slowed until we are around the 3 minute mark, based on the extrapolated speeds/times of an F1 car which should be just as safe) it should be through aero rather than power adjustments.
    Robin Cohen

  4. Paul, Interesting as ever :) Given the 4-hour Test on Wednesday before Qualifying, can teams vary air restrictors/ballast/mapping combos before starting the weekend for real ?? sounds all a little time will tell

  5. Very thought provoking Paul, in fact I've been trying to look a some numbers myself the last few days.

    So this gives two seconds a lap back to petrol powered cars, however these on average are four seconds slower than the diesels. So the Diesels will be 24 seconds ahead after a stint of 12 laps.

    Thus, as the two finish their fuel stops the petrol car should just be drawing level as they pull away in the pit lane, only to lose another 24 seconds in the next stint.

    In agreement with the gent above, we would rather see the petrol car pull up along side on the track - or even at the finish line and on the same lap.

    Again, none of this accounts for the 2 or 3 seconds the diesels have been carrying in sand over the last few months.