The news that 340mm carbon brake discs are to be allowed once again in MotoGP has rekindled a debate that has been going on behind the scenes for some time. The move to allow the discs at all tracks, and not just Motegi where they are already compulsory, has come as both power and weight of the MotoGP machines has grown over the past three years. But the real solution lies in reducing minimum weight.
There was a certain irony in the moment chosen by the Grand Prix Commission to ban carbon discs larger than 320mm. The move – made for reason of cost savings and rationalization – came just as MotoGP was to return to 1000cc, meaning the bikes were about to reach higher top speeds. Compounding the problem, the minimum weight was also increased. The initial proposal was to raise the minimum from 150kg, the weight of the old 800cc machines, to 153kg. However, to make life easier for the CRT machines, the weight limit was raised even further, in two steps, to 157kg in 2012 and 160kg in 2013.
In the space of two years, engine capacity had been increased by 25%, leading to a power increase of around 10%, while weight had also been increased by nearly 7%. It was a recipe for brake problems, and that is precisely what occurred. Ben Spies lost his brakes at Motegi in 2012 – and spurred making them compulsory at Motegi for 2013. All of the Yamaha riders spent 2013 complaining of a lack of braking power, and Cal Crutchlow is still struggling to deal with braking on the Ducati Desmosedici GP14. Allowing 340mm brake discs is the quickest and most immediate fixes, but for the long term, minimum weight needs to be reduced once again.
Such a move is likely to come sooner rather than later, with weight reductions a racing certainty for 2016 when the new set of MotoGP regulations comes into force. With the production-based CRT machines now gone from the scene, a more generous minimum weight is no longer necessary. The new generation of Open class machines are much closer to the factory prototypes than the bikes they replaced, meaning that weight reduction would be relatively straightforward. Even the production-based Open class machines – the Avintia Kawasaki and the ART and PBM machines, using the Aprilia RSV4 engine – are much closer to prototypes after a couple of years of development.
How much will the minimum weight be reduced by? At Jerez, Race Director Mike Webb told us that they were examining proposals to reduce the weight to either 155kg, or perhaps even 150kg, though the former was much more likely than the latter. Both weights are achievable, as is even less. Asked for his opinion on what was manageable at a reasonable cost, former FTR chassis guru Mark Taylor told us that any decent engineer worth his salt should be able to design a MotoGP machine that came in at 150kg. Less than that was more difficult: when asked if 140kg would be feasible with resorting to extremely expensive materials and techniques, Taylor said that it would be possible, but expensive.
The main reason behind the looking weight reduction is not just about braking, however. There is an even more pressing concern than that. As both speeds and weights have increased, so has the distance which bikes travel after they crash. A MotoGP machine traveling at high speed is a massive store of kinetic energy. Accelerating it to 350+ km/h takes an enormous amount of energy. Slowing it down requires the same amount, but applied in reverse. Current run off technology – hard standing, then gravel traps, and then air fences – has reached its limits, with air fences only serving as a catchment of last resort. Ideally, the bike and rider should already have come to a halt before they reach the end of the gravel trap, and not have to use the air fence.
In the past, the barriers where air fences are placed have been moved further and further back, but that process is extremely expensive, bad for spectators (who are further away from the action) and at some tracks, becoming increasingly difficult. Some tracks are simply running out of space to move the barriers further back: Sachsenring's Turn 1 already closely abuts the section between turns 10 and 11; the Ramshoek at Assen has already had the runoff extended almost into the paddock; San Donato at Mugello, at the end of the straight, sits underneath a massive hill, necessitating major excavation work to try to create more run off. If speeds continue to increase – both corner speeds and top speeds – then MotoGP will simply run out of tracks where it can race safely.
There are two solutions to this problem. As kinetic energy is defined as ½mv², the most effective way of decreasing the distance a crashed bike will slide is by reducing the speed at which it crashes. As velocity is an exponential component of kinetic energy, reductions in speed have huge consequences. However, limiting speed is difficult: Dorna are keen to impose a rev limit to cut down on top speeds, but that solution may end up driving up corner speeds once again, as the capacity reduction to 800cc did. Any reduction in top speed would require a similar reduction in corner speed, and that can only be achieved by reducing grip, both by reducing complexity of electronics, and by reducing the performance of the tires. The arrival of Michelin, who come to the series after a period of absence, should give the series a short respite. However, at some point, the French tire manufacturer will start to match the performance of the current generation of Bridgestone tires, and then the series is back at square 1.
Reducing weight has a much smaller effect – the relationship between weight and kinetic energy is arithmetic, not exponential – but it is much easier to implement and to police. All three manufacturers are adding ballast to reach the minimum weight, in some cases switching from titanium and other exotic materials to stainless steel for some components to add weight. Removing ballast would require a lot of set up work and some minor redesigns, but it would not present a major engineering challenge. With a new tire supplier coming in 2016, along with new, standardized and more limited electronics, that season would seem to be a good point to start reducing minimum weights. It is just a question of time.