Analyzing Braking Stability: Why Is Honda So Much Better Than Yamaha?
One of the great privileges which holding a MotoGP media pass allows is to stand behind the armco and watch and listen to the bikes as they go past. At the Sepang test, I made full use of that opportunity, and wandered over to Turn 3 – the glorious, fast right hander, where the riders get sideways driving through the turn and onto the short straight to Turn 4 – to enjoy the spectacle of the best riders of the world showing off their skills.
There is more to be learned from watching at track side than just how spectacular MotoGP bikes are through fast corners, though. The careful observer can pick up clues to what both the riders and factories are doing. With electronics such a key part of MotoGP nowadays, the track is one of the few places where updates are visible. Updated vehicle dynamics algorithms may be invisible from pit lane (or nearly so, with the occasional addition of sensors or torque gauges the only visible clue), bike behavior on the track will sometimes betray them.
At the end of 2013, Marc Marquez and Dani Pedrosa had asked for more stability under braking, and some more corner speed. Listening to the bikes at Sepang gave a possible clue as to how they had achieved that. The differences in engine note between the various bikes were instructive of the varying levels of electronics, engine braking strategies, and gearbox function.
That Honda have been working on braking and corner entry was audible at Sepang. Though the RC213V always sounded smooth under braking, braking for Turn 4 the improvement was noticeable. As they braked and downshifted for the corner, the Hondas of Marquez and Pedrosa sounded more like a big scooter with a constantly variable transmission than a racing four stroke with six separate gears. Engine revs decreased smoothly, downshifts barely perceptible. There was no popping or crackle of extra fuel burning off, just a smooth, booming descending tone.
How should we interpret this noise? It seems safe to assume that it finds its origins in the seamless gearbox. The system Honda has developed provides advantages changing gear both up and down. We have previously measured the advantage of upshifts, and now HRC appeared to have mastered downshifts. Honda riders change down through the box without using the clutch – a feature Yamaha was testing at Sepang, and at the top of the list of Jorge Lorenzo and Valentino Rossi's wish list at the end of 2013 – but Honda also appears to have combined fuel metering and control of the RC213V's slipper clutch to produce a truly seamless downshift.
What are the advantages of such a system? The crackling and popping heard on downshifts, especially on the Open class machines, are all a sign of fuel being wasted. Excess unburnt fuel enters the hot exhaust pipe, where it spontaneously ignites, causing the irregular crackling. On systems with a lot of fuel, this is not a problem, and produces spectacular jets of flame from the exhaust pipe. The Kawasaki ZX-10R World Superbike machine is a notorious flamethrower; to see it in MotoGP, you need to go to Qatar, where the darkness of the night betrays the soft blue flames so vividly caught by Scott Jones1.
Injecting precisely enough fuel to match the engine speed means the engine produces exactly the amount of engine braking required, with all the fuel being burnt, none being wasted. With the fuel allowance reduced from 21 to 20 liters for 2014, saving fuel is paramount, and deceleration and engine braking is a prime area for seeking to reduce fuel consumption. The fact that Yamaha spent much of the test working with fuel strategies to find a set up which worked with the ultra lean fueling, while the Honda riders repeatedly said they had not spent any time on it as fuel consumption was not a problem in the heat at Sepang, is a clear indication that Honda's 90°V is already extremely efficient with fuel.
Saving fuel is one key target, but having exceptionally smooth deceleration offers another significant benefit. Acting like a slipper clutch on steroids, the scooter-like deceleration means that the rear wheel stays firmly put under braking. The changes in braking torque caused by downshifting are being managed perfectly. The rear wheel no longer hops as engine braking increases after gearshifts, keeping the wheels nicely in line. It is a rather neat little irony that HRC appeared to have replicated the downshifting behavior of a two stroke on a 1000cc four stroke, though at an astronomical cost.
How are they managing downshifts so well? It seems likely that the Torductor – the rotating torque sensor on the gearbox output shaft on the factory Hondas, rumored to cost 60,000 euros – plays a key role here. Initially employed to assist with upshifts and smooth power delivery, it can also play a role when changing down through the gears. The sensor detects the torque going through the output shaft, measuring both the engine torque as it drives the rear wheel, but also the braking torque from the rear wheel, as it slows the engine when the throttle is closed. Based on that signal, it would be possible to both monitor engine braking much more closely, and track and respond to it using the engine management system.
By having the combination of electronics, seamless gearbox and slipper clutch manage engine braking torque, this frees the riders up to concentrate on braking. Though they still have to operate the gears (the rules explicitly demand this), precisely timing downshifts no longer appears to be necessary. Instead, the rider can focus more of his attention on just operating the brakes, searching for the best possible point at which to apply the brakes. The rider has more control over the bike, allowing more precise corner entry, with no fear of the bike being upset by engine braking forces. More efficient braking and better corner entry mean more chances to pass other riders on the brakes, while simultaneously increasing corner speed.
This, incidentally, is why fans have been robbed of the spectacle of riders backing MotoGP bikes into turns. A combination of electronics and vastly improved slipper clutches now mean the rear of the bike is under control. That is a much more efficient way of entering corners, and therefore faster, if less visually appealing.
Comparison with the other bikes was illustrative. The most obvious comparison is with the Honda RCV1000R production racer, as that is very close to being a 2013 RC213V with conventional valve springs, a conventional gearbox, more fuel and the Dorna-spec software (popularly referred to as the 'championship software' in the paddock). Watching Nicky Hayden on the Drive M7 Aspar RCV1000R, you could clearly hear his gear changes while braking for Turn 4. The Honda production racer crackled and popped, and moved visibly underneath Hayden as he lined up for the turn. No doubt as the season progresses, the teams will get the championship software dialed in better, and smooth corner entry out. But it will never be as good as the factory bikes.
There was a clear differences between the Yamahas as well. While the Tech 3 riders are still without Yamaha's seamless gearbox – team boss Herve Poncharal told us that they would probably receive the gearbox early in the season – their bikes make the same kind of noise which the production Hondas do, though a little bit more refined. They still crackle and pop, but significantly less.
The factory Yamahas, on the other hand, make a good deal less noise under braking. Jorge Lorenzo and Valentino Rossi were experimenting with Yamaha's new improved seamless gearbox, though it was impossible for me to tell from track side whether they were using it while I was out watching them. The gearbox is still not as sophisticated as Honda's, but it offers some advantages. The factory Yamaha riders' gear changes were smoother and less noisy than the Tech 3 bikes or the RCV1000R. They were clearly audible, but there were only a few pops and bangs, and the revs sounded as if they were being managed better.
The fact that the Yamahas need a different riding style to get the best out of it also makes comparisons harder. Jorge Lorenzo already brakes earlier than the Hondas, letting off the brakes earlier and carrying more speed into the corner. His style is silky smooth and sweeping, and so his downshifting is already optimized as a result of his riding style. Yet the Yamaha's downshifts were still clearly audible, something which it was often hard to hear on the factory Honda bikes.
From the side of the track, it looks like gear changes while braking are the next front in the continuing battle between the two Japanese MotoGP giants. It is a natural consequence of the reduction of the fuel allowance, and the search for ever more speed. From my limited vantage point, it looks as if Honda currently has the upper hand.
I should stress that the above is all just conjecture, based on my own observations from the side of the track. I spent an hour or more watching at the same point, early in the day while all of the riders were posting a lot of laps. There was a difference in engine note that I could clearly hear, and there was a visible difference in the behavior of the various bikes under braking. But the theories of how the system might work are entirely mine. I did not try to confirm them with either HRC or Yamaha engineers, as the engineers have no interest in sharing such information. They would have had reason both to confirm and deny any theory I put to them, and no way for me to know whether I was a victim of disinformation or they were showing me a kindness. For the moment, the above is merely my best guess. And it remains a privilege to be in a position to make such observations, and draw my own conclusions from them.
1: While I was writing this article, I asked Scott if he had a photo of from Qatar showing a Honda producing exhaust flames, either during practice or while the engines were being warmed up. I was confident that Scott would have such a shot, as he is the photographer with the most attention to detail in the paddock. He has a talent for spotting some of the more remarkable parts of racing, and then capturing them on film, with other photographers tending quickly to follow his lead. If anyone had a photo of a Honda shooting exhaust flames, I knew he would. So when he told me that he did not have such a photo, nor had he ever seen the Honda RC213V produce flames in the way that both the Ducati and the Yamaha does, it confirmed to me that there is something in my theory.
Gathering the background information for long articles such as these is an expensive and time-consuming operation. If you enjoyed this article, please consider supporting MotoMatters.com. You can help by either taking out a subscription, buying the beautiful MotoMatters.com 2014 racing calendar, or by making a donation.