Were Honda exceeding the Moto3 rev limit in 2015? This is the accusation made by KTM Sports Director Pit Beirer in a story on the German-language website Speedweek. Beirer alleges that KTM came across the issue when talking to riders who switched from Honda to KTM this year, who were complaining of how abruptly the KTM hit the rev limiter. Beirer further claims that KTM were able to look at the data of the Honda Moto3 machine held by a former Honda mechanic. In that data, he alleges, the Honda ran flat out to the 13,500 RPM rev limit, then gradually tailed off to 13,600 RPM.
These claims, if they are true, would be a massive breach of the Moto3 regulations. Though Beirer does not mention Danny Kent by name, the insinuation was that this may have been a factor in a Moto3 title which ended up being decided by just six points.
We spoke to Peter Bom, crew chief to Danny Kent both this year and last, during his successful Moto3 championship campaign, and a key factor in the Englishman's title. Bom denied the allegations, and explained that the claims can only be based on Beirer misinterpreting the facts. The difference between the Honda and KTM Moto3 rev limiter strategies was marked, Honda having invested a large amount of time and money in optimizing both gear change and rev limiter strategies, making the bike as smooth as possible and as easy to ride.
A primer on rev limiters
To understand the issue at stake, some background is needed. In every race series with a rev limiter, factories expend a lot of energy in optimizing the point at which the rev limiter cuts in. It is not a matter of the bike being under full power at (in the case of Moto3) 13,500 RPM, and all power being cut as soon as it hits 13,501 RPM. If that were to happen, the consequences could be very dire. If a rider hit the rev limit while still leaned over in a corner, they could easily be thrown from the bike and injured.
What happens when an engine hits the rev limit is that the ECU detects that the engine is at the rev limit, and decides to cut power. The speed at which it can make that decision depends on the processing power of the ECU. The spec Dell'Orto ECU is a very basic unit, with limited power, and so cannot react quickly enough. The result is that for a split second, the revs exceed the limit, before being cut by the ECU. As the engine speed drops below the rev limit, the ECU is slow again to return the sparks to the ignition, causing it to drop below a little way below the limit before ignition returns. This causes the engine to sputter as it hits the limiter, the ECU alternating between cutting power and returning it again.
KTM vs Honda
This process appears to be at the core of Beirer's accusation. KTM has made a conscious decision to allow full power all the way up to the rev limiter, making it a very hard transition. As the rev limiter is at or around peak power of the engine, this allows the rider to extract the maximum performance from the bike. The downside is that it is much harder for the riders to manage the transition around the rev limiter. The bike is unsettled, and requires more input from the riders.
Honda have chosen a different approach, putting in a vast amount of work aimed at smoothing the transition where the rev limiter cuts in. Their engineers have worked hard at optimizing engine management strategies to make it less abrupt, while retaining as much power as possible, yet giving the riders the feeling they need to shift up.
Feeling the switch
The accusations by Beirer had stung Peter Bom, and prompted him to go through his data, to see what could have triggered the claims by KTM. Before having Danny Kent under his wing in 2015, Bom was crew chief to German rider Luca Gruenwald in 2014, the Kiefer team using KTMs that year.
"It's true that the young riders switching from Honda to KTM are complaining that the KTM rev limiter is a lot more abrupt," Bom said. "That's just a difference in the strategies the two bikes use. Honda worked really hard on the rev limit strategy, putting a lot of work into getting it right. The rev limiter and gear changes were really strong for Honda, because of the work Honda did on using the spec Dell'Orto ECU. The gear changes on the Honda almost feel like a seamless gearbox. That's just all down to getting the strategies right."
Had Honda been cheating? "I really didn't understand the nature of the accusations," Bom said, "so I went back and looked through my data, comparing it to Luca Gruenwald in 2014. It's a bit difficult to make the comparison, Danny was fighting for the championship, Luca was much further down the field. And the rev limit was changed this year, so the Honda was only allowed to rev to 13,500, the 2014 KTM was still allowed to rev to 14,000 RPM."
Where the difference is
The most accurate comparison Bom could find was at Mugello. Both Kent in 2015 and Gruenwald in 2014 had been fighting in a large group during the race, though for different positions. Both had been leading the group at points, in the slipstream at others, and both had been flat out in sixth gear at the end of the straight just as they crest the hill and start to go downhill. "If I look at the data, I can see that when Danny's engine was on the rev limiter, the revs were bouncing around by about 50 RPM. Luca's KTM was bouncing around the limiter a lot more, maybe 100 RPM or so." Perhaps, Bom said, there was something in the way that the data which KTM had seen which led them to interpret it as having gone over the rev limit.
The engine speed data needs to be treated with some caution in terms of accuracy, Bom explained. "Dell'Orto (who make the spec ECU) define the sampling rate for each of the channels in the ECU. I don't know exactly what the sampling rate is for the engine speed, but it feels way too low. 200Hz would be normal, 500Hz would be ideal, but asks a lot from an ECU." The Dell'Orto spec ECU does not have the processing power to spare on that kind intense workout. As a result, the ECU isn't sampling every single revolution when the engine is at the rev limit. At 13,500 RPM, a Moto3 engine is spinning 225 times per second, and if Bom is correct, and the engine speed is being sampled a much less than 200Hz, then the ECU will be having to average out the signal to calculate the engine speed.
Bom denied outright that the Leopard Moto3 team had exceeded the rev limit last year. "100 RPM is not going to make that much of a difference," Bom said. "The rev limit is fixed by Dell'Orto before they hand us the ECU, so we couldn't break it if we wanted to." Bom also said that his data had been checked several times by IRTA, and been found to be within limits. Everything they had done had been perfectly legal.
MotoGP's Technical Director Danny Aldridge confirmed this. "At every event, the data was taken from the first 3 places, plus 1 or 2 random riders after every qualify and Race," Aldridge told MotoMatters.com. "For example Danny Kent data was taken direct from his machine 20 times in 2015, the most of any rider." Aldridge acknowledged that Pit Beirer had contacted Director of Technology Corrado Cecchinelli and himself a few weeks ago, and IRTA and Dorna were investigating the claims. "Of course we take any alleged cheating very seriously, especially if it comes from a manufacturer. Since the report we have informed Dell'Orto, who in turn are checking the data from 2015."
The process will take some time, Aldridge said. "We are just asking for time to make sure we carry out this investigation correctly," he added. IRTA had not received the information from KTM which the article on Speedweek had alleged they had supplied, Aldridge confirmed. "I am sure you can understand that this is making everything take a lot longer," he said.
Were Honda really exceeding the rev limit by 100 RPM last year, as KTM claim? Was Danny Kent's championship really obtained through fraudulent means? Peter Bom is adamant that it wasn't. The title was earned as a result of the hard work by Danny Kent and his team, and Honda had put in the work to extract the maximum potential from the spec Dell'Orto ECU. One of the reasons the Honda Moto3 bike was so expensive to lease was because of the work HRC had done on the ECU, and making it work for the bike.
The affair is now in the hands of Dorna and IRTA, with Corrado Cecchinelli and Danny Aldridge leading the investigation. They have informed Dell'Orto, who are going through their 2015 data looking for anomalies. There is no timescale of when results are expected, but such serious allegations need to be checked thoroughly and carefully, so it will take some time.
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