

The forces in play with Ducati's torque arm

Ducati has always been known for taking the path less traveled when it comes to their MotoGP bikes. Their willingness to experiment and innovate – and sometimes, pick up old solutions which were dropped in the past – has been put into overdrive since Gigi Dall’Igna took over as head of Ducati Corse, the Bologna factory's racing department.

The appearance of a torque arm on the Ducati GP19s at the Jerez test in November last year is another example of exactly this kind of thinking from Dall'Igna. An idea which was once common practice in racing motorcycles in the 1970s and early 1980s, but disappeared shortly afterward. Why had Ducati reinstated the idea again? What were they trying to achieve?

When we spoke to riders who used the torque arm at the Jerez test, they remained deliberately vague. "For sure there were some positives and negatives to it, and like I said, I think we've got to back check it," Pramac Ducati's Jack Miller said. "It seemed to be a little more stable grabbing the rear brake, and stuff like that. But it's going to take some time to really develop it, because at the moment, it's in its very primitive stages."



Jack Miller tested the torque arm at Jerez in November 2018

Newly promoted factory Ducati rider Danilo Petrucci was similarly ambiguous. The torque arm was an improvement, he admitted, but he was loath to go into detail. "It was more or less an improvement, but there were very, very small differences," he said. "I think Gigi didn’t like to change a lot of things. He always wants to try new parts to be sure if it works or not but it always changes very little not for evolution but you aim to go on the limit to feel the difference."

Something old, something new

I discussed this question with Peter Bom, world championship winning crew chief to Danny Kent and Stefan Bradl. Naturally, a person with Bom's technical background knew what those torque arms used to be used for, and a clear idea of what Ducati is trying to achieve by bringing them back again for 2019.

"Designers used this construction in the past because it helped to prevent the rear wheel bouncing or stamping," Bom explained. "That could sometimes happen with no warning if the rider used the rear brake when braking hard in a straight line."

Better suspension eventually fixed that problem. "Developments in rear suspension helped to solve that problem," Bom continued. "The top out spring was a big step forward in that respect." The top out spring is a small spring used to dampen the impact when a shock or front forks reach maximum extension.

Changing geometry

Ducati's rationale for bringing back the torque arm was different, Peter Bom reasoned. "The result of the torque arm is that it opens up the rear suspension. But it is not so much the case that the rear tire is being pushed into the asphalt with greater force. It's more that the rear of the bike is being pushed upward. That's something you don't really want when you are braking in a straight line."

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