Persistent rear grip problems mean Pol Espargaro is yet to achieve the kind of results he expected when joining Repsol Honda, with a best MotoGP finish of fifth so far this season.

But after trying a radically revised 2022 prototype at the recent Misano test, Espargaro is confident that Honda understands the root cause if the issues faced by all the RC213V riders this season.

Espargaro's team-mate and eight-time world champion Marc Marquez is the only Honda rider to stand on the podium so far this year, courtesy of a Sachsenring victory and Aragon second place.

The covid technical freeze means Honda, like the other non-concession manufacturers, has been unable to modify its engine design since the start of 2020.

However, Espargaro said it was the complete package of changes that made the difference on the '22 prototype, which - in addition to a revised engine - featured a new Yamaha-style square air intake, new aerodynamics, new frame, new rear seat unit with a 'salad box' and relocated exhausts.

"I think that the biggest difference at the test was not the engine for us. The engine was a good step up but mainly the step we did was in the full bike. All the components," Espargaro explained of the 2022 prototype.

"As you can see in the pictures, the bike is so different everywhere. Like the aerodynamics. The engine is different for sure but also how the bike is made, the weight, the height, everything. It makes the bike so different.

"The engine makes so much effect as well, but the biggest difference was not the engine at the test."

Most importantly, the changes addressed the main area that Espargaro, a multi-podium finisher for KTM, has been struggling in.

"Yeah, yeah. It helps a lot [with rear grip]," he replied. "Okay, Misano is a place where the grip is quite good, so we were having different problems because of too much rear grip. But I think we understand the problems we have.

"The most important thing is that we know what's going on. And to improve the problem first you need to know the situation you are having.

"It seems like we know what we are doing and Honda brought something that improved quite a lot the rear grip, then we faced other problems. But as it's a new bike that's normal, natural.

"But yeah, the new bike was better."

Espargaro is 14th in the world championship ahead of this weekend's American round at COTA.