MotoGP champion Marc Marquez put more practice laps on the new carbon-fibre reinforced Honda chassis at Brno on Friday, setting his best lap time with the frame.

Both chassis also had a similar pace, but - just as at Sachsenring - Marquez still doesn't sound convinced the new design is ready to race.

"The most important thing for me on this first day was to try to have the same feeling like the first part of the season with the bike and we did. We also achieved the other goal, which was try to understand the two different chassis," said Marquez, who was second fastest in the pair of track sessions.

"I tried both chassis in FP1 and FP2 because tomorrow the weather looks like not so good and it will be important to have two bikes with exactly the same chassis.

"I did my fastest lap with the new one, but the old one is the old one and I know everything about that chassis. And I know the reactions of that chassis.

"So now the engineers are trying to analyse everything. The pace with both chassis was very similar, but the old one is there, with the new one still we need to work and it looks like tomorrow the weather will be not so good.

"Still it's not decided yet, but we have a Monday test so maybe we decide to will retry [the new chassis] on Monday."

The Repsol Honda rider starts the second half of the season with a dominant 58 point title lead over Ducati's Andrea Dovizioso, which he says makes changing chassis all the more difficult.

"If you are in a not so good situation then it's easier to choose the new chassis. But if you are coming with a good feeling, winning races, being constant in all the race tracks, then it's more difficult to make the decision.

"But of course if we are trying [a different design] it’s because if some positives and negatives. When you put a new chassis the bike balance changes and with the current chassis we know where we can arrive, we know which is the best balance.

"But with the new chassis still we need to investigate, we need to go more deeply in the details because it has very good potential, but still missing some areas.

"What we are doing is trying the new chassis in different race tracks, different grip, different layouts to analyse the strong points and the weak points."

Rookie star Fabio Quartararo (Petronas Yamaha) may have been the fastest rider on Friday but, from analysing the timesheets, Marquez feels title rival Dovizioso is the man to beat.

"It's true that today the difference [over the top ten] was very big if we compare to the last races, but here the first 5 laps is one pace and the next 15 laps is another," he said.

"The rear tyre drops a lot so for that reason the pace is quite difficult to understand because when you put new tyres you improve by nearly two-seconds. Then when the tyre drops you lose 1-1.5s per lap. So it's important to work with the used tyres and it's what we did.

"At the moment the fastest one is Dovi, for me. He is the one that can keep better the pace and even last year he did a great race."

Team-mate Stefan Bradl, again replacing the injured Jorge Lorenzo, was only 22nd quickest (+2.049s)