Romain Grosjean says time spent driving a 125cc gearbox kart reiterated how Formula 1 needs to change, because it left him "more tired" than racing in a grand prix.

The Haas driver and Grand Prix Drivers' Association director has been a key advocate of F1's rules changing so drivers can push more during races.

While this is often expressed in the form of F1 moving away from tyres that are too sensitive to overheating or degradation, world champion Lewis Hamilton has been vocal this season in his desire for a car that is more physical to drive.

Asked by recently whether he shared that view, Grosjean said: "I went go-karting with my friends with a 125cc gearbox and I was more tired than doing a Formula 1 race.

"Why? Because you push all the time, you don't play safe. And most importantly we manage the tyre all the time [in F1].

"At Barcelona it feels like you are driving at 40%, 50% of the capacity of the car, and it's not hard.

"If it was only qualy laps, you would push as hard every lap and then you'd be completely fucked by the end. You'd be tired.

"If we had to refuel you'd be even more tired. When you have to lift and coat for fuel and for tyres, how is it hard on the body, how is it hard on the concentration?"

Hamilton's team boss Toto Wolff has suggested removing power steering to make the cars a greater physical challenge.

But Grosjean said "we've asked many times" for the tools he reckons drivers need.

"I think if we run out of power steering we can't turn the steering wheel," he said. "So I don't think they're going to change much.

"What we need is a car that we can push. Bring refuelling in and then the car is not 100kg [heavier with fuel] at the beginning.

"Have 30kg for each stint and then you go a couple of seconds faster, if not more, and so you are much more tired."

Grosjean admitted he does not have the "magic" solution to F1's apparent problems but stressed the importance for drivers to be willing to make suggestions, even if they get dismissed.

"We're all aware there's room for improvement in a lot of areas," he said. But if we don't change anything, obviously nothing's going to change.

"Maybe what I am saying is bullshit and I am missing completely part of the equation. When I say we should do this, maybe I forget some reason why we shouldn't.

"But at least I'm sending ideas. They could be absolutely wrong, they might be not feasible, but I'm trying."