If a race is declared wet and is started behind the safety car, drivers are obliged to run Pirelli's blue-walled extreme wet tyres.
However, the anomaly is that once conditions become raceable, the wet tyre is regarded as being of little use.
In the Spa sprint, there was a rush into the pits for intermediates once the race got underway, with half the grid coming in at the start, and the remainder at the end of the first flying lap.
“The extreme [wet] tyre is a pretty pointless tyre, it's really, really bad,” said Russell.
“It's probably six, seven seconds a lap slower than the intermediate. And the only reason you'd ever run the extreme wet is because you'd aquaplane on an intermediate. So that needs to be substantially improved.
“The aquaplaning with fairly little water is really substantial. I remember watching the old onboard videos of 2007 with [Felipe] Massa and [Robert] Kubica in Fuji, so much water, they were still pushing flat out.
“I remember doing test days here in F3 and Formula Renault, on Michelin and Hankook, aquaplaning wasn't really a thing, but I appreciate we're doing well over 200 miles an hour. It's not straightforward. But, there needs to be some significant improvements."
Source: Autosport