Charles Pic believes both teams and drivers would face a "big challenge" if the Formula 1's potential switch to 18-inch tyres is given the go-ahead.
The Lotus reserve driver completed 14 laps on Pirelli's experimental rubber during the morning of the final day of the Silverstone F1 test as part of a trial for a possible switch in 2017, or even a year earlier.
The Lotus was run largely in 2014 trim, with only minor changes to allow for the different clearances involved and small modifications to the suspension setup.
"If we go with this type of tyre one day, it will be a big challenge," said Pic when asked by AUTOSPORT whether he believes F1 should make the change.
"For the teams, because they will have to build a completely new car around it because the philosophy is completely different, and also for the drivers because they are completely different.
"And on the looks side, it is different and some people will like it, others not. Honestly, I thought they were a bit too big, but then maybe it is because it was the first time I saw them on the car."
Pic was unable to push hard on the rubber and was forced to adhere to a top speed limit on the straights and keep off the kerb because the tyres are only a prototype.
He found that it made a big difference to the behaviour of the car.
"The goal was to try and run them and see how they react," said Pic.
"The overall grip was very low, I think it was five or six seconds off the pace, mainly for the reason that the rest of the car was made for the normal tyre, not the prototype.
"It is true that they are more reactive and nervous, and then on top of that you lose a lot of aero.
"It is not even like you are in Monza configuration, it is even less because of this type of tyre.
"If you look at handling, of course it is not good - but that was not the point of the test.
"This was really the beginning with this type of tyre and for sure they will improve it.
"I think in the philosophy it will be a type of tyre that will react quickly, and the reaction you get in the steering wheel is more nervous. Each time you get the snap it is quicker [than with the standard tyres]."