Red Bull team principal Christian Horner believes the Formula 1 calendar has reached its “saturation point” and should not expand beyond the current 21 races.

This season equals the most grands prix to be held across a campaign, while the provisional 2019 schedule features the same amount of races with the championship concluding in December for the first time in over 50 years.

F1 owners Liberty Media has previously suggested the calendar could reach as many as 25 rounds, with new races in Vietnam and Miami set to be added in 2020. But the idea of going beyond the current 21-race limit has been met by resistance by a number of team bosses, including Horner.

“Twenty-one races, I think, is about saturation point,” Horner said. “There’s only so many chapters you can have in a book and I think at some point you go beyond what’s relevant. I think to go as low as 15 or 16 I think is too low but I think that 21 is the upper end.

“It’s tough. It’s tough for the guys in the garage, for the traveling staff, it’s tough for everybody involved and I think for the spectator and fans as well, beyond 21 races it reaches saturation, so I think it’s finding that balance.

“I think the really encouraging thing is that there are some great venues that want to host Formula 1 races and events and I think that that should provide natural competition for the venues that are already on the calendar.”

Sauber team boss Frederic Vasseur shared Horner’s concerns about the strain the calendar puts on team personnel and reckons 18 would be an ideal figure.

“For sure we will never go more than 21 because that is, from my point of view, far too much,” he explained.

“I think at one stage also we are losing the exceptional of the event; the more races you are doing, everybody is used to and at one stage we have to keep the exceptional side of the races and for me it’s a bit too much but I will follow the calendar for sure. I won’t stop after 18 next year.”

But according to Toro Rosso team principal Franz Tost, the most important factor is that quality prevails over quantity.

“I think it’s not the number of races or the size, it’s the show which we offer and the level of the entertainment,” Tost added. “If you have 15 boring races people will not watch any more. No, I think we should have around 20, 22 races and I think this is a good number and the exclusivity once more depends how good we are.

“We also should not forget that we are a global player and therefore we need a certain number of races to stay a global player. And I would absolutely refuse to go below 20 races. The year has 52 weeks, therefore we have a lot of time.”