|Degradation on Pirelli tires on Hamilton's Mercedes|
Pirelli has warned that there will be more four-stop races this year because some teams voted down their recommended changes.
"We have 19 circuits this year and that means a lot of variable conditions," Hembery told Autosport Magazine.
"Sometimes we will be in the consecutive band, and sometimes we will be pushing it right to the end level because it is related to the circuit.
"The teams do improve their tire management, as we have seen in the past few seasons where it tends to be lively at the start [of the season] and then by the time we get to Hungary things have leveled out a lot.
"But I think we will have tough races yet. We have Silverstone coming up – and if it is warm then that again can be a hard race from our point of view."
"So we will probably have some races with four stops, which we have said we don't want.
"We would have needed to change the hard compound to avoid that, but to do that we would need the agreement from all the teams and we know that is not going to happen.
"We can do it if asked, but [in the event of four stops], my message would be stick with us for a few races. We talk about averages and over the course of the season we are aiming for an average of two stops."