If FP3 saw plenty of soft rubber trying to cope with the dust around Montmeló, it was time for some hard tyres to come out of their blankets for a hot FP4. That meant that the fastest men of the session mingled in the 1:40s on all the various tyre combinations. Fabio Quartararo eventually took the spotlight off Alex Rins on his final lap, proving that speed is the best pain killer after his highly publicised arm pump surgery. The Frenchman strung together a pretty impressive run of mid 1:40s on a soft front - medium rear, while the Spaniard posted nearly identical times on a medium – hard combination.
Maverick Viñales made a late jump into the top three on his softs but didn’t seem to quite match his Petronas-branded teammate on pace. Marc Marquez had to resort to his favoured hard front and circulated a couple tenths slower than his younger headaches at the front, while Franco Morbidelli rounded out the top five despite doing limited running in FP4 following his painful looking FP3 crash. The Ducatis looked keen on softs as usual and Andrea Dovizioso ran a decent pace on his way to sixth but half a second slower than the lead Yamaha and ahead of Valentino Rossi and Takaaki Nakagami.
Joan Mir and Jack Miller completed the top ten, while Cal Crutchlow limited his track time with a tumble at turn five. Jorge Lorenzo in 12th was the only Honda rider to make the soft front work and although it only brought him within a second of the leader, the Spaniard seemed to struggle less than Danilo Petrucci, the Mugello victor down in 15th and marginally quicker than Pol Espargaro.