Carrefour de l'Arbre is 2,100 m of five-star pavé between Camphin-en-Pévèle and Gruson, and the entry is the worst of it: the pavé de Luchin turns left then right over stones the French reconnaissance write-ups call filthy and sharp-edged, and when it straightens out past the Domaine de Luchin it gets more irregular still. The camber is extreme, roughly 30 cm higher down the middle than at either edge, enough to ground a low car, and the crown carries the least broken stones, so that is the line: middle of the road, chosen early, pedalling the whole way. It does not always hold, because the ridge can be worn down to a sharp spine of grass and dirt, and the ploughed earth verge on the left is far riskier for punctures than the pavé is. After the tarmac crossing, the second half, the pavé Jean-Marie Leblanc, is more rideable and still ugly, on a slight rise that arrives when there is nothing left, ending at the restaurant on the crossroads itself; Gruson, straight after, feels clean by comparison. You reach it off three kilometres of tarmac from Camphin with the last kilometre badly exposed, and a headwind here is what makes it hard to hold the front. Wet, the stones go slick and the edges fill with puddles and mud, and in 2021 the race came through the sector in deep mud. It hurts, and it is still rideable: a public road any day of the year, on the Paris-Roubaix Challenge route, and a journalist got over it upright at a bit over 15 km/h on 35 mm tyres run slightly soft, weight back on the saddle, hands flat and loose on the bars, carrying as much speed into it as she could.