He doesn't actually get a proper chance to answer that. Running like this at an incline on a smooth surface is a lot like running down a steep hill (that's exactly what they're doing but shh): the faster one goes, the harder it is to keep oneself from pitching forward and tumbling to the bottom.

Admittedly, Yuusei was planning on doing that right about now anyway, but he doesn't initiate it on his own accord, simply losing his footing with an alarmed cry and beginning to roll with some pretty impressive momentum. He very much tries to keep Reira from getting hurt somehow by holding her close to his chest and allowing his other limbs to take most of the weight to put some space between her and the ground. Like a big wheel. Yeah.

Hopefully this isn't how Jack feels whenever he crashes the Wheel of Fortune.