Learn how to do fire hopping, which is that after doing a super mini-turbo, using a mushroom, going through a boost panel or tricking on a normal ramp; hop continuously in a left-to-right direction a couple of times, this will keep your extra speed a little bit longer.

Btw, this trick doesn't work on bikes and it's not worth it doing fire hop with just regular (blue) mini-turbo. You can search on YT more about this technique. You can also look in there the Meta of MK8U which is different from MK8DX. I hope that'll help you