When playing the "expert" rules, and double 6 is rolled, and the player chooses to keep it, does both engine damage and wheelie effects apply?
Also, our group feels that the uphill and downhill penalty/bonus should apply as long as you are on the hill.
According to the rules, the penalty/bonus onlt applies when you are on the tile containing the marker.
1) Yes, double six "hits" you twice, if you elect to keep the roll. You make your engine check, and end up doing a wheelie (or "stand up" and take a rear tire damage in a corner).
2) I wondered about this, too. However, I believe you have the correct idea. If you look at track # 10, there are several places where "flat" markers are used. If the "uphill" and "downhill" markers lasted for one tile only, there would be no need for "flat" markers.