My Valkyrie trike has 150/80-17 radial on the front now. Wanting to go to a Bias Rear tire on the front reversed. BT45 or the MPA sounds like what everyone here is using most. I CAN'T FIND THEM IN MY SIZE. Should I go 140/80-17 or 150/70-17, I can find these. One size better than the other ?? Thanks, Brett