I'm just getting back into mountain biking after many years of road-only riding. I'm looking for a crankset, and I'm noticing that most mountain bike cranks come in 175mm and a few come in 170mm. I guess the 172.5mm cranksets are pretty much a thing of the past. I'm not sure which length to go with. I'm just under 5'5" with an inseam of just over 30" (actual measured inseam, not pants inseam). I use 170mm cranks on my road bike. So should I go with 170's or 175's on my mountain bike?