Crankarm Recommendations for XL Flux
I am building up a Flux for XC use and am considering 180 mm cranks. I am 6'4'', 220lbs. I am currently riding a 5Spot and realize the BB on the Flux will be about 1/2'' lower than the Spot, and the 180 cranks puts you about another .2'' lower versus the 175s. Ned Overend says all but the shortest riders should use 175s for XC racing because of the additional power, and since I already use 180s on my roadbike, I thought I would give it a shot. I also like the fact that the longer cranks allow you to sit a little lower on the bike. Anyone have any experience or thoughts regarding crank length for my situation?
I'm about your height, not as heavy. I've been using 180 road cranks on road and MTB's forever. It definitely feels odd if I hop on a road bike with 175's, but I can't say that I can really feel the difference on a MTB. The difference is less than 3%, anyway.
When I set my saddle height, I always go off of the BB spindle, not the low pedal. So, my seat isn't any lower if I use a longer crank. Also, when descending with your weight off the saddle and cranks horizontal, crank length makes no difference to your cg.
I do feel like it makes sense for tall riders to use a longer crank, but they're not readily available long enough to help. I would like to try a 190 or 200 crank (there are a couple of custom ones available), but you would need a higher BB for sure.
Low BB's on full suspension bikes can be a problem. I've had a Blur and Heckler, both of which are fairly low (I found the Blur much too low). I don't know about the Flux. I also think it's unfortunate that nobody (AFAIK) changes the rear triangle of FS bikes for taller riders. If your saddle is very high, you end up with your butt behind the rear axle as soon as you start climbing. Steeper ST angles and zero-offset seatposts help, but longer chainstays are the better solution. I had Curtlo build me a custom road frame with a bit longer wheelbase (I spec'ed all of the geometry), and the handling is much better than anything I was able to find off the shelf.