ASK MBACTION: BB Woes and So Much Pressure
HOW MUCH SHOULD I PUMP?
Q: A bike-shop mechanic just told me that I should pump my rear shock up to my bodyweight, and that’s all I need to do to tune my suspension, is that right?
—Trevor, who has a bad bike mechanic
A: The short answer is no. That’s not all you need to do. Suspension designs are all different. The required pressure varies depending on shock air volume, leverage ratios and damping adjustments. If you’re looking for the simplest solution, set your compression and rebound knobs to the open setting. Then, set your sag, which is the amount the shock compresses when your bodyweight is in the riding position to roughly 20–30 percent of the shock travel. Once you’re there, you’ll have a base setting. Now, you can start to work on fine-tuning the air pressure and damping adjustments to find your ideal setup. Start with the rebound and compression adjustments in the middle of their ranges. Remember also that you can always go back to your “base tune” if the suspension starts working poorly.
BIG BOTTOM BRACKET QUESTION
Q: Is there a BB shell adapter that will let me use a BB30 crankset with a 68- millimeter threaded botton bracket?
—Eric, who wants to put a big bearing in a small hole
A: There isn’t one that we know of. The BB30 requires a larger-diameter bearing than your 68-millimeter BB frame, so there’s no room to fit it all in there. Even if there was a way to mount the bearings outside of the BB shell, it would be tough to find a crank with a spindle that would fit that setup. Bottom line: the 68-millimeter bottom bracket is on its way out. Sorry to be the bearer of bad news.
“Ask MBA” peeve of the month:
Seized bottom brackets. They’re the worst.
THERE ARE SO MANY WAYS TO GET MOUNTAIN BIKE ACTION
Mountain Bike Action is a monthly magazine devoted to all things mountain biking (yes, that’s 12 times a year because we never take a month off of mountain biking). It has been around since 1986 and we’re still having fun. Start a subscription by clicking here or calling (800) 767-0345.