Interesting past few weeks for me. Friends were complaining about their bikes lacking in some area, looking to upgrade and all it took was Shimano's UN55 BB. Which cost all of $17 from REI.

Bike #1 . Bikes Direct Motobecane Mirage SLX. Bottom Bracket Flex: Owner is a big guy and complained the BB area was flexing. Sure enough, riding along side him when he was out of the saddle there was chain rub. Replaced this New VP BB English Square Bottom Bracket Set 68X 126mm VP BC73A Aluminum Cups | eBay and all problems gone.

Bike #2 . Diamondback Bikes - Road Bikes - Century Slow to accelerate and owner wanted a major wheel upgrade. Wheels weighted in at 1900 grams so not light but not super heavy either. Replaced the Chin Haur BB with the UN55 and no complaints.

The cheap BB in the first bike was a bit of a surprise given it cost $500, but the second bike cost close to $1000. Who puts a $8 BB instead of a $17 BB in a well speced bike?

So consider changing out your BB before upgrading other stuff. All it takes is 10 minutes and cost $20.