Chainring switch

[Aaron09]

I am going from a 3 chainring to a 1 chainring. My current BB is 68mm with the spindles measuring 122.5. I am looking to get a new bottom bracket, but I am unsure what size. Any thoughts? The original chainring was 48/38/28 teeth and the new one will be 39t.

 

[dabac]

To me it wouldn't make sense to replace a 38 with a 39 unless the 38 was due for replacement anyhow.
It's a 2.6% difference, far less (say 1/3) than the regularl difference between gears in a cassette rear.

If you find the big and the small so horribly disturbing, why not simply pull them off, switch to a shorter set of chainring bolts and call it done?