Crankset advice

[Novicerider]

Hello, I’d like to change my crankset. It’s currently a Shimano Altus FC-M311 48/38/28. Bottom bracket is Shimano BB-UN26. Cassette is an 8 speed. Bike ridgeback tour. Would like something comparable or upgrade. Generally ride between 30-70 miles with up to 4,000ft of climbing and will be riding coast to coast in July (hopefully). Bit confused by it all tbf (maintainance novice). Like for like Altus cranksets appear to be for bottom brackets of 123mm, but I think mine might be smaller (not sure how to read BB). Part says L117R does this mean 117mm? How significant is The BB size for crankset? Cheers!

[rotavator]

You can check the length simply by measuring it with a caliper/vernier/ruler but I guess it is 117 mm.

BB length but more importantly how far the righthand/drive side sticks out are major controls on your chainline but it is also controlled by the design of the crankset, search for previous threads on this including recent ones.

[531colin]

Whats wrong with the existing crankset? the bit you pictured looks OK.
That BB is definitely 117mm, its printed on it! along with L&R for left and right.
The BB length is determined by the chainset