Hey all, not sure if this is the best place for this question but...
The image here is from the BD website. It just struck me as odd that there would be a hole in the bottom of the bottom bracket housing. What is the purpose?

Drainage.

I had considered that. But I don't think that my bike has a hole on the bottom, maybe it does and I've just never noticed it. Don't know if it's normal for bike frames to get water inside them, but it seems like a bad idea especially with a steel frame.

Leaving water trapped inside a steel frame also seems like a bad idea. Lesser of two evils, and you are correct, not all BB's have holes in them so yours may not.

Decoration.

Decorative drain.

Had a high-end Miyata roadster with such holes. Old-style fixed-and-adjustable-cup bottom brackets were much more susceptible to moisture than are modern sealed units. At best, they had that little plastic cover over the spindle.
Moisture can condense inside frame tubes, and these drain holes would let accumulated water either drain or evaporate.
They were never common, to my knowledge, so there must not have been a consensus that they were a good idea.

Never mind the hole. What kind of bike would put the cables, unprotected, around the bottom bracket like that? Are they sure the powder-coating is that wear-resistant? (And slick?)

3-leaf clover = somewhat lucky

My Specialized globe sport disc has the cables like that.

Yeah, I saw the lack of plastic guide thingy too, and thought the same thing.

I think it's a government plot. Maybe something to do with reducing the consumption of iron ore and steel...

I pulled apart the bottom bracket of my old 3 speed once cause of a grinding sound it kept making. Found several dead bees in there. Maybe they would have survived that. lol.

It's a BD bike, right? That hole is a keyhole. If you find the magical key that fits it, it turns into a Cannondale.

Condensate drain. All metal bikes will have water inside from condensate so it's a good idea to have a drain/vent to control rust/corrosion.

thousands and thousands of great steel bikes run the cables like that.

alot of great frame builders have cutouts like that. I think the whole drainage think is a legand. it was likely done more to prevent rebranding frames.

get off your carbon and smell the steel once and awhile

So if my steel steed doesn't have a condensate hole, should I be worried? I live in Western Washington, it tends to run on the cold and wet side around these parts. I ride in the rain/mist regularly and store my bike in the house (warm/dryish) at night. Maybe I'll pull out my seat post and flip her over.

Oh man, there was no pun or innuendo intended in the last sentence of that last post...

Hey! There's kids on this forum!

If you're really finicky, you could strip the bike and treat the inside of the frame with Framesaver. FWIW: I just got finished reassembling a 20-year-old steel frame bike after having it powdercoated. Despite several years in the Pacific Northwet, everything inside was fine.

There are people who reccomend drilling a small ( 1/8" ) hole in the bottom bracket shell to allow for drainage.

Far better than holes in frames to allow drainage: Buy a TITANIUM FRAME bike! Planet Earth will rot away before a titanium bike rusts or corrodes.

Holes for drainage? You're kidding, of course. Any hole that would allow drainage would allow things to enter as well.

I can't believe that no one has suggested what is obvious: The cutout makes for a lighter bike. Weight settles to the lowest point in the frame: The bottom of the BB is the most effective spot to remove mass from.

I think there is supposed to be a hard plastic sleeve over the front derailleur cable to protect the paint... I could be wrong.

Brad

The cable routing is correct for this style of BB. No plastic or chromed metal guide is used. The guides are built into the cast shell. The paintwork does get worn away. I have this style on my Bob Jackson tourer.

Drainage holes in the BB are not only to prevent the frame from rusting. They also prevent the bottom bracket bearings from running in a water bath. Many of these classic designs were built when BB bearings were 1/4" cup and cone. They had a plastic protection sleeve but otherwise poor sealing.
Cartridge style BB units (eh Shimano) do not have any openings inside the shell so water would not affect them. There are some rebuildable cartridge bearing units that would be affected by running in a water bath. Their seals are not that good.
In practice, nothing gets into the shell and if it did, it would drain out.

I think it was more an artsy thing when the Italians were doing this on the Colnogos and DeRosa's. The also had some cutouts on the lugs with clovers and spades for looks. Also there were silicon sleeves that protected the bearings when for the cup and cone bottom brackets.