Talking about bicycles. You're in luck, young grasshopper. Most bicycle parts can be expressed with Koreanized English (Konglish) words, like "pump," which becomes "pompuh." Here are some others:
bicycle shop: ja-jon-go ka-gae
bottom bracket: beebee (this also means 'beeper')
bearing: bearing (Korea makes fine and cheap bearings, by the way. Stock up.)
puncture: punk (no kidding)
"Where is X?" "X ga oh-dee ee-soy-yo?"
"Let's go!" "Kaja!"
trail: deung-san-ro [note: there is no precise Korean word for trail. 'Narrow mountain way' or 'deung-san-ro' 'is as close as it gets, which can describe a dirt road in the mountains, or a backwoods singletrack. Use 'narrow mountain way' with caution. Sometimes Koreans use the word "course" or "corsuh" to talk about trails.]
alcohol of any type: joo
this way: ee-jok
to the north: puk-jok
to the south: nam-jok
to the east: tong-jok
to the west: seo-jok
to the left: win-jok
to the right: orun-jok
straight ahead: cheek-chin
back, in the opposite direction: ban-dae-jok
You can use the following phrases to alert hikers to your presence. Korean hikers are generally very receptive to off-road cyclists, and are very impressed by the fact that bikes can negotiate the trails. There is little, if any, of the conflict found on US trails, despite huge numbers of trail users in Korea. There's a good chance you'll be the first mountain cyclist they've ever seen, and if you're not Korean, it's highly likely that you'll be the first non-Korean riding a trail that they've ever seen. This surprise sometimes produces a deer-in-the-headlights effect. Some hikers seem not to notice your alert no matter how polite or loud. In these situations you should just do as Korean mountain bikers do: pass them just like the buses and taxis drove past you on your way to the mountain. No really, you should just try to get their attention; most don't expect a bicycle to be on the trails, which tend toward the unrideable scale anyway. To wit:
"Coming through!" (very polite): "Shillye hamnida!"
"Hello." (polite): "Anyong hasaeyo."
"Watch out!" or "Careful!" (a little less polite): "Jo-shim-heyo!"
"It's broken." "Go-jang naseyo."
"I don't comprehend/understand." "Mol-ayo."
"I'm sorry." "Mee-an haeyo."
"Do you speak English?" "Yong-o mal haeyo?"
mountain spring: yaksoo