rollagain

There's a trick for that. You introduce a piece of string into one of the frame openings and put the shop-vac nozzle against the opening where you want it to come out. The vac will suck the string through and you can then use the string to pull the cable housing through the frame.

Paul Barnard

Trimmed the steer tube off of a fork the length of the head tube plus a few spacers. Fortunately that was a large frame and I was building a medium at the same time and there was enough to work with.

bkentr

The dumbest move I've made was also the worst possible, about the most dangerous, and had the most lasting
consequences.

After cleaning off the mud and crud off the Trek 850 , I left the front axle nuts tight, but only hand tight.
No wrench.

After the next mornings ride, about 1/2 hour, the front wheel fell out during a quick jump off a curb,onto a city street

Bikes don't roll well with no front wheel.

The result was a skull fracturing over the handle bars pile driver faceplant.

After I got out of the hospital, one week later, I knew and understood that it was time to change my bike riding
style, give up the gung-ho i can do anything aggressive approach, and adopt a slower, casual and careful one.

That was early 1985. I have been Very careful about my building and maintenance jobs since that time.

That is also the year I started assembling the what I called "fun bikes" out of BMX bikes,started riding
nearly upright , and reduced my top speed.


A side story to that one is the huge number of other people I talked to in the next year that either had, or knew someone who had, have their front wheel fall off while riding.
Those sometimes annoying safety bumps, hooked washers, or something like those have good reason to be there.

One man reported that after some work on his head set, on his Harley Davidson, he left off the top nut.
Sure enough the first "wheelie" he tried lifted the frame off the fork.
Bikes, even motor bikes don't roll well that way either.
He was wearing a helmet, moving slowly,and was not hurt.

kentr

Hondo Gravel

On the Katy Trail last summer 2017 in the dark I put my cycling shorts on backwards. Something didn’t feel right LOL so when the trail was void of people I pulled a quit switcharoo.

randallr

Ok, mine will be the dumbest and most obvious yet - putting crank arms back on and realize I've got them both coming off the same side of the BB, so that pedaling would be a ridiculous two legged synchronized stroke, both sides of the crank going down at the same time, both sides going up . . . you get the idea. At least it wasn't dangerous

Kapusta

My biggest screw-up was re-using the old air when I was changing the air in my tires.

GamblerGORD53

My problem was I used to think chains lasted indefinitely. ha Rode 2 Raleigh derailleur bikes over 10,000 miles, past when they were clunking on the cogs. Probably most of the reason I hated them so much. Plus, the 1940s SS coaster Rudge I rode in high school, which came from my great uncle, now has a chain stretched a whole 1/4". My dad rode it slowly for 40 years after I bought my bikes.

ccccc

Not tightening the headset, thought I had broken my bike...

ericy

Forgetting to properly size the new chain when I replaced a chain.

IrishBrewer

Works especially well if you tie a small bit of cloth to the front end of the string.

WizardOfBoz

After working 7 years in a bike shop, then a MS and PhD in engineering, I still threaded my chain around the jockey wheel separator so that it was being dragged over solid aluminum and not the jockey wheel...
And didn't notice for a week or so.

(I really need a "forehead slap with butt of hand" emoticon).

WizardOfBoz

His pride and bank account sure were, though!

bkentr

Yes, pride and the pocket book, both can be damaged with ease.

while I am not proud of my dumb mistake, it did not take long to understand there was no way to "undo" the result.

I offer the story in the hope that someone else might be more careful to check or double check such things.
While I'm sure that most riders are careful, if this story saves even one broken neck, it was worth the telling.

kentr

BBassett

Paying the wrong person to maintain and service my Rohloff Speedhub.

rumrunn6

just realized I mounted a tire backwards, meaning rotational direction, despite my writing on the tire in TWO kinds of marker what the correct direction should be DOH!

WGB 

Hillbilly me gets his first fancy road bike.

The valves were longer and skinnier than Schrader valves usually were. Well, I thought they must be special racing valves and then I saw they had these fancy little nuts on them and so I guessed you had to unscrew them to add air. And so I did. The first nut seemed defective because it snapped off. So, resolving to return the bike and review the defect with the retailer I moved to the other tire and it's valve nut snapped off too. And that's when I learned there were valves called "presta"...

hman0217

broke the head off a bolt off in my new ti frame's rear rack eyelet. Then I had the bright idea that I would thread a bolt from the inside to push it out. Broke the head off that bolt too. The tried drilling out the outside bolt. Left-handed drill didn't do it and the hole was approaching getting too big. So I hammered a torx bit in there and tried counter-clockwising it with vice grips. Broke the torx bit in there. And it was carbide so it just laughed at me when I tried to drill it out.

Then I found that the inside bolt (second one I put in) was sticking out just enough that the old dremel trick would work and so I cut the notch and was able to get it out with a flat screwdriver. Then I tapped out the torx bit from the inside.

At that point, I surrendered and took it to the LBS. Took him a good 20 minutes to get it out so I didn't feel too bad. But boy did I botch it up trying!