I just took one of my 3 speeds out for a spin and it has developed a strange thing - it pulls really hard to one side, as though there is a heavy basket on the bars (there isn't). This isn't a matter of the bike pulling, but the bars wanting to swing wildly to the left!

What could be doing this? Help!

Is one of the brake cables hooked on something? maybe you have been turning right too much and have the turning mechanism wound up the wrong way. Is your bike a Democrat?

Bike must be a Democrat and is voicing its opinion. I'll check the brake cable. Where
is the turning mechanism (or is this a joke that I am just not getting?)

I'm no mechanic, but could it be headset issues?

Not to hijack the conversation, but as someone who considers himself firmly left of center, a Democrat bike wouldn't be swinging wildly left; it'd be veering slowly right!

Don't think it would be headset - it was totally overhauled/rebuilt in the summer. Gonna have to have a good look at it.

OH yes major kidding on that one

This is gonna sound stupid but my friend had a similar problem. he was complaining that he had a very hard time turning the bike in one direction. And the handlebars wanted to pull to one side. He also said that he thought I hooked up the brake cables wrong. He was not a tech person in the least.

The problem was that he accidentally spun the handlebars around 360 degrees so that his brake cables were wrapped around the stem. Caused all sorts of weirdness. Flipped the handlebars back around the other way and all was well with the world.

OMG. I am a moron.

Fork's bent?

A large number of things could be happening.
Wheel not set in the fork
bent fork
twisted frame
Cable issues as mentioned
troubled headset time for a repack perhaps, and check the fork out of the bike.
Sight the frame to begin with.
Does the bike track straight? line up the bike on a line, wheel it backwards steering the front wheel on the line, let the rear wheel go as it will keep the bike vertical. Watch what the rear wheel does, stay on the line or go off? The rear wheel can effect steering just a much as the front. Rear wheel could be not centered in frame, out of dish (doubtful unless you trued the wheel recently) Frame bent behind the bottom bracket.

The problem can be found, but it might take some time.

Anything preceding this or did it just begin the problem one day?

nothin preceeding this. Just today. Bike was perfect the last time I rode it! What about overinflated tires?

No, tire pressure wouldn't be an issue unless you inflated the right tire more than the left tire.

I'm with repechage. Either one of the wheels isn't in the dropout right, or something is bent. Try riding in a straight line through a puddle, while holding both hands on the handlebar. Does it make one water trail, or two? If two, then either one of the wheels isn't in the dropout right, or something is bent.

Make sure first that the brake cables did not get tangled around head tube. If that's not the case make sure the tire is sitting right in the dropouts. Then you can look at frame damage. To me it sounds like brake cable routing problem.

Can you take a picture of the bike especially the front?

Is your stem bolt tight? Do the bars move up and down with little resistance?

First thought, bent forks.

Second though, missing (or toomany) ball barings in the headset? I had this recently.

The simplest thing would be a loose or out of alignment wheel. Check that the wheel is tight, and check that the wheel is centered between the fork at the crown. If it is not then the bike will pull to one side or the other.

If the front wheel is centered, then check the rear wheel. If it is loose on one side or otherwise not centered the bike won't track straight. Although this feels a lot different than if the front wheel is out of alignment.

90% of the time this is the problem.

Did this situation just start? Was something done to the bicycle just before the problem. That's where I would look first. Next, look at the head set. Has it managed to tighten itself up? If so, that will cause your bicycle to pull one way or the other.

Hmmm....the situation just righted itself as quickly as it happened!

Sorry for the moronic post. My friend had asked if I would sell it to her and I'd agreed and she was on her way to ride it...then I test rode it and found the problem!!

What was the problem !!! ??? We are all wanting to know after our bunch of suggestions!

Don't leave us hanging!

Double check for loose hub cones too.

Is it a Raleigh? The front wheel has a 'fixed' side-putting it in backwars will over tighten the adj cone and ruin the bearings. Just a thought.

She gets me every time, girl.

Actually I have no idea what happened! I suppose it must have been a cable. I went and fiddled a bit. The right brake cable was a bit loose - it's loose in the guides/tie thingies. I thought it might actually be the right side pushing the bars to the left. Anyway that may have fixed it.

I bet the first time you rode it your rump was off center, a bit a spinal lean compensated but sent the bike off course. The next day, you managed to center your "arse" on the saddle and "bingo" problem solved. I would further my speculation if strong drink or medicinal herbs were involved prior to the first ride.