I have a vintage road bike, and I want to put a mountain bike stem on it. Can you tell me what size of adapter to buy.
25.4mm or 22.2mm?

Neither, you can find quill stems for this and avoid that.

And welcome aboard, glad you found us.

We need pics of any and all "vintage" bikes, you need 5 posts X 2 days to post them, its an anti spam measure that serves us very well.

Go around, say Hi AND comment on any threads that interest you.

Try and upload to your albums and somebody may move them here.

Thanks for the warm welcome! I will definitely get around to doing that.

I understand that this solution is heavier, and ugly; but there are a few reasons I thought it would be better to do it this way:

• I have handlebars from a mountain bike that I want to try, and it seems hard to find a quill stem that can fit thick handlebars.
  
• I'm going away on the 16th, so whatever I order has to be amazon prime, or similar next day delivery.
  
• It doesn't have to be perfect. I just want to try it out, and I can always go back to the original stem and bars.
  

I ordered both sizes in the hope that one would be right. Will I have a working solution? Or should I try to find thin riser bars, or a quill stem that can fit the thick ones I have.


Thanks for you help.

Your welcome and bars for a quill can sometimes be a challenge to find so the adapter is the way to go, just be sure that the whole wedge of the adapter is below the threaded part of the steerer tube as you are adding to the leverage that can damage it. It is a "simpler" solution but a kludge to be sure. Also keep in mind the cables being long enough for the additional height, if their not you can keep it lower until you sort it out.

You might want to give us some background so we know how much to help, IE, can you do the cables if need be and do you know how the steerer tube threads can be a problem?

Also tell us what bike you are working on, somebody here has likely worked on one and may have insight on any kinky pitfalls you may encounter.

The adapters usually have a minimum insertion line but it's not always good enough.

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Two variables to consider here- quill diameter of your bike and "steerer" diameter of the stem you want to use.

Quills can be 21.15mm, 22.2mm and 1-1/8". Since you say it is a road bike, and it must not be junk or you wouldn't be spending money on it, 99.9% certainty your bike is 22.2mm.

The steerer end of the threadless stem is usually 1-1/8" although some older and very uncommon stems are 1".

So, based on above, you most likely want 22.2mm x 1-1/8 adaptor. The 25.4mm diameter you mention would be the other end of the stem that clamps to the handlebar.

I seem to have made a mistake while removing the stem. I loosened the top bolt, but the stem wouldn't budge, so I hit the bolt lightly with a hammer. The bolt went completely into the hole, and now the bars can turn independently of the wheel. But the stem is still stuck, and now the bolt doesn't bite at all. What can I do?

I don't know what the model name is. It's Leleu branded, and was sold by Cycles Roger. The frame is blue, yellow, white, and faintly pink.
Assuming I can get the stem out -- the gears are on the frame, so I'll only have to handle the brakes, and I've ordered some new cables in case I need them.

Thanks for you help.

That all makes sense, except that the 25.4mm diameter is definitely the quill end. They have an annotated picture showing it.
They have two sizes. Both have steerer diameter of 28.6mm, and length of 150mm. One quill is 22.2mm, and the other is 25.4mm.

This is where we will probably need pics as we may have veered off into "oh no" territory.

You can loosen the top nut of the headset and see what happens, maybe even loosen completely so it slides up above the threads, if that doesn't help then turn the bike upside down and remove the front wheel and see if you can nudge the wedge back into place and resecure everything back to zero, you may have to remove the front brake to do this.

You may be in the take it to the shop phase as what you describe may be out of your realm, anybody you know really good with bikes or is there a DIY co-op type place near you?

Respond to all the posts here to get your count up so we can get pics, we really need them now as we need to make sure we are talking about the same thing for sure, very hard to know without them.

And get some good pics uploaded to your album too, we need em now.

Do the stem and bars only rotate or do they move up and down some at all?

Here is pic from OP's album. Both emulate 1-1/8" threadless. That is the 28.6mm dimension. On the bottom end of the adaptor, 22.2mm is for a 1" threaded steerer and 25.4 is for a 1-1/8" threaded steerer. Unless you have a "one-piece crank" road bike or one of the few other Schwinns that take a 21.15 stem, you want the adaptor to the right.

The rotation of the bars independently of the wheel started out stiff, but now I can turn the bars quite easily while holding the wheel still. There is absolutely no vertical play in the stem. Removing the nut doesn't help.

I'm going to bed now. Tomorrow I'll take pictures of everything, make an album of them, and try nudging the stem from the bottom.

Thanks for all your help.