Odd sized drop handlebars

[loz]

hi guys, I've bought some ITM drop handlebars , the clamp area has a diameter of 25.6mm. I can't find any stems for this size, and according to sheldon this size shouldn't exist either!

http://www.sheldonbrown.com/gloss_ha-i.html#handlebar

think a 25.8 stem would be ok?

 

[jimboalee]

That's the 'small' size, 1".

Some MTBs have this size.

 

[davidad]

That's the 'small' size, 1".

Some MTBs have this size.

Not quite. 1" is 25.4mm.

 

[Hilldodger]

ITM do the stems as well.

 

[jimboalee]

Not quite. 1" is 25.4mm.

What happens is the handlebars are just oversize from 25.4mm. The stem clamp diameter could be undersize, which is OK, correct, which is also OK, or oversize. If the stem clamp diameter is oversize, the stem would clamp the bars on only a portion of the circumference and an unsuspecting bike builder would have bars that could move.
If the stem is undersize or correct, the bars are shaved to shape and the clamp is firm.

 

[loz]

looks like i've caught myself out again, think i'll buy some more bars of a size i can get a suitable stem for (i couldn't find an ITM stem for 25.6mm)

thanks all, another lesson learned

 

[Crepello]

What happens is the handlebars are just oversize from 25.4mm. The stem clamp diameter could be undersize, which is OK, correct, which is also OK, or oversize. If the stem clamp diameter is oversize, the stem would clamp the bars on only a portion of the circumference and an unsuspecting bike builder would have bars that could move.
If the stem is undersize or correct, the bars are shaved to shape and the clamp is firm.

So, is the oversized stem acceptable?...if it is 0.2mm over? I know that front loading stems are generally accepted as fine if the stem is .2 over. But what about a one bolt, classic quill stem clamp? I have ITM 25.8 bars in a 26. quill stem and all so far seems fine. I had no reason when installing the set up that I was pushing the stem clamp to far. But I could be wrong! Is .2 difference acceptable?

I ask with genuine enquiry.

 

[MartinC]

Many (all?) of us used to mix and match 25.8 and 26.0 'old fashioned' bars and stems from ITM, 3TTT, Cinelli and Deda all the time. The only things that weren't compatible were even older UK stuff at 25.4 and old Cinelli at 26.4.

 

[jimboalee]

So, is the oversized stem acceptable?...if it is 0.2mm over? I know that front loading stems are generally accepted as fine if the stem is .2 over. But what about a one bolt, classic quill stem clamp? I have ITM 25.8 bars in a 26. quill stem and all so far seems fine. I had no reason when installing the set up that I was pushing the stem clamp to far. But I could be wrong! Is .2 difference acceptable?

I ask with genuine enquiry.

The single bolt Quill type stem wraps the stem's clamp band around the bars like a Jubilee clip. AHead stems that are two piece castings clamp the bars by pulling the outer casting in toward the stem. Castings have very little flexability, so it is advisable to get a stem with slightly lower diameter than the bars so the stem scrapes a shiver of paint off the bars to fit snug and tight.

There are MTB stems with 1" ( The industry terminology ) clamps.

 

[jimboalee]

Also, if a stem is bought that is a real sloppy fit, get a sheet of thin Aluminium from a hobbyists store and make a shim.

Motorcycle scramble handlebars do not have the 1" bulge for a bicycle stem clamp. Shimmed with aluminium sheet, they were used on 'Tracker' bikes pre BMX and MTB.

 

[mickle]

What happens is the handlebars are just oversize from 25.4mm. The stem clamp diameter could be undersize, which is OK, correct, which is also OK, or oversize. If the stem clamp diameter is oversize, the stem would clamp the bars on only a portion of the circumference and an unsuspecting bike builder would have bars that could move.
If the stem is undersize or correct, the bars are shaved to shape and the clamp is firm.

Eh? Wrong. Bars are never 'shaved' to fit. Never. This is very bad and misleading advice.

Bars and stem sizes should match, it's not difficult.

 

[mickle]

Also, if a stem is bought that is a real sloppy fit, get a sheet of thin Aluminium from a hobbyists store and make a shim.

Motorcycle scramble handlebars do not have the 1" bulge for a bicycle stem clamp. Shimmed with aluminium sheet, they were used on 'Tracker' bikes pre BMX and MTB.

There's a more cheaper and more convenient source; aluminium soft drink cans are precicely 0.2mm thick which happens to be the increment between handlebar and seat post standards.

 

[jimboalee]

Eh? Wrong. Bars are never 'shaved' to fit. Never. This is very bad and misleading advice.

Bars and stem sizes should match, it's not difficult.

Maybe I should have said 'Crimped' by the stem clamp.

Remove a pair of aluminium bars and see how the metal has been swaged by the clamp.


Apparently, Loz is finding it difficult.

 

[jimboalee]

This is my mistake. Mickle is somewhat of a perfectionist when it comes to bike building. I'm a 'hairy arsed engineer'.

 

[zigzag]

Eh? Wrong. Bars are never 'shaved' to fit. Never. This is very bad and misleading advice.

Bars and stem sizes should match, it's not difficult.

ideally the sizes should match. jimbo's posts, while entertaining, should always be taken with a pinch of salt