Bicycle Mechanics - What is internal diameter of road dropbar?

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Ritterview
09-12-05, 08:29 AM
I have been trying to find the internal diameter of a standard road drop bar at the grip end.

According to Sheldon Brown's Bicycle Glossary the external diameter of the standard drop bar is 25.4 mm (1") at the clamp and 23.8 mm (15/16") at the grip.

After much Googling, however, I have been unable to ascertain the standard internal diameter at the bar end.

Can anyone help me out?

ofofhy
09-12-05, 08:32 AM
Can you measure your drops? It probably naries with material.
Ritterview
09-12-05, 08:50 AM
Well, it probably does vary somewhat, but the manufacturers of drop bar taillights appear to assume a standard internal diameter for them to sell lights without specifying material or type.

Example of drop bar lights:
http://www.serfas.com/lights/TR-1.html

HillRider
09-12-05, 09:46 AM
Actually the "standard" diameter of road bars at the stem clamp isn't standard at all and it certainly isn't 25.4mm. That diameter was used only by manufacturere of low line bars for installation on lower-line bikes.

The most common diameter at the bar clamp is 26.0 mm or 25.8 mm depending on manufacturer. The old Cinelli diameter was 26.4 mm but they now use 26.0. The new "oversize" standard is 31.8 mm.

As to internal diameter, that will certainly vary with material type and wall thickness. Bar end accessories (mirrors, shifters, lights) are made with an expander clamp that is initially small enough to fit the thickest wall diameter bar but expands to hold in what ever you put them in.