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Handlebar Diameters

Repair & Tech Info - Bikeman Tech Info

I like to break bars down to three different options: Mountain, Road, and Cruiser.  There are two major measurments to consider when looking at a new bar - the stem clamp size (the 'bulge'), and the overall width of the bar.

Formerly mountain and road bars used different clamp sizes, 25.4 and 26.0 respectively.  Now many bars are switching over to the newer standard for both mountain and road, 31.8.  The oversize clamp adds stiffness to the bar and it also reduces the amount of stems manufacturers need to produce.

One other measurement that is easily forgotten is the diameter of the bar off the bulge (where your grips go) which is typically most important when setting up a cruiser or a commuter bike, see below (Cruiser / Commuter Bars).




Mountain Bike Bars - Flat Bars, Riser Bars
Mountain Bars come in two different clamp sizes - the older 25.4mm, and the newer 'oversize' 31.8.  Widths vary widely, many bars are made to be cut down so you can buy it wide and work it down to what you like.  Check with the manufacturer of the bar to see if that's an option.  A 25.4 mountain bar shouldn't be used in a 26.0 road stem.

Road Bike Bars - the Drop Bar
Road bars now mainly come in two different clamp sizes - the older 26.0, and the newer oversize 31.8.  Widths vary and some manufacturers measure the outside to the outside of the widest point of the bar while some measure the center to the center of the widest point.  If you are unsure of how they are measured check with the manufacturers web site or shoot us an email.  A 26.0 bar shouldn't be used in a 25.4 mountain stem.

Cruiser / Commuter Bars - Mustache, High Rise, Randonneur, Multi-Position
Here is where you will see the most variety - and here is where you need to keep in mind not only the clamp size of the stem you have or want to use, but also the diameter of the bar off of the bulge.

Mountain bike brake lever and shifter clamps are designed to fit a diameter of about 22.2mm.

Road bike brake and shift levers (Shimano STI, Campagnolo Ergopower, stand-alone drop bar brake levers) are designed to fit a diameter of about 23.8mm.

This is why you need to be sure to match up what shifters or brakes you plan to use with the grip area of the bar, along with the clamp size of the stem.

BMX Bars - BMX Riser Bars
BMX bars use the same diameter for both the stem clamp area as well as the grip area, 22.2mm.  What's the signifigance of 22.2mm?  It's actually the same as 7/8", which was how they started out being measured.

Here's a list of the most common sizes and their use:

31.8 Common clamp diameter for modern oversize bars.  Interchangeable mountain and road use.

31.7 Deda Elementi oversize clamp size (compatible with 31.8)

26.4 Clamp size for old school Cinelli bars, no longer in use (though some stems may still be available).

26.0 Formerly the most common size for road bars (previous to the oversize 31.8 clamp).

25.8 Used by ITM, Ritchey, and 3T. For road use.  Compatible with 26.0 stems/handlebars.

25.4 Formerly the most common size for mountain bike bars (previous to the oversize 31.8 clamp).  Also used on some Japanese and Taiwanese road bars (Nitto for example).

23.8 Grip area of road bar.

22.2 Grip area of mountain bar as well as the clamp size of BMX bars.

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