I have a new-ish Bianchi Cortina hybrid that I'm trying to find suitable drop bars for, but I can't figure out the proper size to get. It seems like the bars mostly come in 25.4mm, 26mm and 31.8mm. But do you get this size from the bars, or from the stem clamp?

When I measure the bars on the outside of the clamp, it looks to be about 25.4. When I measure the space in the clamp itself it seems closer to 31.8. When I measure the bars directly under the clamp (where it fattens up a bit) it seems somewhere in between. Help?

  • Are you measuring it with the parts disassembled? You really should do that (even if you just slide it to the side a bit). By the way, the size is got from the bars, since the clamps are always a tiny bit larger while unclamped. Mar 15, 2012 at 3:36

1 Answer 1


Measure the handlebar itself, while unmounted from the bike, at the center most point of the bar. Use a digital or vernier scale caliper.

The bar from the 2009 Bianchi Cortina is a 25.4mm MTB handlebar, with about 2 inches of rise. I expect yours will be as well. Do not use a 26mm bar, although you can likely mount it on the stem, because the installation will damage it, and it will fail, probably at some future point when you are riding it.

If you want a drop bar, you will need a new stem as well as handlebar. 25.4mm road drop bars are rare or non existent, since 25.4mm was the mountain bike standard.

I hope that helps.

  • 1
    You don't need to unmount the bar entirely, just loosen the clamp and slide it to one side so you can access the center of the clamp area on the bar. Measure the bar twice, the second at 90 degrees from the first, and average the two numbers if different. Mar 15, 2012 at 12:11

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