Positron400

Hey,

can I fit any STI/brake lever on a drop handlebar or am I limited to the diamter? Could I, for excample fit a Di2 Dura Ace STI on a 80ties road bike with "old silver" drop handlebars?

Thanks
BR
P!

Hondo6

Depends on the grip area OD of those "old silver" drop handlebars.

ISO spec for drop bar grip area OD today is 23.8mm (15/16"), and I'm pretty sure that predates the introduction of STI's. I'm thus pretty sure all STIs are designed to fit that OD.

However, some older steel drop bars used a grip OD of 22.2mm (7/8"). I don't know if the clamps on all STIs will contract enough to mount securely on bars with the smaller OD. A difference of 1.6mm isn't that much, but depending on the clamp design it might be just enough to prevent proper fit. Haven't tried it personally.

Older French bars (25mm clamp) used a grip area of 23.5mm, so I'd guess those would very likely work. I'd certainly expect STI clamps to accept a difference of -0.3mm from nominal, as that's less than -0.012" smaller than the ISO spec.

You could try it if you already have the bars and are dead-set on using STI shifters (and will thus be getting a set of STIs anyway). But you may or may not end up needing a new set of bars in that case.

Shims of thickness around 0.7-0.75mm placed between the clamp and a old bar with 22.2mm grip area would also theoretically work. Keeping them in place during mounting might prove difficult, though.

More info on handlebar dimensions can be found here.

Andrew R Stewart 

A common alloy drop bar diameter (not at the stem clamp) is 23.5mm and for chromed steel bars 22.2mm. However dimensional standards back in the 1960s and earlier 1970s were more national or brand ones and not strictly shared across boarders or between brands. So, a test fit will give you the final determinate.

Not asked, but... I found long ago that the comfort of Al bars, compared to steel, is much better. Between the larger diameter offering one's hands a nicer fit and the bars greater flexibility they just feel nicer to me and many others. So if P400 has steel bars and if the STI levers don't fit them well I suggest considering finding some Al ones. Andy

Iride01 

Any, no.

Some, yes.

Kontact 

If the bar uses a 25.4 stem clamping area or larger, you are 99% going to be fine

Andrew R Stewart 

Please explain. Andy

Kontact 

As this chart shows, all the drop handlebars with grips less than 23.8mm take stems under 25.4.

https://www.sheldonbrown.com/cribsheet-handlebars.html

And while there certainly might be exceptions, those exceptions are unlikely to be the kind of thing you're going to run into. Which is why I said 99%, though I should have said 99.9%.

You can't mount an STI lever on a bar not designed for a drop bar brake lever, so 25.4 flat bars do not apply.

Positron400

Thanks, good to know if I want to switch from brake levers to STIs in the future. Much appreciated.