Lovegasoline

I plan to upgrade my brakes levers to Tekro Aero plus buy and install Tektro interrupter (cyclocross style) brake lever(s) (https://www.tektro.com/_english/01_pr...r&sort=1&fid=3) on my French made mid 1980’s Motobecane Grand Tourer with Weinmann center pull brakes. The bike is stock and has alloy drop bars. This upgrade is to replace the stock Weinmann brake levers and rubber handlebar grip (not grip tape). The grip is an 'imitation leather' wrap (including stitches) made of rubber, looks like it was almost 'shrink-wrapped' onto the handlebar & brake hoods, can't be removed without being destroyed, and the entire cockpit is anti-ergonomic: I have to move my hands a good distance to grab some brake. As is, no adjustment to the brake lever position is possible without cutting off the rubber grip.

I've read about the utility and ergonomic benefits of upgrading to Aero brakes (ride/brake from the hoods), it's not prohibitively expensive, and I'm sold on it (the bike is a tad big for me and I'd also like to replace the stem for one with a shorter reach). As long as I'm going to do the Aero swap and put on bar tape (and hopefully swap the stem), I plan on putting on the interrupter brake lever(s). Most my riding is playing in NYC traffic and my thinking is I really only need the interrupter lever for the front brake (left side) because if I 'm going fast enough to need the rear brake I'll probably be in the drops anyway: 90% of my NCY riding is on the bar tops (can't really grip the stock Weinman hoods due to anti-ergonomics).

The Tektro Interrupter brake levers are sold in three sizes intended for different (outside diameter) handlebar sizes:

RL720 - For use with 24mm OD handlebars
RL721 - For use with 31.8 mm OD handlebars
RL726 - For use with 26.0 mm OD handlebars

I measured my handlebars’ OD with calipers at the ‘top grip area’, where the rubber grip ends and the bare handlebar is exposed: I get a measurement of about 23.62mm. However, I notice that the handlebar’s OD is slightly, but noticeably, larger at its center point where it’s held by, and makes contact with, the stem (I didn’t unscrew the handlebar from the stem and measure). Which of the two dimensions, grip area or stem area, is the one which designates handlebar size?

Further, looking over standard handlebar sizing charts is somewhat confusing and some measurements differ by just half a millimeter: what size handlebar would mine be classified as?

Thanks a bunch.

fietsbob

It depends on how close you want the brake levers to be,
31.8 and 26 are fitting on the center where the stem clamp is
gripping the bars..

if you want them a bit further apart ,
[and not shim down the larger clamp sizes]
get the 24mm

AEO

FYI, only get the 24mm if you have 44cm or wider bars.
26mm will work on 31.8mm bars, but you can't mount them right next to the stem and you'll need a rubber shim.
31.8mm mounts near the stem on 31.8mm bars, but IMO, it gets too close and causes cable routing problems. It is possible to mount it closer to where you actually hold the bars, but you'll need a rubber shim, because the bars taper off to 24mm at that spot.

FastJake

I believe it's grip size that they are referring to. In any case, you definitely don't have 31.8mm bars. That's a new thing. So cross that one off the list.

As fietsbob said I think it depends where you want to mount the lever. Once you remove your old grip tape you'll see that the handlebar gets noticeably smaller at the point where the grip tape ends and the center section begins. Measure the place you want to put the lever and buy accordingly.

I'd expect 26.0mm if you want it jamming up against the stem (bad placement IMO), or 24mm if you want it in the area currently occupied by your grip tape.

Lovegasoline

I’m a little confused by the replies.

My handlebar ‘s OD appears to be constant (no tapering to speak of) excepting a very small area positioned directly underneath, and gripped by, the stem: the latter section doesn’t extend past the width of the stem for more more than 1/8” on either side.

The overall width of my handlebars are about 42cm: you're saying the 24mm Tektro lever fit my bar? I'm not comprehending how the handlebar width impacts the size of brake lever, or where it is mounted?

FastJake

I think what AEO meant to say is that if you have narrow bars you'll want to mount the brake lever right up against the stem. But wider bars will allow you to mount it further away, in the section that has a smaller OD. Personally I don't think this is a big deal and would mount the lever wherever I wanted regardless.

But since your bars have a constant OD that entire point is moot. Are they steel or something? All aluminum bars I've seen have the bigger center section (extending an inch or two on each side) and the rest is smaller. Have you removed the grip tape to check?

In any case, I'd go with the 24mm lever. I won't guarantee it'll fit, but I'm like 95% sure.