Analyzing The Compatibility of STI Shifters and Flat Bars

Description of the Situation

You’re wondering whether STI brake-shifters can be combined with flat bars.

It’s possible to install STI brake-shifters on flat bars if you use a shim to compensate for the smaller diameter of the handlebars.

However, the combination of STI shifters and flat bars results in poor ergonomics and insufficient brake actuation because the two components aren’t designed for each other.

The Problems With STI Shifters On Flat Bars

Below you will find a list of inconveniences that originate from installing STI shifters on flat bars:

1. Ergonomic Nightmare

STI and other shifters with similar characteristics are created specifically for drop bars. They have hoods (the black bases) playing the role of handles providing a comfortable riding position and quick access to the brakes.

When installed on flat bars, the hoods create ergonomic problems because brake-shifters are supposed to be in a vertical position (levers perpendicular to the bars) rather than in a horizontal one (levers parallel to the bars).

As a result, shifting becomes uncomfortable and distracting because you have to push the switch levers down and up rather than to the sides as intended.

It won’t be surprising if your fingers and wrists report pain from “digging” for the little levers and pressing them.

2. Sub-optimal Braking Performance

STI and other brake-shifters are engineered for handlebars with curves. When you put them on flat, risers, or bullhorns bars, the brake levers end up touching the bars before reaching maximum travel.

This leaves the rider with two options – to pre-tighten the brakes almost to the point where the pads/shoes are rubbing against the rim/rotor or to ride without the ability to maximally trigger the brakes.

Both alternatives are sub-optimal and could result in an accident due to insufficient braking power or poor brake modulation.

The term brake modulation describes the rider’s ability to control the braking force.

If a set of brakes has too much modulation, the levers will bottom out (reach the end of their travel) before full braking power has been applied to the rims or disc rotors.

If there’s too little modulation, braking is stiff, there’s little feedback, and the brakes work in on/off mode with no phases in-between.

3. Incompatible Clamping Mechanism

Drop bars have a 23.8mm clamp-on area whereas that of flat bars is 22.2mm. As a consequence, you will have to place a shim around the bars before installing the shifters to increase the diameter of the mounting spots.

Some people would find this solution non-aesthetically pleasing, but it’s the only way to securely tighten brake-shifters to flat bars.

4. Poor Aesthetics

STI shifters on flat bars look out of place. Many cyclists consider the combo visually disturbing.

Better Solutions For Switching From Drop to Flat Bars

If you’re wondering whether you can install STI shifters on flat bars, there’s a high chance that you’re trying to convert a road bike from drop to flat bars.

If that’s the case, you can consider some of the following options:

1. Flat Bar Road Shifters

The most straightforward way to switch from drop bars to flat on a road bike is to use flat bar road shifters.

Those models pull and release just as much cable as STI shifters and have clamps with a smaller diameter designed specifically for flat bars.

Tip: Brake-shifters are among the most expensive parts of a road bike. If you sell yours at a good price, you would make more than enough money to buy flat replacements.

2. 1 Road + 1 MTB Shifter

Shimano’s 8, 9, and 10-speed rear Road derailleurs have the same rear shift ratio as Shimano’s 6,7,8 and 9-speed MTB rear derailleurs.

The rear shift ratio of a derailleur describes how much the derailleur moves per 1mm of cable pull or release by the shifter. If two derailleurs have the same capacity and rear shift ratio, they’re interchangeable.

Therefore, if your road bike has 9 speeds or less you can use an MTB shifter for the cassette.

For the front, however, you will need a road shifter for optimal shifting experience.

You could also consider using a friction shifter mounted on the stem, the downtube, or the bars. Friction shifters move as much as the user wants them to and allow you to mix road and MTB parts.

3. Thumb Friction Shifters

Another option is to install a pair of thumb friction shifters that can support the number of gears that you have.

The downside of friction shifters is that they come with a learning curve and a bit of discomfort that cyclists accustomed to modern index shifters may find annoying.

Below is a list of thumb friction shifters:

Model Number of Speeds*Weight
Sunrace SLM105-7126g
Falcon Friction5-7N/A
Dia-Compe ENE Thumb Shifters8-10116g
Microshift Flat Bar Shifters9-10110g
Shimano Deore SL-MT62 5-7N/A
Shimano SL-M1505-7N/A
Table 1

*The number of speeds is derived from the cogs of the cassette, not by multiplying the cassette cogs by the chainrings.

Tip: You can find many old-school friction shifters on the second-hand market. Check your local websites for second-hand goods.

4. Bar-end Shifters + Thumbies

The company Paul Components makes mounts allowing you to attach bar-end shifters to flat bars. The product is called Thumbies.

Alternative Handlebars

If you insist on keeping your brake-shifters but still want to change the handlebars, you could consider alternative handlebars with a curve that won’t limit the movement of the brake levers.

The options are:

Mustache Handlebars

Mustache handlebars are essentially a mix between flat and drop bars and work just fine with road brake levers.

That said, the shifting isn’t super comfortable when using brake-shifters because the gear levers aren’t easily accessible.

For that reason, most users of mustache handlebars have shifters and brakes independent of each other. The most common combination is road brake levers + bar-end shifters.

Sparrow Bars

Sparrow bars are similar to mustache bars. The main difference is that they’re often shorter and have a bit more drop. Similarly to mustache bars, they permit the use of road brake levers thanks to the curve.


What You Need To Know

1. It’s possible to install STI shifters on flat bars if you use a shim.

2. STI shifters on flat bars offer poor ergonomics and affect the braking system negatively because the lever bottoms out against the bars early on.

3. If you want to make a drop bar to flat bar conversion, it’s recommended to use flat bar shifters rather than brake-shifters.

4. Curved alternative bars (e.g., mustache bars) accept road levers and give you a mix of drop and flat bars.

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