Condensed Answer: Trigger shifters are designed for handlebars with a grip area that has a 22.2mm diameter. Meanwhile, drop bars are 23.8mm thick.
Consequently, the clamps of trigger shifters are too narrow to fit on a set of modern drop bars without modifications.
How To Install Trigger Shifters On Drop Bars
Trigger shifters may not fit on drop bars by default, but there are ways to make the combination a reality:
- Filing The Clamps
One of the ways to make trigger shifters compatible with drop bars is to file the clamps of the shifters from the inside until they fit on the bars.
The difference in thickness between modern drop bars and flat handlebars is 1.6mm. Thus, you will have to file down the clamps by about that much.
It’s possible to use a hand file to complete the task, but the procedure will be faster if you rely on a rotary tool. If you don’t have a rotary tool, you can use a standard drill (preferably one allowing you to control the RPM) with a sanding attachment.
If you have a caliper (preferably a digital one), you can measure the initial/original thickness of the clamp and periodically re-measure it while filing. Once you get close to removing 1.6mm, you can check if the shifters fit on the drops.
FAQ: Will filing the clamps weaken them?
Yes. By removing material from the clamps, their overall strength will be hurt and in some cases, the procedure will void the warranty of the shifters even though the clamps do not influence the mechanism.
That said, the clamps of the shifters do not have to be extremely strong because the overall weight of the shifters isn’t that much.
Nonetheless, a failure of the clamp could cause trouble, especially if the shifters and the brake levers are part of the same unit and thus use one clamp.
The risk isn’t insanely high, but it’s present.
FAQ: Can’t I just open the clamps with a flathead screwdriver?
The clamps are often made out of aluminum which isn’t a material that likes to be bent excessively. By opening the clamps with a screwdriver, you risk breaking them.
- Old School Drop Bars
Old school drop bars made of steel have a 22.2mm diameter and will therefore allow you to slide standard trigger shifters on them. You should be able to find a fairly cheap model on a site for second-hand goods or a Facebook group.
The downside of using old bars is that they have a slightly different shape and weigh more because they’re made of steel.
- Trigger Shifters Designed For Drop Bars
Shimano A050 are indexed shifters that fit on modern drop bars. Hence why you find them on bikes such as BTWIN Triban 100.
Note: These shifters are indexed but not exactly trigger shifters because most of the work is done by the thumb rather than the index finger.
- SRAM Shifter Adaptor
There’s a special adapter allowing you to mount any under-bar SRAM trigger shifter to a 31.8mm drop-bar. (read more)
- Replace the Clamps of the Shifters With Seat Post Collars
Another option is to remove the existing clamps and replace them with seat post clamps. To make this work, it will be necessary to file the lip preventing the seat post clamp from sliding down. (read more)
FAQ: Can I install a trigger shifter on the stem?
Modern threaded stems are very thick and cannot accommodate a trigger shifter.
Only old French quill stems can accept a trigger shifter because they have a 22.2mm diameter. Those stems are rare and made for the aforementioned thin bars.
If you have a thin French quill stem and bars that fit on it, you will be able to install a trigger shifter on the handlebars too.
You can’t install a trigger shifter on other quill stems because they will be either 25.4mm or 28.6mm in diameter.
The Benefits of Installing Trigger Shifters On Drop Bars
- Drivetrain Mixing
Installing trigger shifters on a road bike makes it possible to use MTB derailleurs, cassettes and chainrings. Thus, if you want to add extra low gears to your bicycle while still having indexed gears, trigger shifters will help.
Modern brake-shifters combine a brake lever and an indexed shifter designed specifically for drop bars.
Brake-shifters are often the most expensive parts of a road bike – sometimes more expensive than the frame and wheels.
For that reason, they are often absent from the cheapest road bikes which use either grip shifters or other cheap shifters that would fit on the bars.
Meanwhile, trigger shifters are extremely affordable and reliable. The entry levels series of Shimano offer decent performance for years without breaking the bank.
This makes trigger shifters a fairly cheap way to add index shifting to a road bike.
- Unique Look
A road bike with trigger shifters is essentially a Frankenbike. Some people like the aesthetics of such bicycles.
- No Downtube or Bar-end Shifters
By using trigger shifters, you will eliminate the need to mess around with shifters that aren’t on the handlebars (e.g., downtube shifters, bar-ends shifters…etc.)
The Downsides of Installing Trigger Shifters On Drop Bars
- Extra Work
Regardless of which method you choose, installing trigger shifters on drop bars will take more work than simply buying dedicated drop bar shifters.
- Tops Only Action
Trigger shifters are designed for flat bars and risers. Thus, it makes ergonomic sense to install them on the tops (flat part). If you place them anywhere else, using them will be quite difficult.
However, by putting them on the tops, you instantly lose access to them (and the brakes if you’re using a combo set) when riding in the drops or the hoods. Some people will find this practice inconvenient.
- Real Estate Loss
By installing a set of trigger shifters on the tops, you will lose handlebars real estate that could otherwise be used for a smartphone mount, a light…etc.