Description of the Situation
You have standard drop bars and STI shifters but want to try alternative handlebars such as bullhorns and wonder whether your existing brake-shifters are compatible.
Condensed Answer: While it’s possible to install STI brake-shifters on bullhorns, the combination is not common because it complicates cable routing and prevents you from fully engaging the brake due to the lack of room.
The Problems With Installing STI Shifters On Bullhorn Bars
1. Reduced Breaking Actuation
STI and other brake-shifters are engineered specifically for the curves of drop bars. For that reason, STI brake levers bottom out against the bars when installed on bullhorns.
The result is a limited actuation of the brakes and sub-optimal braking performance. The problem is less pronounced on bullhorn bars with a larger curve near the ends.
To fix this issue, some riders reduce the slack in the brake cable to a minimum via the barrel adjuster and sometimes even manually pre-flex the brakes ever so slightly while tightening the pinch bolt. As a result, the brake lever doesn’t have to move as much to maximally trigger the brake.
This practice has the following downsides:
1. Limited Brake Modulation
By artificially shortening the brake cable and pre-flexing the calipers, the modulation of the brakes is reduced to unpleasant levels.
The term brake modulation describes the rider’s ability to control the amount of braking power applied at any given time.
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.
Running STI Shifters Backward
Another way to circumvent the brake lever actuation issue is to install the STI shifters backward – the end that doesn’t go into the hoods will be facing forward. This orientation allows the lever to maximally contract and makes cable routing a bit easier.
The disadvantage of this approach is that shifting becomes “inverted” and may feel weird and uncomfortable, at least in the beginning. For that reason, this set-up is more common when the brake levers and shifters are independent of each other.
2. Poor Cable Management
The cables and housing of brake-shifters come out of the base (handle) and go back towards the tops of the handlebars. If the cyclist uses drop bars and wraps them correctly, the result is a fairly neat set-up.
When installed on bullhorns, however, brake-shifters complicate cable management because the cables are going forward and up with no bar to support them. The solution is to make a loop so that the cables go back towards the rider.
Unfortunately, cable loops have a negative effect on the lever’s actuation.
3. Lower Mechanical Advantage
When cycling in the drops, the rider can apply more force on the brake levers because:
- The lever is triggered near its end and thus the moment arm is longer (more leverage).
- Most of the force comes from the index and middle finger which are much stronger than the last two digits.
However, when the STI shifters are placed on bullhorns, you can’t squeeze the levers with the same mechanical advantage because the index and middle finger are far away from the bottom of the lever.
4. Compromised “Grip” Ergonomics
The hoods of STI shifters reduce the gripping area when mounted on bullhorns. As a consequence, the cyclists cannot comfortably grab the “horns”. This peculiarity harms one of bullhorn bars’ best features – the extra leverage provided by the handlebars during climbing.
Many cyclists consider the aesthetics of a bicycle just as important as its functions.
Truth be told, STI shifters look out of place on bullhorn handlebars because the two aren’t made for each other. If you think that this set-up is ugly, you’re not alone.
Shifters and Brake Levers Compatible With Bullhorns
Below you will find a list of set-ups (shifters and brake levers) compatible with bullhorns:
Part 1: Brake-Shifters
1. Shimano Metrea Brifters
Shimano’s Metrea series has a variation designed specifically for bullhorn handlebars. The brake-shifters are installed at the end of the bullhorn bars and offer neat cable management. The Metrea series is more popular in Europe.
Note: Metrea levers operate with disc brakes only.
2. Shimano Di2 TT Brake-Shifters
Shimano’s Di2 TT brake-shifters are another option. They are built for time trial and can be installed at the ends of the bullhorns.
Part 2: Separate Shifters and Brakes
A cheaper way to equip your bullhorns is to use brake levers and shifters independent of each other.
You cannot use regular flat bar brake levers on the horns of the handlebars because the orientation of the cable would be wrong.
Bullhorns operate with the so-called reverse brake levers designed for time trial and triathlon. Reverse brake levers have their cable and housing inserting from the opposite side and facilitate installation and cable routing.
If you plan to install brake levers on the tops, however, you can go with regular flat bar levers or small inline brake levers which work in conjunction with your main brakes placed on the horns of the bars.
As far as shifters are concerned, the following options are available:
- Downtube shifters
If your frame has mounts for downtube shifters, you can consider a set. The con of downtube shifters is that you have to move your hands away from the bars during shifting – an impractical solution when riding in heavy traffic
- Bar-end shifters
Bar-end shifters are a very popular choice because you can trigger them without moving your hands away from the brake levers.
- Stem shifters
You could also install old-school stem shifters. They’re closer to you than downtube shifters but still require you to move your arms to reach them.
Note: Some people consider stem shifters dangerous during an accident because they’re fairly close to the cyclist’s abdomen.
- Grinded MTB shifters
MTB shifters are designed for bars with a smaller diameter (22.2mm) and don’t fit on drop bars and bullhorns by default. However, some people file the inside of the clamp and put them on road bars anyway.
You can use an MTB shifter for the rear because Shimano’s 7,8,9 and 10-speed road rear derailleurs have the same rear shift ratio as Shimano’s 7,8 and 9 MTB rear derailleurs.
- Old-school Shifters Mounted Next To The Brake Levers
Some bullhorn fans install retro thumb shifters right under the brake levers. Old school shifters have a friction mode which allows you to mix MTB and road parts because the movement of the shifter is guided by the rider. One example of such shifters would be Shimano SIS SL-MY20.
Note: Search for shifters that have a band-style clamp and replace the bolt with a longer one. This is necessary because bullhorn bars have a 23.8mm clamp area.
- Paul Thumbies
The company Paul Components makes a mount that allows you to install bar-end shifters on flat bars. The product is called Thumbies. You can use it to attach thumb shifters to bullhorns.
What You Need To Know
1. When installed on bullhorns, STI brake-levers bottom out against the bars.
2. STI shifters on bullhorns result in less than optimal cable routing.
3. For optimal performance, it’s recommended to use brake-shifters designed specifically for bullhorns or time trial bikes.
4. A set-up separating the shifters from the brake levers is the most economical way to equip your bullhorn bars.