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Basic Knowledge

The main source of incompatibility complicating the conversion of a road bike with an Ultegra group set to flat bars are the shifters.

Modern bicycles have indexed shifters. The movement of index shifters is segregated into clicks corresponding to the number of gears that the bike has. Each click equals an up/down shift.

The rider doesn’t decide how much cable is pulled or released during the clicks of the shifter. The movement of the shifter is pre-set and non-changeable.

The rear derailleur has pre-determined movement too described by a property called rear shift ratio.

The rear shift ratio indicates how much the derailleur moves per 1mm of cable pulled or released by the shifter. For example, if the rear shift ratio is 1.7, then the derailleur moves 1.7mm for every millimeter pulled or released by the shifter.

The pre-set values of the shifter’s pull and the derailleur’s ratio result in a fixed travel of the derailleur. This makes shifting fast and predictable but complicates the mixing of shifters and derailleurs due to the dissimilar values of the variables (cable, derailleur ratio).

Incompatibility

Shimano Ultegra is a road groupset. And since road bikes use drop bars by default, the cable pull of brake-shifters is designed for road rather than MTB derailleurs.

However, flat bars are dominant in the MTB market. Consequently, the vast majority of shifters for flat bars have an MTB cable pull and cannot be used with road derailleurs.

Possible Solutions

To determine the viable combinations, one needs to become familiar with the cable pull and shift ratio of popular road and MTB components.

Shift Ratios

Cable Pull

*There isn’t accessible data that can reveal the cable pull of 12-speed Shimano MTB and road shifters. It’s known, however, that the numbers are different from those of 11-speeds parts.

Conclusions

10-speed Shimano road derailleurs have the same rear shift ratio as 8/9-speed MTB derailleurs, namely 1.7.

Consequently, the following combination is possible: 10-speed road derailleur + 8/9 MTB/Road Shifter + 8/9 MTB/Road Cassette.

The only requirement for this combo to work would be to get a cassette that is compatible with the derailleur. Note: Road derailleurs are designed for smaller cassettes.

Or in other words, if you have a 10-speed Ultegra derailleur, you can technically combine it with an 8/9 speed system + 8/9 flat bar shifters when doing the flat bar conversion.

The main downside of this approach is that you will be downgrading to a drivetrain with fewer speeds. 8 and 9-speed cassettes come with larger jumps between the gears. This makes it harder to maintain a smooth cadence.

The term cadence indicates the number of crank rotations per minute. In general, a higher cadence such as 90RPM is associated with more efficient energy expenditure and thus higher average speeds.

Dedicated Flat Bar Shifters

Another option is to use dedicated flat bar shifters designed for road bikes.

The viable options, in this case, are made for 10 and 11-speeds:

• SL-RS700 (10/11-speed)
• Shimano SL-RS700 (11-speed)

Note: Shimano has many flat bar shifters but most are designed for MTBs. Those don’t fit in the Ultegra drivetrain unless you want to downgrade the bike to 8/9 speeds.

Friction Shifters

The final option is to rely on friction shifters mounted either to the downtube (old school) or the bars.

Friction shifters are not segmented into clicks. They move smoothly, and it’s up to the rider to determine how much the shifters have to travel for a shift to occur. This property makes friction shifters a good choice for people who want to mix all sorts of drivetrain components.

The downside is that friction shifters are slower and less user-friendly.

The Advantages of Switching From Drop Bars to Flat Bars

• Upright position

The main incentive to switch from drop bars to flat is to ride in a more upright position and reduce the stress on the back that comes with leaning forward. People with poor flexibility or back problems greatly appreciate the reduced stress.

• Better compatibility with a front rack

Drop bars limit the number of front racks that you can install as well as the size of the cargo that you can carry on them. For that reason, people who rely on front racks often install flat or comfort handlebars.

• Simplicity

Flat handlebars add simplicity to the setup.

• Light weight

Flat bars (especially short versions) can be extremely light.

The Downsides of Switching From Drop to Flat Bars

• Drag

The main purpose of drop bars is to allow the rider to lean forward and assume a more aerodynamic stance. Flat bars take that possibility away.

• Fewer hand placements

Flat bars offer one main hand position whereas drop bars offer 3. For that reason, drop bars are still seen on many touring bikes. The longer the trip is, the higher the chances of experiencing wrist discomfort due to relying on a single hand placement.

• Limited setup

As already explained, the component options for flat bar road bikes are fairly limited. It’s also highly possible to run into incompatibility issues.