from Rookie’s keyboard
Hello, friends
My shift ended. I did my bike commute and now I am in front of my 15-year-old laptop ready to write another bike post.
Today, I decided to talk about the compatibility of road shifters with non-road derailleurs.
Are you ready?
Let’s go.
Index shifting
Modern shifters are indexed. This means that each click of the shifter pulls or releases a pre-determined amount of gear cable.
The goal is to simplify the shifting process by limiting the needed input from the rider.
If you want to shift, all you have to do is trigger a single click.
Rear Shift Ratio
The rear shift ratio describes how much a derailleur moves per 1mm of cable pulled or released by the shifter. The rear shift ratio depends on the number of gears on a bike.
If a derailleur has a 1.7:1 rear shift ratio, the derailleur moves 1.7mm per 1mm of cable pulled or released by the shifter.
The rear shift ratio is essential when determining compatibility between road and MTB parts.
Friction Shifting
Friction shifters are old-school. They don’t pull or release a pre-determined amount of cable. Instead, the user moves the lever as much as needed to make the desired shift.
Friction shifters are the equivalent of a manual car whereas indexed shifters are an automatic transmission.
The advantage of friction shifters is that the rear shift ratio becomes irrelevant because the user can compensate for any descrepency.
Many rookies are totally unaware that they can combine indexed road shifters with MTB derailleurs when the transmission has up to 9 speeds.
A 10-speed road drivetrain can also be combined with an MTB derailleur designed for 9 or fewer speeds.
Indexed road shifters should match the number of gears on the cassette.
If the shifters are the friction type, they are compatible with all MTB derailleurs that can cover the entire cassette.
If you plan on using friction shifters, any derailleur that can cover the cassette will operate with the system. This is the main advantage of friction shifters.
That said, friction shifters have the following cons:
- Instability (Your hands move away from the handlebars.)
- Complicated for Beginners (An inexperienced rookie will have a hard time dealing with friction shifters.)
Indexed Shifters
Modern road bikes use brake-shifters a.k.a. brifters. Brake-shifters combine a brake lever and an index shifter in one unit designed specifically for drop bars.
Indexed road shifters can be used only with derailleurs that have a rear shift ratio matching that of the corresponding road derailleur.
For example, if the bike has a 10-speed cassette and road shifters, it will be compatible with any derailleur that has the rear shift ratio of a 10-speed road derailleur.
If this condition isn’t met, the shifter will not move the derailleur as much as necessary, and the chain will fail to go onto the targeted cog.
Example:
The rear shift ratio of 10-speed MTB Shimano derailleurs is 1.2 whereas the rear shift ratio of 10-speed Shimano road derailleurs is 1.7.
The cable pull of a 10-speed road shifter is 2.3mm.
One click of the shifter would move the 10-speed MTB derailleur only 2.76mm.
The same click, on the other hand, will move the original road derailleur 3.91mm.
Therefore, a 10-speed MTB derailleur won’t be moving sufficiently when used with a 10-speed road shifter.
There are two ways to solve this issue.
The first one is to replace the road shifter with an MTB one. A 10-speed MTB shifter has a 3.4mm cable pull and will therefore move the same derailleur 4.08mm – a number that’s fairly close to the required 3.91mm of travel.
However, in this case, we want to keep the road shifter. Therefore, the only option is to replace the derailleur.
Luckily, 6 to 9-speed Shimano MTB derailleurs and 6 to 10-speed road derailleurs rely on the same rear shift ratio (1.7).
You can combine a 9-speed MTB derailleur with a 10-speed road shifter as long as the derailleur can cover the entire cassette.
| Number of Speeds | MTB Rear Shift Ratio | Road Rear Shift Ratio | ||||
| 8 | Shimano – 1.7 | SRAM – 1.1 | Shimano – 1.7 | Campagnolo – 1.4 | ||
| 9 | Shimano – 1.7 | SRAM – 1.1 | Shimano – 1.7 | Campagnolo – 1.5 | ||
| 10 | Shimano – 1.2 | SRAM – 1.3 | Shimano – 1.7 | Campagnolo – 1.5 | SRAM – 1.3 | |
| 11 | Shimano – 1.1 | SRAM – 1.12 | Shimano – 1.4 | Campagnolo – 1.5 | SRAM – 1.3 |
The table above contains the rear shift ratios of many road and MTB derailleurs.
Another requirement for successful pairing is to match the number of cogs with the number of speeds that the shifter is designed for.
For example, if the cassette has 10-cogs, the shifter should be designed for 10-speeds too.
This is necessary because the cable pull of the shifters varies with the number of gears.
Below are tables containing the cable pulls of different shifters sorted by brands and the number of gears:
Shimano
| Number of Speeds | Type | Cable Pull |
| 6 | Road + MTB | 3.2 |
| 7 | Road + MTB | 2.9 |
| 8 | Road + MTB | 2.8 |
| 9 | Road + MTB | 2.5 |
| 10 | Road | 2.3 |
| 10 | MTB | 3.4 |
| 11 | Road | 2.7 |
| 11 | MTB | 3.6 |
Campagnolo
| Number of Speeds | Type | Cable Pull |
| 8 | Road | 1.4 |
| 9 | Road | 1.5 |
| 10 | Road | 1.5 |
| 11 | Road | 1.5 |
SRAM
| Number of Speeds | Type | Cable Pull |
| 7 | MTB | 4.5 |
| 8 | MTB | 4.3 |
| 9 | MTB | 4.0 |
| 10 | MTB + Road | 3.1 |
| 11 | Road | 3.1 |
| 11 | MTB | 3.5 |
Cassette Interchangeability
MTB and road cassettes up to 10 speeds made by the same brand are interchangeable and many consider the terms “road” and “MTB” marketing specifications rather than a necessity.
You can use a 10-speed MTB cassette on a 10-speed road bike as long as the derailleur can climb all the way to the final cog.
Road bikes have higher gears (smaller cassette cogs), and many road derailleurs are too short to cover a wide-range 10-speed MTB cassette.
In other words, the shifter may be compatible with the cassette, but the MTB sprockets will require an MTB derailleur too.
10-speed MTB derailleurs are not compatible with indexed 10-speed road shifters. In that case, it’s necessary to use a wide-range 9-speed MTB derailleur.
11-speed MTB and road cassettes are not directly interchangeable. 11-speed road hubs are wider than 11-speed MTB hubs.
The purpose of this modification is to push the largest cog of the 11-speed road cassette further away from the spokes. The largest cog on a road cassette could come in contact with the spokes without this change.
MTB cassettes do not have this problem because the lowest gear is larger. Consequently, the periphery of the big cog is further away from the hub and the widest section of the wheel.
An 11-speed MTB cassette is too narrow to cover an entire 11-speed road hub. This problem can be circumvented by installing a 1.85mm spacer on the hub before sliding on the cassette.
Unfortunately, I have to end this post as I just got a call from the boss. They need me early tomorrow and I have to go to bed now.
Until next time,
– Rookie
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