**Condensed answer: ****10-speed rear derailleurs do not work accurately with 11-speed cassettes when coupled with index shifters.**

The only exception are SRAM’s 10-speed *exact actuation* road derailleurs which have the same rear shift ratio as SRAM’s 11-speed road (exact actuation) and 10-speed MTB (exact actuation) derailleurs.**Note:** If one uses friction shifting, a 10-speed derailleur can operate with an 11-speed cassette.

**Indexed Shifting**

Indexed shifters pull or release a pre-determined amount of cable with each click. This simplifies the shifting process and the necessary input. If the gears are properly adjusted, a single click is all it takes to shift.

**However, the “rigidity” of indexed shifting is also a source of incompatibility between drivetrain components.**

**Rear Shift Ratio**

**The rear shift ratio of a derailleur describes how much a derailleur moves per 1mm of gear cable pulled or released by the shifter.**

The rear shift ratio of a 10-speed MTB derаilleur is 1.2 whereas that of a 10-speed road derailleur is 1.7.

Or in other words, a 10-speed MTB derailleur moves 1.2mm per 1mm of cable movement initiated by the shifter while a 10-speed road derailleur moves 1.7mm.

**Cable Pull**

Indexed shifters pull a different amount of cable per click. For example, the cable pull of an 11-speed road shifter is 2.7mm whereas that of an 11-speed MTB shifter is 3.6mm.

How much the derailleur moves is decided by the derailleur’s rear shift ratio and the cable pull of the shifter.

**Since 10 and 11-speed rear derailleurs have a different rear shift ratio as shown in the table below, they are not interchangeable when used with index shifters.**

Type | Speeds | Rear Shift Ratio |

MTB | 10 | 1.2 |

Road | 10 | 1.7 |

MTB | 11 | 1.1 |

Road | 11 | 1.4 |

Type | Speeds | Cable Pull |

MTB | 10 | 3.4 |

Road | 10 | 2.3 |

MTB | 11 | 3.6 |

Road | 11 | 2.7 |

**NOTE: **The data in the tables is for Shimano derailleurs and shifters. Other brands such as SRAM and Campagnolo operate with a different rear shift ratio and cable pull.

If you combine a 10-speed derailleur with an 11-speed shifter (a requirement to run an 11-speed cassette), the derailleur will move too much per 1mm of cable movement and will tend to over-shift.

How much can be calculated by multiplying the rear shift ratio by the cable pull.

The possible scenarios are:

**MTB**

If you combine a 10-speed MTB derailleur with an 11-speed MTB shifter, the derailleur will move **1.2 x 3.6 = 4.32mm** per click.

Conversely, an 11-speed MTB derailleur combined with an 11-speed MTB shifter moves **1.1 x 3.6 = 3.96mm**.

Thus, a 10-speed derailleur will move 0.36mm more than needed to shift across an 11-speed cassette.

**Road**

A 10-speed road derailleur combined with an 11-speed road shifter moves **1.7 x 2.7 = 4.59mm** per click.

Meanwhile, an 11-speed road derailleur combined with an 11-speed road shifter moves **1.4 x 2.7 = 3.78mm**.

Therefore, a 10-speed road derailleur will over-shift by 0.81mm when put on an 11-speed drivetrain.

**Note: **11-speed drivetrains are particularly sensitive to slight inaccuracies because the space between the cassette cogs is quite small.

**The Exceptions**

**SRAM’s 10 Speed Exact Actuation Derailleurs**

SRAM’s 10-speed exact actuation road derailleurs have the same rear shift ratio as SRAM’s 11-speed road derailleurs and SRAM’s 10-speed MTB derailleurs.

Thus, one can theoretically use a 10-speed SRAM road derailleur in conjunction with an 11-speed cassette.

**Friction Shifters Make Everything Compatible**

Friction shifters (e.g., the downtube shifters on retro road bikes) allow cyclists to easily mix road and MTB parts of different speeds thanks to the absence of indexing. It’s up to the rider to move the shifter to a position that would trigger and maintain a shift.

**If you have a friction shifter, you will be able to combine a 10-speed derailleur with an 11-speed cassette as long as the derailleur has the capacity to cover the entire cassette. **

The downside of friction shifters is that they’re slower and a bit more difficult to operate, especially for beginners.

**Parts Needed for a 10 to 11 Speeds Conversion**

A conversion from 10 to 11 speeds requires the following list of new parts:

1. 11-speed cassette

2. 11-speed rear derailleur if using index shifting (unless you have a SRAM 10-speed exact actuation derailleur)

3. 11-speed chain (a 10-speed chain can work on an 11-speed cassette, but the shifting won’t be optimal)

4. 11-speed shifter (unless you use friction shifters)

5. New gear cable and housing (optional)

**What Are The Benefits of Converting From 10 to 11 Speeds**

A conversion to 11-speeds has the following benefits:

**Larger gear range**

11-speed cassettes can offer a large low gear. For example, some modern mountain bikes have a 50th big cog at the back.

The extra gearing makes a 1x drivetrain (the current MTB standard) a lot more viable.

**Smaller jumps between gears**

An 11-speed cassette comes with smaller gear jumps. The smaller jumps ensure smooth pedaling by making it easier to maintain high cadence.

Cadence is a term referring to the rotations of the cranks per minute. High cadence (e.g., 90RPM) is associated with greater average speed and minimized fatigue.

**What Are The Downsides of Converting to 11 Speeds**

The main downside of an 11-speed conversion is the price tag. 11-speed components are not cheap and the final cost can quickly climb up, especially if you insist on getting high-end parts.

And if you don’t feel comfortable doing the mechanical work yourself, the bill would be even greater as you will have to pay a bike shop for the labor.

**Summary: What You Need To Know**

- 10 and 11-speed derailleurs have different rear shift ratios. The only exceptions are SRAM’s 10-speed exact actuation derailleurs which have the same rear shift ratio as SRAM’s 11-speed road exact actuation derailleurs.

- The different rear shift ratio of 10 and 11-speed derailleurs causes inaccurate shifting because 10-speed derailleurs move more than necessary to make a shift when controlled by an 11-speed shifter.

- A friction shifter will allow you to combine almost any 10-speed derailleur with an 11-speed cassette. The only requirement is to get a derailleur with sufficient capacity to cover the entire cassette.