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Good news.

Tiagra shifters can be combined with Ultegra’s mech.

Rear Compatibility

Tiagra 4500 rear shifters are compatible with Ultegra’s 10-speed rear derailleurs.

Tiagra 4600 rear shifters can work with Ultegra’s 10-speed rear derailleurs.

Tiagra 4700 rear shifters can operate with Ultegra’s 11-speed rear derailleurs.

Front Compatibility

Tiagra 4500 front shifters aren’t compatible with Ultegra’s front derailleurs.

Tiagra 4600 front shifters are compatible with Ultegra’s 10-speed front derailleurs.

Tiagra 4700 front shifters are compatible with Ultegra’s 11-speed front derailleurs.

How is this possible?

The compatibility between a derailleur and a shifter depends on two values:

• The shifter’s cable pull
• The derailleur’s rear shift ratio

Cable Pull

The shifter is the control unit that tells the derailleur when and how to move. When the rider presses the shift lever, the shifter pulls or releases a certain amount of gear cable. Pulling the cable pushes the derailleur toward the larger cogs. Releasing it allows the derailleur to go back to its original position.

The cable pull is a value that depends on the following factors:

1. Bike type (road, MTB…etc.)
2. The number of gears that the shifter is designed for
3. Brand
4. Category within the same brand
5. Year of release

The cable pull alone is not enough for total control over the derailleur. The derailleur itself has to be programmed specially. This outcome is achieved via a property known as the rear shift ratio (or pull ratio).

Rear Shift Ratio

The rear shift ratio of the derailleur is a setting that determines how much the derailleur moves per 1mm of cable moved by the shifter. For instance, if the rear shift ratio is 1.7 to 1, the derailleur would move 1.7mm for every millimeter moved by the shifter.

By controlling the values of the cable pull and the rear shift ratio, one can predetermine the location of the derailleur after each shift.

This programming makes indexed shifters so easy to use. The rider doesn’t have to overthink. One press of a button/lever moves the derailleur from one cog to the next. As a result, shifting is very fast and accurate, provided that the adjustments of the derailleur are correct and the gear cable tension is adequate.

When two derailleurs have the same rear shift ratio and the needed capacity for the drivetrain in question, they are interchangeable regardless of bike type, brand, or year of production.

If you replace a derailleur with one that has a smaller rear shift ratio, it will not move sufficiently to trigger a shift. This is called an undershift.

If the new derailleur has a larger rear shift ratio, it will overshift. In both cases, the drivetrain will suffer and may even be completely unrideable unless the user avoids shifting altogether and uses the derailleur simply as a chain tensioner.

Enough technical introduction, let’s return to the original story – Tiagra + Ultegra.

Tiagra 4500

Tiagra 4500 is an old-school group set designed for 9-speeds that appeared in 2006.

As surprising as it may seem, it is compatible with an Ultegra 10-speed derailleur.

How so? Both 9 and 10-speed Shimano rear derailleurs have a 1.7:1 rear shift ratio. Consequently, if you install an Ultegra 10-speed model on a drivetrain with a Tiagra 4500 rear shifter, the derailleur will move as expected.

Don’t forget that derailleurs don’t have brains. They’re pre-programmed robots and do as they’re told. They aren’t speed-limited either (unlike cassettes and shifters).

However, you can’t use Tiagra 4500 with an 11-speed derailleur as 11-speed models have a smaller gear ratio and won’t be able to move the chain sufficiently to trigger a shift on a 9-speed cassette.

Tiagra 4600

Tiagra 4600 is the 10-speed successor of the 4500 series. Tiagra 4600 derailleurs have the same rear shift ratio as Ultegra’s 10-speed models and can therefore also be used with an Ultegra unit.

Tiagra 4700 – The 11-speed Samurai In a 10-speed Body

Tiagra 4700 derailleurs were originally designed for 10-speeds, but the derailleur has an 11-speed rear shift ratio (1.4:1).

This property gives us the following options:

A. Tiagra 4700 shifter + 11-speed Ultegra rear derailleur + 10-speed cassette

B. 11-speed Ultegra shifter + Tiagra 4700 rear derailleur + 11-speed cassette

The above are the only viable combinations for 2 reasons:

• Tiagra 4700 shifters are 10-speed and have a unique cable pull that is neither 10 nor 11-speed.

• Tiagra 4700 derailleurs have an 11-speed rear shift ratio and can therefore operate with 11-speed road shifters.

Front Derailleur Compatibility

Tiagra 4500

Tiagra 4500 front derailleurs are technically not compatible with the Ultegra’s front derailleurs.

Tigra 4600

• Tiagra 4600’s front derailleur is compatible with Ultegra’s 10-speed front shifter.
• Ultegra’s 10-speed front derailleur is compatible with Tiagra 4600’s front shifter.

Shimano’s compatibility chart backs that up.

Tigra 4700

Tiagra 4700 is designed for 10-speeds, but it isn’t compatible with 10-speed front shifters. Instead, it works only with its own (4700) and 11-speed models.

Why?

The secret is found in the front derailleur’s design.

10-speed derailleurs have a short swing arm whereas Tiagra 4700 front derailleurs and those designed for 11-speeds have a long swing arm (image above).

The short swing arm offers a smaller mechanical advantage (leverage) than the long swing arm.

As a result, the shifter connected to the short swing arm derailleur doesn’t have to pull as much cable to trigger a large movement of the front derailleur.

It sounds illogical, I know because people naturally associate more leverage with smaller effort exertion.

However, when a lever has a lower mechanical advantage, it actually causes a greater output displacement.

Conversely, when a lever has a greater mechanical advantage as is the case with long swing arm front derailleurs, the shifter/lever pulls more gear cable.

If we use the long arm of a lever to insert force, we benefit from a greater mechanical advantage multiplying our effort.

The long arm (the one with more mechanical advantage), has a longer travel than the shorter one. (image below)

In other words, the input is longer than the output.

Note: I explain the concept in more detail here. (The post is about brakes, but the principles are applicable here too.)

Weight Comparison Between Tiagra and Ultegra Rear Derailleurs

The table below compares the weight of Tiagra and Ultegra rear derailleurs.

Conclusion. As expected, Ultegra derailleurs are slightly lighter. But in the best-case scenario, one would only save 50-80 grams. This is way too little to matter in practical settings.

The Advantages of Combining Tiagra Shifters With Ultegra Derailleurs

We have to be honest, here.

The difference between Tiagra and Ultegra isn’t massive. The consensus is that Ultegra is lighter and offers slightly smoother shifting. But the reality of the situation is that most people can’t tell the difference, especially in day-to-day riding.

Therefore, the main practical advantages of combining Tiagra and Ultegra are:

• Extra choices

Having more components to choose from can’t be bad, right? Imagine that you’re looking for a Tiagra derailleur new or used, but you can’t find one. Well, you have one more option – a compatible Ultegra unit.

• Setting yourself for a future upgrade

You can take advantage of Tiagra 4700’s 11-speed compatibility with 11-speed derailleurs. If your bike is equipped with Tiagra 4700, and you want to transition to 2×11, for example, you can do so by replacing the cassette, the chain, and the shifter.

The derailleurs as well as the front shifters can stay. A chain is needed because 10-speed chains aren’t compatible with 11-speed cassettes.

The outer width of a chain decreases as the number of speeds on a cassette increases due to the reduced proximity between the cogs.

The chainrings can stay too as the difference between 10 and 11-speed chainrings is too small to create an incompatibility. The inner width and 10 and 11-speed chains are the same. Thus, they’re made for chainrings of the same thickness.

That said, the spacing between the chainrings on 10 and 11-speed cranksets could be slightly different and may require a small readjustment of the front derailleur. The difference isn’t massive, though.

The table below contains the inner and outer widths of 10 and 11-speed chains.

As you can see, the inner width is the same while the outer width difference is between 0.3 and 0.4mm.

The Disadvantages of Combining Tiagra and Ultegra

As long as the dependencies explained above are respected, there aren’t major downsides other than the classic “why bother?”

“Why bother?” is a simple phenomenon to understand but difficult to respect.

Very often in life, we are looking for a change that isn’t necessarily justified. Then we end up spending time and other resources on variables that aren’t as fundamental as we expect/want them to be.

In other words, if your current Tiagra setup is in good shape, it may be wiser to keep pushing it until its last breath before upgrading/changing a part.