So 105 is moving into 12-speed Di2 territory. Great! At least I think so. And if you're reading this site, you probably agree.

However, not everyone is a fan of electronic shifting. And that's OK! With Shimano making DURA-ACE and Ultegra Di2-only, some readers have raised concerns that 105 will end up the same - Di2 only.

Will there still be a mechanical version of 12-speed 105? I think so - it won't be this year though.

This is a Di2 site, so let's take some time to discuss all the new 105 Di2 components:

Taking full advantage of the concept of trickle-down technology, Shimano's FD-R7150 is very similar to the older Ultegra FD-R8050. Comparing it to the 12-speed FD-R9250 / FD-R8150 two things come to mind:

Not aero
The more expensive 12-speed front derailleurs feature a tiny, 'aerodynamic' profile. The 105 version doesn't have that. While I really like how the more expensive front derailleurs look and sound, there's nothing wrong with this shape - it'll shift great all the same.

Top limit bolt
Since this front derailleur is essentially a rebranded Ultegra FD-R8050, it has a (top) limit bolt. The DURA-ACE and Ultegra front derailleurs don't have that bolt.
Besides adjustment bolt, this derailleur also has the familiar support bolt - used to fine-tune the front derailleur's angle.

The FD-R7150 is meant to be used with a 44.5mm chain line, just like Shimano's other 12-speed road front derailleurs.

FD-R7150 weighs 142g, compared to 116g for FD-R8150 and 96g for the FD-R9250.

While the 105 front derailleur is very similar to a previous version, the rear derailleur is brand new!

It doesn't just shift the bike, but has other functions too:

• It houses the charge port.
• Its function button lets you interact with the system
• There's a status LED that'll tell you about the battery status, shift mode, etc.

It also supports Synchronized Shift, which will either shift the front derailleur automatically when the rear derailleur reaches a certain gear, or compensates for front derailleur shifts by automatically shift the rear derailleur up/down a gear or two.
Manual mode is still the default, and using that is perfectly acceptable too. In fact, all of my bikes are set to manual mode most of the time.

RD-R7150 weighs 302g, compared to 262g for RD-R8150 and 197g for the RD-R9250.

One of 12-speed Di2's main feature is its wireless shift levers. Naturally this feature also made its way to 105 Di2.

Having a wireless front-end greatly reduces the time needed to build bikes, especially since most bike manufacturers nowadays seem to insist on routing wires and hoses through headsets and stems in the pursuit of "more aero".

Each shift levers has one E-Tube port (SD300), and no satellite shifter port.

Shimano resources (like the ST-R7170 manual) claim that the E-Tube (SD300) port is not used, and that it is not functional. CyclingTips state that you can connect the levers to the rest of the bike by wire.

I double-checked this with Shimano, and they said that you can not run the system wired.

Also, TT compatibility is currently restricted to Ultegra R8100 and DURA-ACE R9200. You cannot build a 105 Di2 TT bike by connecting older TT/Tri shifters to the levers.

No hood buttons. Two CR1632 batteries

Sadly, one of my favourite Di2 features - hidden hood buttons - is missing from 105 Di2. I get it, 105 is the cheaper groupset and compromises have to be made... but I'll definitely miss the hood buttons.

Each of the ST-R7170 shift levers takes not one, but two CR1632 batteries. They'll last for about 3.5 to 4 years.

Disc only

Yep - 105 Di2 is Disc only.
The ST-R7170 levers have full free stroke and reach adjustment, just like the DURA-ACE and Ultegra shifters.

I'm in the Disc Brake Death Squad myself, so this makes perfect sense to me. Other rides are still firmly attached to their favourite rim brake bikes or framesets though.

If this is you, 105 Di2 probably isn't for you... although there is a workaround. You see, 105 Di2 is fully compatible with Ultegra R8100 and DURA-ACE R9200, and you can in fact build a 105 Di2 bike with Ultegra rim brake levers.

A pair of ST-R7170 weighs 423g, compared to 391g for ST-R8170 and 350g for ST-R9270.

Cassettes & Chainrings

12-speed Di2 has been out in the wild for a year now, but so far only two cassettes have been released 11 - 30T and 11 - 34T (DURA-ACE and Ultegra versions).

105 Di2 will be released with an 11-34T, and the 11-36T will follow later - that last one is going to be a climber's favourite, I think!

• 11 - 34T: 11 - 12 - 13 - 14 - 15 - 17 - 19 - 21 - 24 - 27 - 30 - 34T (361g)
• 11 - 36T: 11 - 12 - 13 - 14 - 15 - 17 - 19 - 21 - 24 - 28 - 32 - 36T

You can also use the DURA-ACE or Ultegra cassettes - they're all fully compatible.

The available chainrings will be 50 - 34T and 52 - 36T. They'll come in all the crank arm lengths you'd expect, from 160mm all the way to 177.5mm. The Q-factor is 148mm.

New wheels! C32 & C46

Yep, Shimano are releasing a couple of new wheelsets as well - the C32 and C46 WH-RS710 wheels. While they're technically not 105 / R7100, they're close enough.

Just like last year's Ultegra wheels, they'll take 11-speed and 12-speed Shimano cassettes.