While Ultegra and Dura-Ace 12-speed front derailleurs don't have any limit bolts, the 105 one does.
The top (high) limit for the 105 front derailleur is set using an adjustment bolt, and the low limit is set electronically.
Before your start, make sure you have correctly set up your front derailleur height, angle, and support bolt. Have a look at the 12-speed front derailleur installation guide for information on how to do that.
Adjusting the top adjustment bolt
You will need a size 2 hex wrench to set the top adjustment bolt.
The first step is to shift the front derailleur to the large chainring and the rear derailleur to the largest sprocket.
Next, turn the top adjustment bolt to set the correct clearance between the chain and chain guide inner plate. You’re looking for 0 – 0.5 mm of clearance.
Set the low limit
There may not be a low adjustment bolt, but that doesn’t mean you do not need to set it up. To start, shift the front derailleur to the small chainring and the rear derailleur to the largest sprocket.
Now press and hold the button on your rear derailleur until the LED next to it lights up yellow. This should take about 2 - 5 seconds.
You have just put the bike in adjustment mode.
The final step is to set the correct clearance between the chain and the chain guide inner plate. This time you’re looking for about 0 to 0.5 mm of clearance.
You adjust the derailleur by pressing the left (front derailleur) shifter buttons.
This front derailleur can move 18 steps inward and 18 steps outward from the initial position (37 steps total). It can be easy to lose track of the current position, but if you find that it doesn’t move when you press a button you’ve probably gone too far.
You can get the current adjustment value by connecting to the bike using the mobile app. Note that you can also set the low limit using the mobile app.
Note that when you’re in this adjustment mode the chain guide will overrun slightly and then move back in an exaggerated manner, so that you can check the adjustment direction. When checking the positions of the chain guide and the chain, perform the check after the front derailleur has moved back and come to a stop.
Press and hold the button on your rear derailleur to leave adjustment mode. Now shift the front and rear derailleurs through all gears and make sure chain rub does not occur in any gear. If it does, go back into adjustment mode and tweak the chain clearance.
That's it - your derailleur should now be working just fine, without any chain rub. Take the bike for a ride, and tweak the settings if necessary.
Is the front derailleur giving you a hard time? Feel free to send me a message any time!