With the 11-speed 105 groupset, there has been quite a lot of technology which has filtered down from the top groupsets of Dura-Ace and Ultegra. The Tiagra groupset is heavier. As with pretty much everything in road cycling, you pay more to have lighter components. Dual Brake Levers - Mechanical

So it looks like you'll pull 3.78mm when you really want 3.92mm on a 10 spd cassette (the pitch tables say 3.74mm and 3.95mm - presumably due to rounding effects) This design isn't something we're used to seeing on the 105. It's only been available on Dura-Ace and Ultegra. please note, that the new rear derailleur geometry follows the design of the 11speed groupsets, and, it is for a longer cable pull with decreased derailleur actuation ratio. Therefore, the shifting is less sensitive to cable stretch and the extra friction of the concealed cable routing of the shifters. My plan to increase the size of my cassette to 32 teeth got very complicated when I was informed that Tiagra had a different cable pull to 105. Phase 1 saw me making do with 30 teeth which works fine with the 105 mech( despite it having a nominal maximum of 28 teeth). Both Shimano Tiagra and Shimano 105 use the same ratio of gear cable pull to rear derailleur movement, so you can fit a 105 derailleur in Tiagra system if you want to

The Tiagra brakes are impressive too. They don't fail to offer the stopping power riders want (and need). However, Tiagra does offer a triple chainset option ( 50 - 39 - 30). If that option interests you, then you will need to consider compatibility with your left-hand shifter along with the front derailleur. Right now my fitness isn't what it was so finding myself spinning on the smaller front ring just for bigger hills, which I never used to need to do. However I think this will only be tempory as fittness is noticably getting better again day by day. When it comes to rear derailleurs, this is where the 105 groupset differs from the Tiagra. The 105 R7000 is very different from the previous 105 models. It stems from the Ultegra R8000 design from the previous year.

The other major difference between the two groupsets is that the 105 brakes are considerably better than Tiagra ones. They are a real highlight both in terms of all-out power and fingertip control. The hoods are comfortable to perch on and the levers to use, and there’s a solid feel to the shifting and braking. The 105 isn't the only model that has benefited from upgrades. Tiagra's cables now run beneath the bar tape, which is how the higher-end Shimano groupsets have it.

Shimano Ultegra R8170 Di2 Disc Groupset

I replaced the long cage Tiagra 4700 with a shortcage, and went for the 105 10 speed (5700) which you would think would be a straight swap... It's not. Shimano presents these brakes as having the capacity to take up to 28mm wide tires. What we found is that the newest 105 - the R7000 has more drop than it used to (51mm vs 49mm). As you can see there isn't a huge amount of difference in the weight of these two so the biggest difference is that the Tiagra brake levers run a 10-speed system whereas 105 is an 11-speed. Shimano says both 105 and Tiagra have room for tyres up to 28mm wide. However, the latest 105 R7000 brakes have slightly more drop (the distance from the mounting bolt to the brake pads) than before: 51mm v 49mm. That implies you should be able to run 30mm tyres with the right frame.