This is a decent read so copied it just incase it gets taken down ~ here is the original DOCUMENT
Shimano currently offer seven levels of road bike components. From most expensive to cheapest, they are:
A Di2 groupset costs more than ten complete Sora groupsets, so what are the differences? Starting from 2200, I’ll explain what the extra money buys you in terms of features and design.
Shimano 2200 is the cheapest of the groupsets and the most basic. It is an 8-speed system, offering eight gear ratios on the rear cassette and two or three chainrings at the front. The STI gear shifters shift up using the brake lever, but shift down using a small button on the inside of the lever, similar to Campagnolo levers.
The most significant upgrade from 2200 to Sora is the additional sprocket, from eight to nine speed. The Sora STI levers include a built-in gear indicator, so you can see what gear you’re in without looking back at your cassette. Sora also uses an integrated bottom bracket rather than the traditional square taper bottom bracket on 2200 and has a much more sophisticated forged crankset. This arrangement is much stiffer, allowing for a more confident pedalling feel during sprints and hard climbs. Sora is generally much better made and finished than 2200 and is a much more attractive and modern-looking groupset.
This groupset also offers a 9 speed system like Sora, but has generally better finish and quality. The most significant upgrade is to the STI gear levers. Rather than the thumb button used for downshifts on Sora and 2200, Tiagra features a small paddle behind the gear lever. This allows for much easier shifting from the drops, which is an essential feature for racers and fast group riders.
This is the first group to use 10-speed shifting, using much of the technology from Dura-Ace in a more affordable package. 105 also offers a HollowTech crankset, which is lighter and stiffer than those on lower groupsets. The 10-speed groupsets also offer internal cable routing – this routes both sets of cables under the handlebar tape, allowing for better aerodynamics and a cleaner look to the front end
Ultegra and Dura-Ace
These groupsets offer essentially the same technology as 105, but with progressively better materials and machining. As the flagship groupset, Dura-Ace features many parts in Carbon Fiber and exotic parts like fluorine coated bushings. Notably, Dura-Ace does not currently feature a Triple crankset and is available only in Double or Compact configurations.
Shimano’s most advanced groupset, Di2 uses electronic shifting to offer the smoothest, fastest possible gear changes. Di2 is slightly heavier than standard Dura-Ace due to the added weight of the system battery, but offers significantly better shifting. The big advantage of Di2 is that shift buttons can be placed wherever needed, making it ideal for time-trial bikes or for sprinters who need to shift from deep in the drops. Di2 can be shifted under very heavy pedalling load, as the electronic derailleurs are ‘intelligent’ and can identify the perfect moment to shift.
Weight savings across the groups are small but significant. Exact weights change often, but there is about a 1kg difference between 2200 and Dura-Ace. Each successive group offers marginally lighter parts than the last.
There is a great deal of debate about the shifting performance of different groupsets. The general consensus is that Sora shifts much better than 2200, Tiagra is a big improvement over Sora, but from 105 upwards there is little difference. For most people, gear changes are as smooth and easy on all 10-speed groupsets. The main improvements from Ultegra and Dura-Ace are weight and better aesthetics.
Mix and Match
With the exception of Di2, components can be freely mixed among the same speed setup: 9-speed with 9-speed, 10-speed with 10-speed. Many entry-level bikes feature a mix of Sora and Tiagra, using Tiagra on the most critical parts like the rear derailleur to get the most “bang for the buck”. Many riders build their own machines with a custom choice of components, or slowly upgrade a stock bike with improved parts.