Groupsets

Yes, but... Make sure the flat-bar shifters will work with road derailleurs. Either use gear shifters designed for flat-bar road bikes or you might need to also swap to MTB transmission. Brake lever 'throw' and leverage could also be different with flat-bar brake levers compared to drop-bar lever braking. Online searches & youtube are good to confirm compatibility - the chances are, if you are thinking about doing something with a bike, someone has already made a youtube video about doing the same thing.

Gear shift levers are designed to work with specific derailleurs, cassette and chain. The best way to ensure that your bike performs at its best is to use matching groupset components. There are some exceptions though, for example, Shimano 11 speed 5800, 6800 and 9000 work together, as do some Sram and Campagnolo groups. Always check compatibility online if you are unsure.

Yes. Providing stock is available, you can select options such as crank length, cassette ratio, bottom bracket type and derailleur cage length, this allows a good level of customisation for your new build.

Yes, it is more cost effective to buy a full groupset rather than individual components. Buying a groupset from Merlin allows component options too (providing stock is available), so it is also easier to get exactly what you would like.

This is a largely personal choice on which most bike riders have an opinion. Different manufacturers provide their own options for all types of bike riding, each manufacturer has their own particular slant on each component and the technology of how they integrate together. While some riders prefer the solid clunk of Campagnolo, others prefer the cutting edge technology of Sram Wifi or the smooth, effortless performance of Shimano. Campagnolo supplied the winning (disc brake) groupset for the 2021 TDF winner, Tadej Pogacar (UAE Team), recent Shimano and Sram wins suggest that at the top end of road racing at least, there isn't too much to choose between manfacturers.

This depends on how long your legs are, typically taller people have longer legs. Smaller riders would be better suited to shorter 165 - 170mm cranks, average size riders usually go for 172.5 - 175mm and larger riders usually choose 175 - 180mm. Cranks are available in 2.5mm increments from 165mm to 180mm although some sizes can be more difficult to find, especially at the shorter and longer extremes..

Road bike chainsets tend to come with 2 chainrings. The options of chainring sizes are usually; Compact - 34 50 chainrings, Semi compact - 36 52 and the classic race option, 39 53. More and more riders are choosing compact and semi compact chainsets which allow for smaller gear ratios for easier, faster pedalling over climbs.

Yes, there are warning lights on the junction box of Shimano Di2. In the event of the battery fully running down, the front derailleur stops first, at that point there's still usually around 100 shifts of battery power for the rear derailleur. Modern batteries last so long, they can be taken for granted and not checked regularly - it's a good idea to check the battery life indicator every few rides.

Solid Green light - 75 - 100%

Flashing Green light 50 - 75%

Flashing Red light 25 - 50%

Solid Red light 0 - 25%

Some riders who live in flatter areas, or race on flatter courses, might need a close ratio cassette such as 11-23. At the other extreme, riders who climb hills or mountains might require a wider ratio cassette such as 11 - 34. Many road riders fall between these two examples and ride with a 11-28 cassette which gives a good range of gears for road riders using compact or semi compact chainsets.

This depends on the groupset and the chainset. The big groupset manufacturers recommend using all their components in a groupset, however some smaller manufacturers such as Hope, Rotor and DMR make chainsets which integrate with various different groupsets.

No. Bottom bracket shells in framesets vary hugely, depending on your bike / frameset manufacturer. They vary in both diameter, width and also in how they fit the frameset. Some are threaded (Italian or BSA British Thread) and some are pressfit. The best way to ensure a new bottom bracket will fit, is to look at your bike's existing bottom bracket and try to match. Check online for fit and compatibility if you are still unsure.

If you are replacing a like-for-like chainring, choosing the chainring should be relatively straight-forward. If you are aiming to match chainrings for a specific crank, chainrings have a couple of things to consider. Firsly the number of 'arms' on the right hand crank arm usually 5 or 4. The bolt circle diameter (BCD) is the measurement of a circle diameter which passes through the centre of all 4 or 5 bolt holes. If you are unsure google your bike's crank BCD.

The number of teeth on the chainring also needs a little thinking about, particularly if you are running 1X transmission.

Yes, a smaller chainring will help. It might be more cost effective to replace your bike's cassette instead. Check your rear derailleur's maximum sprocket size. For example, changing from a 25 sprocket to a 28 biggest sprocket with a 39 chainring would give a similar gear to 34 X 25.