Rear derailleur

Yes, within the same brand and with the same number of speeds, cross-series compatibility is generally guaranteed. A Shimano 105 R7100 12-speed rear derailleur works perfectly with Ultegra R8100 Di2 12-speed shifters, and vice versa. This flexibility allows you to upgrade or replace a broken component without changing the entire groupset. However, 11-speed and 12-speed derailleurs are not interchangeable, as the cable pull ratio differs. Between brands (Shimano/SRAM, SRAM/Campagnolo), mixing is not possible on modern indexed groupsets.

Adjustment is carried out in three stages: limit stops, cable tension, then fine-tuning. First, check the alignment of the derailleur hanger (if it is bent, straighten it using a hanger tool). Position the chain on the small chainring and the small sprocket, then loosen the cable completely. Adjust the top limit (H screw) so that the pulley is aligned under the smallest sprocket, then the bottom limit (L screw) under the largest sprocket. Tighten the cable by hand, then retighten the screws. Test all gear changes on the road. Adjust the tension using the adjustment wheel if any gears shift too late. A new cable and clean cable housings are essential for a precise adjustment.

Yes, always if the hanger is bent, even slightly. The derailleur hanger (or anti-derailment hanger) is a sacrificial aluminium component designed to bend before the derailleur or frame is damaged. Even a slightly bent hanger causes the derailleur to be misaligned, making adjustment impossible and increasing wear on the drivetrain. The hanger is specific to the frame (references by frame make and model) and costs between €10 and €30. Simple check: after removing the derailleur, check that the hanger’s contact surface is perfectly perpendicular to the wheel’s axis.

No, a short-cage derailleur is not designed to accommodate the necessary chain length difference.With an 11-34 cassette and a 50-34 crankset, the total capacity is (50-34)+(34-11) = 39, which far exceeds the capacity of a short cage (≤ 29). Forcing this setup results in the chain being too tight on the large sprockets, risking chain breakage and making gear changes impossible. You need a long-cage derailleur (GS from Shimano, identified in the product code) that accommodates a large sprocket of 34 to 36 teeth, depending on the model.

Yes, particularly on mid-range groupsets where the gains are measurable. The original nylon or POM (polyoxymethylene) pulleys work well but generate more friction than machined pulleys with ceramic bearings. Aftermarket ceramic pulleys (CeramicSpeed, Kogel, Ceramic Bearings) reduce friction by 1 to 3 watts, as measured in standardised tests. On a 105 or Ultegra groupset, upgrading to ceramic pulleys is one of the best value-for-money modifications (€50 to €150 for a 2-watt gain). On a Dura-Ace Di2, the original pulleys are already high quality and the gain will be smaller.

A derailleur rarely comes off its mount, unless there has been a fall or direct impact. In 90% of cases, problems with imprecise gear changes are caused by a tight cable, a kinked cable housing, a bent hanger or a worn chain: adjust before replacing. The real signs that a derailleur needs replacing: the body is cracked or bent following a fall, the upper pulley bearings are seized despite cleaning, the cage tension spring no longer returns to its original position, or the stops no longer work properly even with a new spring. A well-maintained derailleur lasts 30,000 to 50,000 km.

No, feedback from the field on Di2, AXS and EPS is unanimous regarding their reliability. Electronic groupsets undergo rigorous durability testing (water resistance, impact, temperature) and are used by professionals in the most demanding conditions. Cyclo-cross, the ultimate muddy discipline, adopted electronic groupsets as early as 2015 without any major issues. The difference: a mechanical fault (broken cable, spring) can be repaired at the roadside, whereas an electronic fault (damaged connector, faulty firmware) often requires a bike mechanic with the right tools. Both types of fault remain very rare, however, with normal maintenance.

No, modern derailleurs are strictly linked to the brand of the drivetrain. The cable pull ratio is specific to each brand: a Shimano cable pulls 2.7 mm per gear, whilst a SRAM cable varies depending on the range. Mixing a Shimano lever with a SRAM derailleur (or vice versa) results in incorrect indexing and imprecise gear changes. The only partial exception: friction derailleurs (older models or certain Microshift models), which operate independently of the cable pull ratio. On a modern indexed groupset, you must stick to the same brand.

A light lubrication every 500 to 1,000 km on the pivot pins and springs is sufficient. First degrease the pulleys and the derailleur body with a diluted bike degreaser, wipe thoroughly, then apply a few drops of light oil (chain oil or special derailleur oil) to the pivot pins. Never grease the pulleys with thick grease: it attracts dirt and creates an abrasive paste. After any ride in the rain or on muddy roads, rinsing with clean water followed by drying and re-lubrication is recommended to prevent corrosion of the pivot pins.