Tech Talks Presented by Park Tool is a monthly video series hosted by Park Tool's own wrench whisperer, Calvin Jones. The series will cover the A to Zs of some of the most prevalent repair jobs, with the seventh episode demystifying derailleur limits and cable tension.
Contrary to what it sometimes seems like, your derailleur is not controlled by a mix of witchcraft and luck, but rather by cable tension and limit screw settings. Those two things are independent of one another, but they also both need to be adjusted correctly in order for your shifting to work properly. Below, Calvin Jones explains how limit screws and cable tension affect your shifting, as well as how and when to adjust them.Tech Talks - Derailleur Limits and Cable Tension
Need more Calvin in your life? Episode #1 - Tubeless tire installation and conversion Episode #2 - Saving that bent disc rotorEpisode #3 - Derailleur hanger alignmentEpisode #4 - Shimano and Crankbrothers pedal serviceEpisode #5 - Trailside wheel repairEpisode #6 - Trailside chain repair
Stay tuned for more mechanical how-to videos with Calvin returning on the last Thursday of every month to show you the easiest way to get the job done. Want to know more? Park Tool's how-to section
has you and your bike covered. www.parktool.com
Corrosion on cables or deteriorated housing can cause poor shifting and are common issues. Especially for bikes that don't have a full run of housing from shifter to derailleur. Even if the exposed cable doesn't have rust/corrosion, inside the housing could be different.
Also check for proper routing, kinks, breaks or if the housing is too short.
A little lube down the cable housing when replacing a cable goes a long way for smooth shifting.
To your point, in the hands of the competent individual with the experience to dictate actions, lube can be the answer. For a lot of stuff...
On bikes that have exposed cable with too much friction, I always take the housing out of the housing stops and drop a few drops down the housing and slide it up and down the cable. It cleans out any dust from corrosion. If there's a lot, use WD-40 carefully to clean out the housing and then lube it after. You can take some sand paper and lightly sand down any rust off of the cables as well.
Keep in mind there are some cables that you shouldn't put lube on. Shimano has a few cables that have PTFE coatings that act as lubrication. They recommend as soon as the coating wheres off or enough of it has strung out and bunched up, to replace it. (if you haven't seen these cables, it looks stringy when the coating starts coming off. It can bunch up when it enters the housing)
Side note: I get customer needing to keep costs low, but when I see any rust on the cable I usually suggest it's mandatory or else I can't guarantee how long the "fixed" cable will last. Of all the things on the bike, the small dollars spent on a new cable/housing can get you the best return on performance, especially when there's rust involved.
Mech hangers can go to hell, but yes, they're the first thing to check when your gears are dodgy.
The issue you'll have is since you've adjusted the b-tension so the derailleur won't contact that largest cassette cog, It now puts the derailleur further away from the smaller cogs.
This may not be an issue but depending on the wear and age of your drivetrain, It can make adjusting your gears more finicky. It may also make your drivetrain go out of adjustment more often as well. Another issue you may have, since the screw is dialled most of the way in, the B-tension screw may slide off of the derailleur hanger(or what the screw contacts) that it's supposed to push against.
The new derailleurs that have the appropriate range, climb the cassette at a different angle than previous gen so it can be as close as possible without contacting the largest cogs.
The issue with using a longer B-tension screw is that it still puts the derailleur too far from the smaller cogs. If you're going through rough terrain, you may jump gears. It's not as bad as what i'm explaining though. Many people have modified their cassettes using one-up conversions and I've actually tuned a bike that had an oval chainring with a one-up conversion in his cassette. It worked perfectly fine after I adjusted it. I'm a bike technician and have taken shimanos s-tec courses. I think you'll be fine.
That's why shimano makes GS and SGS cage options. GS is a medium cage capable of doing 1x and most 2x options and SGS is for 3x.
The suspension curve only affects chain length. The jockey wheel placement barely moves in relation to the wheel through suspension travel. The pivot between the axle of the rear wheel and where the derailleur attaches to is too small for a suspension curve to affect it.
Even if it did affect it, it still would have the same space between the cassette and jockey wheel as it would when the travel is neutral because the cassette is a circle and the derailleur would pivot around the wheels rear axle since it's in a fixed position.
Hope that makes sense lol.