Hi MBA, I was wondering if the modern clutch style rear derailleurs can affect the performance of some dual suspension bikes. I understand that suspension designs such as the DW Link, VPP and Maestro designs rely on chain tension to create anti-squat. If the tension is increased by the rear derailleur, would this influence suspension performance and under which conditions.
My bike is a VPP design running 1x10 with a 32-tooth front chainring. So I was also wondering if the change to one-by (instead of the 3x10 stock) has resulted in any compromises.
Excellent Questions Mike! With many suspension systems, the length of the chainstays increases as the bike moves through its travel. This can be the case on both the short-link four-bar designs that you’ve referred to (DW Link, VPP, Maestro etc.), as well as single pivot and Horst Link systems.
Depending on the bike, you can expect the chainstay length to increase by around 15 to 30mm on a typical 150mm travel trail bike. In some cases the rate of chainstay lengthening will vary throughout the travel, with this effect being more pronounced in the earlier part of the suspension movement.
The increasing chainstay length is closely tied to the ‘anti-squat’ effect that we often refer to, and suspension designers use it to make the bike feel firmer when you’re pedalling hard and putting lots of torque through the drivetrain.
As the effective chainstay length grows and shrinks with the suspension movement, the rear derailleur compensates for the varying chain length. With a clutch equipped derailleur, the actual spring tension isn’t really tighter but they do have more resistance to movement—it’s as if the derailleur cage has a degree of ‘breakaway force’ limit chain slap.
In theory, this added resistance from the clutch will make the suspension less willing to react to bump forces. However the forces that your suspension is dealing with are quite substantial and will easily overcome the small amount of resistance created by the derailleur clutch—at least that’s my take on it. Do a little test by compressing your suspension with the derailleur clutch on, and then try the same thing with the clutch disengaged or the chain removed. This will give some indication of whether the clutch affects the quality of your suspension.
If you feel the suspension is compromised, you may wish to run a relatively low clutch force on the derailleur (assuming the clutch is adjustable). A lighter clutch setting will also improve shifting performance and give a softer feel at the gear lever. Go too light and you’ll be forever losing your chain, so there’s always a compromise and you’ll need to find a balance that you are happy with.
In regards to your drivetrain set-up, on most bikes the size of the chainring will have a bearing on the amount of suspension anti-squat. A smaller chainring commonly creates more anti-squat and you’ll get less in a bigger chainring.
While some anti-squat is good for pedalling efficiency, you can have too much of a good thing. There’s usually a correlation between anti-squat and the amount of feedback that you get through the drivetrain when pedalling over bumpy ground. Too much anti-squat can compromise traction when climbing. In extreme cases it’ll even make a bike rise up in its travel and ‘pogo’ along the trail.
Ideally you want a chainring size that plays well with your particular bike, matches your ride preferences (some people prefer more active ride with less anti-squat for example) as well as providing a suitable gear range for your trails.
Sometimes a multi-ring drivetrain can play well with the variable anti-squat found on most suspension systems. You’ll get a firmer ride with more anti-squat in the smaller chainrings, and that’s usually good for climbing. Shift to the big ring and you’ll get less pedal kickback and more active suspension for descending.
Obviously this ‘on-the-fly variable anti-squat’ is mostly lost with a one-by drivetrain, but it shouldn’t be too much of an issue if the suspension performance matches your preferences in the single chainring that you choose.
Hope that all makes sense.