Does gearing affect suspension performance?
As 1x drivetrains have become more popular, more and more users are spec’ing 28-tooth and smaller chainrings. But what does that mean for suspension performance? (click to enlarge)
As 1x drivetrains have begun to push the front derailleur to the brink of extinction, we’ve noticed more and more riders running small chainrings, a huge bailout cog, or some combination of the two. Following a number of arguments over post ride beers about how these different setups might affect suspension performance, we decided it was time to ask an expert. Enter Chris Cocalis, front man of Pivot Cycles, who has been building and designing mountain bikes since the late 1980s. Here’s what Cocalis had to say in this exclusive interview with Mtbr.
Mtbr: Do you design suspension dynamics around a specific gearing?
Chris Cocalis: Yes. Gearing is a key part to every suspension design in the market. In the old days (like 2008), we only had a triple ring set up that had either a 34 or 36 middle ring. At that time, we would optimize around the middle ring. In general, as you went to a bigger ring it would have less affect or interaction with the suspension and as you went to a smaller ring it would have a greater effect. On dw-link bikes this worked out great because the smaller chainring generated higher levels of anti-squat at the point when you wanted it (while climbing). On newer designs, we have to look at the range and design more around a smaller ring in general. For instance, back in 2007, we would not have considered that a 30T front ring would be used for pedaling on flats and descents. So if this gearing is run on one of those older bikes, then hard pedaling forces will stiffen up the suspension and generate more anti-squat then we would optimally want. Current models take this into account and we take these smaller gear choices into account from the onset of the design.
Mtbr: So how then does replacing the stock chainring or cassette with something smaller or larger alter performance?
CC: In the case of our dw-link models, going down to a 28-tooth ring has a minor effect. Other designs in the market develop a lot of bob and pedal feedback if a smaller ring is installed versus what the bike was designed for. Going larger is generally not an issue. On the rear, the effect on the suspension from the smallest cog to the largest is generally only a 1-2 percent difference, so this really does not play into the equation. Within the current range of 10-45 (in the case of the One-Up cog), there are no appreciable effects on the suspension related to what gear you are using in the range on rear cassette.
Mtbr: Is there an extreme at either end of the spectrum (smaller or larger) that can negatively affect performance?
CC: We design around the current range of 30T-36T. If something as small as a 26T is installed on the front, a very in-tune rider might be able to notice some pedal feedback and suspension stiffening under hard pedaling efforts on our bikes, but it will be pretty negligible. At the other end of the spectrum, tire clearance vs chainring clearance becomes more of the issue so some of our newer designs are not designed to accept over a 36T front ring. However, if they did put something larger on the bike, then the result would be slightly lower levels of anti-squat on the climbs.
Pivot’s Chris Cocalis (R) with Mtbr founder Francis Cebedo.
Mtbr: We’ve noticed a number of manufacturers are releasing the same model in 1x specific or 2x compatible versions, what kind of challenges does this pose?
CC: Other than designing mounts and clearances to accommodate the range of options, it really does not pose an issue. With a modern Shimano 2X, the front is either going to be 24/34 or 26/36. The big ring falls within our optimal range and the small ring is intended to be used on steep climbs where the increased anti-squat is a benefit. On the 1X, most of our customers appreciate a 30T which kind of splits the difference between the 2X set ups and offers good all around performance across a wide range.
Mtbr: From a suspension perspective, what are advantages or disadvantages of building a 1x specific frame?
CC: The only suspension advantage would be if the gear range that the frame was designed for was really small like designing the frame for a 36T single ring in the case of a downhill bike. However, in most other applications, the designer needs to expect that anything from a 26T-36/38T could be used on the frame so you are still working around averages that are similar to the range used in 2X systems.
Mtbr: Clutch rear derailleurs are a nearly universal feature on high end mountain bikes. Do you have to take the damping forces these derailleurs exert on chain extension into consideration when designing suspension? And do you feel that has any impact on performance?
CC: Clutch derailleurs do have an impact on the damping forces. When they first came out, there were a lot of designs where this had a major effect on the bikes performance.
However, it is the standard now and shock tuning and in some cases suspension design has adapted to compensate. It’s not something that you can isolate out, and during the time that the clutch rear derailleurs came into play, there was also a lot of new shock development going on, so shock tuning was being developed for the newest models and being tested on bikes that had clutch derailleurs. If the shock is working well on a bike with a clutch, it may not perform as well on a bike without a clutch rear derailleur. However, that’s a non-issue as everything we test has a clutch derailleur.
To learn more about Cocalis and the bikes he designs visit www.pivotcycles.com
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