by Damon Rinard
Over the years, I have wondered about chain stiffness. Lateral stiffness of course, as any chain's vertical stiffness is virtually nonexistent, and even the most laterally stiff chain will quite easily flex vertically to wrap around even the smallest of cogs. I am talking about the side-to-side flexibility a chain has, not stiff links that bind where they are supposed to pivot.
I measured the lateral stiffness of several chains by placing them on the garage floor with the axes of the pins level with the floor, then bending the chain to form an arc. Naturally, stiffer chains form a larger radius arc, and measuring this radius is one way to determine relative stiffness among chains. The radius is half the diameter. This chain's radius is about 15 inches.
Chain Lateral Stiffness on Multi-speed Bikes
Lateral flexibility of the chain may be a benefit to modern multi-speed bikes, but a certain amount of lateral stiffness is sometimes needed on older derailleur bikes whose jockey pulleys are farther from the cogs. These bikes seem to shift better with a little lateral stiffness in the chain. The greater the distance between the jockey pulley and the cogs, the less precisely the derailleur controls the chain's placement onto the desired cog. In this case excess lateral flexibility in the chain makes shifting even less precise.
I'm not sure if a laterally stiff chain affects front shifting, though I would believe it if Shimano claimed a certain amount of lateral flexibility helped SG-X shifting. In this design the chain engages two chain rings at once over a fairly short circumferential distance, where the chain must bend quite a bit. Maybe a highly flexible chain helps here.
Chain Lateral Stiffness on Fixed Gear Bikes
In my experience, too much lateral chain flexibility can be dangerous on fixed gear bikes, whether they are used on the road or track. On rare occasion a laterally sloppy chain can climb the chain ring's teeth and come off. On a fixed gear bike especially, that can be disastrous! But don't get the wrong idea. While chain stiffness is certainly helpful in preventing accidental derailment, in my experience proper chain line and avoiding a "too loose" chain tension adjustment are more important factors. Nevertheless, it is interesting to see how chains vary in lateral stiffness. Witnessing a rider suddenly spinning and going nowhere in the middle of a bunch sprint is one of the reasons I became interested in the lateral stiffness of chains.
There are many influences on chain derailment: poor chain line, flexible chain, too loose chain tension, bumps that make the chain swing, or burrs on the chain ring teeth. I don't know how important each of these influences are, but on a fixed gear bike, given the choice I'd rather have a little more security with a good chain line, tall cog teeth and ... a stiffer chain.
In the table below,
CHAIN is the make and model of the chain tested.
STIFFNESS (RADIUS) is the radius of the smallest arc formed by the chain, in inches. A larger radius means the chain is stiffer.
BUSHED indicates whether the chain uses bushings or not. It is thought that bushless chains are more flexible than bushed chains.
WIDTH is the nominal width of the chain, sometimes erroneously called pitch.
WEAR is the increase in length due to wear, in percent. I consider 1.0% to be worn out. I am not sure how much wear affects lateral stiffness.
COMMENTS describe any other useful information.
Chains are listed from stiffest to most flexible.
CHAIN STIFFNESS (RADIUS) BUSHED? WIDTH WEAR COMMENTS Regina Record ORO 38 Yes 3/32 new silver with holes in outer links Sedis track 31 Yes 1/8 0.1% black KMC Taiwan BMX 27 Yes 1/8 new silver TAYA TB-700 20 3/32 new middle model: sil outer, blk inner Regina America SL50 19 3/32 0.4% hollow pins DID SuperLanner #2 18 3/32 asymmetrical silver/black KMC "Z" (Z610HX) 18 3/32 new "Specially heat-treated Bull's-eye Riveted pins" TAYA TB-500 17 3/32 new cheap one: blk outer, sil inner Regina America SL50 17 3/32 hollow pins Shimano HG 16 3/32 600 Ultegra 8 speed Dura-Ace CN-7700 16 3/32 0.1% 9 speed Sachs/Sedis PG 15 3/32 0.3% square riveted Shimano IG 14 3/32 0.4% all silver Dura-Ace 14 3/32 0.5% 8 speed "Narrow" Sachs/Sedis PG 14 3/32 0.1% step riveted HKK "Z" 13 Yes 3/32 0.5% silver/black Dura-Ace CN-7700 13 3/32 0.3% 9 speed DID SuperLanner #1 11 3/32 asymmetrical silver/black KMC Super Shuttle 11 3/32 0.5% CN-SS91S
Take a close look at the ranking in the STIFFNESS column. A larger number here means the chain is stiffer. A smaller number means it is more flexible. This is the number with which you want to compare chains.
I have listed two SuperLanner chains; there is no difference that I know of between the two that would explain the different radius measurements. I called them #1 and #2 just because I had two of them.
It is interesting to note that with the exception of the Regina Record Oro, the stiffest chains are the wider 1/8" width.
It is also interesting to note that the three stiffest chains use bushed construction. Of course, the HKK "Z" chain uses bushed construction too, and it is the second most flexible chain, so clearly not every bushed chain is stiffer than every bushless chain.
Also of interest may be a list of chains I've weighed.
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