I run a single chainring on my time trial bike, and until recently haven't bothered with a front mech or any sort of chain guide. However, since a recent upgrade to SRAM Rival cranks (with a Stages power meter) my chain dropped off the chainring twice during a time trial - when I was changing gear. To cure this, I could have fitted a front mech and all the cabling/lever that goes along with it - allowing me to get the chain back on without stopping.
To actually prevent the chain unshipping however (and to save all that un-necessary weight), I decided to custom-build a chain-stay that attaches to the front mech mounting points and is rigid. The photo shows what it looks like, fashioned from a sheet of 2mm stainless steel - involving lots of tough sawing, filing, hammering and drilling.
To demonstrate just how much the chain can flex when changing gear, here is a slo-mo video. Note that I did this under "no-load" conditions, ie, wheel spinning freely and turning the crank by hand, so it's probably a worst-case of chain flex. It's kind of scary just how much it wobbles left and right during the gear change:
Join the Team Zwatt campaign for a discounted power meter - available single-sided or dual-sided!
I've supported the Team ZWATT campaign on #Indiegogo and will get my affordable power meter soon.
30 April 2017 (Sunday): Duff Morgan / Iceni Velo Road Race
01 May 2017 (Monday): Ixworth Cycle Races
10 May 2017 (Wednesday): CC Breckland 10-mile time trial
14 May 2017 (Sunday): Ken Wright Memorial Road Race
20 May 2017 (Saturday): ECCA 10-mile time trial champs
|Learning basic skills :|
|Getting into shape :|
|Fun snd safe riding with others :|
|Training for races :|
|Not at all :|