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triple to double

Chris Roan2020-11-18 18:38:19

As our tandem is away for a respray we are wondering about refreshing the current gearing.  Currently running 30 speed 105 with a triple chainset and considering changing to 22 speed Ultegra with a double chainset.  Views appreciated especially regarding gap between gear changes. For info tandem is an Orbit Spirit which if anyone is considering one we have been extremely pleased with it and with the help and guidance provided by JD Tandems.

Chris

Martyn Aldis2020-11-20 12:32:40

I see the Sudden Ramp Trap as a disadvantage of triples on tandems and we do get caught now and again when a road I don't know suddenly steepens at a corner or turn, going from sensible climb to a ramp, and we can't get the change to the inner ring in time. We do a called two rotation sprint then ease off routine for changes to the little ring but if the change of slope is sudden and steep enough this doesn't always work especially if we have luggage on board.

Unmodified road gearing, double or triple, does not give us the low gears we need. For our 2009 Cannondale RT2 which came with 10 speed road triple 52,42,30 rings and 12-27 cassette, I replaced the 30 with 26 teeth and put on a 12-30 Ultegra cassette. This keeps reasonably close spacing in the higher gears which can be good on gentle profiles and when working into a head wind and gives us 23.5 to 117 gear inches which is OK for day rides. Putting a smaller inner ring onto a 130 or 135mm BCD road chanset can cause problems with the chain getting inside the spider of the outer rings but it has been OK with our FSA chainset.

Our 26" wheel tandems have 9 speed 11-32 cassettes with smaller BCD chainsets as used on mountain bikes and tourers. These allow a wide range of reliable gears with a lowest gear below 20 gear inches and the gear steps aren't so wide as to be annoying very often.

I can see that in theory at least, the newer very wide 11 speed cassettes used for todays MTB and gravel bikes, largest sprocket 40+ teeth, could make a double chainring arrangement attractive if combined with a typical compact chainset ring sizes. 50,34 rings and 11-42 would gives 22 to 122 ger inches, bigger but probably not perceptibly bigger range than our modified triple on the Cannondale with steps similar to 9 speed 11 - 32. The big benefit would be no Sudden Ramp Trap. If I was to build up a fairly light weight tandem from scratch, I would certainly give this a try.

If your team strength and chosen routes mean you never use gears under 29 gear inches a road double could be the way to go but there don't seem to be many tandem teams in that category at least in the UK.

Matthew Stephens 2020-11-26 13:09:19

Our main tandem is a Landescape 700c 22speed 105 with 50/34 double cranks & 11-32 cassette.

I like this, probably more than our other tandems with triples on, and would recommend it.

The cassette is still relatively close ratio. This is important as I like to find the gear which feels just right for our optimum cadence, rather than a gear just a bit too high or just a bit too low with wider ratio cassettes. 

Another important aspect is that we dont run out of gears when going fast. Well at least when we do find some good hills to descend! On 26" Cannondale with 53/39/30 & 11-25 cassette, we 'spin out' at 32-35mph, but this is partly due to reduced wheel diameter of gatorskins, effectively reducing the gearing. Less of an issue on 700c wheels & standard groupsets.

The 'loss' of the 8 gears, from 30 to 22 is just redundant/ duplicated gears, so not a concern. 

I'd definitely recommend compact or semi compact, but to do such a change is a large financial investment for a marginal improvement. None of the existing 10spd groupset can be used except brakes. Chainset can usually be kept, but you'd have to see if works ok & not if you're after the compact chainset ratios. You would need new; 2x brifters, 2x derailleurs, chain. 9 speed or below & the derailleurs can be used for 8 or 9 speeds as same lever shift ratio in road & mtb groupsets, but 10 & above use different lever pull ratios for different speeds & whether you use road or mountain group sets. Your choice obviously! 

Happy upgrades! 

Tim Dowson2020-11-28 19:22:06

How much life do you get out of a 2 x ll setup? It sounds as though it can function well while in good condition but I could imagine that with the narrower sprockets you would be forever changing the cassette and chain, at least, on a tandem.