A bit text heavy this week but continue reading if you are interested in drop bars and low gears.
Traditionally touring bikes have run low gear ratios, the reason being that if you are carrying load you want a lower gear to spin up hills and climbs. This has been mainly achieved by mixing mountain bike and road components. Up to 9 speed with a Shimano system the cable pull of a long cage rear mtb derailleur matched STI’s and indexed bar end shifters. This enabled a wide ratio at the rear e.g. 11-32 or 34 coupled with a road front mech and ‘touring’ triple chainset (usually 48/38/28 or 46/36/26) to give you a nice spread of gears.
If you wanted to go super low you could try adding a mountain bike chainset up front although with modern chainsets that use external bearings you would generally have to use a mountain bike front mech in order to push your chain far enough out onto the outer chainring*. This is possible with bar end shifters where the left hand works still on friction and isn’t indexed but drop bar STI levers have a different cable pull so won’t function correctly. You also need to consider the chainline and rear spacing of your frame, a touring frame with a 135mm spaced rear will work, with a 130mm (i.e. road) spaced rear then it is likely there will be chainline issues that affect the shifting.
Enter 10 speed and things start to get more difficult, we’re not there yet but as 10 speed travels down the Shimano ranges then it is going to be harder to either find 9 speed components or get components of sufficient quality. You can still get 8 speed shifters but the STI’s are now ‘no name’ items at the bottom of the pecking order, although the bar end shifters are still pretty good quality. If you are going to be doing lots of miles on a tour day after day, you want quality, not necessarily light weight mind just solid and reliable.
The problem with 10 speed is that Shimano have completely divorced road and mountain bike groupsets, whilst also working heavily on the assumption that you will use a full Shimano groupset throughout rather than picking and choosing brands that might be ‘compatible’ but offer alternative chainring ratios for example. This means you can’t use a 10 speed long cage mtb mech and an 11-34 cassette with a 10 speed road shifter. You can get round this problem if you use a 9 speed mtb derailleur as the distance it travels is the same and it will index, I haven’t seen or heard how this holds up long term though. Alternatively Shimano have increased the capacity for 10 speed medium cage road derailleurs to 11-30 with a triple chainset or 11-32 with a double chainset but this isn’t as low as you can get on a 9 speed system.
10 speed also has issues at the front too, Shimano assumes you will use their road chainsets with their chain rings as part of a groupset of components. So the front derailleurs are generally designed to work with 50 or 53 outer rings and a spread of no more than 20 teeth for a triple. They do work with other ratios that are close but as you lower the gearing you risk problems like the deep back plate of the modern front mechs catching the middle ring.
So if 9 speed components do start to get phased out (no confirmation either way yet) and 10 speed is the future then how do we achieve low gears on a drop handlebar set up? The 2013 Salsa Fargo may hold the answer, Sram. There are two models of full Fargo bike, the more expensive of which features a Sram X7 front derailleur and X9 rear derailleur paired with Sram Apex road shifters. The limitation here is that you can only have a double set up from Sram, but with the ability to run a mtb double at the front and an 11-36 cassette at the rear very low gear ratios are again possible.
Sram’s compatibility between road and mountain bike groupsets coupled with their ‘Wifli’ range in the road spectrum also gives you choice. There are medium cage Apex and Rival derailleurs which will accept 11-32 cassettes although I would have thought they might struggle if you have smaller than the 34t inner chainring they are designed to be used with up front, but then if you want to go lower a Sram mtb rear mech can be used instead.
This is more a theoretical discussion rather than necessarily practical as I sadly don’t have the resources to test everything, but it is based on the bikes/equipment that cross my path both at home and at work.
*My current set up is based on a 9 speed double with a 42/29 mountain bike chainset at the front and a 12-28 rear cassette. As the chainset I’m using is square taper I have reduced the axle length to try to combat any chainline issues, not something you can do with a chainset designed for external bearings. I have got it to work with Tiagra 9 speed STI’s and a Tiagra double front mech although the outer stop is all the way out and there is some slight rubbing when in the highest gear so it isn’t perfect.