Low gearing on a road bike - Part 1/3: "Finding the best solution"

A standard road bike used to be equipped with a 2-chainring crankset: 53 or 52-teeth large ring and a 39-teeth small one. Within the last few years (roughly since 2006) we witnessed the (re-)introduction of a "compact" version with 50T/34T chainrings. I believe that many cyclists welcomed this option wholeheartedly, as the usability of the large 53T ring was somewhat questionable. Not everyone can be Lance Armstrong to spin that huge 53T chainring on local roads effectively.

Still, sometimes even the 50T/34T combination can be very limiting, especially that the largest rear cog available in a standard road cassette is only 30T (Shimano) or 32T (SRAM). This means, steep hills remain a challenge for weaker riders that are left on the road without a truly low (<1:1 ratio) gearing. Actually, achieving such a low gearing on a road bike is not that hard at all, but the tricky part is to do it with integrated shifters (such as Shimano STI). If we don't mind giving up on our indexed STI shifters, the best option seems to be to build a road bike with mountain bike components, as these come with smaller chainrings and larger cassette sprockets.

Or is it?

I am running a typical cyclocross crankset on my road/cross/touring bike. It has a 46T/38T chainrings, which combined with a 12-30T, 10-speed cassette gives me a decent range of gear ratios. Yet, in some situations, I wish I had even lower gears available. Unfortunately, the cranks (a standard road type) have the BCD (bolt circle diameter) of 130mm and the smallest chainring I can install on these cranks is 38T. In order to increase the gear ratio, I would have to install compact cranks, with a 110mm BCD. However, the smallest chainring available for such cranks is only 34T and combined with a 30T rear sprocket, it is not the sub-1:1 ratio I would be looking for. What options do I have then?

1. Use compact cranks. Change the cassette.

This seems to be a decent solution, especially that compact road cranksets are readily available and SRAM makes large-sprocket, Shimano-compatible cassettes with 32T and even 36T cogs. The problem is the rear derailleur capacity. Road derailleurs are not designed to work with sprockets larger than 28-30T. Recently, SRAM introduced the new WiFli road derailleurs that can now handle a 32T sprocket, which means that a 12-32T cassette may work with a standard derailleur in some circumstances, but choosing a 12-36T cassette means that the derailleur will have to be replaced with a long-cage MTB model. Unfortunately, these are rarely compatible with road group components. One known to work with 10-speed road cassettes and STI shifters is the Shimano Deore RD-M592 9-speed (!). Other options exist as well.

RD-M592 rear derailleur - 9 speed but works with 10 speed STI shifters. (Source: shimano.com)

 

There is a fundamental problem with this solution, though. Instead of just decreasing the chainring size, which could reduce the crankset weight as well, we have to increase the weight of the bike's rear end by using a huge (and heavy) cassette with the huge 36T sprocket. Also, there is no way of lowering the gear ratio past 0.94 with a 34+36T setup (a 34T chainring for compact cranks and a 36T sprocket in the cassette). To do it, the entire crankset would have to be replaced as well. That's why it clearly looks like an all-wrong, dead-end solution.

2. Keep the same cassette. Change the crankset.

This would be the best option of them all. The goal is to use a smaller than a 34T chainring and relatively large cassette sprockets. Theoretically, by reducing chainring size, we can not only lower gear ratios but also decrease the weight of the bike. We don't necessary have to change the rear derailleur for a one with a longer cage (although this depends on the final chainring selection) nor STI shifters. This means we need a crankset with a BCD smaller than 110mm, designed for road bikes. And this is the problem, as very few of such cranks exist. There is a bunch of retro-looking cranksets for square taper bottom brackets, but if you would like to use modern cranks with outboard bearing cups, your selection is very limited. The notable example is Sugino OX801D, which comes with 110/74mm BCD for a wide range of chainring combinations, down to 24T. Unfortunately, it costs $500 and it's availability is limited anywhere outside of Japan.

Sugino OX801D - one of its kind?

Alternatively, a triple crankset could be used, set up as a double, with the largest chainring installed in the place of the middle one. I am not sure how smoothly such contraption would shift, but theoretically, it is possible to achieve a 0.75 gear ratio with a smallest 24T chainring in the front and a 32T sprocket in the cassette. There are some issues with this solution. Front road derailleurs are designed to work with a 16T difference between chainrings so this setup may work if we stay with e.g. 46/30T or 44/28T rings. Such combination looks potentially promising as it allows for a 1:1 or even lower gear ratio. The q-factor (width between cranks) may suffer a little but it should be still smaller than when using mountain bike components.

I will discuss this option more in part 2. Stay tuned.

3. Settle for the middle. A compromise.

The third option is to settle for something simpler - a compact crankset with a 34T chainring and the largest cassette a road derailleur can handle. This would probably be a 12-32T cassette with a medium-cage derailleur. It may be a stretch on some frames, especially those with a shorter derailleur hanger. Obviously, this way we won't have the 1:1 ratio, but it will be close. The winners are bicycles set up with all-SRAM components, as they can take advantage of WiFli derailleurs and shifters.

This finally brings me to the point of this post - we desperately need manufacturers to follow Sugino's example and introduce more modern road cranksets with smaller BCDs. Sure, a 34T chainring is nice, but a 28T or even 26T is nicer.