I’ve recently had a new Dolan GXC gravel bike and I plummed for the di2 12-speed wireless gears which comes with a 10-51 cassette on the rear. It’s like riding with a plate on the back wheel. It’s huge.
Now that’s fine, I’ve been a long-time strong advocate for lower gears vs higher gears for us average joe’s and I’ve often said the industry got it wrong with 50-34 compact chainrings for years. I was shown the light over 10 years ago by a friend who built a custom 1x di2 rig to race on with a 46T chainring. He was way ahead of his time. It intrigued me enough to look into it and hey presto! ever since I’ve regularly swapped my big rings out for lower citing the greater need for lower gears
The 51 tooth cog on my cassette got me thinking. How low is it to what I currently ride and will I need it? My lowest gear at the moment is 30×34 which sits on my original 2x Dolan GXC and I have to say 1. that is already very low and 2. I don’t think there has been anything I couldn’t get up on it in terms of steepness. Only slippy or technical trails have prevented me climbing, not being over-geared.
So lets dig into the numbers.
Using a basic gear calculation, 30×34 gives me 0.88 revolutions of the wheel per pedal rev or a 0.88 gear. Anything, below 0.9 is a very low gear in my book
FYI, to work out gear ratios, simply divide your chainring teeth with your sprocket teeth. 30 divided by 34 = 0.88
For my 51 tooth cog, I’m running a 40T front chainring, so 40 divided by 51 = 0.78. That’s not a massive difference in number but a big difference in how the low the gear will feel.
For comparison, to get near my original 30×34 gear on a 40T chainring, the rear cog would have to be between 45 & 46
My gut instinct is the 51 will definitely be too small and will be redundant most of the time but I will ride it on some steep inclines first before I change anything.
So my options are:
- Do nothing, suck it up and stop moaning
- Change the cassette to a 10-45T
- Change the chainring to a 42T or 44T
I’m also a fan of oval chainrings so I think for me, when I’ve spent sometime riding the bike and tested the low gears. If I decide it is too low, an oval Stone 42T or 44T chainring is probably what I’ll go for ( I have a 38T on my Dolan GXA)….and so you know for reference 42×51 is 0.82 and 44×51 is 0.86, both still tiny but will eat up some of the low gear redundancy
Adios
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As much as x1 are the current trend, lighter and less to go wrong etc etc, it was a leap of faith for me when I ordered my Dolan gravel bike. So in the end I went for the 2x Di2, 31/48 with a 11/36 cassette.
But then by the time you add about 13kg of camping equipment I suspected that even that gearing might not be low enough. I did originally think about swapping out the chain set for a 30/46, but the rewards for a lower gear simply was not worth the expense, plus I would lose out more on the top end.
So to cover all bases, I’ve just purchased a 11/45 cassette from Ali Express and I have to say it works a absolute dream, just a minor adjustment on the B screw that’s all.
In fairness, it will only get used when fully loaded, and if I cannot get up on that gearing, well then I’m just happy to walk!