This is going to be a controversial post, for only one reason; we all ride at different paces. I need gears you won’t, you’ll want gears I don’t and vice versa. It’s quite simple, really. For newer cyclists, I lump the noob, “years ago”, me in that grouping, it can all be confusing, and that’s what I aim to sift through.
There’s a blog I follow, the author of which thinks the compact chainset is the root of all evil. He’s a passionate fella, let me tell you. He rides a 46/30 set. I, on the other hand, ride the aforementioned compact 50/34 chainset on both of my road bikes and both bikes came with 52 tooth big ring chainsets originally.
Now, we could very easily get lost in the woods here, because there are a lot of combinations – and I’m not even going to cover the 1x setups (with only one chainring – usually for gravel bikes, but they are breaking into road cycling, slowly – I would prefer never riding a 1x on a road bike).
There’s one important factor that drives what we choose for our chainring set: SPEED. I loved my 52/36 setup on my Venge, until I tried an 11-28 cassette on the back. The big jumps in gears in the cassette 21, 24, 28 are all wrong with the 52 tooth chainring if you happen to average between 19 and 22-mph on your fast rides. There’s a cadence hole between 18-1/2 and 22-mph so at speeds in between, you always feel like you’re pushing the wrong gear (too hard or too easy). The remedy is to use an 11-25 tooth cassette. That eliminates the three and four tooth jumps, but also limits your climbing in the little ring. With that 36 tooth little ring, it’s nice to have that 28 tooth last gear. The 36/25 front to back combo is manageable on steep hills but I’ve found myself wishing for another gear on more than one occasion.
Now, I just happen to know top speed pedaling a 52/11 gear selection is around 45-mph, maybe 48 if you really want to crank up the cadence. I used that combo once or twice a year, only going downhill. My max sprint on our fast group ride (on a flat stretch) was around 35-mph with no tailwind – 38 if we had a good push. This meant my 52/36 setup was a little on the big side, but workable.
The compact 50/34 tooth chainring combination I put on the Trek, with that same 11 tooth small cog, is around 40-mph top speed. Also, I’m here to tell you, a 34/28 combination is a whole lot better for steep climbing than the 36/25 I had on my Venge. So my top-end speed better matches my ability, and I can climb anything I’ve ever run into with the 34/28… and the 11-28 cassette works better with the 50/34 chainring combination because the “cadence hole” is at a lower speed. In other, simpler terms, the 50/34 fits my riding style perfectly. So much, I took the 52/36 chainrings off my Venge and swapped them for 50/34.
Going back to my blog friend’s 46/30 setup, he’s almost going to be able to climb up a wall with a 30/32 low gear combination. On the other hand, there’s no chance he’d be able to keep up with our Tuesday B Group, let alone the A Group, or win a sprint. That’s just a little too small (you might get away with a 48 but I’ve got friends who won’t use less than a 52 in the A Group). The key is, it works for him and that’s what’s important. Choosing the right combination of chainrings all about the top-end and low-end speeds you need.
As gravel bikes go, they typically come with smaller chainrings (mine’s a 48/34 combination) or a 1x setup. I could switch to something smaller, but I end up down in that 48/11 pretty often so I don’t think that’d be wise. I’ve got an 11/32 9 speed cassette, too, and that last gear 34/32 is more than enough low-end gear for anything I’ll encounter on that bike. I’m a lot slower on my gravel bike, so the smaller chainrings work. If I were to use my gravel rig as a road bike as well, I’d have to rethink that combination to get a little more top-end out of it.
Finally, a note of caution: We have to be very careful when we go swapping chainrings. Sadly, the front derailleur hanger/bracket can be a little tricky. We have to make sure we’ve got enough room to raise or lower the front derailleur so the cage is 2-3 mm above the chainring teeth. Any more and the front derailleur will shift the chain into the bottom bracket when you shift from the big to little chainring in the two biggest cogs on the cassette. Any less, well, you’ll be grinding chainring teeth with your front derailleur cage… and that simply won’t do. You’ll also, when you get down to those odd combinations (that 46/30 I mentioned above), have to make sure the chainrings work with your groupset. For example, if you’ve got a 53/39 setup, forget about switching chainrings. You’ve likely got a 130 BCD crank and 53/39 is all that works on a 130. You need a 110 BCD crank and the chainrings… and it’ll be likely your front derailleur hanger won’t work, anyway. Point is, do your homework before you go buying parts that won’t fit on your rig. Unless you know a welder who can fix your derailleur hanger to work with anything.