So you want a larger or maybe smaller sized chainring? This article is best suited for those looking to change their current chainring to something smaller to help get you up those rather steep hills easier. I am looking for a smaller chainring for my gravel bike to climb tough hills without getting off the bike. I go into detail about what you need to know to fully understand the differences in chainring sizes and hopefully inform you so you can go out and make a decision based on what you current bike setup requires.
Can I Change Chainring Size?
Yes yeah can but you cannot just change your current chainring for something that does not work with your current setup. Meaning the new chainring you get for your bike needs to works with your current chainset. Your cranks will have a specific bolt layout or fitment spec. As your chainring wears down from use over time, you will eventually need to replace your chainring as the teeth show signs of heavy use.
Things to consider when changing chainrings. You need to make sure if you are running a 1×11 speed for example, to get the same chainring to match. But you need to make sure that the new chainring you get has the same number of chainring bolts as your previous one. For example 4 bolt chainrings can only be replaced by 4 bolt chainrings. Also it is important to make sure that the BCD (Bolt Circle Diameter) is the same for both chainrings. Also if you have a front dérailleur this may require adjustment to move up or down depending on the chainring size. But how do you come to the conclusion for what chainring size?
How Do I Choose Chainring Size?
When it comes choosing a chainring size. Now it is rather challenging for us to be able to tell you exactly what chainring size and gear ratio will work best for you. But we will try our best to help describe to you how these chainring rings variations impact your ride.
This type of riding results in different terrain and impact on overall riding. For example are you bike touring with 4 fully loaded panniers weighing your bike down and you plan to ride steep climbs, with a lot of altitude gain? You will need a variety of options and something that can give you a rather low granny gear to get that heavy bike up the hills. Figuring what type of trails you plan to ride for MTB and gravel bikes is important. Same goes if you are riding up long climbs. You will be better off with a smaller chainring. But if you are road cycling and riding in mostly flat areas with short and steep climbs, it is recommend that a larger chainring is best.
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It is also worth noting what type of cadence you prefer to ride? Is your preferred cadence high or low? Do you like spinning your legs in faster rotation or more of a slower and harder push? If you like spinning quick then smaller chainring will get you spinning the cranks like you want. But if you like pushing the big gears, go for a larger chainring.
Also consider your fitness level when combined with the terrain. For example, I rode my Kins Sutra LTD that comes stock with a RaceFace Aeffect 36t crankset. And when I rode the Victoria Divide over MT Buller. I really struggled at times when climbing the steep sections with my bikepacking gear. The 36 teeth was too large a chainring for the ride when combined with my fitness. I like to consider myself very fit but maybe the chainring just is to big. And this is partly way I am writing this article so I can figure out with chainring size I should next get for my Sutra. So maybe a chainring size like 34 or even 32 tooth might be what I get for my bike. But more on that later.
Also you want to consider your bikes current cassette numbers and figure out what ratio is ideal for your type of riding. This is the comparison between front chainring and a given rear cog. For example a lower gear for a gravel bike should fall in the range of 1:1. This means something like a (42:42, 34:34, etc.). If you go much lower, traction and balance can become issues. This also brings up the importance of figuring out what your gear range is. You work out the gear range of the cassette by dividing the biggest cog by the smallest of the rear cassette. Using my bike as an example it has a 10 tooth smallest cog and 42 biggest cog, so 42/10 = 4.2= 420%
Furthermore once you understand this you can get the gearing ratio by dividing the teeth of the chainring with the teeth of the cog on the cassette. So back to my bike again (42/10 cassette numbers) lets say I take its current lowest cog number (42t). And a divide the current chainring size to the lowest cog. The lowest gear has a ratio of 36/42 = 0.857. And you can calculate the highest gear ratio is 36/10 = 3.600.
So if I wanted to achieve a similar climbing ratio to something like the Kona Unit X (Mountain/Crosscountry bike) which someone I know has and is able to climb the same very steep hills with ease. I would have to change to a smaller chainring and using out gearing ratio conversions when can more easily compare and find out what chainring would work best for achieving our goal. So the Unit X has a lowest gear ratio of 32/50 = 0.640 (0.857 Sutra) and highest gear of 2.909 (3.600 Sutra). So as you can see in out example the Sutra at stock has more gearing to ride down hill while the Unit X would spin out more on road. But the Unit takes the cake with a lower number then the Sutra for climbing easier up steep hills and this is where we want to get for the Sutra. So if we were to get a 28t chainring on the Sutra this would result in a 0.667 lower gear ratio and a 2.800 highest gear. Which is fairly close to the Unit x for climbing. But my only concern with this small a chainring is the spinning out that I can see happening on steep road downhills. So I might want again to go for something around a 30, 32 to 34 tooth. But you can see if you play around with these numbers you can find an ideal range for you. It is a good idea to compare to other bikes and how well the perform for the type of climbing you have in mind.
What Is The Best Chainring Size?
Again the best chainring size really depends on what trails and terrain you plan to ride and what type of bike your have. We cannot promise an ideal chainring size as everyone is different. But we are going to give you examples for each type of bike. As we discovered the chainring size is not the end all be all. You need to convert the numbers and figure out the gear ratio so you are comparing oranges with oranges.
Also wheel size does depend on what effect this has on your overall bike performance and gear ratios too. If you want to play around with some numbers and potential crank sizes to see what potential km/h you can expect for each gear. I suggest taking a look at this bike gears calculator.
So the question makes more sense if we ask what is the best gear ratio for climbing for example. And the more I research it seems people are saying something like 0.610 is around the ideal ratio. But again it depends on your wheel size and grade of climbs. In general it seems this number is best. So back to my bike for example if I want to achieve this ratio or close to it I would need the 28t chainring to get a 0.667 ratio for climbing.
This article is outside of the realm of talking about touring bike gearing and all that. As I was just trying to focus primarily on 1x chainrings. But maybe we will leave that for another blog post.
How Does Chainring Size Affect Speed?
How does this effect speed? If I was to get say a 28t chainring it will definitely effect my down hill speed. But it will increase my efficiency and ultimately my speed and ability to climb better, especially on the really steep stuff (not walking). So put simply the larger the ring the more pushing required which results in a faster speed when the rotations are maintained. The smaller the faster you will spin resulting in a slower speed.
Chainring Teeth Difference
This change in chainring teeth results in the differences in speed. The number of teeth in the chainring determines the output you create in moving the bike forward while you pedal. For example, a 28t chainring will feel lighter and have less resistance when pedalling while a 36t chainring will feel harder to pedal against and have a strong resistance when pedalling. Especially on the climbs. The result however is that you will travel farther, and faster, per pedal with the 36t chainring vs the 28t. But obviously requiring a larger effort to spin the larger size chainring.
Oval Chainrings Vs Round
So where do oval chain rings fit into this? Well we wrote a article all about them. But it is stated that oval chainrings, provide greater pedalling efficiency. In theory when it comes to saving your limited power output and instead based on product design allowing you to make the most of your energy to pedal more efficiently. While also you get a smoother delivery of power or torque to the rear wheel. A round chainring results in a uneven pedal stroke which means your cadence becomes jerky and irregular. Surprisingly a oval chainring smooths this out. Which also increases you overall traction thanks to the the increased torque.
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