An oval chainring next to a normal one.

How to find the right chainring size

Theresia 26. June 2017

Finding the right chainring size can be hard. Read the following blog post and see how our two World Cup riders do it.

It took a long time for my brother and me to find the right chainring size. I usually ride a 34 tooth ring on my Eagle drivetrain and when things get steep I switch to a 32 tooth. Robert on the other hand rides a 38 tooth every time. We are both very different riders with different needs. What type of rider are you? What factors are most important when you are choosing a chainring? Read on to get some answers.

Robert’s Scott Spark with a 38t chainring

Robert’s Scott Spark with a 38t chainring

How do you decide?

1. What trails do you ride?

First things first, what type of terrain do you ride? Do you crank up long climbs or go on longer tours with a lot of altitude gain? Then a smaller chainring is definitely what you need. However, if you ride in mostly flat areas with short and steep climbs, I would recommend a larger chainring. 

Theresia killing it uphill.

Theresia killing it uphill.

2. What kind of ratio are you riding?

When it comes to getting up hills and bombing down them, you need to know how many teeth the upper and lower sprockets of you cassette has. The table below shows you the difference in ratios between various cassettes on different sized chainrings. The lower the number the easier it is to turn the cranks. For the upper sprocket, this can mean getting up the hill easier and on the lower sprocket spinning out when riding downhill. A lot of times this decision is a compromise, so it is important to have your terrain in mind.

50t (Sram Eagle) 46t (Sram, Shimano, e*thirteen) 42t (Sram, Shimano) 10t (all) 9t (e*thirteen)
28t 0.56 0.61 0.67 2.80 3.11
30t 0.60 0.65 0.71 3.00 3.34
32t 0.64 0.70 0.76 3.20 3.56
34t 0.68 0.74 0.81 3.40 3.78
36t 0.72 0.78 0.86 3.60 4.00
38t 0.76 0.83 0.91 3.80 4.23

2.1. How does the ratio change with a larger chainring?

The table below shows how the ratios change on an Eagle cassette depending on the chainring size. Here, the larger the chainring the larger the gear jumps. This can lead to your cadence being disrupted when you can’t find the ‘right’ ratio on you cassette.

50 36 28 21 16 12
36t 0.72 1.00 1.29 1.71 2.25 3.00
32t 0.64 0.89 1.14 1.52 2.00 2.67
28t 0.56 0.78 1.00 1.34 1.75 2.34
Grinding away.

Grinding away.

3. What type of cadence do you hold? Lance Armstrong or Jan Ulrich?

Here it is important to know if you prefer to keep up a high or low cadence. Or another way to put it: do you keep your legs spinning like Lance or do you crank out the gears like Jan? If you are more the Lance type, then a smaller chainring will get you spinning the cranks like you want. But if you like pushing the big gears like Jan, go for a larger chainring.

Robert taking on an uphill in Nové Mesto

Robert taking on an uphill in Nové Mesto

What is your fitness level?

Of course, your fitness level is an important factor when it comes to chainring choice. If you don’t ride that often, but still ride in mountains / hilly terrain, I would recommend riding a smaller chainring. This keeps you pushing the same cadence as you switch gears to head up the mountain. For a long time, I thought I could ride a 34 tooth chainring on every type of trail. When I decided to test out a smaller ring, I found that I was saving tons of energy riding uphill sections because my cadence remained the same. If your have the feeling that you don’t have enough gears halfway up the mountain, you should also switch to a smaller chainring. However, when you are riding downhill and you cadence increases to out of control, you might want to consider looking into a larger chainring.

An oval chainring next to a normal one.

An oval chainring next to a normal one.

What is with oval chainrings?

Robert and I used to ride oval rings. We notice a huge difference compared to round ones. An oval 32 tooth chainring feels very different because the cadence is no longer round. When I was riding a 32 t oval ring, I thought I was on a 34 t. This is due to the amount of power you need to push over the longer section of the ring. As soon as there is an oval SRAM Eagle chainring on the market, we are definitely going to give it a try. Just make sure not to switch to oval before a race or longer tour. It is important to get used to them first because of how they affect your cadence.

Robert’s Scott Spark with a 38t chainring

Robert’s Scott Spark with a 38t chainring

Final Thoughts

Choosing a chainring can be difficult. The best way is to try out different sizes until you find the right one for you. Knowing your cadence preference, terrain and ratio will help you make that decision before you buy, however. Don’t forget about your fitness level either and riding a smaller ring is never a bad thing. Keep in mind what you can do and stick to it!

Related articles

Blog comments are published with first name and first letter of surname.
Blog comments are published with first name and first letter of surname.
  • Dragos B. 17. September 2019

    Hi guys, great article, really useful,I will also add the importance of knowing your gear range and how to, in my opinion this makes a huge difference, i.e I use Sram PG1130 / 11-42 T that give me a gear range of 382% therefor a smaller chainring like 30t is more suitable than an 38t that will go great on an SRAM Eagle 10–50 with a gear ratio of 500%, Spec sheets usually mention the largest and the smallest cog of your cassette, where the smallest cog in a 11-42 cassette has 11 teeth and the largest has 42 teeth. You work out the gear range of the cassette by dividing the biggest cog by the smallest, so 42/11 = 3.81 = 382%. One thing I still struggle to understand is the actual chain length, how will this impact wile changing the chainring and/or cassette, if I change my chainring from 30t to 34t, do I need to change the chain as well ?

    Thanks,
    Dragos

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
  • lalit t. 14. August 2019

    i have a scott scale 765 having 1x setup as below.

    it has sram nx1 gxp pf 32t Chain set and Sram PG1130 / 11-42 T cassette.

    During my rides which is 60 % city roads and 40 % off roads, i found that i am using 11th and 10th gear more and the 9th and lower gears are too free/easy to match my pedalling.

    I wish to increase my top speeds and at same time wish that the 9th,8th,7th gear also match up with my pedalling power ,so which chainring should i change from existing 32t ?

    Also if I opt for 36t oval ring, will it give benefits of both?

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • bike-components 26. August 2019

      Hello Lalit,
      I would recommend to enter all your data into a ratio-calculator.That way you can compare all of the ratios. It could be possible that a 34 teeth option is more helpful than only to increase the top speed with a 36 teeth option.
      An oval ring will not have an influence on the ratio. But the way you rotate feels smoother and your muscles can work more efficient and you can partially compensate the dead center of the crankset while rotating.
      best regards, Christopher

  • Romans K. 12. May 2019

    Hi I found this discussion. and wanted to ask. I want to switch sram 11-42 30t to 11-42 38t due to lack of speed. just I dont know will it fit my frame and will 38t will be enough. I ride mostly flat roads. how can you tell?
    My frame(L size) and set up:
    https://www.hargrovescycles.co.uk/scott-scale-935-2018-mountain-bike.html

    thank you.

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Marcel 15. May 2019

      Hi Romans,
      according to the Scott manual, a 38 tooth chainring is actually the max chainring size that you can run on your Scott Scale 935. So you are good to go.
      Feel free to double check:
      https://s3.amazonaws.com/assets.scott-sports.com/manuals/2018/bike/bikes/2018_Scale_EN_web.pdf
      Regards, Marcel

  • Adrian C. 25. November 2018

    IMHO, all your article does is argue for the case of keeping triple cranks. No one is going to carry different cranks and spend 15 min on the road side changing them if you do, well that's why they have double and triple cranks.

    For me, I have Sora r3000 and as your article says, being unfit makes a difference, and I want either lower granny crank or larger rear cassette.

    On both aspects, Shimano has limited me. I have bought a 9 speed Deore from this site, and intend to get a 11-40t 9 speed. I tried mountains last month touring, and was breathing hard on 30front/34 rear, which was the lowest.

    Thanks for a nice article.

    Adrian

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Robin 6. December 2018

      Hello Adrian, it seems as if you would be talking about a touring / road bike equipped with SORA. Theresia's Blog post is about finding the right chainring size for your one-by equipped mountainbike. In order to find the right gearing for you, I would advise you to contact my colleagues of our customer Support via info@bike-components.de or just give them a call via 02405-450045.
      Regards, Robin

  • Morgan O. 23. October 2018

    Nice article :) novice here and I could use some advice please! I've acquired a new cassette and chain for my ht and have decided I might aswell get new chainrings at the same time. I'm currently running a standard 3x9 setup, but I'm thinking I could save money and weight by getting 2 instead of 3. Problems I can think of: not enough range, I don't do a lot of massive climbing and was thinking that some rings which are in the middle of the standard range for 3x9 might be okay?
    Having 3 positions to switch to, would the middle ghost gear just effectively help the transition so long as I move the limit screw things?

    Hope it's not too silly a proposal or question, just can't seem to find an answer on Google!
    Cheers

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Robin 9. November 2018

      Hi Morgan, in this case I would go for 36-26. It could be possible to use your 3speed-front derailleur, but this requires a very detailed setup of the limit screws. In the end I would advise you to completely change to a 2-by or 1-by Setup in order to get the most efficient drivetrain. Cheers, Robin

  • Neil H. 12. October 2018

    Hi i currently run sram 1x11 & i find i run out of gears going down hill
    I'm about to switch over to sram 1x12 Eagle & thinking about changing the front ring to a 36T i ride mixed terrain do you think this is the right set up ?
    good article by the way.

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Robin 16. October 2018

      Hey Neil,

      in this case I would suggest to get a bigger front chainring as you already mentioned. For mixed Terrain, a36t is perfect in combination with the widespread EAGLE-Cassette. Regards, Robin

  • Norman B. 24. September 2018

    Thanks very helpful as I am currently looking at the Sram force 1x and can't make up my mind whats the best front chainring. It comes with a standard 40T but will I be better dropping to a 38T, with an 11-42. I ride mostly in hilly terrain.

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Robin 28. September 2018

      Hi Norman, thank you for your Feedback. The choice is very individual. I run a one by-setup with 40-42 as the lowest gear as well and it isabsolutely enough - even for longer climbs on gravel or loose surfaces. I would suggest to try out the 40t - you can always go lower if you'll need it. Regards, Robin

  • Brook T. 1. September 2018

    Thank you. Good article. yes, I am going to a smaller chain ring because I like to go up steep single tracks and I am 65 years old and not as strong as I use to be . I think I will go from a 32T to a 28T for my 1 by 12 (10-50). I bet I won't have to walk my bike up hill as much!

    Blog comments are published with first name and first letter of surname.
    Blog comments are published with first name and first letter of surname.
    • Robin 4. September 2018

      Hey Brook, thank you very much for your Feedback! I am sure you have the right gearing for your style of riding once you make the Switch.Enjoy riding! Regards, Robin