Popular Question and Answers

Why Oval Chainrings?

To start I think it would be best to dispel some of the myths or misinformation on oval chainrings.

Peddling will feel odd or weird… it would be difficult to tell if you're riding an oval and some have said an oval actually feels more round or more natural.

It will damage a clutched derailleur… It will work the clutch slightly more than a round ring, but this is the motion derailleurs are designed to make and after many years of use it hasn’t shown to make much difference.

There are few upgrades in this price range that will make a noticeable improvement in performance. An oval really begins to stand out when the trail gets technical or if you're pushing the pace. Maybe you're chasing some Strava segments or doing some races or just trying to make that difficult climb. It can be hard to explain exactly how it helps because it's so subtle. You may just feel faster or the ride feels easier, or now you can make that climb that seemed to always hang you up.

In the simplest of terms, most notice an increase in acceleration(spin up faster/easier) and since mountain biking is constantly slowing and accelerating this is very beneficial.

 

Why only 30 and 32 tooth oval chainrings?

  There are a couple reasons for this, first they are simply the most popular size, with the modern 11 or 12 speed systems these two sizes cover a wide range of riders. Usually if someone is looking for a 28 or 34 tooth chainring they are still in the "round" chainring mindset. 

  Let me explain that a little more, obviously with a round chainring the gear ratio stays the same for the full rotation. But our power output as we pedal certainly does  not stay the same during the full rotation. With a round chainring we are trying to find the balance that allows optimal power delivery during low and high output power. Generally this doesn't work out well, and most prioritize either climbing or top speed when deciding on a size. 

  Now with ovals you get the best of both worlds, for example a 30 tooth oval acts more like a 28T during the lower power portion of the rotation(more vertical crank position). But at the high power output portion(more horizontal crank position) it acts more like a 32T. The same goes for the 32T oval, it acts like a 30T and 34T depending on the rotational position. So if a 30T oval covers the range of 28-32 and a 32T covers 30-34, these two sizes should provide the majority of your needs.  

  I do find quite often that riders have too large of a chainring, I can tell this by looking at their cassette. If the smaller cogs are nice and clean with little wear and all the larger cogs show lots of wear its very likely this rider would benefit from a smaller chainring.

  For reference purposes here's the top speed calculations, this is using a 175mm crank arm length at a rotational speed of 90RMP and a 10 tooth rear cog. 

28T -> 36.1kmh

30T -> 38.7kmh

32T -> 41.2kmh

34T -> 43.8kmh 

As you can see there isn't much top end speed difference, and I would think most would feel much better making that tough climb because of the smaller chainring, than squeaking out those couple kmh's on the descend. You can always pedal faster to make up the difference of the smaller chainring, but nothing will help stalling out on that climb because the gear wasn't low enough:)