How Do Oval and Round Chainrings Impact Motion?

Hello This is Saita from LEOMO. In this article, I would like to take a look at the changes which occur in LEOMO Motion Performance Indicators (MPIs) when a cyclist switches from a round chainring to an oval chainring. In addition, we’ll review the changes which take place in MPIs as a cyclist gets used to riding an oval chainring..

I have noticed that there are a lot cyclists who are interested in oval chainrings, including some who are riding at the ProTour level.

Based on my experience, I imagine that many cyclists who made the switch to oval chainrings may have found the experience of riding oval chainrings odd right after making the change. Some of those individuals, unable to get used to the odd sensations, likely changed back to round chainrings as a result. Conversely, I know that there are cyclists who now feel that oval chainrings are all they can ride with!

One of the MPIs which reflects these new pedaling sensations is DSS, or Dead Spot Score. Let’s take a look at the changes which occurred in DSS in conjunction with PSI using a cyclist who made the switch from a round gear to an O’symetric oval gear on August 21st, 2017 as an example.

First, let’s look at how DSS changed over the long term:

Figure 1: Chronological Change in Magnitude of DSS by Power Range

Immediately after making the switch to oval chainrings, DSS is shown to be increasing . Over time, we clearly see that DSS becomes smaller and smaller as the cyclist continues to use the oval chainring.

Next, let’s narrow down our filter and look into the DSS・PSI seen during training on an almost identical course (approx. 170km) including both flat sections and ascents.

Figure 2: DSS and Ant+ Data for a Long Ride

We can see that the cyclist’s DSS increased immediately after changing from a round chainring to an oval (8/23), and DSS continually decreased afterwards on 9/6 and 10/11 (Figure 1).

Figure 3: PSI on a Long Ride by Cadence (81–100rpm / 61–80rpm)

Let’s take a look at PSI by cadence on the same long ride (Figure 2).

With a round chainring at a cadence of 81–100 rpm, DSS occurred between the 11 and 1 o’clock positions and slightly at the 6 o’clock position on the left. The right leg saw this occur between the 10 and 12 o’clock positions and 4:30 and 6 o’clock positions. We don’t see a particularly large change in the DSS of the left leg with the oval gear, but this phenomenon is now mostly gathered around the lower dead spot (around the 6 o’clock position) for the right leg.

Looking at a cadence of 61–80 rpm, the DSS was occurring between the 6 and 8 o’clock positions for both left and right legs when using the round chainring at lower cadences (61–70 rpm). With the addition of the oval chainring, DSS was now occurring between the 10 and 12 o’clock positions on 8/23. We can also see that the DSS of the right leg in particular decreased as the cyclist adapted to the oval chainring.

Lastly, let’s look at an example of a 5-minute VO2 Max race.

Figure 4: DSS and Ant+ Data for 5-Minute VO2 Max Races
Figure 5: PSI and PCD for 5-Minute VO2 Max Races

There was an increase in DSS during 5-minute intervals when using an oval chainring (9/7) as compared to a round chainring (5/24) (Figure 3). The range of the position where DSS occurs is larger for the oval chainring, and the frequency of occurrence is higher as well (Figure 4).

As can be seen above, the position and frequency of occurrence, as well as the magnitude, of DSS varies between round gears and oval gears. We can also say that DSS characteristics undergo changes as the body adapts to the use of an oval gear. For all those who may be considering a switch to an oval chainring, or who have tried using one in the past but gave up on it, I would suggest using the data outlined in this article as a reference for the long term effects of the switch and giving an oval gear a try.

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