don't buy it on Wiggle

A 9-tooth cog in a 1X will wear out SUPER quick because of so few teeth and because you HAVE to use it to keep up with riders who can use use a 12 tooth cog. Also, a 9-tooth cog causes a lot more friction with the chain because of excessive angles the chain has to contort to.

I also don't recommend sprinting on a 9-tooth cog, very likely to jump your chain because of so few teeth to handle sprint power.

And nobody has mentioned the elephant yet.
There is about a 7% speed variation tooth to tooth due to chordal action.

Q rings for your cassette but with no consistent alignment with pedal strokes.

A 9-tooth cog in a 1X will wear out SUPER quick because of so few teeth and because you HAVE to use it to keep up with riders who can use use a 12 tooth cog. Also, a 9-tooth cog causes a lot more friction with the chain because of excessive angles the chain has to contort to.

I also don't recommend sprinting on a 9-tooth cog, very likely to jump your chain because of so few teeth to handle sprint power.

So, a sprinter would either not use the 9t cog (maybe keep it in the 10 or 11, depending on the rest of the course and cassette option chosen), or simply stick with 2x whatever, like they do now.

I almost never sprint, and when I do, I'm almost never in my very biggest gear.
So, this wouldn't be any sort of dealbreaker for me.
YMMV.

Care to translate that for laypeople? :)

And nobody has mentioned the elephant yet.
There is about a 7% speed variation tooth to tooth due to chordal action.

Closer to 6%.
An 11 tooth is already 4%. How much do you feel that?

Yea, I've done a fair amount of bike race sprint finishes and I've never been in the biggest gear. Probably not even much beyond thr middle of the cassette.

Closer to 6%.
An 11 tooth is already 4%. How much do you feel that?

Care to translate that for laypeople? :)

Can't wait to hear Tom A.'s take.

Potential random mini-torque spikes.

I knew it! Micro-accelerations! Exactly what I need for my physics model.

Edit: I'm not serious. But it does look like you would ride very jerky if you used a 9-tooth cog in a group ride and people tried to draft you. You could become unpopular with a reputation for not riding smoothly at high speeds.

Hybridlete wrote:
GreenPlease wrote:
Potential random mini-torque spikes.

I knew it! Micro-accelerations! Exactly what I need for my physics model.

Edit: I'm not serious. But it does look like you would ride very jerky if you used a 9-tooth cog in a group ride and people tried to draft you. You could become unpopular with a reputation for not riding smoothly at high speeds.
You're not serious about your physics model? I think most of us already knew that ;)

You may feel the "chordal action" due to a small sprocket via the pedals but I can't see any reason why it would bother anyone else. It's not going to be the least bit perceptible to anyone else from your bike speed. You don't need a fantasy physics model to realise that the frequency is far too high for any perceptible variation in bike speed due to this.
However in case this isn't intuitively obvious to you, let's just look at an example of the sort of numbers involved. Lets say your speed is 36km/h (22.5mph), which is very slow to be riding in the 9 tooth sprocket anyway, even for a real grinder on a small 36T chainring. At that speed your rear wheel is rotating at a little over 4.5 times per second (about 273rpm). You have 9 teeth so the frequency of any torque or speed changes due to "chordal action" is about 41Hz (273*9/60). That sort of frequency may be noticed as vibration through the pedals by the cyclist but there's not a chance in hell that it results in bike speed changes that effect fellow riders in a group. How much do you think your bike slows down and speeds back up in 24 milliseconds? And it's not even that power is switched on and off every 24 milliseconds. No, we're talking about less than a 10% reduction from peak to minimum power during that 24 millisecond cycle. If you ride your bike and stop pedaling for a moment you'll find that a thing called inertia (may have cropped up in your "physics model") prevents the bike from suddenly coming to an abrupt halt. Neither aerodynamic drag, gravity, rolling resistance, nor bearing or other losses, are capable of providing sufficient braking effects in the world of cycling for this to be a problem. This should be a surprise to no-one.

Your pedalling frequency and smoothness has much more scope for variation in than the "chordal action" in question. This has a typical frequency of about 2.5-3Hz for both feet combined (assuming cadence of 75-90). So pedalling inconsistencies would have 15 times more impact based on the frequency and thus the time available for the bike to decelerate and accelerate between peaks. And that's if the variation in output was comparable. In fact, I'm certain that pedalling variation is a lot more than 6 or 7% being suggested for the sprocket chordal action. Also bear in mind that my example uses a rather unrealistically low speed. At higher speeds the effect would be even more negligible. So, in conclusion, there is absolutely no truth to the suggestion that this could gain you a reputation for not riding smoothly at high speeds. That's just nonsense - surprise.

Oh good, if only this had been around for a year.

https://bythehive.com/...ts/trs-race-cassette