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I am curious what the difference would be when pedaling If I made a change on my bike:

I got 30T and 9-46 and 175mm crankarms. The combo is working decent for me.

I was looking at getting new crsnks. Rather thsn a straight upgrade, I could consider going to a shorter arm. 170, even 165 and compensate for a smaller spinning radius by dropping to a 28T ring.

I’m curious how this would affect the quality of the ride when climbing and descending?

30-46 is a fine climb gear for me, I don’t need more leverage, but I hardly ever use the 9 either. I climb with high cadence. The 9 seems a pavement gear and so I basically never use it with my 30.

so besides gear ratio, I’ wondering if other folks have experimented with short arms and how you liked it?

If it matters, I am tall. Dunno if thats enough reason to stay 175
 

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I have no idea why people think you need to go down a chainring size when you reduce your crank length.

Shorter cranks == smaller circles

This means you feel like you're spinning more. The less leverage thing is BS.

Use the chainring size you have now with the shorter cranks, then decide.

Watch this for a crank length experiment:
 

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I have no idea why people think you need to go down a chainring size when you reduce your crank length.

Shorter cranks == smaller circles

This means you feel like you're spinning more. The less leverage thing is BS.

Use the chainring size you have now with the shorter cranks, then decide.

Watch this for a crank length experiment:
They say less leverage because the lever arm (crank) is shorter. Same force from the riders leg, shorter distance from the fulcrum/rotational center. It's the same reason that a breaker bar has more torque on a nut or boot, than than a shorter one, just in reverse.

So you compensate with easier gearing. Seems pretty straightforward to me.

The guy from hardtail party in the video you linked even calls out the effect, by saying he needs to be in an easier gear when riding/climbing on the smaller cranks. He says it a couple times as he goes down in crank sizes iirc.
 

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I swapped from 170 to 165 on one of my bikes and I felt like if it was noticeable it was barely. Like one of those things where I wasn't sure if I was actually noticing it or just trying to convince myself that there was something to notice.

So fairly subtle, if at all.
 

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Reducing the crank length from 175mm to 170mm is a 2.9% reduction in length.
Reducing the chainring from 30 to 28 teeth is a 6.7% reduction.

I think that means the chainring change will make about twice the difference that the crank change does, so the net effect is it will feel like a ~3% smaller chainring on the original cranks, i.e. about a 29T on a 175mm.

FWIW I have almost exactly both of these setups: One bike with 175mm cranks with a 32/10-51 and another with 170mm cranks and 30/10-51. The shorter crank bike feels like it is slightly lower geared but I'm not even sure I could tell them apart blindfolded.
 

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I am curious what the difference would be when pedaling If I made a change on my bike:

I got 30T and 9-46 and 175mm crankarms. The combo is working decent for me.

I was looking at getting new crsnks. Rather thsn a straight upgrade, I could consider going to a shorter arm. 170, even 165 and compensate for a smaller spinning radius by dropping to a 28T ring.

I'm curious how this would affect the quality of the ride when climbing and descending?

30-46 is a fine climb gear for me, I don't need more leverage, but I hardly ever use the 9 either. I climb with high cadence. The 9 seems a pavement gear and so I basically never use it with my 30.

so besides gear ratio, I' wondering if other folks have experimented with short arms and how you liked it?

If it matters, I am tall. Dunno if thats enough reason to stay 175
I went from 175 to 170 and much better clearing rocks ect but then I needed to adjust my seat ? but I really enjoy the shorter crankarm.
 

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Chain-ring size is matched to crank-size but not because of decreased torque. Shorter cranks change your functional cadence range.

When you go a shorter crank you preferred cadence increases. Someone who likes to spin at 90rpm on 175mm will naturally spin at 95rpm on 165mm. You match this with a change in change rings.
 

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I totally get that the applied power doesn't change. Seems there is consensus on that one.

anyone with real world experience, even if using the same chainring size?
Yes, I've gone from 165 to 160 to 155 over the past 10 years. Each time I felt more spinny, not less.

I went from a 165mm/28t to a 160mm/30t. The 28t with the 160mm felt waaaay too spinny for my personal tastes.

I've kept the 30t chainring for the 155mm, and it really feels spinny, but I'm trying to get used to it rather than go to a 32t this time.
 

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They say less leverage because the lever arm (crank) is shorter. Same force from the riders leg, shorter distance from the fulcrum/rotational center. It's the same reason that a breaker bar has more torque on a nut or boot, than than a shorter one, just in reverse.

So you compensate with easier gearing. Seems pretty straightforward to me.

The guy from hardtail party in the video you linked even calls out the effect, by saying he needs to be in an easier gear when riding/climbing on the smaller cranks. He says it a couple times as he goes down in crank sizes iirc.
The thing is, if your cranks are already too long for you, and you're not able to get enough leverage, going to a shorter crank makes it feel like you can get enough leverage rather than needing to go to a smaller chainring.

He does, but it's not necessarily been my own experiences. The comment about leverage is always interesting, because if you're running too long of a crank length, you're probably not getting the right leverage in the first place.

I'm 5'4", with a 29.5" inseam and short femurs. I'm pretty sure I'm not able to get the same leverage as a male with longer femurs and is much taller than me (referring to @Whiterabbitt who calls himself "tall" :) ).
 

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The thing is, if your cranks are already too long for you, and you're not able to get enough leverage, going to a shorter crank makes it feel like you can get enough leverage rather than needing to go to a smaller chainring.

He does, but it's not necessarily been my own experiences. The comment about leverage is always interesting, because if you're running too long of a crank length, you're probably not getting the right leverage in the first place.

I'm 5'4", with a 29.5" inseam and short femurs. I'm pretty sure I'm not able to get the same leverage as a male with longer femurs and is much taller than me (referring to @Whiterabbitt who calls himself "tall" :) ).
Ah, so you mean bio mechanical leverage/physical power output at certain crank lengths, not mechanical leverage. I was talking about pure mechanical leverage.

As it happens, Dylan Johnson has an interesting video on crank length, where he covers a couple of research studies on crank length and power output. It's worth watching (as are most of his other videos, I quite like how he dives into the available data).

There were a bunch of tests using all sorts of different crank lengths (from as small as 120mm, to as large as 265mm), and they also had tests for short vs long legs. The most interesting part (IMO) was seeing that cranks that were~80% different in length, only had a 4% difference in overall power production from the cyclists. And that crank length and cadence do seem to correlate. Sounds like if you prefer a high cadence, shorter cranks are probably the way to go.


From what I've seen/read it really just seems to come down to preference. I've never actually changed crank lengths (just using the stock 175mm's my bike came with), so my opinion probably isn't worth much. But due to the research, I'll probably try shorter cranks next time, and will pay attention to if I need any different gearing.

But honestly my desire to try short cranks is mostly about pedal strikes. So if I can ride 165mm cranks, and get the same power/efficiency (or close enough) as my current 175mm cranks, then that seems like a win to me.
 

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Ah, so you mean bio mechanical leverage/physical power output at certain crank lengths, not mechanical leverage. I was talking about pure mechanical leverage.

As it happens, Dylan Johnson has an interesting video on crank length, where he covers a couple of research studies on crank length and power output. It's worth watching (as are most of his other videos, I quite like how he dives into the available data).

There were a bunch of tests using all sorts of different crank lengths (from as small as 120mm, to as large as 265mm), and they also had tests for short vs long legs. The most interesting part (IMO) was seeing that cranks that were~80% different in length, only had a 4% difference in overall power production from the cyclists. And that crank length and cadence do seem to correlate. Sounds like if you prefer a high cadence, shorter cranks are probably the way to go.


From what I've seen/read it really just seems to come down to preference. I've never actually changed crank lengths (just using the stock 175mm's my bike came with), so my opinion probably isn't worth much. But due to the research, I'll probably try shorter cranks next time, and will pay attention to if I need any different gearing.

But honestly my desire to try short cranks is mostly about pedal strikes. So if I can ride 165mm cranks, and get the same power/efficiency (or close enough) as my current 175mm cranks, then that seems like a win to me.
The not-hitting things is one of the reasons my husband is going to 160mm cranks. Hopefully he doesn't hate them, but we'll find out after his bruised ribs heal.

So hear me out: One of the things a lot of these videos does leave out is the human factor of strength, hyperextension (which is not good for hips and knees), femur/tibula lengths, and I'm curious if seat angle matters too. A few years ago, I went through the whole bicycle inseam measurement (29.5") and did the calculations according to Sheldon Brown, and it said I should run ideally 163mm cranks, but I found that 155mm works for me. The reason that the really short work for me is I have hypermobility in my joints, so it's really easy for me to hang at the end range of my range of motion, and that pretty much turns off my muscles and I hang on my joints. So it's better for me to use the shorter cranks so I'm engaging my muscles than hanging off my bones.
 

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The not-hitting things is one of the reasons my husband is going to 160mm cranks. Hopefully he doesn't hate them, but we'll find out after his bruised ribs heal.

So hear me out: One of the things a lot of these videos does leave out is the human factor of strength, hyperextension (which is not good for hips and knees), femur/tibula lengths, and I'm curious if seat angle matters too. A few years ago, I went through the whole bicycle inseam measurement (29.5") and did the calculations according to Sheldon Brown, and it said I should run ideally 163mm cranks, but I found that 155mm works for me. The reason that the really short work for me is I have hypermobility in my joints, so it's really easy for me to hang at the end range of my range of motion, and that pretty much turns off my muscles and I hang on my joints. So it's better for me to use the shorter cranks so I'm engaging my muscles than not.
Ha. As it happens, I'm just getting recovered from two broken ribs and a shattered toe (toe got caught between the pedal and a root at speed somehow, and folded under the pedal). So I know exactly the feeling. Hopefully he recovers well :).

Some of the studies that Dylan covers in his video do talk about strength, and power output (that's the part I was mentioning where they tried tons of crazy crank lengths, and measured power output, o2 usage, etc), as well as leg length. But you are right, I don't think he mentioned if that study accounted for different ratios of femur/tibula lengths, or seat angle (but there was a really interesting separate video on seat heights and how that impacts stuff). I'd be very interested in any future research on that front for sure.

And, of course you should always do what works best for you. Sounds like you've spent some time on it, and experimented a bit, which is great. I hope to try out some shorter cranks in the future as I said. I'm not sure if I'll go with 170's, or be bold and try 165's for my next build.
 

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I have 2 slayers. One with 170, one with 175 crank. Both with same gearing. I can't tell the difference in cadence or power... I can tell the difference in not as much tagging of stuff on the shorter crank.

I would not change chainrings if I was you. Keep the same gearing.
 

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I can tell you from first hand experience that a reduction in crank length must also include a reduction in chainring, by the aprox same percentage. Due to a busted knee i was forced to go from 175 mm to 115mm (shortened zee crankset, i had to drop to lowest possible chainring (26t nw) to retain the overall effective gearing, it would be better to drop to a 24t nw but cant seem to find one.

if you dont reduce the chainring you will run out of gears very quickly uphill and you never use the smaller gears (way to tall). How big this effect will be depends on the ammount of crank reduction.
 
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