change gears?

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Eric Reid AeroFit | Instagram Portfolio
Aerodynamic Retul Bike Fitting

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I think the answer is "it depends". On climbs, some people can easily maintain the same power by switching to a higher cadence (lower torque resulting in lower gear, but maintaining power by having a higher cadence). Some have more challenge doing so.

Within pro cyclist, you see difference in pedaling styles too. Quintana stands out with running 172.5 cranks while being quite a short rider, but it clearly works for him. On the same team, Valverde, who is 4" taller uses shorter cranks.

Froome is 6'1", runs 172.5
Valverde is 5'10", runs 170
Bernel is 5'9", runs 170
Landa is 5'8", runs 170
Quintana is 5'6", runs 172.5

Yes, I tend to be a high cadence guy. I suspect I've become slower on climbs because my cadence is dropping down out of my "sweet spot." With the higher gears, I'm finding it more difficult to keep my cadence up. So a gearing change is in the works. I'm just wondering if it's worth ALSO going back to the longer crank.

SHORT CRANKS suck dogsh*t when it comes to climbing.
And don’t give me the bullshit that time gained while in aero neutralizes the extra time climbing nonsense. :)

When you run shorter crank, you lose torque. At the same gearing, you might struggle to push the crank, resulting in lower cadence / speed.

The question is... can you bring your cadence even higher than your old cadence with a lower gear. If you cannot (maybe that requires you to be in such a high cadence that it's unnatural for you), you should stick with the longer crank.

You can switch the gear and see if that's something your body can respond to. I have switched to lower gears over the years (from 175 to 172.5 to 170, and then tested out 165). The sweet spot for me was 170. I simply cannot bring my cadence high enough to compensate for the loss in torque on climbs when i switched from 170 to 165. I still run 165 on my TT bike though.

Also, this is not an exact science. Track riders (very powerful riders) usually run 165mm cranks, so this is something you might be able to adapt to. Again, this depends and you have to test it out and decide what works for you.

Consider that you might be looking at correlation and not causation.

Of course, track riders need the clearance. Digging a pedal into the wood while trying to hold your position is a drag. (Pun not intended, really.)

When I was young and fast, I rode 175mm. Not intentionally. It was just what I had. About five years ago, I went to 172.5 as an experiment. It seemed to work fine. A year ago, I went to 170mm on my TT/triathlon bike and did fine, so I switched my road bike to be more consistent. (Was it Emerson who said, "Consistency is the hobgoblin of small minds"?) I'm definitely having more than second thoughts about this change.

Nope...especially not for just 2.5mm. Crank length is a PART of the total leverage between the foot and the ground. So, if you go smaller on the crank length, then to compensate you should go with lower gearing. Your cadence might be higher, but your "tangential foot speed" (i.e. the thing that feels "right" to your body...how quickly your foot moves in the "push" phase) will be the same. People can make equivalent power over quite a fairly large range of cadence. Cadence is basically a dependent variable ;-)

In short, you did a double-whammy on your gearing by going to the larger small chainring AND the slightly shorter crank length.

BTW, one can dramatically shorten crank length and still maintain power as long as the gearing is changed to compensate and keep the foot speed constant. Here's one example: http://bikeblather.blogspot.com/...erwithin-reason.html

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http://bikeblather.blogspot.com/

You can run some torque numbers here: https://www.sensorsone.com/...e-calculator/#torque

300w = 221.27 ft lbf/s

Interesting. Thanks for the reference! 2.5mm clearly makes a difference.

Not really it is only 1.4% difference. That would be like switching your 36 tooth chainring to a 35.5 tooth chain ring.

Your gearing change is much larger factor.

Is the gearing change a much larger factor? Sure it is. That's been a basic premise of every post in this thread.

But, as for crank length (the subject of this thread), if force and velocity remain the same, you may be correct that speed doesn't change that much. But if force and velocity remained the same (i.e., if I were a machine), we wouldn't be talking about this. Because I know the force and/or velocity change is the key change, I'm not setting them as constant. I'm setting torque as the constant. I'm concerned with how force application changes to obtain a given torque given the change in lever length. If you're looking at the force applied to the pedal, the difference is about 3.5 to 4 pounds of force even at around 200 watts. (Higher at higher watts.) To me, that's a difference worth recognizing. At the top of a brutally steep climb (of which we have many around here), it could mean the difference between topping the climb in the saddle and walking part of it.

Yes, and you would also lower the force the same amount if you could run a 35.5 tooth chain ring instead of a 36 tooth. You are arguing over a 1.5% change in the force on the pedals. I think you need to recheck your math if you think the difference is going to be 3.5 to 4 llbs, you are not putting down 250lbs of force on the pedals.

Why are you keeping torque as the constant?

Look at the Quadrant Analysis plots in that blog post I linked to above. With appropriately changed gearing, there was NO difference in Average Effective Pedal Force, Circumferential Pedal Velocity, Power, or HR when switching between cranks of 175mm and 150mm. The only change was cadence, which as I said above, is a DEPENDENT VARIABLE in this system.

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http://bikeblather.blogspot.com/

Why would your pedal force change? Typically, the way one adjusts to making the same power on shorter cranks is increasing cadence. Usually you wouldn't even notice it because the circumference of the circle your foot has to travel for 1 revolution is smaller.

So force applied at the pedals is the same, but torque is lower because of the shorter lever and angular velocity is higher because of the higher rpm over the smaller circle.

For 2.5 milimeters these are all very small changes.

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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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I complete agree... just stick with what you are used to, I tried 175 and 170 and have riden 172.5 my whole life and hated both the shorter and longer, I am 6"1'. I found the short crank I was not feeling enough power and longer crank I couldn't get Over the gear and was fighting all the time. I think its just 20 years of using one crank length has my brain used it, I really thought I wouldn't notice 2.5mm but I did both ways.

Within pro cyclist, you see difference in pedaling styles too. Quintana stands out with running 172.5 cranks while being quite a short rider, but it clearly works for him. On the same team, Valverde, who is 4" taller uses shorter cranks. //

Ya, but how tall you are is not what matters, it is how long your leg levers are. I'm way taller than my wife, but she has longer legs, this is what you would need to know if you want to do comparisons. And I think you are talking road cranks here for the guys? A bit different when you go to a tt position...


And 2.5cm is no big deal at all, bet if I came and changed them while you were sleeping, and a couple other little tweaks, you would not even notice...


And I think most cyclists and triathletes ride a tiny bit longer cranks on their road bikes, much different position and needs..

Qinatana's saddle height is 69 cm as Valverde's is 75 cm.

Louis :)

Qinatana's saddle height is 69 cm as Valverde's is 75 cm.//

Great, thanks. that is the number that is much more pertinent to any discussion on crank lengths that overall height..Road bikes I assume??

Yes.


Louis :-)

I assumed OP climbs in a normal road position when summitting a 8-10% hill, and did not think this was a discussion regarding crank length's impact on TT position, but rather crank length impact on power generation in road position. Very different discussion if we are talking about crank length in a TT position.

Also, listing height is to illustrate a point. I think there are merits to simplification at times. The point is people (in my illustration, well known climbers) have different pedal length preferences. Quintana is a bit known to have a slower cadenced pedal style (70-75 while climbing).

Agreed that height is not perfect and reality is far more complicated. Two athletes with similar saddle height, their ideal pedal length could be very different if they have different portions in terms of upper leg, lower leg, foot size, and point of contact with pedal.

My ss cx rigs have 177.5mm cranks over my normal 172.5mm on most of my other bikes. To me it sometimes makes the difference of clearing a steep spot or having to dismount on the ss bike. Maybe it is in my head, but I don't think so. When the rpms are way down in the low numbers a little longer lever is noticeable. At 80-100 rpms, I don't think you would notice.

Reportedly pantani would run 180’s in the mountains. I’m not sure how much of this has to do with light riders and seated vs standing, but if you are 120-130 pounds you could see how extra crank leverage out of the saddle *might* help.

There’s very little work on metabolic load/parameters on seated vs standing but clearly they are at least slightly different activities.

Maurice

I'm sure I'd notice 2.5 cm

((((Sorry))))