# Will I be able to tell a big difference in 165mm vs 172.5mm cranks?



## ZachUA (May 18, 2013)

My current cranks are 172.5 and I spotted a deal on a 165mm crankset. I've heard there is a recent trend towards shorter cranks? Is this true? Have there been any studies to determine if shorter crank offer advantage? I am average height with 33" inseam if that matters.


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## DaveG (Feb 4, 2004)

They are only a deal if you need them, which it sounds like you don't. I am not aware of any studies that show shorter cranks are better.


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## ZachUA (May 18, 2013)

I guess I should have worded my original post better.

I am building a new bike. my current cranks on my current bike are 172.5. If I put 165mm cranks on my new frame will I be able to tell a big difference (negative or positive).


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## DaveG (Feb 4, 2004)

ZachUA said:


> I guess I should have worded my original post better.
> 
> I am building a new bike. my current cranks on my current bike are 172.5. If I put 165mm cranks on my new frame will I be able to tell a big difference (negative or positive).


I cannot but everyone is different. I am tall and run 175's. For a while I used a cheap old 10-speed on my trainer with 165's and I really did not notice


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## mikerp (Jul 24, 2011)

ZachUA said:


> I guess I should have worded my original post better.
> 
> I am building a new bike. my current cranks on my current bike are 172.5. If I put 165mm cranks on my new frame will I be able to tell a big difference (negative or positive).


Depends on how you ride and how many miles you put in. If you are casual and do a few miles it probably won't matter, if you put in a lot of miles and race I'd suggest you stick with one configuration. TT bikes are the exception as they have a different setup.


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## headloss (Mar 3, 2013)

I doubt you'll notice, once your body adjusts. Stroke will be reduced by 7.5mm downward, so I imagine you will want to raise your saddle 7.5mm to compensate. Obviously, you may have to make other adjustments in response to that. In which case, it comes down to a personal feel and you won't many good answers asking the internet.

I don't really notice a difference myself, short vs. long crank in terms of spinning and mashing.


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## MarshallH1987 (Jun 17, 2009)

No benefit to shorter cranks, it is more of what feels better to you riding. Shorter cranks spin in a smaller circle. Worry about fit and not the deal. And yes, you will notice a difference at 7.5mm until your body adjusts.


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## aa.mclaren (Jun 25, 2008)

One of the standard bike-fit rules is adjusting your saddle height by 2X the difference of the change in crank lengths, when going longer or shorter. For changing from a 172.5mm crank to a 165mm, you would be recommended to raise your saddle 15mm. If you were going for a 175mm crank from 172.5s you would have to lower your seat by 5mm.


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## Kerry Irons (Feb 25, 2002)

ZachUA said:


> Have there been any studies to determine if shorter crank offer advantage?


Lots of studies. Many conclusive. They disagree with each other. No consensus despite what those pitching a given formula will tell you. Crank length is personal preference. The only thing we can be sure of is that your seat will be higher with shorter cranks and you will find it easier to spin higher cadences.


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## wim (Feb 28, 2005)

aa.mclaren said:


> One of the standard bike-fit rules is adjusting your saddle height by 2X the difference of the change in crank lengths


Never heard of this, and it's a bad idea. The standard recommendation is to raise/lower your saddle by the amount of crank length change. Doing that will re-establish your customary saddle-to-pedal distance (and knee angle) at crank bottom dead center while changing your knee angle at top dead center to an acceptable degree.

Following your "rule" would screw up leg extension at bottom dead center and introduce a major change in knee angle at top dead center. Whoever put out this twice-the-difference rule forgot that a crank length change has opposite effects for bottom dead center and top dead center. For example, going shorter reduces pedal-to-saddle distance at bottom dead center, but increases it at top dead center.


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## wim (Feb 28, 2005)

Kerry Irons said:


> you will find it easier to spin higher cadences.


In fact, just riding the way you normally ride will increase your cadence with shorter cranks. At one and the same leg speed, cadence will increase with shorter cranks—like it or not.


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## spdntrxi (Jul 25, 2013)

it's not that noticeable…. and like others have said higher cadence.

I go from 165 to 172.5 all the time… I get lazy and use my wifes bike on that sits on the trainer instead of strapping mine in.


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## Jay Strongbow (May 8, 2010)

I definitely feel a difference jumping from 172.5 to 165 or visa versa just like I'd feel a difference if someone moved my saddle 7.5 mm.

Feeling a difference and getting better or worse performance are two different subjects though. As far as that goes there's no difference that I can detect.
Seeing as though this is a second bike I'd just stick with what you have on the first one.


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## tom_h (May 6, 2008)

Track bikes (fixed gear) typically have 5-7.5 mm shorter cranks for the same nominal frame size, so that on steeply banked tracks the uphill pedal doesn't strike the ground.
IME, the body adjusts within 10 minutes or so, and you stop noticing it.

If you plan on racing criteriums, shorter cranks will provide more ground clearance when pedaling thru turns. I have 32" inseam and 172.5mm cranks, in hindsight I wish I'd gone with 170mm.

On triathlon forums I've read they are favoring short cranks because somehow it "saves" the legs for the running segment, but I don't understand the physiological basis -- and it might even be a fad, I don't know.


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## headloss (Mar 3, 2013)

tom_h said:


> On triathlon forums I've read they are favoring short cranks because somehow it "saves" the legs for the running segment, but I don't understand the physiological basis -- and it might even be a fad, I don't know.


longer crank = knee goes higher? i.e more extreme movement stressing legs...
shorter crank = more spin => let gears do the work...


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## AndrwSwitch (May 28, 2009)

I have 165 on a track bike and 175 on a road and a mountain bike, with something in between on another couple. I do notice a difference, and I like the shorter cranks marginally better. I don't think they effect my efficiency or power output within that range, though.

I don't think I change my saddle position by as much as the difference in crank length. The vertical position relative to where I exert the most force in my pedal stroke changes by less than the change in arm length.


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## Edhunt (Sep 1, 2012)

I have bikes that are 170, 172.5 and 175. I am a masher and my "natural" cadence is around 75-80 rpm. I can't really tell the difference between the 172.5 and either of the other two, but if I have been riding my bike with 175 for a while when I hop on the 170, it takes me a little longer (5-7 more reps ) to get up to speed after a light, and hills seem harder.

On long flats, the 170 bike is easier to spin, but into a headwind or uphill I prefer the 175. 

A different perspective with the same topic: it depends.


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