# 172.5 or 175 crank arms. Big difference?



## Special Eyes

Is there going to be much difference to me, as a 6 foot tall rider on a 56cm frame, between 172.5 or 175 crank arms? Are the longer ones generally for taller riders?


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## Mike T.

Special Eyes said:


> Is there going to be much difference to me, as a 6 foot tall rider on a 56cm frame, between 172.5 or 175 crank arms? Are the longer ones generally for taller riders?


There are many threads on this topic. Use the search function and you will find them.


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## rubbersoul

After wrestling with this issue for a while, I finally made the jump from 172.5 to 175. Makes a big difference in torque, ie for climbing or pushing a bigger gear on the flats. Well worth it to me. 6'1" by the way.

Cheers


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## lamazion

I'm 6ft and years ago I made the switch to 175. Last year I gave 172.5 a try and prefer the way I can "spin" them. I'm in the process of moving my bikes back to 172.5.


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## JCavilia

> Is there going to be much difference to me


No. Difference will be small, if you can notice it at all.


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## woodys737

JCavilia said:


> No. Difference will be small, if you can notice it at all.


+1. I use 172.5's and had the opportunity to ride a set of 175's for a week while my cranks were being worked on. While spinning I could almost convince myself I could tell I was on 175's but, while in the middle of hard efforts crank length never entered my mind. 

The only thing I can say is that after hard efforts my gluteus medius or something very close was sore. I did lower the saddle to compensate for the longer crank.

THIS is always a good link to reference for muscles used while pedaling.


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## dracula

Special Eyes said:


> Is there going to be much difference to me, as a 6 foot tall rider on a 56cm frame, between 172.5 or 175 crank arms? Are the longer ones generally for taller riders?


I am 180cm, inseam 83 cm and ride 175cm on all my bikes. 

There is an interesting Figure comparing inseam length (Schritthoehe) versus crank length (Kurbellaenge): 

http://www.customcranks.de/de/Kurbellaenge_komplex.html

scroll down to the bottom. Armstrong with a comparatively small inseam rode a 175cm.


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## Oldteen

I'm 6'/34" inseam & have 172.5 and 175 cranks on different bikes. No difference I can tell. MUCH more difference in pedals (stack height).


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## Ventruck

I'm 5'10-11", 34in inseam. I personally didn't realize my current bike had 172.5's - as opposed to the 175's I've used long previously - until months into riding it. While this, and pretty much every above poster's reference would be far from pointing you to a perfect fit, there's no question that either may just work for you.

Now 170mm cranks, I totally felt the difference and personally hated them.


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## Kerry Irons

*Big difference*



rubbersoul said:


> After wrestling with this issue for a while, I finally made the jump from 172.5 to 175. Makes a big difference in torque, ie for climbing or pushing a bigger gear on the flats. Well worth it to me.


No, it doesn't make a big difference in torque. Simple math says it's 1.4%. And a longer lever arm does nothing to extract more power from a rider's legs. If you've been paying attention, you would know that study after study has been done on this topic, and the conclusion is thatt there are a bunch of inconclusive studies. You may like longer cranks while somebody else may not, but neither likes nor dislikes constitute a "big difference."


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## chas0039

I have 6 bikes with an equal mix of both. The only thing I do differently is adjust the seat setback to deal with a longer or shorter crank. When I am riding, no difference at all and I can't tell which on is on which bike.


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## dougo14

Hi, I have been running a 172.5 crank arm and have just recently changed to a 175. I have noticed there is less spinning and am not sure if I like that or not. I have question though I have been professionally fitted up to my bike before I changed over my cranks. I just wondering if I should put the seat up or down or ford or back. I have noticed a sore pain in my knees but it doesn't last that long after a ride. Can you please help my. I am also 15 years old if that helps. Thanks


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## wim

> _Hi, I have been running a 172.5 crank arm and have just recently changed to a 175. I have noticed there is less spinning and am not sure if I like that or not.
> _


When changing to longer cranks, the conventional wisdom is to lower the saddle by the difference between the old and the new crank (2.5 mm in your case). This will re-establish the knee angle at bottom dead center of the crank circle you had with your shorter cranks.

However, this will also introduce a 5 mm change at top dead center (2.5 mm longer crank + 2.5 mm lower saddle), so the knee angle at top dead center will have changed quite a bit. Because of this, there are some riders and coaches who advise not changing saddle height when changing crank length.

Your spin has suffered a bit because the crank circle is larger with the longer cranks. So at the same leg speed, it takes your foot just a tad longer to complete one crank revolution. If you want to regain your former spin, you need to increase leg speed a little.

To me, the obvious solution to your problem is to go back to your old, shorter cranks. Crank length has no proven effect on performance unless you're talking about grinding uphill at painfully slow cadences. Doing that, the longer crank will give you a small advantage.


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## crit_boy

dougo14 said:


> Hi, I have been running a 172.5 crank arm and have just recently changed to a 175. I have noticed there is less spinning and am not sure if I like that or not. I have question though I have been professionally fitted up to my bike before I changed over my cranks. I just wondering if I should put the seat up or down or ford or back. I have noticed a sore pain in my knees but it doesn't last that long after a ride. Can you please help my. I am also 15 years old if that helps. Thanks


It is a bit concerning that you are 15 years old and having knee pain. You should not be having knee pain. 

If the 172.5 were not giving you pain, I would think that is a simple way to start. However, there are other questions/issues. Have you grown since you fitting (limbs, feet, etc.), are you pushing too large of gears, probably other stuff to consider. 

Since you had a fitting, I would assume you have some support from your parent(s). You may want to mention it to them. Hopefully, they can get you to the right help (more fitting, Dr. with juniors sports knowledge). You don't want bad knees when you are less than 20. They just get worse over time.


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## ToffieBoi

dougo14 said:


> Hi, I have been running a 172.5 crank arm and have just recently changed to a 175. I have noticed there is less spinning and am not sure if I like that or not. I have question though I have been professionally fitted up to my bike before I changed over my cranks. I just wondering if I should put the seat up or down or ford or back. I have noticed a sore pain in my knees but it doesn't last that long after a ride. Can you please help my. I am also 15 years old if that helps. Thanks


As a 15 years old rider, you should really listen your body carefully. I know a few young riders, whose riding career finished because of knee problems before they are even 18.

From 172.5mm to 175mm, you have only 2.5mm difference. We set our saddle height when the pedal is at 6 o'clock position. So you should lower the saddle for 2.5mm, since your pedal is 2.5mm lower than it was.

For the horizontal alignment of the saddle, we put the pedal on 3 o'clock position. Now, your pedal is 2.5mm further than it was, so you should move the saddle 2.5mm forward.

In practice, those measurements will not change anything I guess. You move more than that during a ride and there is no difference in knee pain for sure.

That's why, I recommend you to observe your riding style and also see a doctor for your current pain in knee to not make it worse.


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## velodog

I've gone from 170's to 172.5's and prefer the 172.5's.

I can't honestly say that I can feel the difference, but I still prefer the 172.5's. 
I don't know if I feel a difference that doesn't register or if I am just playing head games with myself, but there's no going back to the 170's for me.


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## masont

Biggest difference to me is in bike fit. If you're looking to get as low as you can go in the front (or you have a bit of a lunch muscle) a shorter crankarm - in addition to causing your saddle to go up 2.5mm, will also be 2.5mm shorter at the top. So you'll get 5mm of extra space that you can either use to take a spacer out or not knock your gut with your knee.


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## ToffieBoi

masont said:


> Biggest difference to me is in bike fit. If you're looking to get as low as you can go in the front (or you have a bit of a lunch muscle) a shorter crankarm - in addition to causing your saddle to go up 2.5mm, will also be 2.5mm shorter at the top. So you'll get 5mm of extra space that you can either use to take a spacer out or not knock your gut with your knee.


I bet that, you or your body will not notice the difference on your bike, if I secretly change your saddle 2.5mm forward and 2.5mm downwards.


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## wim

ToffieBoi said:


> I bet that, you or your body will not notice the difference on your bike, if I secretly change your saddle 2.5mm forward and 2.5mm downwards.


The corollary to that is that he would feel no difference if you'd secretly exchanged his cranks for 2.5 mm longer ones. That's part of the idea behind not messing with the saddle at all after making a crank length change.

My take on this was that he experienced knee pain _after_ the crank length change. But I could have read this wrong.


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## ToffieBoi

wim said:


> The corollary to that is that he would feel no difference if you'd secretly exchanged his cranks for 2.5 mm longer ones. That's part of the idea behind not messing with the saddle at all after making a crank length change.
> 
> My take on this was that he experienced knee pain _after_ the crank length change. But I could have read this wrong.


This two is a bit different in my opinion.
With a bigger crank, your feet follows a relatively bigger route. Even if it is 2.5mm, movement is different. Bigger diameter, longer route. That can effect the pressure on knee, or muscles. 

But 2.5mm on saddle is not a difference at all. When you switch from thin padded bibshorts to thick ones, you will go higher more than 2.5mm. In winter times, I sometimes wear 2 padded bibshorts and no kneepain whatsoever.
When you move the your hands from tops to hoods, you move more than 2.5mm to front. 
Your body does not stay still on saddle at all. You move more than centimetres during rides and there is no change 

I hope I could be more clear now about my opinion


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## wim

ToffieBoi said:


> This two is a bit different in my opinion.
> With a bigger crank, your feet follows a relatively bigger route. Even if it is 2.5mm, movement is different. Bigger diameter, longer route. That can effect the pressure on knee, or muscles.


I see your point. For what it's worth: a 2.5 mm change in crank length will change the crank circle (the line followed by the foot) by 16 mm. That in itself doesn't change pressure on the knee all that much. But as you also said, it's the larger diameter that can hurt you when lengthening cranks. This is especially true when lowering the saddle by the amount of the crank length increase.


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## cranecamsou

There are really a couple questions at work here: 
1) Difference in performance? As others have said, this is arguable and likely small.
2) Difference in feel/fit? Just like moving your saddle/stem/bars 2.5mm in any direction can cause a significant change in comfort, changing crank arm length can greatly impact the feel of your spin motion. Ankle, Knee, & Hip angles will change for the better or worse - depending on you. 

I'm 6'3"/33-34" inseam and find that I have greater deep hip fatigue when riding the 175 on the 'cross, still a fun bike though.

In general, I'm a fan of switching out components and trying out new contact point positions....but always in pursuit of a better fit - rarely for performance.


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## pmf

I've use both and I cannot any difference. If one is on sale and the other is not, I get what's on sale. Its a 1.4% difference. Measure out 2.5mm and see what you're worrying over. Cleats and/or shoe soles probably differ by more than 2.5mm.


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## multirider

Ventruck said:


> I'm 5'10-11", 34in inseam. I personally didn't realize my current bike had 172.5's - as opposed to the 175's I've used long previously - until months into riding it. While this, and pretty much every above poster's reference would be far from pointing you to a perfect fit, there's no question that either may just work for you.


I purchased a CX bike and rode/raced it for 6 months before realizing it had 172.5mm cranks and my other 3 bikes have 175s. I'm 6'2" tall if that is relevant.


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## grandsalmon

Well, I have bikes w both, FWIW and can always tell in the spin


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