# Accidentally got 170mm cranks instead of 172.5....is this going to be an issue?



## PruneJuice (Oct 21, 2010)

I accidentally got a pair of 170mm cranks, my old pair was 172.5 because thats what was one the bike when i got them new.

I am 5' 9.5" tall - will the 170mm cranks work? I know spinning at a higher cadence will seem easier, will I notice that much of a loss of power when climbing?

Unfortunately I can't try them out because I don't have a new bottom bracket yet.

Thanks for any help!


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## xxl (Mar 19, 2002)

PruneJuice said:


> I accidentally got a pair of 170mm cranks, my old pair was 172.5 because thats what was one the bike when i got them new.
> 
> I am 5' 9.5" tall - will the 170mm cranks work? I know spinning at a higher cadence will seem easier, will I notice that much of a loss of power when climbing?
> 
> ...


The cranks will work. You will almost assuredly not notice any differences between the new and old. Old skool rules-of-thumb (leg?) might suggest you use 170s anyway, and that's just a guideline--no empirical evidence.


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## Mapei (Feb 3, 2004)

Some people are sensitive to crank arm length. Some are not. I am. Ninety percent of the folks on these forums aren't. If you don't have your bottom bracket yet, and you've found you are sensitive to these sorts of measurements, maybe you can just exchange the 170's for the 172.5's. Heck, you're already waiting on stuff, anyway.


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## PruneJuice (Oct 21, 2010)

Just figured out that the cranks on my mtb are 170 as well. I'm less concerned now.


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## Mike T. (Feb 3, 2004)

You won't notice anything. I have bikes with 165 (my track bike), 170 and 172.5 and had 175's too on an older mountain bike. The best winter training bike I had had 165 cranks and I loved that bike. I couldn't tell ya what cranks I was using just by feel.

I'm 5' 9" too and 170's are my preferred length for road.


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## axlenut (Sep 28, 2010)

Hi, with your MTB running 170s you should be fine with the same on your road bike. My MTB has 175s on it and I'm so used to spinning the longer cranks that when I get on a bike with shorter cranks I can really feel the difference. When I place the order for my SS road bike I decided to go with the same 175s on it too. Really glad I did as the long cranks give me a lot punch on the hills and I think it helps me on the MTB staying with the same crank length. 

I once heard a saying from a fly fishing instructor that went something like: 

Practice makes perfect, if you practice doing something wrong long enough you can end up doing it perfectly wrong ;-)

I'm perfectly happy spinning too long of a crank now. 

BTW - I'm 5'10"

Later, Axlenut


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## pmf (Feb 23, 2004)

2.5 mm is such a small difference that I can't see how anyone would be able to perceive it. Then again, some folks here swear they can tell whether their seatpost is carbon or aluminum. 2.5 mm is 0.25 cm, or roughly 0.1 inches. Take a dollar bill and fold it in half six times (if you can). That's a little shy of 0.1 inches. There's got to be a ton more variance in the thickness of shoe soles and cleates than 2.5mm. 

I went from 172.5 to 175.0 once just because I wanted the new cranks, they were on sale, but only in the 175 mm size. I could tell absolutely no difference. I don't even recall changing my saddle height.


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## FBinNY (Jan 24, 2009)

2.5mm out of 170 is something on the order of 1.5%. Not exactly an earth shaking difference either way. You certainly won't notice a change in leverage or climbing power.

But if you're a spinner with highly ingrained pedaling motion and are sensitive to such things you might notice a slight difference in the pedal circle, something you'll get used to pretty quickly.


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## BikeFixer (May 19, 2009)

Mostly psychological I'm thinking


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## Cableguy (Jun 6, 2010)

It would be interesting to see how many of the people who claim they can feel the difference with 2.5mm would actually have no clue if they didn't *know* what they were using. Kind of like how many wine "experts" are unreliable in a blind fold test. If you believe cranks of X size are the best, for whatever reason, and you think you're using them, you will ride differently... regardless of what cranks you actually *are* using... 

Cyclist: "Oh yeah, I can definitely tell it's easier to spin with these cranks"

Tester: "Well, you know how we told you we put on the 170mm cranks? You're *still* using the 172.5mm"

*awkward silence*


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## tconrady (May 1, 2007)

The only difference you're going to notice is that you'll need to raise your saddle height by a couple mm to make up for your foot not going quite as far down at the bottom of the pedal stroke. I made the same mistake but in the other direction (accidentally got 172.5 instead of 170) and once I readjusted my saddle position down I was good.

think of it this way....the diameter of a complete pedal stroke revolution has just decreased by 5mm...that's pretty small if you think about it.


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## Kuma601 (Jan 22, 2004)

You'll get accustomed to it and or you'll prefer the 172.5 to make a swap.


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## cwg_at_opc (Oct 20, 2005)

erg. more stuff to fan the flames. read this:

http://www.pezcyclingnews.com/?pg=fullstory&id=8845&status=True&catname=Latest News


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## BikeFixer (May 19, 2009)

cwg_at_opc said:


> erg. more stuff to fan the flames. read this:
> 
> http://www.pezcyclingnews.com/?pg=fullstory&id=8845&status=True&catname=Latest News


   :thumbsup: :idea: <fan flames>

LMAO perfect


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## MShaw (Jun 7, 2003)

It always amazes me that the people that can't tell a difference don't believe there's people out there that can. When I'm riding every day (not right this now, its winter) I can even tell between thick and thin socks! I solved that problem by buying thin cycling socks. 

I'll get back to y'all here in the next few months. I have one bike that I upgraded to a Red crank that's 172.5mm and the rest of my stuff's 170mm. We'll see how things go. I may end up with all of em 172.5 or I may end up with all of em 170mm.

M


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## SystemShock (Jun 14, 2008)

MShaw said:


> It always amazes me that the people that can't tell a difference don't believe there's people out there that can.


Not only that, but some ppl who can't seem to get a little _mad_ at the ppl who can. :lol:

Whatever happened to 'ride and let ride'? :idea:
.


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## rudedog55 (Aug 10, 2009)

cwg_at_opc said:


> erg. more stuff to fan the flames. read this:
> 
> http://www.pezcyclingnews.com/?pg=fullstory&id=8845&status=True&catname=Latest News


that is a great article, thanks for that link.

FWIW, i have 177.5 on my TT bike, 175 on my cross and road bike and 172.5's on my Crit bike, i cannot tell the difference getting on one bike from the other in regards to crank length.


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## NJ_Pirate (Nov 1, 2010)

I ride 172.5 on my road bike and need to replace the crank arms, and the only thing i could find cheap were 175's. I've been riding my MTB this week as a replacement and the crankarms felt like they were spinning faster and therefore must be much shorter. I just went into the garage, and see that I have been pushing 175's on my MTB. I guess there isn't as much difference as I thought!


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## zyzbot (Feb 3, 2004)

Cableguy said:


> It would be interesting to see how many of the people who claim they can feel the difference with 2.5mm would actually have no clue if they didn't *know* what they were using. Kind of like how many wine "experts" are unreliable in a blind fold test. If you believe cranks of X size are the best, for whatever reason, and you think you're using them, you will ride differently... regardless of what cranks you actually *are* using...
> 
> Cyclist: "Oh yeah, I can definitely tell it's easier to spin with these cranks"
> 
> ...


Actually I noticed the difference when my new crankset turned out to be 172.5 instead of the 175 that I was used to. I noticed right away that something was different but I didn't quite what it was. Weeks later I noticed the length difference when cleaning the bike and realized that a 172.5 had been ordered instead of the 175. I kept it and got used to it.


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## izzyfly (Jul 10, 2009)

cwg_at_opc said:


> erg. more stuff to fan the flames. read this:
> 
> http://www.pezcyclingnews.com/?pg=fullstory&id=8845&status=True&catname=Latest News


Experimented with two crank sizes 170's, and 172.5's and the difference was what was described in the article, namely getting to maximum power faster with the shorter (170 crank), since you can spin it up faster. One additional observation is that with the longer cranks means lower saddle position to 'make up' for the lower bottom pedal position (since the crank is longer), and on the 12o'clock apex position, the lower seat plus the longer cranks meant I needed to bend my knees at a more acute angle. This more acute bending meant I needed more effort to straighten my legs out when I pedal from the 12o'clock position to the 6o'clock pedal position. Doing this especially on a climb seemed to drain me faster than with a shorter crank, since with a shorter crank I don't have to bend my knee as much on the upswing; it's like 2.5mm less knee hitting my lower torso on my pedal upswing. Just try doing squats where with longer cranks you need to bend more than with shorter cranks. In both cases, you need to straighten up your knees - with the longer you're coming from a more bent position, and thus more effort to straighten the knees. That's just my observation after a one month period of experimenting between 170 and 172.5 cranks. I suggest sticking with the shorter crank if your bike fit gives you the choice between two crank sizes.


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## MShaw (Jun 7, 2003)

My first ride with the new cranks wasn't too different than the last ride on the old cranks. Feet spun slower tho. Not by much.

I haven't ridden the other bike with the shorter cranks on em lately. We'll still hafta see.

M


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## Bocephus Jones II (Oct 7, 2004)

PruneJuice said:


> I am 5' 9.5" tall - will the 170mm cranks work? I know spinning at a higher cadence will seem easier, will I notice that much of a loss of power when climbing?


no...


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## satanas (Nov 8, 2002)

Nobody can really answer this for you. The only way to tell if you notice/care is to try it personally.

It doesn't matter how many dismissive and or self-righteous answers you get here, YOU need to do the experiment for yourself to get a valid answer. YMMV.


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## AndrwSwitch (May 28, 2009)

NJ_Pirate said:


> I ride 172.5 on my road bike and need to replace the crank arms, and the only thing i could find cheap were 175's. I've been riding my MTB this week as a replacement and the crankarms felt like they were spinning faster and therefore must be much shorter. I just went into the garage, and see that I have been pushing 175's on my MTB. I guess there isn't as much difference as I thought!


Having read some of the articles out there, I'm in the "it's no biggie" camp. But it's always made sense to me that someone who gets a lot of saddle time on one size would notice a change, even if they got accustomed to it fast and it made no difference after a half hour or so.

So here's a theory for you. Maybe your MTB's crank felt smaller because instead of having to adjust to the longer crank arm, at least at the beginning of the ride, you were already accustomed to that arm length. Since you were used to the MTB crank arms feeling a little slower to push, when they didn't, they felt like they must be smaller.

For whatever reason, all my bikes have come out of the box with 170mm crank arms. I haven't felt any great need to mess with the sizes, so if I've ever been on a different size as an adult, it's been briefly, test-riding someone else's bike.


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## ewitz (Sep 11, 2002)

After eight months of riding almost daily on my two good bikes with 172.5, this weekend i broke out the winter bike that has 170's. 

Yes, I can tell the difference. However, I am sure a few more rides and I will have adapte enough that it doesn't bug me. But I still prefer 172.5 and wouldn't race the 170's as I find that it forces you spin a gear lower than I would prefer to be in.


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## serious (May 2, 2006)

That article is deceiving. Crank size is not supposed to do much for power output. It is supposed to make it more efficent to *spin*. I have to believe that most people can tell the difference between a 160mm and a 175 mm crank when it comes to spinning.

In the gym the spin bike has 160mm cranks and it clearly easier to spin at 90+ rpm than my 175mm mtb cranks (for long periods of time).


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## saifix (Apr 12, 2014)

i had a 50-34 170mm cranks on my daily beater.26'' wheels.
tried a used 48-36-30 triple crank with 175mm arms.
it was like night and day the difference.very slow cadence,and uncomfortable leg positioning.also the bike handled differently more unstable,slow-ish style.changed back to 170 asap.

now i found a good deal on a 172.5 shimano 105 and from my previous experience im hesitating to put it on my road bike.it has 170mm also.
79.5 cm inseam.


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## cxwrench (Nov 9, 2004)

saifix said:


> i had a 50-34 170mm cranks on my daily beater.26'' wheels.
> tried a used 48-36-30 triple crank with 175mm arms.
> it was like night and day the difference.very slow cadence,and uncomfortable leg positioning.also the bike handled differently more unstable,slow-ish style.changed back to 170 asap.
> 
> ...


Good thing this thread is _only_ almost 4 years old or some people might give you grief for dredging up a dead thread...not me of course, I'd never do anything like that. 

You might want to check the date of the last post in a thread before posting.


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## twinkles (Apr 23, 2007)

Get the 105 crankset, I'm sure you'll like them more than 175s and maybe better than 170s. You'll never know til you try. If you don't like them, you can always dump them on RBR classified, craigslist or ebay. Pssst..............I think it's ok to add to an old thread.


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