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changing from 172.5 to 175 cranks

post #1 of 34
Thread Starter 

I am switching to compact cranks for some upcoming ultra distance events.  What are the drawbacks of switching from a 172.5 mm crank length to 175 mm?  I know longer length means more leverage but is it going to kill my knees or hips to switch?

post #2 of 34

i migrated from 170 to 172,5

i adjusted my seatpost so that the leg distance to the pedal remained the same,

i haven't got any problems but cannot tell the difference really, i don't ride that much nowadays though,

post #3 of 34

The difference in length is 2.5 millimeters or about 1.5 percent, you probably wont notice a thing. I have 175mm cranks on my road bike and 172.5 on my tri-bike, I notice no difference.

post #4 of 34

You may not notice a difference.  Assuming you drop your saddle 2.5mm for the extra length, your knees will come up ~5mm higher at the top of the stroke, which shouldn't hurt you.  A few years ago I was trying different crank lengths (I was deciding between 172.5s and 175), and each time I switched between the 172.5s and the 175s, it just felt like I'd lowered the seat a bit. This kinda annoyed me, so I stuck with 172.5.  I reckon I woulda been just as happy with 170s, but my local shop had deals on 172.5 Dura-Ace cranks, so.....

 

What's your inside leg length (not pants inseam)? 

post #5 of 34
Quote:
Originally Posted by beyeker View Post

I am switching to compact cranks for some upcoming ultra distance events.  What are the drawbacks of switching from a 172.5 mm crank length to 175 mm?  I know longer length means more leverage but is it going to kill my knees or hips to switch?

 

We aren't you and we cant see you, so we can't really give you a firm answer. Many people have experimented with longer cranks (including me), but there appears to be no scientifically determined evidence to suggest that there is a gain or loss in performance from changing crank length in small increments.  Usually this is becasue no bike fitting parameter can be changed in isolation from other parameters.

 

For example a crank length change will lead to a saddle position change which can lead to a stem position change etc etc etc. By the time you've settled in to the different position you can't possibly know which of these subtle changes has actually resulted in a gain or loss (or injury).

 

The mechanics of the situation are simple.  Generally you will typically end up pedalling at slightly lower rpm in a slightly larger gear for the same speed.  Whether this matches well with your physiology or not depends on you.

 

However I disagree with the blanket statement that you won't notice any difference.  My switches in the past have lead to subtle (but noticable) changes in pedaling style, and has affected the onset of back pain that occasionally plagues my riding.  If you've been, and will continue, doing long distances in the saddle (as stated in your post), then I think you will be quite atuned to your current setup and any changes you make to it.  I would at least budget for some time to adjust to the new cranks and the positional tweaks required, and be prapared to call it a failed experiment if it ends up hurting you.  Of course it may never happen, but it is foolish not to embark on such experiements without eyes wide open.

post #6 of 34
Quote:
Originally Posted by 531Aussie View Post

 I reckon I woulda been just as happy with 170s, but my local shop had deals on 172.5 Dura-Ace cranks, so.....

 same reason for me but on Ultegra, twice ! one time for a 53/39 and the second time for a 50/34, just two days ago...

i guess stores tend to sell less of the 172,5 so then they put them on sale ?? 

 

 

post #7 of 34

Longer crank length also gives you less ground clearance in cornering so be careful. 

 

Read this for more info: http://www.nettally.com/palmk/CRwives.HTML

and this: http://www.nettally.com/palmk/Crref.html

post #8 of 34
Quote:
Originally Posted by vspa View Post

..

i guess stores tend to sell less of the 172,5 so then they put them on sale ?? 

 


Ha! Very probably.  Yep, from what I gather, 172.5 is the most ubiquitous length (or at least it was for a long time), perhaps just ahead of 170.

 
 

 

post #9 of 34

I forgot this site too: http://www.sheldonbrown.com/cranks.html

post #10 of 34

I think many people give too much importance to an "ideal" fit. A fit that is close enough is sufficient.

 

I have 2 bikes one with 175 cranks and one with 170 cranks. I have no problems going from one to the other. There is less overall positional difference between going from one set of cranks to the other than there is going from the hoods to the tops of the handlebars. Bicycling is all about being comfortable in a wide range of positions. If you ride in one position all the time, perhaps there might be some problem with slight changes but ...

post #11 of 34


 

Quote:
Originally Posted by An old Guy View Post

I think many people give too much importance to an "ideal" fit. A fit that is close enough is sufficient.

 

 


I agree with this!  I know a guy who spent $800 for a pro fit plus the recommended goodies and he came out worse in the end, I've known others who came out worse too, I would venture to guess in the 40 years of riding about 1/2 came out worse and the other 1/2 came out better, in other words a flip of coin if it works or not.  I have 9 bikes and not one is exactly the same as another, and I can ride any one bike and not be wishing I took a different bike, and none have ever been pro fitted, I've done my own dialing in.  I think a lot of fit issues are psychological, but that's just me, I guess if your a pro rider then it may be necessary to get the exact ultimate position for performance, but their fittings are a far cry from the crap we get at LBS's, and they get theirs for free including the parts we don't get that luxury.  You can get plenty of fit help right off the internet without resorting to some expensive pro fit.  And of all the people you would think should have a pro fit is me, I raced Cat 3 level for 5 years never got a pro fit; I'm now 58, in other words older then dirt to most of you, I rarely see someone my age riding, you would think with age comes problems and such problems need a pro fit to help with...nope.

 

post #12 of 34

 

Quote:
Originally Posted by Froze View Post

 I rarely see someone my age riding, you would think with age comes problems and such problems need a pro fit to help with...nope.

 


we have here an active number of master riders who compite every sunday, from your age and more !

proper fit is something i don't miss after leaving competitive cycling, in those days a 1/2 centimeter change seemed outrageous and you even risked injuries for such a small change,

the more you trained on the bike the more fragile your legs were,

 

 

  

post #13 of 34


 

Quote:
Originally Posted by vspa View Post

 


we have here an active number of master riders who compite every sunday, from your age and more !

proper fit is something i don't miss after leaving competitive cycling, in those days a 1/2 centimeter change seemed outrageous and you even risked injuries for such a small change,

the more you trained on the bike the more fragile your legs were,

 

 

  


Where I live older people don't ride much, and the ones I do see are pedaling along at 8mph on a comfort bike.  There are only a handful of older riders around here that are any good at riding.  

 

I never had an injury from a ill fitting bike, so a 1/2 a centimeter isn't going to do anything, your talking 3/16th of an inch!

 

What did you mean by the more you trained on the bike the more fragile your legs were?  If this is in reference to some part on your bike being off by 3/16th of an inch I find that incorrect.  The human body has a wonderful way of adapting, and it will adapt to differences and thus your legs will improve over time just as it would if the bike didn't have that 1/2 cm difference.  Maybe if you were talking an an inch too high or low in the seat making your knees too straight or too bent you could have a point, but not 1/2cm, that's psychological.  Kind of like a gambler going out to gamble and takes a certain set of clothes each time he goes because he thinks he wins more wearing those specific clothes.

 

post #14 of 34

 

cycling legs with many kilometers on them are potentially easy to injure for example doing other sports, that is the reason why competing cyclists don't do any sports different from cycling during the race season, ok lets make it 1 inch change but assuming someone (a competing cyclist) lift or lowered the saddle that amount in one go, he could easily get tendonitis, Fignon injured his achilles tendon from barely touching it with his pedal, in his words, after a training ride,

 

it was precisely a master rider who told me once that cycling legs should be treated as ballet dancer legs, i got tendonitis once and it was so annoying that i started paying special attention as to how to avoid it ! 

post #15 of 34

 As a professional rider, I used 180mm cranks for classic races and time trials. On the track I used 170mm and in criteriums 175mm. But that was a long time ago...now I only ride for pleasure and especially the Alpe d'HuZes event, on one single day we climb the Alpe d'Huez six times....and fundraise more than 42 million Euro for the Dutch Cancer Society in 6 years.

This year I got an Magnesium Segal bike sponsored (www.segalbikes.eu). It had a SRAM Force groupset on it and I was very pleased with it. It had only a 170mm crankset (53/39) and I wanted a longer crankset. Because the bike sponsor didn't have the crankset in stock I searched the internet and found Zinncycles. ({C}www.zinncycles.com{C}) Finally I climbed the Alpe d'Huez this year with 200mm cranks (compact), with my 1.95 meter and inseam of 94 centimeters it felt great! With long legs you need to consider longer cranks. Zinn offers also the possibility to try longer adjustable cranks so you can find out what comforts you. You need to try them for a few weeks before your muscles are adjusted. But I agree that a switch of just 2.5mm won't be a problem.

....oooh yes, I can tell everybody that mine is 20cm! ROTF.gif

 

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