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172.5 or 175 crankset(9 posts)

172.5 or 175 cranksetgtrguy
Oct 12, 2003 8:54 AM
I'm 5'10" and ride a Trek 5500 I have been riding a 175 triple and really died not know it I decided to upgrade to dura ace and ordered a 172,5 thinking that is what I had. I know that the larger crankarms are beter for mashing. I think 172.5 is standard. Any thoughts?
You beat me to the question - I to am curious how does thewild
Oct 12, 2003 3:10 PM
175 compare to the 172.5 (which I have) to climbing hills and flats.

Much thanks
re: 172.5 or 175 cranksetrussw19
Oct 12, 2003 3:34 PM
Most here will agree that you won't be able to tell the difference. The difference is the width of a nickle. I made a jump from 172.5's to 177.5's and didn't notice the difference. The school of thought is that each 2.5mm increment translates to about 3 to 5 RPM defference on your spinning. You will get used to it in a week of riding and won't ever notice it after that.

On the other hand there are people here who swear they are "in tune" with their bodies and can tell the two apart. They also claim that they can sleep on a stack of 15 mattresses with a pea under the bottom one and still feel it. I have my doubts about these people, but that's simply my opinion about it. But then that's what you asked for.

Lol :-) Thanks russw19 (nm)wild
Oct 12, 2003 4:32 PM
Oct 13, 2003 10:15 AM
I have 170mm cranks on one bike and 175mm cranks on another. I switch between bikes regularly and can not tell any difference in the way I ride or spin. Chances are unless you'll never feel a difference in a 2.5 mm change.
“Power”, “Leverage”, “Spin”????...TFerguson
Oct 13, 2003 4:13 PM
I like your answer because none of this has ever made any sense to me. Changing your chainring from a 53 to a 52 will give you the about same change as going from 172.5 to 175 and your legs can't tell the difference. If you want to change your "leverage", just shift. One cog equals about 10mm.

The only possible difference I can see from different length arms is how far your knee has to bend to get to the top. This may be important, but has nothing to do with the above.

Oct 21, 2003 5:39 AM
Unfortunately I don't have 15 mattresses handy to test whether or not I can feel the pea, however the ability to detect differences in crank length is *not* hypothetical, though it does vary considerably from person to person.

I am one of those strange people who can tell 2.5mm difference, while I would describe 5mm as being vast, huge, humungous, etc. I have friends who don't notice - and others who do.

I suspect it's a similar thing to the fact that most people don't care much about gaps between the gears as long as the range is big enough; ie "what's the point of 10 speed, 5 is enough", etc....
Whatever makes you happyKerry Irons
Oct 13, 2003 4:52 PM
It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems. That said, an extra 5 mm in crank length may only take away 3-5 rpm of spin, so it is not a large effect. A triple will help in making sure you have low enough gears to keep your cadence high while climbing - pushing hard at a low cadence while climbing is a major source of knee problems.

Every increment of crank length is about 2-3 rpm. Going from 170 to 175 is about 5 rpm. Spinning is more physiologically efficient, all else equal. It is also something you have to practice - you can't say "I can't spin" unless you have spent some serious time working on it, day after day over a season or two. The primary disadvantages to low cadence like you use are 1) harder to accelerate quickly starting from a lower cadence, 2) you'll have less left late in a ride, 3) risk of knee problems, and 4) you have less "turndown ratio" in your gears. If your total range of cadence is 50-60 up a steep hill to 80 on the flats, you need to have a wider range of gears to get you everywhere you want to go. If you can comfortably spin up to 110, then you can go 35 in a 53/13. If 80 is your comfortable cadence, you need a 53/11 to just go 30.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. What little research has been done on crank length suggests that people adapt to different crank lengths and there is no optimum or formula related to body proportion. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

The short answer is: if it feels better and measures faster, do it. If it doesn't feel better but measures faster, maybe you should do it and hope to adapt. And even if it doesn't measure faster, you may adapt and get faster. Simple, eh? NOTE: measures faster means repeat timed distances on different days in different weather, not just "faster on my nightly ride" which can be masked by the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.
re: 172.5 or 175 cranksethphoto
Oct 19, 2003 1:30 AM
I'm not an expert cyclist, but I can definitely tell between 165, 170, and 172.5 cranks when riding them. The other day I test rode a new roadbike and within a couple of minutes I can tell that the cranks are longer than 170 (they were 172.5). As someone already mentioned, I can "feel" by how much my knees come up, not by the rpm or power.

I'm 5'8", ride a 52cm frame and 170mm cranks.

I think it comes down to personal preference - there really is no standard. I'm used to 170mm cranks on roadbikes so I stick with them.