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170 vs 172.5 vs 175 crankset(7 posts)

170 vs 172.5 vs 175 cranksetPaulCL
Sep 25, 2003 5:41 AM
Following on the "Mirage vs Veloce" thread below. I have an opportunity to buy a 170mm crankset very cheaply. The problem is: I ride a 175mm now. Will I notice 5mm of difference on my second bike?? I doubt it, but was looking for input.

Thanks. Paul
maybe, but maybe notlaffeaux
Sep 25, 2003 11:18 AM
I have a set of 170mm cranks on one bike and 175 on the others. I personally can not tell a difference. Some people claim they can. Maybe I'm just insensitive (I have been told that before). :)
re: 170 vs 172.5 vs 175 cranksetMShaw
Sep 25, 2003 11:34 AM
If you can buy then cheaply, try it and see for yourself. If you can feel the difference and don't like it, sell them. If you do it right, you either don't lose money, or could possibly make some...

Mike
No answer possibleKerry Irons
Sep 25, 2003 4:15 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.
Pennywise, pound foolish?Fez
Sep 25, 2003 7:14 PM
If you feel like experimenting, go for it. It may feel odd at first, but the body has a way of adapting pretty quickly. I don't know how weird it would feel to ride the 170s 3 days a week and the 175s the other 3 days.

If you are a big guy and you are comfortable with what you ride now, and you are happy with your cadence, then I would stick with 175.

FWIW, I am a medium sized guy with medium length legs and femurs. I ride 172.5 cranks.

I rode 170s for most of the last decade. When I bought a bike sometime in the 1990s, something just didn't feel right, but I couldn't put a finger on it. I had no idea for weeks until I looked at the back side of the crankarm. It turns out the dumbass in the store mistakenly installed 165 cranks (5mm less than I was supposed to get). The shop corrected that mistake.

While the difference from 165 to 170 was very noticeable, the difference from 170 to 172.5 was much less noticeable.

However, when I went from 170 to the 172.5, I made a conscious effort to improve my cadence. The result is that despite going to a longer crank, I improved my normal cadence from 90 to 100 and I think I spin better at all speeds.

Good luck
Could bePaulCL
Sep 26, 2003 8:05 AM
I've decided to hold off and buy the 175's. No sense stressing the knee joint in any way - its' too, too important. The price difference is only $15 anyway!
go check out analytic cycling.comMShaw
Sep 26, 2003 2:55 PM
They have a power comparison for crankarms. Most interesting!

Mike