I am using 175 cranks on my road bike the tt bike i am going to buy has 172.5 could this be a problem?
I have a bike with 170 mm cranks and one with 175 mm cranks. I can notice the difference, but it’s not a problem. I think you shouldn’t worry.
2.5 mm will make almost no difference. You will be hard pressed to notice. However, neither length may be the one you should be riding. I rode 175s for 10 years before trying 180s and finding I liked them better. After a little more research into some things Leonard Zinn was writing I went to 190s and that was better still. Just for curiosity, punch you inseam into the formula:
Inseam (measure this acurately standing flatfooted up to your crotch)
in millimeters (inches x 25.4)
x .21 or .216 = crank length proportionate to leg length in mm
For example:
34.5 inches x 25.4 = 876.3 x .21-.216 = 184-189
If you do mostly tris and time trials go with the longer length. In some case this may mean that your cranks are too long. If you fall in that range that hits 170-175 then you are one of the lucky ones because everybody makes a crank for you. If not then things become harder.
Chad
Thanks, I come out at a 185 crank length now thats got me thinking,Did it give you more power what about rpm,it could become an expensive exercise to find the right size
.
I first tried out the 190s on my mountain bike for a while, but since I only had a double my low gear was 38x34. It didn’t matter. With the long cranks I was climbing stuff that I couldn’t believe I could manage without a triple.
I have no problem spinning them on the road bike at a high rpm, but on the few occasions I tried, I was most impressed with how hard I could accelerate. Not a useful thing in triathlon, but I wish I had the longer cranks 10 years ago when I was bike racing. The only thing I can liken the feeling of longer, proportionate cranks is this: imagine you are trying to pull the nut off a bolt that is really tight using a short wrench. Now switch to the longer wrench and see how much easier it is to loosen.
I was so convinced I had Frank Day make me some 190mm PowerCranks and I have been riding them ever since. By the end of the spring race season my rpm for races on the 190 PCs averaged between 87-92. Since my computer counts coasting as zero and most of the races were hilly, then the actual rpm was higher.
I cannot for the life of me remember the company that made my first set of long cranks. I think they supply Zinn cycles with his long cranks and you can buy them from Zinn, but he marks the price up by close to $100 from what I paid and my cranks look exactly like the ones on his website. I paid about $200, but I saw the last time they were up to $240. Still, that was better than the Zinn price of $360 (which does include a BB) and less than you pay for the Shimano, Campy or high-zoot carbon cranks than come in very limited lengths. If I think of the name I’ll let you know.
Was the 185 using the .21 or .216?
Here is the web page I ran across initially.
http://www.nettally.com/palmk/Crankset.html
Chad
I will check out the site my range was 186-191 it makes sense in what you are saying it makes me wonder why shimano and others do not offer a wider range i think my i am a fairly average build 5-11 78 kgs.
Dave
$$$$$$$$$$$$$
That is the bottom line for the companies who make components. It is not very economical to offer up a range of sizes from 150mm-220mm. Most people will likely fall within the 165-180 range, so why let people think they might need something that is longer or shorter if it cuts into your profits?
Chad
Hi again,
I don’t know why it occured to me out of the blue, but I remembered the name of the company.
High Sierra Cycle center:
http://www.hscycle.com/Pages/customcrankset.html
New cranks are $240, no rings. You can get a regular 130mm or even 110mm (the so called compact size that has been around forever), or even the crazy campy sizes in 135 or 144. That means you can keep using whatever rings you have right now. They don’t take returns, though, since the cranks share a common spider and they build them for you after you order.
If you fall out in the 186-191 range then I would buy the 190s. You will not regret it. Do think about a couple things though:
-
Ground clearance. If you are only a triathlete this isn’t an issue. If you race bikes in criteriums then you won’t be able to pedal through the corners.
-
If you go to a much large crank your saddle height is going to drop and make some corresponding changes in your position.
-
It only comes in square taper, not octalink or any of the new funky BB types. You may also need a new, longer bottom bracket depending on the design of your frame and arm clearance. This might will increase q-factor. Not an issue in my book.
It is well worth the money.
Chad
Thanks for the help
.
After years of running and riding everywhere (no car) with a 172.5, I switched to a 175 a year ago: huge difference (more power) BUT I now have knee problems for the first time ever., …may very be a complete coincidence… probably going back to 172.5.
PS. The formula puts me at ~180
It is funny to see this post here!! I posted something very similar the other day and people was not able to explain me what would define my crankset size.
I also think (the physic explain it) about the “imagine you are trying to pull the nut off a bolt that is really tight using a short wrench. Now switch to the longer wrench and see how much easier it is to loosen.”
Some friends told me about the knee problem it can cause and so on. I have been trying the 175 (used to use 172.5) and I am liking it. I cannot tell it is a hole lot of difference but I also changed my small ring to 42 and I am liking the new set up.
Peace,
Bruno
I have given the issue some thought,as to why the manufactures make that particular size range and not say start the range at 175. Now i maybe way of the mark here but most pro cyclist probably fit into the 55kg-65kg and height range to suit which would probably bring the formula for them at 170-175. triathletes generally are taller and with a weight range of 70-80 kgs i know weight is not the factor but i am looking at proportionatley, so maybe we do not fit the norm make sense?
This issue is a bit more complex than “Multiply leg length by X” and “longer cranks gives more power”…
a) The leg muscles are most powerful when close to fully extracted - advantage shorter cranks.
b) To change into 5 mm longer cranks, the seat must be adjusted 5mm down. At the top, the pedals will be 5mm+5mm higher; making it more difficult to sit in low aero position - advantage shorter cranks.
d) Knee problems, pedalling style, race type etc…
Get the right crank lengt, not the longest!
Now i maybe way of the mark here but most pro cyclist probably fit into the 55kg-65kg and height range to suit which would probably bring the formula for them at 170-175.
This statement is truer than you know. If you looked at the link for the Kirby guy, somewhere on his page I think I remember him talking about the average size for pro cyclists in the 70s. It showed that a 170-175 crank range would fit 90 percent of them. I’m sure that is still the case if you factor in the size of women. The common range fits a large percentage of them.
However, if you are outside that range, it may not. I have never had knee problems and never noticed any other issues when I went to 190mm cranks. I just kept getting faster.
Chad
This issue is a bit more complex than “Multiply leg length by X” and “longer cranks gives more power”…
I don’t think anyone advocates buying the longest crank possible, just one that fits. For a large percentage of the population that means using one of the common sizes.
What is wrong with using a formula to determine crank length? Muscles are muscles and if a specific range of motion is good for one person, it will be good for another.
a) The leg muscles are most powerful when close to fully extracted- advantage shorter cranks.
I fail to see how this argument supports shorter cranks. Using this philosophy I could give you 150mm cranks, raise your seat and say “There you go, your legs are making full extension” but are you going to be better on 150mm cranks? I doubt it. Why, because they are too short for you. Why would a much taller person be any different?
b) To change into 5 mm longer cranks, the seat must be adjusted 5mm down. At the top, the pedals will be 5mm+5mm higher; making it more difficult to sit in low aero position - advantage shorter cranks.
This may be true–though I never had a problem with it–but doesn’t take into account the fact that a difference of 5mm on your frontal areas is negligible when compared to the size of your whole body. And if going to longer cranks is appropriate, it may increase your power and more than offset any loss of aerodynamic, if there was one.
c) Knee problems, pedaling style, race type etc…
I went from 175 to 190, and never had any knee problems. I have no idea where this comes from. If ever this fallacy had a chance to work it, should have been me, who increased by 15mm. Never a problem. Pedaling style? I can spin 190s as at 100+ rpm or climb easily at 75 rpm, so it comes back to the question of range of motion—do muscles work the same or are they different? Race type? I already mentioned you don’t want to corner on long cranks if you are still riding a frame made for shorter ones. Other than a criterium, I can’t see how longer cranks would not be a benefit. Ect… ? What other reasons do people have against longer cranks besides the traditional “that’s the way we have always done it.”
If you can’t tell, I’m a big advocate of longer cranks for those who should be using them. That’s not everybody and longer is not necessarily better, but if have very long legs then pedaling on a 170 or 175 is like riding a tricycle.
Chad
Here are the aero, power, and knee issues in a little bit more detail. If you go to shorter cranks, by say 5mm, then to get the same leg extension at the bottom of the pedal stroke you will have to raise your sadle 5mm. At the top of the pedal stroke, your leg will now be 10mm more extended than before. This means you’ll be developing power from a less compressed (knees in your chest) position. Of course, if you’re sitting up then this isn’t an issue because of the more open angle, but in the aero position it is an issue.
Note that this is also related to power. The more flexed (bent) your knee is, the longer your quad muscles are stretched, and the less power output you’ll have at that position. I’m not referring to force-to-torque conversion related to moment arm, I’m talking about the force of muscular contraction, which for the extensors is reduced at full joint flexion.
Longer crank arms increase the total amount of flexion and extension with each rotation, which rotates the knee joint through a larger angle range. For some people this is no problem. For many others, though, decreasing the range of knee angles, and especially the range through which force must be applied, is a significant benefit.
Aero, power, and knee health issues all argue in favor of shorter cranks. Longer cranks increase the torque (for the same force) at the point of maximum power, and therefore would be expected to be advantageous in mountain biking if the low range is gear-limited. But now that there are 24- and even 22-tooth chainrings, why should a mountain biker be gear-limited?
At the top of the pedal stroke, your leg will now be 10mm more extended than before. This means you’ll be developing power from a less compressed (knees in your chest) position. Note that this is also related to power. The more flexed (bent) your knee is, the longer your quad muscles are stretched, and the less power output you’ll have at that position.
This is a very interesting explanation and certainly not something I could have come up with. It reminds me of doing squats; the farther down you go the harder it is to get all the way up. However, it still begs the question of optimum range of motion. Surely there is an optimum range of motion as you are describing it, but it isn’t very logical to me that the range should be the same for everyone.
If I go back to the comparison with weightlifting, when I do squats (I don’t anymore, but let’s pretend) and I am six feet tall with long legs, I could go down a certain distance until my knee is at a right angle and then raise up with the weight fairly easily. However, if a five foot tall person did the same squat, his range of motion is going to be far less than mine, even if we were of the equal strength.
If I were to imitate his range of motion, I would probably not be traveling very far with the lift and would not gain the maximum benefit. If the shorter person were forced to go through my range of motion he might end up going all the way down to his heals and not be able to rise because he was too stretched out.
To me the same logic follows for longer cranks. If I have long legs and am using a crank that is too short proportionately, then I am limiting my range of motion from the optimum. It would be like making someone who should use a 170mm crank arm make do with a 150mm.
Tell me where my supposition breaks down. I really liked your previous explanation but think it supports rather than hurts the need for proportional length crankarms.
Chad
CDW, I agree with you. Longer legs should go with longer crankarms, for exactly the reasons you describe.
But longer than WHAT? I suspect crankarm length formulae were originally derived by comparing historically “normal” crank length with normal inseam length, and then scaing everyone else proportionally. What’s missing is detailed physiology research identifying the actual optimum length. The few studies I’ve seen on this contradict each other to a certain extent (best I can remember), and I don’t know if this has ever been studied in the triathlon context where efficiency matters more than raw power.
So yes, as you say, surely there must be an optimum length. But it’s probably not 170mm, or 170 x some proportionally-derived coefficient. For pure bike racing, maximum power may well come at 170mm for the typical male bike racer. Traditional bike dimensions seem to have an intriguing way of turning out to be pretty close to optimum after the research is done. But again, triathlon geometry is different, and this will probably turn out to be true for crank length as well.
One final thought. I’m 49, and have spent too much of my life in the sedentary state. I ain’t gonna win a triathlon; that’s not why I’m here. For me, triathlon is not a race to be won, but a celebration of life, sport, health, and the great outdoors. If it turns out that shorter crankarms are better for the long-term health of the cartilege meniscus in my knees but give away a little bit in total power, I’ll take those 165s, please.