Forum menu
In the market for a replacement crankset but I've been presented with an option of 170 or 175mm. Which one should I choose and for what reason?
Bike is an Orange 5 if that matters.
175mm is pretty much the norm, 170mm allows better ground clearance and is better for spinning, you often find shorter cranks on smaller bikes or on ladies models.
I would get 175mm.
One of each, 175 drive side, 170 lh. Or even the reverse to counter balance the weight of the chainrings?
172.5 is available sometimes, I suggest matching it to your size/terrain. My road bike has 175.2, fixed gear had 170 (toe overlap reduction) and my fs has 175. Paired crank length 😉
I like the wider "attack" stance of 175, 170 feels quicker on a climb.
5ft 9 , and just swapped down to 170. I was surprised the 5mm does make a difference on ground clearance, and i find i can put the power down quicker and more so in undulations, although this may be more to do with stiffer SLX cranks
175 on the MTB. I like 170 on road, makes it easier to spin smootly, but for technical stuff I'd much prefer 175.
And yes it IS noticeable for me.
175mm means you can have your saddle 5mm lower for a bit more clearance.
Generally speaking crank size seems unimportant for people of average height, therefore worth giving consideration for the taller/smaller rider.
Taller riders > 180cm (6ft.) might consider 177.5cm cranks
Smaller riders < 165cm (5’5”) should be on 170cm length of crank or less
I have only spotted a few studies on this subject (I’m certain there must be more) focusing on the optimal crank length. Findings suggest that crank length was optimal for power (product of resistance and cadence) production when the crank arm was set at 41% of tibia length (lateral knee joint space to lateral malleolus); however this had a very small sample size at 16 trained young adult cyclists. Also the pedalling cadence optimal for power output was found to decrease with increasing crank length. Therefore, an increased crank length increases the lever arm, so the cyclist does not have to pedal as quickly to achieve the desired power output. A longer crank arm may be desirable for power production for a cyclist who style refrain from a high cycling cadence.
Also worth considering crank sizes if
1. You are experiencing biomechanical problems such as knee pain
2. Min increase in ground clearance- if you are between the common sizes of 170-175 (172.5 would be harder to get) and your bike has an extremely low bottom bracket, you may find that the extra clearance from the shorter crank might just be enough to prevent your pedals grounding.
Different cyclists have different leg lengths. It seems obvious that crank length should be proportional, so long legged cyclists should have long cranks, short-legged cyclists should have short cranks....and yet, 99.9% of adult bicycles have crank lengths between 165 and 175 mm. Have the bicycle manufacturers joined in a great conspiracy to force everybody to ride the same length cranks, regardless of their needs?
This is a common misunderstanding. The "leverage" of a bicycle drive train, also known as "gain ratio" depends on the crank length, wheel diameter and the sizes of both sprockets.
Yes, if you go to longer cranks without changing any of the other variables, you will have more "leverage", which is another way of saying you'll have a lower effective gear...but on a multi-speed bike, you can change gears at will!
Ay, there's the rub! Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.
S.Brown.
Shorter cranks are easier to spin, and kinder on your knees if you have knee troubles at all, as well as giving you more ground clearance.
Longer cranks give you more leverage.
Buy what suits you... Though if you are extremely tall, or short, you should be using cranks longer or shorter than the norm anyway to suit the length of your legs. Personally though, despite being bang on average height, I prefer to use 170mm cranks cos I can spin them better and they're kinder on my dodgy knees.
Hmmm, I'm 5'11" and like the idea of more leverage since i dont have powerful legs
Stroke length is also a factor on technical terrain in MTBing. You might have to use one pedal stroke to clear something before you can make another, for instance. I reckon it's easier with long cranks, but I can't quite explain why currently.
Its crazy isn't it.
someone 6'2" would ride 175mm
someone 5'2" would ride 165mm
Thats only 10mm difference (20mm dia) between someone 1 foot taller than another!
188cm tall, 180mm cranks on SS. Can notice the difference but it's not night and day.
Did some research before deciding and settled on 180mm because basically I'm taller than average, so should run longer than average cranks.
Knee pain and the need to buy a new crank (due to a new build), forced me to look into the same subject. Basically, the shorter your legs are, the shorter your crank arm length should be to gain optimal power - if you think of the extremes, a really long crank will not allow your knee to bend in such a way to gain maximum downward force onto the pedals. This will mean less power, and also most likely knee pain. Road bikes seem to have shorter cranks from what I've read.
For a 30" leg, I would get 170mm
31" + 175mm
Thats all you get from Shimano, Middleburn etc would prob offer more variety