Crank Arm Length
 

Hi all yes I’m a Newbie. Just got back into cycling after almost 15 years. Very long story but been adding things to my Giant Defy. Last thing was a power meter. I trusted guy I got bike from and ordered 175 mm crank meter. My Lbs installed it and 30 seconds later a second mechanic said you gotta a problem. He could immediately see my cranks were 172.5 not 175. Place I got Stages power meter from said it was my fault and I’m stuck with it. Called Stages and they were super but couldn’t help me as I didn’t buy it from them. So long story but bought the the drive side in 175 had it installed today. I had read many articles about length and majority of them say makes no difference, just adjust saddle height. My fitter didn’t even have to do that. Looked at my knee position and said it looks ok and to try it for a while. So paired it to my Garmin 830 did zero reset and just threw my shoes on and went for a ride around block 1.8 kilometers. Since back riding it’s been a pure pleasure no pain no burn, until I did my heart rate threshold test lol but in this short trip around my block my thighs were burning. Do you guys think I need to get use to new length or could this jump in size be a problem. Possibly since the arc is longer my legs need to get use to it ??
thanks for help
I’m 6 foot tall. I’ve gone from 172.5 to 175 mm cranks

Shorter cranks?

You didn't say how tall you are. But, you should be fine. 2.5mm difference in length. You'd probably never have noticed if you hadn't looked at the labels.

Two competing physical things.So, the two are a wash. The energy is the same. You may find you're doing a slightly higher cadence in slightly lower gears with the shorter cranks.

As long as both sides are the same, your body will get used to it.

Hi I went longer. Thought they were 175 but I actually had 172.5 So I bought 175 drive side also so now I’m running 175 and I was running 172.5 and I’m 6’ foot tall

Ahh, so they're 2.5mm longer... Bought one, then a second to match. Still, you are pretty tall. Not Wilt Chamberlain, but not short either.

Depending on how hard you hit it, it may take a little to get used to change, but many people ride on multiple crank lengths on different bikes.

You may need to lower your seat by about 2.5mm (unless it was previously low).

I'd turn off the power meter, and give the new cranks a good shake-down before you decide whether you like them or not.

I'm 5'11" with 33" inseam and have bikes with 170, 172.5 and 175 cranks. I can tell a little difference if I haven't ridden one for awhile, but adapt pretty quickly so I don't notice the slight difference... when my health is good (explanation follows).

When I first got the bike with 175 cranks, I set the saddle too high based on how my cadence felt, and soon has lower back/hip aches. I video'd myself riding and realized I was rocking in the saddle. After lowering the saddle a bit the problem cleared up. With the correct saddle height my knee is a bit higher at the top of the stroke and there's slightly more quad engagement, so if I haven't ridden that bike for awhile my quads may tire a bit sooner on seated climbs. When I stand to pedal the longer cranks feel like they offer a bit more leverage. Hard to quantify this stuff.

And a couple of donor frames came with 175 cranks -- one with a cracked aluminum frame I'm cannibalizing for components to put on the other, a carbon fiber frame that included only an Ultegra crankset in 175. So I'll ride that crank as-is for awhile and it'll probably be just fine.

There are various theories about longer cranks offering more leverage and maybe favoring riders with choppy cadence (guilty), shorter cranks being better for smooth spinning (mine isn't very smooth), etc. But in actual testing by various magazines using power meters, and reports from interviewing pro teams that test bike/rider fit to the nth degree, there isn't much evidence to support any of these theories. They've even tried 160 cranks on riders who are around 6 feet tall. Reportedly, Jacques Anquetil (5'10", TdF champion between the late 1950s-early 1960s) experimented with everything from 160-190mm cranks, although it's hard to find definitive bike setup info. In still photos, his distinctive toe-down style and thigh position relative to top tube at the top of his stroke indicates he seemed to experiment a bit with saddle height as well. Mostly it comes down to what the rider prefers in terms of subjective feel.

For 2017-early 2019, I rode an older '89 Ironman steel frame bike with mostly original components, including 172.5 cranks. The only concession I made to recovery from injury and illness in 2018 (hit by a car, then complications from Hashimoto's, a decades-old auto-immune disease that killed my left thyroid lobe in late 2018 and left me pretty weak for a year), was to swap out the original 52/42 chainrings in favor of 50/39, then 50/38, and the 7-speed freewheel from 13-24 to 13-28.

Then starting in spring 2019 I switched mostly to an early Trek 5900 from 1993, which the previous owner had fitted with 170 cranks and Biopace 52/42 -- those oblong eccentric chainrings (not quite oval, sorta squared off). I was curious to try 'em but figured I'd get tired of the experiment and switch to conventional round chainrings soon. Nope. I liked the Biopace rings... but only on that bike. The only adaptation I made was to slow my cadence from the usual 90 rpm to around 75-80 rpm, which seemed to work better for me -- a bit more power, a bit faster climbs.

Last month I had to put the Trek aside to service the old Chris King headset (yup, even those need attention after 27 years of neglect). So, out of curiosity, I swapped the Biopace rings over to my Ironman with 172.5 rings. It felt herky-jerky, not smooth as it did on the Trek with 170 cranks.

Within a week I had foot pain and knee twinges -- not quite unbearable or persistent aching, but definitely something wrong. I rarely have knee problems. I tried saddle adjustments -- height, fore/aft positions, etc. -- everything I could think of, but nothing helped. Last week I switched back to round chainrings. Still no help. And the foot pain, while familiar, has in the past always been corrected with proper shoe fit and good insoles (I like ProFoot Miracle insoles). But I'm wearing the same footwear and insoles that have worked perfectly for me for years, including replacing the insoles as needed (they're good for 4-12 months depending on the user).

At this point I'm not even sure the knee twinges and foot pain have anything to do with the crank length, chainrings or anything about the bike. I've also been battling a persistent problem with sinus and respiratory inflammation, psoriasis and psoriatic arthritis (all related to the Hashimoto's syndrome). And I'm getting the same foot pain with any shoes and boots I wear for walking. So that's probably just another manifestation of the arthritis-type symptoms that accompany Hashimoto's.

So, long boring story short... it's likely my swapping chainrings and crank lengths had nothing to do with my recent knee and foot twinges. And it occurred to me that maybe other folks have also mistakenly blamed the bike for unrelated physical discomfort, and just assumed crank length, chainring types, etc., were at fault.

Ask me again in a week or so after I've finished the new-to-me bike build with that 175 Ultegra crankset.

Hi thanks for all the info. Honestly I haven’t ridden in a week with all the power meter crank length and trying to return it or should say swap it so maybe that’s why my quads got so sore so quick. I’m gonna just try not to think about it and ride. I plan on starting a training peaks plan on Monday.

I raised the the same issue a few weeks ago, also involving a purchase of a Stages power meter. A 2.5mm increase in crank length increases your peddle distance between the top and bottom of your stroke by 5mm. If your particular leg length is proportional to your height, 175mm cranks should be no problem.

https://www.bikeforums.net/general-c...illimeter.html

2.5mm is not that big of a difference. You will adapt.

I have had the opposite recently due to a mishap with a crank arm. A ruined NDS crank arm necessitated a change from 170mm to 175mm crankset that I already had. I definitely can feel the difference. I found and acquired another NDS 170mm crank arm and this morning I am going to change the crankset back to 170mm. All my bikes will once again be 170mm.

Your height has nothing to do with crank length, it's your leg length and saddle height that are relevant. FWIW, I'm only 5'-6" tall, but my cycling inseam is 32-5/8 or 83cm and my saddle height is 73cm. I switched from 170mm to 172.5mm many years ago and really didn't notice the change. Going up from 172.5 to 175 should not be a big deal. How people set their saddle height varies a lot. If you feel over-extended at the bottom of the stroke, the saddle might need to come down 3mm, but then your knee will be even higher at the top of the stroke. Start with no change to the saddle height and go from there.

Hi. That’s what I’m gonna do. Try as us for a while. I rode for a hour today looking at my knee position on top and bottom and it’s flexed both ways. It didn’t seem that bad. I only have a 1x so I’m thinking why I’m feeling a little more strain from new crank length is I only have the 50 tooth chain ring and going longer cranks has made each cassette cog a little harder to turn

Longer cranks give your legs a tiny bit more leverage over the gear, not less.

More leverage, but going through a larger circle.

Right. I'm not claiming that free power is being summoned from the aether, but pointing out that the extra length should not make a given gear "harder to turn" (unless there's a fit issue involved).

I just got back home after a 37 mile ride, on my Lemond Tourmalet, with the crankset changed back to 170mm from 175mm. Much more comfortable and efficient for me. Hard to believe that a 1/5 inch per arm can make such a difference.

I'm 6'1" and if average proportions. I've always used 175s and find them comfortable.

I wouldn't decide the longer cranks are harder on your legs until at least a few rides. Depending on your recovery state, how much sleep you got, etc etc, you could make them burn with your old ones too.

I don't think the extra 2.5mm is the cause of your thigh pain over the course of 1.8km. I'm kind of with the others who say that 175mm should be no issue for someone 6ft tall. Understood that it's leg length that should determine size but unless you have extra weird proportions, your leg length should be fine given your height. I'm 5-7" and run 172.5 on two bikes and 170 on another. I could feel a little difference when riding the 170 for the first time, but that only lasted a few minutes. Lastly, if you didn't have the bike in hand before you ordered the power meter, I would let the seller know he's an idiot for giving you the incorrect specs.

I don't buy the idea that leg length has anything to do with the size crank you should get. From my viewpoint, if you generally like to ride at low cadence, then longer cranks might be desirable. If you like to ride and fast cadences then shorter cranks might be the thing.

Extra leverage IMO, doesn't compare to going to the next lower gear, however if you run out of gears then leverage is certainly some benefit for a moment or so before you either have to push the bike or make it over the hump.

With a 34.5 inch inseam, I've been quite happy on 165 mm cranks. Shorter cranks keep my knees from beating my chest to death when very aero and fast. I also like that it gives me a little more road clearance on my pedals for pedaling while in turns and clearance for road furniture and debris.

Granted, it's not a lot of difference, so preference I think is more what one is used to and not so much that leg length dictates adherence to some axiom that is still IMO sketchy after 40 some odd years.

crank arms are so twenty-teens..... NuBike ? Mountain Pro
- and who doesn't love the idea of reviving early 1990s advertising!

Not a problem just adjust your seat height.
I have 5 road bikes with 175mm cranks, one with 172.5mm and my track bike has 170mm.
I only difference I notice on my track bike is no freewheeling :D

I'm 6 foot with a 33 inch inseam. TBH crank arm length isn't so much of a big deal. I've been all over the map & honestly I think it comes down to personal preference.

On 170's I felt bound up after a while & for what ever reason it felt like my quads were being favored more. My speed/power remained the same.
On 175's my cadence noticably slowed, I feel like I pedal square unless I consciously make a deliberate round stroke, but after a while my hips started acting up. My speed/power remained the same.
For me, 172.5's seems to be the best happy medium from a personal physiology perspective. (Hip issue & pedal coordination.)

I found that 172.5's, for me anyway, paired with oval rings (Absolute Black, Rotor) seem to offer the smoothest power application & easily the highest cadence.

My wife is quite a bit shorter than I am. She uses 170's. For her 175's are a disaster. So, yes it does matter, but a lot of it is coordination & personal feel/preference.

If anything, you've got a powermeter crankset. It wouldn't be hard to sell it for a reasonably high percentage of it's "new" price.

Crank length determines a fixed distance between the pedal at the top of the stroke and at the bottom, and that distance should be proportional to leg length. In theory. Assume that for a given rider there is an ideal knee angle and position of the foot at the top of the pedal stroke and a ideal position at the bottom, then the ideal crank length would be half the distance between the two positions (adjusted of course for the stack height of foot above the pedal axis). If the cranks are longer than that ideal, then either the knee will be bent too much at top of the stroke, which could cause knee pain problems, or the pedal will be too low at the bottom of the stroke, making pedaling awkward and more difficult. If the cranks are shorter than the ideal, that’s a much less serious problem; it would simply result in the legs not being flexed as much and extended as much as they could be to make fullest use of the capacity of the leg muscles used in pedaling. For most of us nonprofessional riders, this is not so bad, because we are rarely pushing ourselves to the maximum limit of our muscle capacity, so we could ride for 40 years with cranks that are shorter than ideal and not notice it. If you became as obsessive as a weight weenie about squeezing the most watts out of your body on a bike, then you could spend a hunk of cash on a pricey bike fitting to determine your ideal crank length and then buy a new crankset. But it would probably be more effective and certainly cheaper to just become a weight weenie.

One of the benefits of appropriate crank length is not having your knees touch your upper-body, when pedaling in the drops, however slight it may be.

I can believe that. I was 6'1/2" but all arms and legs BITD. Never rode anything bigger than 170/171 until I bought my Fuji Pro as a second year racer with its 175s. Riding the same wheels and gears, I was instantly minutes faster around my 45 mile training loop. For me, 170 is too short and I pay a real penalty. No upside. Perhaps I would benefit going even longer but my knees really do not like even small crank length changes (I've had crhrondomalacia patellae the past 42 years) and 175s work so I haven't experimented further.

No, I am not saying everyone should go longer because it worked for me. I am saying that for some of us, there is real benefit to be gained (and felt immediately) by going to the correct length for that person. (And it is my belief that this is so personal that it cannot be looked up in a book.)

Ben

I believe crank length has a lot to do with Your pedaling style. Riders that tend to pedal high cadences will gravitate to shorter cranks. Those with strong legs able to turn big gears will go for longer cranks.