What’s my correct crank length

[novetan]

I bought my bike quite a few months back but without realizing the crank length is 172.5mm until one day I saw the marking when I overturn the bike for a wash. I’d have thought the standard stock length is 170mm.

I wish to get it right. I’m 5’ 5” (1.66m) and inseam is 29.5” (0.75m). I tried several web computation and got different results (varies from 165 to 170mm). Is there a preferred crank length for certain type of rides (such as sprint or endurance) or its strictly governed by ht and inseam. My rides are mostly endurance and with some climbs.

Anyway, being not so technically inclined, I wonder whether that minute 2.5mm does make any difference.

 

[on the road]

It probably doesn't really matter all that much, I'm 5' 6" with an inside leg of 30" and according to the calculations I should be on a 165, but I've always stuck with 170 and I see no need to change, although I'm reluctant to go higher than that.

 

[on the road]

If the 172.5 works for you then why change it?

 

[numbnuts]

if it ain't bust why fix it

 

[biggs682]

if it ain't bust why fix it

could not agree more

 

[novetan]

Thks guys for all the replies. This my first road bike and there isn’t anything for me to compare. But the riding seems ok so far. Guess it’s a kind of psycological thing.

I reckon it’s similar to golf club. I recalled yrs ago Freddy Coupled (I think) was testing some golf club and he hit very well in one particularly club. When the grip was removed revealing the length of shaft, it was actually 5mm longer than his usual club length. Then after the hitting was terrible.

 

[TheJDog]

Sheldon Brown has a bike with child-length cranks (like 150, or something), and other bikes with regular lengths. He says he doesn't notice much of a difference. For very high cadences I think the general thrust is towards something slightly shorter than the amateur rider is used to..

 

[Ningishzidda]

Sheldon Brown has a bike with child-length cranks (like 150, or something), and other bikes with regular lengths. He says he doesn't notice much of a difference. For very high cadences I think the general thrust is towards something slightly shorter than the amateur rider is used to..

I have a bike with 5 1/2" cranks. I can certainly tell they are shorter.
I have bikes with 6 3/4" and 170mm cranks. I cannot tell the difference.
I have a bike with 175mm cranks. After about 30 miles continual riding, I can feel my leg flexion is greater than with 170mm cranks, and get a niggle in the knee behind the patella, as if the saddle was low.
One bike fitting service advises 18.5% the height of the centre of your hip ball.

Its bang on 170mm for me. ( lucky me ).
One of the bikes with 170mm cranks is a Spesh SWorks. I can ride that bike all day long.

 

[SpokeyDokey]

I bought my bike quite a few months back but without realizing the crank length is 172.5mm until one day I saw the marking when I overturn the bike for a wash. I’d have thought the standard stock length is 170mm.

I wish to get it right. I’m 5’ 5” (1.66m) and inseam is 29.5” (0.75m). I tried several web computation and got different results (varies from 165 to 170mm). Is there a preferred crank length for certain type of rides (such as sprint or endurance) or its strictly governed by ht and inseam. My rides are mostly endurance and with some climbs.

Anyway, being not so technically inclined, I wonder whether that minute 2.5mm does make any difference.

Do you race at a high level? Are you on your bike hundreds of miles a week? Is your whole life devoted to cycling? Are you cycling at close to 100% of your body's maximum performance?

If not then these things matter very little in the real world - trouble is nth degree fine tuning from the stratosphere tends to get webbed into the world of the rest of us.

A while back there was a huge thread on a Stateside forum about the merits of a rider losing 20g off the weight of his FD - seriously; the world is a barmy place at times.

 

[Ningishzidda]

Sheldon Brown has a bike with child-length cranks (like 150, or something), and other bikes with regular lengths. He says he doesn't notice much of a difference. For very high cadences I think the general thrust is towards something slightly shorter than the amateur rider is used to..

6" cranks were fitted to 24" wheel youth's / girls bikes. They were usually 42 rings and 18 SS freewheels, resulting in 56" gear.
My 5 1/2" cranks ( 140mm ) are on a 14" wheel child's bike with 52 ring and 15 sprocket on a Sach Torpedo coaster. A 49" gear.

 

[TheJDog]

I have a bike with 5 1/2" cranks. I can certainly tell they are shorter.
I have bikes with 6 3/4" and 170mm cranks. I cannot tell the difference.
I have a bike with 175mm cranks. After about 30 miles continual riding, I can feel my leg flexion is greater than with 170mm cranks, and get a niggle in the knee behind the patella, as if the saddle was low.
One bike fitting service advises 18.5% the height of the centre of your hip ball.

Its bang on 170mm for me. ( lucky me ).
One of the bikes with 170mm cranks is a Spesh SWorks. I can ride that bike all day long.

If I remember what SB said, yes, he could tell the difference, but he so quickly got used to it it didn't matter.

My hip ball is 100cm exactly, and I have 175 on all of my bikes and I have no niggles in my knees, just my ankles. 115 miles a couple of weeks ago. I would try something longer but that would mean all sorts of eBay action.

I reckon if your saddle is at the correct height you can't go too far wrong with the crank lengths that came on your bike.

 

[Ningishzidda]

If I remember what SB said, yes, he could tell the difference, but he so quickly got used to it it didn't matter.

My hip ball is 100cm exactly, and I have 175 on all of my bikes and I have no niggles in my knees, just my ankles. 115 miles a couple of weeks ago. I would try something longer but that would mean all sorts of eBay action.

I reckon if your saddle is at the correct height you can't go too far wrong with the crank lengths that came on your bike.

You have cranks which are 17.5% of your hip ball height and your ankles suffer.

If you buy an Off The Peg bike, the manufacturers did all the physiology homework and put the close-as-dammit crank length on the particular frame size.

 

[TheJDog]

You have cranks which are 17.5% of your hip ball height and your ankles suffer.

If you buy an Off The Peg bike, the manufacturers did all the physiology homework and put the close-as-dammit crank length on the particular frame size.

I actually have niggles in my ankles because I tore ligaments and partially tore my achilles playing hockey. Cycling has been very good to them. As opposed to running . But I should have mentioned that sooner. Perhaps longer cranks would put even less stress on my Achilles, but on long rides, I barely exert them, and I only feel it in long rides. I'll think about it.