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Crank length rule of thumb? (Toe?)

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Crank length rule of thumb? (Toe?)

Old 04-10-24, 07:49 PM
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Originally Posted by Kontact
Why would cranks that come in 2.5mm increments require "radical" BB height changes?

Or have you seen road bikes made specifically for 140mm cranks?
“Different” in that a 10mm longer crank puts the pedal 10mm closer to the ground. The common 2.5mm (or 2%) increment is almost irrelevant when people vary 20% in height.

There’s a fair amount of experimentation with short cranks (140mm to 160mm) in the recumbent bike and trike community. Mostly this is done to facilitate faster spin and lower stress on old, creaky knees.
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Old 04-10-24, 07:53 PM
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I recently put 175s on my PX-10 just for the heck of it, and not really expecting that I'd notice a difference from the 170s, but..... I really do notice the diff, and I like it. My comfort-zone cadence is pretty high, and that's probably come down a bit which is fine, but it's on hill climbs that I really notice the longer cranks- it just feels easier. And now I'm all, I've got to put 175s on all my bikes! I really want to try 175s on my Holdsworth Pro, but the toe overlap on that bike is already kind of extreme, so it might not be the wisest more....

[edit] data point to add- I was just a bit over 6', now I'm a bit under 6', ground down by the weight of years; 36.5" inseam.

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Old 04-10-24, 08:09 PM
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Originally Posted by cyccommute
And where do you shop for these mythic short cranks? I’ve been trying to find them for 40+ years and so far have come up with nothin’. I even had to go so far as to make them myself.
Da Vinci:
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Old 04-10-24, 08:22 PM
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Originally Posted by Jeff Wills
“Different” in that a 10mm longer crank puts the pedal 10mm closer to the ground. The common 2.5mm (or 2%) increment is almost irrelevant when people vary 20% in height.

There’s a fair amount of experimentation with short cranks (140mm to 160mm) in the recumbent bike and trike community. Mostly this is done to facilitate faster spin and lower stress on old, creaky knees.
But that doesn't have much to do with pedal strikes. The range might be 140 to 180, but since road bikes are built for 170 or longer, it isn't like the lower end of the range matters.

And then there's the fact that pedals have increased cornering clearance since the late '80s, so cornering with 180s now is like riding Campy quill pedals in the early '80s.

Just to put some numbers to this, my hypothetical bicycle has pedal clearance to 29.7 degrees with 170 cranks. Cornering drops by 2.5 degrees to 27.2 with 180s. That's the same amount if you use pedals that are 2cm longer. I don't think 2.5 degrees is significant compared to what people believe they are getting out of more suitable crank lengths.

And then if you have gotten on board with big tires, your 35c tires make up for 180 cranks compared to 25c.
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Old 04-11-24, 07:04 AM
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Most of my bikes have 170 mm cranks, a couple have 175, and one is 172.5. My inseam is 32 inches and my normal cadence is around 80 rpm. Whatever length is on the bike I start off with is what feels like the ideal length. If I jump between a 170 and a 175, I can feel the difference for a few miles, then my legs adapt and forget about it. I'm sure there might be some scientific testing that could determine if one length is better, but for my riding, I can use them all. Last year I was looking for a crankset at the bike swap and passed up a bunch of nice 165mm cranks because I thought they were too short. Several were only $10, so I probably should have bought one to try out. Memory Lane and Ann Arbor are only a month away, so I'll add that to my shopping list.
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Old 04-11-24, 09:09 AM
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Guess why they're cheap and consider better uses for the $10

Jus sayn
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Old 04-11-24, 12:07 PM
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Originally Posted by Robvolz
Sounds like I should get rid of my 175 campy Strada, from before date stamps. (1968-1973)
Maybe, maybe not.

For your size, 170s would likely have been spec'd for as long as I can remember. 175s might feel just fine to you, or they may not. There is only one way to find out - try 'em, being sure to adjust your saddle height accordingly. If they feel wrong to you, or (especially) if your knees start hurting, then go back to 170s and move the 175s along to someone else. For comparison, you know how big I am. I ride 175s on most bikes, including the bike you saw me on at Cino last year. However, I do have 180s on the bike you saw me on at Eroica last year. When I ride the 180s, I feel the difference for about two minutes - after that, it's just riding.

As for scraping pedals, I would think that the vast majority of us are long past the days when we are cornering so aggressively that pedal strikes are an issue.
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Old 04-11-24, 01:04 PM
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For years, I had 175s on my go fast bike with a complete Dura Ace 7700 group. I attended a training with Rahsaan Bahati who is taller than me but leg length is the same. I asked him what crank length he uses and he informed me that he uses 172.5 because his coach told him to change from 175. After that training I picked up a 172.5 7700 crankset. My rule of thumb states that if it's good for Rahsaan it can't hold me back.
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Old 04-11-24, 08:59 PM
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I like 175’s. They seem to work better for me than 170’s.
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Old 04-11-24, 09:38 PM
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I just stumbled upon this video. It's about crank lengths for MTBs. There's an innovative crank that offers a huge number of lengths, all so that you can determine which length you like.

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Old 04-11-24, 09:50 PM
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Long cranks, short cranks. Take the average of all the trends = 170mm.
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Old 04-12-24, 09:19 AM
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Originally Posted by bikingshearer

As for scraping pedals, I would think that the vast majority of us are long past the days when we are cornering so aggressively that pedal strikes are an issue.
Agree that pedal strikes are something I’ll never worry about again. Now fender strikes are another story. Put some 175s on a fendered bike that I had been riding with 170s. Balancing at a light, I swung the wheel. The slightly longer cranks meant my foot brushed the fender and down I went. Kept the 175s but made sure the new fender was set Up a little closer to the tire.
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Old 04-12-24, 11:53 AM
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Originally Posted by Robvolz
...I’ve read the longer cranks give more leverage but are harder on the knees. shorter is better for those who prefer to spin more? ...what’s the real rule of toe?
Bernard Hinault's book 'Cyclisme sur Route/Spourt pour tout' was published in 1986. It's English translation 'Road Racing Technique and Training' was published in 1988. RRT is well worth having, for lots of insight on various aspects of fitting.

Lots of used copies of RRT are available:
https://www.amazon.com/Road-Racing-T...s%2C145&sr=8-1

RRT has an extensive discussion of crank length (pages 74-77). Also mentioned in the discussion is that a lot of top pro riders used long cranks BITD without ill effects.

Per the book:
Standard (traditional) crank length: Inseam of 74-80cm = 170mm; 81-86cm = 172.5mm; 87-93cm = 175mm.
Daring, new solutions crank length: Inseam 74-77cm = 170mm; 78-81cm = 172.5mm; 82-85cm = 175mm; 86-89cm = 177.5cm; 90-93cm = 180mm.
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Old 04-13-24, 07:59 PM
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Originally Posted by cyccommute
And where do you shop for these mythic short cranks? I’ve been trying to find them for 40+ years and so far have come up with nothin’. I even had to go so far as to make them myself.
I had some 152 mm, 4 x 110 bcd from Amazon a couple of weeks ago, seem reasonable quality if not the lightest. Stronglight Impact single or double, 5 x 110 bcd comes in 130, 145, 150, 155, 160, 165, 170, 175 mm.
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Old 04-13-24, 11:19 PM
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Originally Posted by Andrew_G
Bernard Hinault's book 'Cyclisme sur Route/Spourt pour tout' was published in 1986. It's English translation 'Road Racing Technique and Training' was published in 1988. RRT is well worth having, for lots of insight on various aspects of fitting.

Lots of used copies of RRT are available:
https://www.amazon.com/Road-Racing-T...s%2C145&sr=8-1

RRT has an extensive discussion of crank length (pages 74-77). Also mentioned in the discussion is that a lot of top pro riders used long cranks BITD without ill effects.

Per the book:
Standard (traditional) crank length: Inseam of 74-80cm = 170mm; 81-86cm = 172.5mm; 87-93cm = 175mm.
Daring, new solutions crank length: Inseam 74-77cm = 170mm; 78-81cm = 172.5mm; 82-85cm = 175mm; 86-89cm = 177.5cm; 90-93cm = 180mm.
Quoting:

"In 1980, he was forced to abandon the Tour because of a bad knee and was forced to miss the Tour in 1983 because of a knee operation."
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Old 04-13-24, 11:35 PM
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Originally Posted by grumpus
I had some 152 mm, 4 x 110 bcd from Amazon a couple of weeks ago, seem reasonable quality if not the lightest. Stronglight Impact single or double, 5 x 110 bcd comes in 130, 145, 150, 155, 160, 165, 170, 175 mm.
The 110 BCD is a dumb chainring to use in either a double or single, especially for a short armed crank. Short cranks are meant small people who have less muscle mass than larger people. The 110 BCD is limited to 34 tooth size. That’s kind of a high gear for a small person.

The other problem for me, personally, is the lack of triples. I’m large and strong and won’t ride without a 22 tooth inner mated to a 34 or 36 (or even 40) tooth cog on the back. I’m not going to ask my 5’ tall wife to ride something that is geared far higher than my bikes. And before the suggestion is made to get a modern bike with something like a 11-52, small bikes that are capable of using that technology are difficult to find in small enough frames. For example the Specialized Diverge Expert E5 EVO comes with a 11-50 cassette and a 38 tooth chainring. That makes for a 21” gear, which is almost respectable. That’s for $2600.

The Specialized Sirrus 2.0 comes with a 11-32 cassette with a 46/30 crank and an 11-32 cassette. That’s a bit taller low of 26” which isn’t all that great but the Sirrus sells for $650 which makes it a better platform for making changes.

The other problem is that the smallest size th Diverge comes in has a standover of 732mm. The Sirrus comes in an XXS with a standover of 692mm. That an extra 40mm (1.5”) of clearance for someone who is short. The Diverge is just too big for an extremely small rider. The standover height of Sirrus can be reduced further by changing the wheels to 26” which isn’t a problem if shorter cranks are used.

The $1800 difference in the bikes means that you can spend money on making the Sirrus into a better bike for a short rider…including having someone like Wheel Smith make short triple cranks for it.
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Old 04-14-24, 03:38 AM
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Originally Posted by cyccommute
The 110 BCD is a dumb chainring to use in either a double or single, especially for a short armed crank. Short cranks are meant small people who have less muscle mass than larger people. The 110 BCD is limited to 34 tooth size. That’s kind of a high gear for a small person.

The other problem for me, personally, is the lack of triples. I’m large and strong and won’t ride without a 22 tooth inner mated to a 34 or 36 (or even 40) tooth cog on the back. I’m not going to ask my 5’ tall wife to ride something that is geared far higher than my bikes. And before the suggestion is made to get a modern bike with something like a 11-52, small bikes that are capable of using that technology are difficult to find in small enough frames. For example the Specialized Diverge Expert E5 EVO comes with a 11-50 cassette and a 38 tooth chainring. That makes for a 21” gear, which is almost respectable. That’s for $2600.

The Specialized Sirrus 2.0 comes with a 11-32 cassette with a 46/30 crank and an 11-32 cassette. That’s a bit taller low of 26” which isn’t all that great but the Sirrus sells for $650 which makes it a better platform for making changes.

The other problem is that the smallest size th Diverge comes in has a standover of 732mm. The Sirrus comes in an XXS with a standover of 692mm. That an extra 40mm (1.5”) of clearance for someone who is short. The Diverge is just too big for an extremely small rider. The standover height of Sirrus can be reduced further by changing the wheels to 26” which isn’t a problem if shorter cranks are used.

The $1800 difference in the bikes means that you can spend money on making the Sirrus into a better bike for a short rider…including having someone like Wheel Smith make short triple cranks for it.
I'm with you on the sensibly low gears, although maybe not that low, my Stronglights go down to 28t with a 28 or 32t on the back. It might be possible to graft a granny sprocket inside a double*, the one I bought went on a recumbent trike with a 20 inch rear wheel so lower overall than a regular setup. I picked up a nearly new Liv Avail in XS for my short person, it doesn't look weird and manages to squeeze in 650B wheels but it did need some work as it's a bit basic - 1 x 10 with a mid drive does the job, and a dropper so she can get her tiny feet on the ground. The cheap battery has yet to explode demonstrate its full ability, I'm hoping it will at least be reliably crap (I bought it years ago for another project that got no further than a brief test ride - I could test it on my e-trike except that doesn't currently have reliable wiring).

* I'm thinking custom chainring with mounting tabs for the granny, can you weld Zicral I wonder? ... apparently not, it's 7075 and subject to microcracking unless you use voodoo.
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Old 04-14-24, 03:46 AM
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Originally Posted by Trakhak
Quoting:

"In 1980, he was forced to abandon the Tour because of a bad knee and was forced to miss the Tour in 1983 because of a knee operation."
That had more to do with the massive gears pros turned in those days with nothing lower than a 42x19 or 21, even in the mountains. Not crank length.
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Old 04-14-24, 05:43 AM
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Originally Posted by nomadmax
That had more to do with the massive gears pros turned in those days with nothing lower than a 42x19 or 21, even in the mountains. Not crank length.
All the pros were riding the same gear ranges in that era. All the racers I rode with used the same gear ranges as the pros. (One teammate used 44/18 as his low gear for even the hilliest races and training rides.)

I know of no pros other than Hinault in that era who skipped races because of a knee operation, let alone two performed a few years apart. (There almost certainly were some, though - just none with the prominence of Hinault in either the general or cycling-specific press.)

You're right that those knee problems might have had nothing to do with his crank arm choices, of course. They could easily have resulted from crash damage to his knees.

And, of course, from the Badger's determined nature. Quoting from memory from a book on the 1980 Giro and Tour: "Hinault gloried in his ability to tolerate pain." Great for winning races. Not so great for avoiding season-ending injuries.
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Old 04-14-24, 12:45 PM
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Originally Posted by noglider
I just stumbled upon this video...
Yes, the 'new' theory of using much shorter cranks. Interesting. Hmph.

Suddenly Sheldon Browns' Gain Ratio comes into its own.

FWIW, the recumbent trike world is big on 155mm & shorter crank arms.
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