Short cranks for short person
05-03-20, 12:13 PM
#26
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TA made cranks in lengths from 150mm to 188mm; I put a set of 155mm arms on my wife's bike. You may need to special-order arms outside the 165-175mm range, though. Otherwise, Mark Stonich of BikeSmithDesign offers a crank shortening service, where he drills and taps a new pedal eye at the radius of your choice and cuts off and finishes the extra material from the arm:
Short Bicycle Cranks
Finally, BMX cranks are available in a range of lengths as well, some of them very short. You may need to be a bit creative in mounting multiple chainrings, selecting the appropriate bottom bracket etc. But in many cases, it can be done.
Short Bicycle Cranks
Finally, BMX cranks are available in a range of lengths as well, some of them very short. You may need to be a bit creative in mounting multiple chainrings, selecting the appropriate bottom bracket etc. But in many cases, it can be done.
05-04-20, 10:25 AM
#27
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I just went to measure it and it's definitely 110mm. The bike is a 2015 model and most of the components are Shimano 105. Specifically reading off the cranks it says "FC-R563/R565/RS500", but that doesn't mean much to me.
I also read the Hambini article on BB86 and 30mm crank axle and I see the point of refraining from that practice. Fortunately, Rotor also has a 24mm axle for their cranksets. Does this mean that that axle will fit perfectly in my current bottom bracket despite being from different manufacturers(Rotor and Shimano)?
So I would go for crank arms, axle(24mm) and spider mount(110x5)? Only these three things? I'm just fishing for confirmation here to calm my nerves once I decide to order
I also read the Hambini article on BB86 and 30mm crank axle and I see the point of refraining from that practice. Fortunately, Rotor also has a 24mm axle for their cranksets. Does this mean that that axle will fit perfectly in my current bottom bracket despite being from different manufacturers(Rotor and Shimano)?
So I would go for crank arms, axle(24mm) and spider mount(110x5)? Only these three things? I'm just fishing for confirmation here to calm my nerves once I decide to order
.“Standard ALDHU is not compatible with 24mm ALDHU Axles.”
You’re really stuck between a rock and a hard place here. If you had a BB386EVO or BSA frame you’d be totally fine.
I think the BBinfinite solution will be satisfactory. Specifically the Abec-7 one piece. Just verify you don’t have anything blocking your BB shell first.
05-06-20, 02:56 PM
#28
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bruken: I wish I had something useful to offer on the specific technical problem here, but I wouldn't even have understood the dimensions of the compatibility problem without smashndash's well-informed comments. I used those to search tech data sites to try to get a grip on this, as I've never dealt with those 86.5 bottom brackets.
The one positive thing I can say is that you're definitely doing the right thing by going for those short-arm cranks for your wife, who by your description is within a centimetre of my height. I began using them about 20 years ago and was pleasantly surprised at what an improvement they made. Surprised, because I was pretty old school, racing bike trad, and had absorbed a lot of advice on how big a deal 2.5mm crank length changes could be. That seems funny to me now. I went from 170mm down to 155mm in one go and it took all of a day to adapt to it - less actually: on the return commute from work that day the ride felt completely natural and easy. I've got several bikes now with cranks from 150 (TA Zephyr), 152 (Sugino XD 600), & 155 (Thorn, Origin8, TA Carmina, & Sugino Mighty Mignon). Clearly, I've bought the farm on the short crank concept. This was much easier for me to do as all my bikes have standard 68mm BB's, except for one that has a 70mm ITA shell.
My original motivation to try short cranks was knee preservation. Sounds like that's a concern for your wife as well. I acquired a fairly high cadence (90 - 105) while still young for that reason, and I was pleased to find that the shorter cranks seemed to enable it, and I did get some relief from knee pain. There was an added bonus though: after just a slight seat height adjustment to get my ankling right and no other change but that, I was surprised at how much better the entire bike seemed to fit me. And that goes to explain that list of cranks above. Most on that list are 110-74 bcd triples, and I like them all, from cheap to pricey, but I really like the Sugino Mighty's, which are a 110 bcd double, 5 arms, standard phase, with a set of 50-34 Rotor Q rings. Nice to get back to a low Q-factor with these, which is also a little better for my knees. And they look great! (The cranks, not my knees).
I hope you'll get back to us with the outcome of your modifications, and let us know if your wife likes the change.
The one positive thing I can say is that you're definitely doing the right thing by going for those short-arm cranks for your wife, who by your description is within a centimetre of my height. I began using them about 20 years ago and was pleasantly surprised at what an improvement they made. Surprised, because I was pretty old school, racing bike trad, and had absorbed a lot of advice on how big a deal 2.5mm crank length changes could be. That seems funny to me now. I went from 170mm down to 155mm in one go and it took all of a day to adapt to it - less actually: on the return commute from work that day the ride felt completely natural and easy. I've got several bikes now with cranks from 150 (TA Zephyr), 152 (Sugino XD 600), & 155 (Thorn, Origin8, TA Carmina, & Sugino Mighty Mignon). Clearly, I've bought the farm on the short crank concept. This was much easier for me to do as all my bikes have standard 68mm BB's, except for one that has a 70mm ITA shell.
My original motivation to try short cranks was knee preservation. Sounds like that's a concern for your wife as well. I acquired a fairly high cadence (90 - 105) while still young for that reason, and I was pleased to find that the shorter cranks seemed to enable it, and I did get some relief from knee pain. There was an added bonus though: after just a slight seat height adjustment to get my ankling right and no other change but that, I was surprised at how much better the entire bike seemed to fit me. And that goes to explain that list of cranks above. Most on that list are 110-74 bcd triples, and I like them all, from cheap to pricey, but I really like the Sugino Mighty's, which are a 110 bcd double, 5 arms, standard phase, with a set of 50-34 Rotor Q rings. Nice to get back to a low Q-factor with these, which is also a little better for my knees. And they look great! (The cranks, not my knees).
I hope you'll get back to us with the outcome of your modifications, and let us know if your wife likes the change.
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05-21-20, 05:01 AM
#29
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Got the stuff!
I ordered all the parts in my opening post and an extra 30mm spacer kit also from Rotor. I received the parts yesterday and as I half expected things did not go smoothly. Embarrassingly I didn’t order any bottom bracket tools so when i got the cranks removed all I could do was to look at those press fitted bearings for a while before reverting to the old cranks and going online to order the tools. You live you learn I guess.
But I must say, when reading about bottom brackets online it’s not very clear what you’re dealing with. One fact that I learned is that the bottom bracket consists of two parts: the bottom bracket bearings and bottom brackets shell. In instructional videos about removing your ”bottom bracket” they some times seem to be referring to only the bearings when they say bottom bracket and sometimes they mean both the bearings and the shell. Furthermore, what does it mean when a bike frame is advertised to have a BB86 bottom bracket? Does this mean that only BB86 will fit? Or is it rather that the diameter at the bottom bracket of the frame is 68mm and the width is 86.5mm?
Before I installed my old cranks again I had a look at the bearings that were currently installed. I took my new bearings and sized them up against the bottom bracket. It seemed like they ought to fit once I had removed the current ones. However, to my dismay I also noticed that further inside the bottom bracket shell it was quite narrow. I looked up the model name of the shell: Shimano SM-BB71-41. From what I could tell the the inner diameter at the ends where the bearings go was 41mm as expected. But again, the middle part was way narrower. I didn’t have a caliper but with some primitive sizing and squinting I could confidently say that the inner diameter in the middle was 24mm. Exactly the size of the crank axle that currently sits there. So regardless of which tools I have or don't have that bottom bracket shell has to go since the new axle I have is 30mm.
On the official site(Rotor) of the bearings I purchased it says:
and furthermore
This would have me believe that it would work with my current bottom bracket shell, but obviously it won’t.
On another site(wheelsmfg) that sells the exact same bearings(Enduro Dual-Row ABEC-3) says:
This would have me believe that I don’t even need a bottom bracket shell. Is this even possible to do?
I’m quite confused about how all this works but this setback hasn’t demoralized me. I am looking forward to what I will discover when I get the tools to get the the bearings out and maybe also the shell out. I appreciate all the response I’ve gotten. Feel free to add any information that you feel may help me on my quest!
But I must say, when reading about bottom brackets online it’s not very clear what you’re dealing with. One fact that I learned is that the bottom bracket consists of two parts: the bottom bracket bearings and bottom brackets shell. In instructional videos about removing your ”bottom bracket” they some times seem to be referring to only the bearings when they say bottom bracket and sometimes they mean both the bearings and the shell. Furthermore, what does it mean when a bike frame is advertised to have a BB86 bottom bracket? Does this mean that only BB86 will fit? Or is it rather that the diameter at the bottom bracket of the frame is 68mm and the width is 86.5mm?
Before I installed my old cranks again I had a look at the bearings that were currently installed. I took my new bearings and sized them up against the bottom bracket. It seemed like they ought to fit once I had removed the current ones. However, to my dismay I also noticed that further inside the bottom bracket shell it was quite narrow. I looked up the model name of the shell: Shimano SM-BB71-41. From what I could tell the the inner diameter at the ends where the bearings go was 41mm as expected. But again, the middle part was way narrower. I didn’t have a caliper but with some primitive sizing and squinting I could confidently say that the inner diameter in the middle was 24mm. Exactly the size of the crank axle that currently sits there. So regardless of which tools I have or don't have that bottom bracket shell has to go since the new axle I have is 30mm.
On the official site(Rotor) of the bearings I purchased it says:
The Press Fit 4130 is the "yes" component to "Is this compatible with my press fit 41mm diameter BB shell for a 30mm axle?”
Designed to work with BB86, BB89 and BB92 bottom brackets
On another site(wheelsmfg) that sells the exact same bearings(Enduro Dual-Row ABEC-3) says:
BB86/92 bottom brackets for use with 30mm spindle cranks and 41mm inside diameter BB shells. This is a direct-fit system where each flanged bearing presses directly into the frame.
I’m quite confused about how all this works but this setback hasn’t demoralized me. I am looking forward to what I will discover when I get the tools to get the the bearings out and maybe also the shell out. I appreciate all the response I’ve gotten. Feel free to add any information that you feel may help me on my quest!
05-21-20, 08:36 AM
#30
Senior Member
You should think of the "bottom bracket" (the bearings) as an adapter to fit the cranks (the arms) to the frame. The BB must fit BOTH the cranks AND the frame.
05-21-20, 10:33 AM
#31
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I ordered all the parts in my opening post and an extra 30mm spacer kit also from Rotor. I received the parts yesterday and as I half expected things did not go smoothly. Embarrassingly I didn’t order any bottom bracket tools so when i got the cranks removed all I could do was to look at those press fitted bearings for a while before reverting to the old cranks and going online to order the tools. You live you learn I guess.
But I must say, when reading about bottom brackets online it’s not very clear what you’re dealing with. One fact that I learned is that the bottom bracket consists of two parts: the bottom bracket bearings and bottom brackets shell. In instructional videos about removing your ”bottom bracket” they some times seem to be referring to only the bearings when they say bottom bracket and sometimes they mean both the bearings and the shell. Furthermore, what does it mean when a bike frame is advertised to have a BB86 bottom bracket? Does this mean that only BB86 will fit? Or is it rather that the diameter at the bottom bracket of the frame is 68mm and the width is 86.5mm?
Before I installed my old cranks again I had a look at the bearings that were currently installed. I took my new bearings and sized them up against the bottom bracket. It seemed like they ought to fit once I had removed the current ones. However, to my dismay I also noticed that further inside the bottom bracket shell it was quite narrow. I looked up the model name of the shell: Shimano SM-BB71-41. From what I could tell the the inner diameter at the ends where the bearings go was 41mm as expected. But again, the middle part was way narrower. I didn’t have a caliper but with some primitive sizing and squinting I could confidently say that the inner diameter in the middle was 24mm. Exactly the size of the crank axle that currently sits there. So regardless of which tools I have or don't have that bottom bracket shell has to go since the new axle I have is 30mm.
On the official site(Rotor) of the bearings I purchased it says:
and furthermore
This would have me believe that it would work with my current bottom bracket shell, but obviously it won’t.
On another site(wheelsmfg) that sells the exact same bearings(Enduro Dual-Row ABEC-3) says:
This would have me believe that I don’t even need a bottom bracket shell. Is this even possible to do?
I’m quite confused about how all this works but this setback hasn’t demoralized me. I am looking forward to what I will discover when I get the tools to get the the bearings out and maybe also the shell out. I appreciate all the response I’ve gotten. Feel free to add any information that you feel may help me on my quest!
But I must say, when reading about bottom brackets online it’s not very clear what you’re dealing with. One fact that I learned is that the bottom bracket consists of two parts: the bottom bracket bearings and bottom brackets shell. In instructional videos about removing your ”bottom bracket” they some times seem to be referring to only the bearings when they say bottom bracket and sometimes they mean both the bearings and the shell. Furthermore, what does it mean when a bike frame is advertised to have a BB86 bottom bracket? Does this mean that only BB86 will fit? Or is it rather that the diameter at the bottom bracket of the frame is 68mm and the width is 86.5mm?
Before I installed my old cranks again I had a look at the bearings that were currently installed. I took my new bearings and sized them up against the bottom bracket. It seemed like they ought to fit once I had removed the current ones. However, to my dismay I also noticed that further inside the bottom bracket shell it was quite narrow. I looked up the model name of the shell: Shimano SM-BB71-41. From what I could tell the the inner diameter at the ends where the bearings go was 41mm as expected. But again, the middle part was way narrower. I didn’t have a caliper but with some primitive sizing and squinting I could confidently say that the inner diameter in the middle was 24mm. Exactly the size of the crank axle that currently sits there. So regardless of which tools I have or don't have that bottom bracket shell has to go since the new axle I have is 30mm.
On the official site(Rotor) of the bearings I purchased it says:
and furthermore
This would have me believe that it would work with my current bottom bracket shell, but obviously it won’t.
On another site(wheelsmfg) that sells the exact same bearings(Enduro Dual-Row ABEC-3) says:
This would have me believe that I don’t even need a bottom bracket shell. Is this even possible to do?
I’m quite confused about how all this works but this setback hasn’t demoralized me. I am looking forward to what I will discover when I get the tools to get the the bearings out and maybe also the shell out. I appreciate all the response I’ve gotten. Feel free to add any information that you feel may help me on my quest!
You have a BB86 bike. This means that your frame has a bottom bracket shell (hole) of 41mm diameter and 86.5mm width. You can verify these numbers quite easily. Any number of cranks and bottom brackets will fit this shell. The “shell” is NOT the bottom bracket marked “SM-BB71-41”. The “shell” is the hole in your frame. Either bare carbon or metal. It should not be 24mm in the middle. In fact, the middle of the shell is usually larger than 41mm.
A BB86 bottom bracket for Shimano Hollowtech II cranks aka the SM-BB71-41, consists of several parts. There is housing, which is what you refer to as a shell - I think. This is a disposable part, and cannot be reused. It consists of 2 37mm ID, 41mm OD plastic cups around the bearings and a plastic center sleeve.
Then, there are the 6805 bearings, which have a 37mm outer diameter and a 25mm inner diameter with a plastic reducer that measures 24mm ID. Sometimes, you might have a bearing that has a 24mm ID with no reducer. These are obviously not compatible with your 30mm cranks.
Some pictures would also be handy.
Last edited by smashndash; 05-21-20 at 10:40 AM.
05-25-20, 01:47 PM
#32
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Before you do anything hasty, let’s go over the basics again.
You have a BB86 bike. This means that your frame has a bottom bracket shell (hole) of 41mm diameter and 86.5mm width. You can verify these numbers quite easily. Any number of cranks and bottom brackets will fit this shell. The “shell” is NOT the bottom bracket marked “SM-BB71-41”. The “shell” is the hole in your frame. Either bare carbon or metal. It should not be 24mm in the middle. In fact, the middle of the shell is usually larger than 41mm.
A BB86 bottom bracket for Shimano Hollowtech II cranks aka the SM-BB71-41, consists of several parts. There is housing, which is what you refer to as a shell - I think. This is a disposable part, and cannot be reused. It consists of 2 37mm ID, 41mm OD plastic cups around the bearings and a plastic center sleeve.
Then, there are the 6805 bearings, which have a 37mm outer diameter and a 25mm inner diameter with a plastic reducer that measures 24mm ID. Sometimes, you might have a bearing that has a 24mm ID with no reducer. These are obviously not compatible with your 30mm cranks.
...
Please watch this video and then let’s try to figure out where the problem is.
Some pictures would also be handy.
You have a BB86 bike. This means that your frame has a bottom bracket shell (hole) of 41mm diameter and 86.5mm width. You can verify these numbers quite easily. Any number of cranks and bottom brackets will fit this shell. The “shell” is NOT the bottom bracket marked “SM-BB71-41”. The “shell” is the hole in your frame. Either bare carbon or metal. It should not be 24mm in the middle. In fact, the middle of the shell is usually larger than 41mm.
A BB86 bottom bracket for Shimano Hollowtech II cranks aka the SM-BB71-41, consists of several parts. There is housing, which is what you refer to as a shell - I think. This is a disposable part, and cannot be reused. It consists of 2 37mm ID, 41mm OD plastic cups around the bearings and a plastic center sleeve.
Then, there are the 6805 bearings, which have a 37mm outer diameter and a 25mm inner diameter with a plastic reducer that measures 24mm ID. Sometimes, you might have a bearing that has a 24mm ID with no reducer. These are obviously not compatible with your 30mm cranks.
...
Please watch this video and then let’s try to figure out where the problem is.
Some pictures would also be handy.
05-26-20, 08:37 AM
#33
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I’m planning on buying a brand new crankset for my wife’s bike. She has been getting back into riding recently and we are both discovering that some parts of the bike are not well suited for her geometry. She is 158cm tall and has an inseam of 70cm. The bike came with 170mm cranks, which by all metrics seem to be way too long. However, I’ve been kind of let down by my LBS who sold the bike. Neither do they think the crank length is a bad match for her nor do they stock cranks that are shorter than 165mm. So I’m a bit on my own now.
Any input is appreciated!
Any input is appreciated!
05-27-20, 04:10 PM
#34
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Also did your friend try 165mm/170mm cranks, not like them, and put on 175mm cranks? Or is that just what was on their bike?
As crazy as it sounds... there is a very predictable trend for crank length. The shorter you are and the more aero you want to get, the shorter your cranks need to be.
