Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

Typical stiffness discrepancy between crank arms.

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Typical stiffness discrepancy between crank arms.

Old 10-30-19, 01:40 PM
  #1  
Nyah
Member
Thread Starter
 
Join Date: Sep 2018
Location: Shenandoah Valley, Northern Virginia.
Posts: 30

Bikes: '99 Trek 520.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Typical stiffness discrepancy between crank arms.

This question is in regards to conventional crank design. I don't ride bicycles regularly anymore and have not done much distance cycling. The most recent cycling trip of considerable distance that I took was somewhere around 52 miles total over two days. Afterwards, I could feel that my right leg was considerably more fatigued than my left. I narrowed the cause of this discrepancy down to the fact that the crank arm of the right side of the bike has a bar (or pin) that drives the spider/chainring. I would like to know if this phenomena has a name or, if this bar/pin crank design has a name or, if there are any alternative crank designs which attempt to spread the driving force evenly between both of the rider's legs. Thanks!

Edit: The bike is a Trek 520 touring bike, which I bought new from a bike shop. The frame size is appropriate for my physiology.

Last edited by Nyah; 10-30-19 at 01:43 PM. Reason: Bike size context.
Nyah is offline  
Old 10-30-19, 01:48 PM
  #2  
BlazingPedals
Senior Member
 
BlazingPedals's Avatar
 
Join Date: Dec 2004
Location: Middle of da Mitten
Posts: 11,142

Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, Catrike Speed

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 995 Post(s)
Liked 95 Times in 69 Posts
It's possible that the left crank arm flexes a tiny bit more than the right by virtue of the spyder reinforcing some part of the arm; but I highly doubt that you could tell the difference by pedaling. And I don't see why lack of flex would give you a sore right leg. More likely you have uneven muscle development or you were pushing unevenly.
BlazingPedals is offline  
Old 10-30-19, 01:50 PM
  #3  
Flip Flop Rider
Senior Member
 
Flip Flop Rider's Avatar
 
Join Date: Apr 2016
Location: South Carolina Upstate
Posts: 1,279

Bikes: 2010 Fuji Absolute 3.0 1994 Trek 850

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 489 Post(s)
Likes: 0
Liked 97 Times in 57 Posts
this is a tough one. Is one of your legs shorter than the other or have an injury that the other one does not?
Flip Flop Rider is offline  
Old 10-30-19, 01:59 PM
  #4  
rosefarts
Senior Member
 
Join Date: May 2015
Posts: 819
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 329 Post(s)
Liked 77 Times in 38 Posts
I have occasionally been much more sore one one side than the other. Either in the leg or back.

It's a hip and hamstring stiffness issue. Also possible that it's a different cleat position on the pedals issue but I don't think that is your particular problem.

I highly doubt that the soreness is from the slight inherent difference in the left to right balance of the bike. More likely it's your own balance and flexibility that should be improved.
rosefarts is offline  
Old 10-30-19, 02:05 PM
  #5  
livedarklions
Cyclesomatic
 
livedarklions's Avatar
 
Join Date: Jun 2018
Location: New England
Posts: 5,264

Bikes: Trek FX 3; 1994 Specialized Allez Pro; Motobecane Fantom CX; Giant OCR A1

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 2708 Post(s)
Liked 1,072 Times in 655 Posts
Originally Posted by Nyah View Post
This question is in regards to conventional crank design. I don't ride bicycles regularly anymore and have not done much distance cycling. The most recent cycling trip of considerable distance that I took was somewhere around 52 miles total over two days. Afterwards, I could feel that my right leg was considerably more fatigued than my left. I narrowed the cause of this discrepancy down to the fact that the crank arm of the right side of the bike has a bar (or pin) that drives the spider/chainring. I would like to know if this phenomena has a name or, if this bar/pin crank design has a name or, if there are any alternative crank designs which attempt to spread the driving force evenly between both of the rider's legs. Thanks!

Edit: The bike is a Trek 520 touring bike, which I bought new from a bike shop. The frame size is appropriate for my physiology.
What makes you think it's the crank? Have you done similar rides on different bikes without this happening? Frankly, unless the arms are different lengths, I can't see how having the pin on one side has anything to do with making the effort different for your legs.
livedarklions is online now  
Old 10-30-19, 02:10 PM
  #6  
shelbyfv
Senior Member
 
shelbyfv's Avatar
 
Join Date: Jun 2007
Posts: 5,784
Mentioned: 25 Post(s)
Tagged: 0 Thread(s)
Quoted: 1290 Post(s)
Liked 318 Times in 203 Posts
Not your crank but it would be interesting to hear how you came up with that idea. Unique!
shelbyfv is offline  
Old 10-30-19, 02:11 PM
  #7  
Nyah
Member
Thread Starter
 
Join Date: Sep 2018
Location: Shenandoah Valley, Northern Virginia.
Posts: 30

Bikes: '99 Trek 520.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Flip Flop Rider View Post
this is a tough one. Is one of your legs shorter than the other or have an injury that the other one does not?
No, for both questions. I have a regular running/walking gait.
Nyah is offline  
Old 10-30-19, 02:13 PM
  #8  
CliffordK
Senior Member
 
CliffordK's Avatar
 
Join Date: Nov 2014
Location: Eugene, Oregon, USA
Posts: 23,531
Mentioned: 182 Post(s)
Tagged: 0 Thread(s)
Quoted: 9761 Post(s)
Liked 320 Times in 253 Posts
Originally Posted by BlazingPedals View Post
It's possible that the left crank arm flexes a tiny bit more than the right by virtue of the spyder reinforcing some part of the arm; but I highly doubt that you could tell the difference by pedaling.
Likely something that sends shivers up the spines of developers of crank based power meters (that use absolute flex to determine power input)

However, I agree, this is likely a training issue, or perhaps one leg had something like a sore knee throwing everything off.

Was the bike assembled from parts? Double check that the crank arms are the same length. If you use foot retention like clipless/cleats, are the cleats set the same on both shoes, or right for your feet?
CliffordK is online now  
Old 10-30-19, 02:22 PM
  #9  
Nyah
Member
Thread Starter
 
Join Date: Sep 2018
Location: Shenandoah Valley, Northern Virginia.
Posts: 30

Bikes: '99 Trek 520.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 23 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by rosefarts View Post
I have occasionally been much more sore one one side than the other. Either in the leg or back.

It's a hip and hamstring stiffness issue. Also possible that it's a different cleat position on the pedals issue but I don't think that is your particular problem.

I highly doubt that the soreness is from the slight inherent difference in the left to right balance of the bike. More likely it's your own balance and flexibility that should be improved.
I seem to remember the injury being in my hamstring. As I implied in the other post though, I wasn't injured until after the ride. It wasn't a cleat issue for me, because I was wearing street shoes, with toe-clips properly arranged to the pedals.
Nyah is offline  
Old 10-30-19, 02:30 PM
  #10  
livedarklions
Cyclesomatic
 
livedarklions's Avatar
 
Join Date: Jun 2018
Location: New England
Posts: 5,264

Bikes: Trek FX 3; 1994 Specialized Allez Pro; Motobecane Fantom CX; Giant OCR A1

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 2708 Post(s)
Liked 1,072 Times in 655 Posts
Is this the crank in question?https://www.ebay.com/i/173739985391?...caAuzuEALw_wcB


I don't see how this is any more "imbalanced" than any other crank--one arm has to be on the drive side and the other on the non-drive side.

Not trying to be a wise-guy, but is your seat on straight? What about your handlebars? It sounds like you're riding off-kilter somehow.
livedarklions is online now  
Old 10-31-19, 01:26 PM
  #11  
Phil_gretz
Journeyman Bike Commuter
 
Phil_gretz's Avatar
 
Join Date: Aug 2009
Location: Alexandria, VA
Posts: 5,244

Bikes: '71 Jeunet 630, '79 Peugeot PXN10LE, '88 Fuji Saratoga, '13 Motobecane Fantom29 HT, '16 Motobecane Turino Pro Disc, '16 Motobecane Gran Premio Elite, '18 Velobuild VB-R-022

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 670 Post(s)
Liked 171 Times in 106 Posts
You could to a sports physical therapist and have a full flexibility and strength rundown done on yourself. You'd be shocked what you'll discover. As others have said, it's likely some mechanical imbalance in you, rather than with the bike.

There are simply too many variables to say without a PT exam, but relative crank arm stiffness would be very, very far down on the list of likely contributors.
Phil_gretz is offline  
Old 10-31-19, 01:40 PM
  #12  
mstateglfr 
Sunshine
 
mstateglfr's Avatar
 
Join Date: Aug 2014
Location: Des Moines, IA
Posts: 9,215

Bikes: '18 class built steel roadbike, '19 Fairlight Secan, '87 Schwinn Prelude, Black Mountain Cycles Monstercross V4, '89 Novara Trionfo, '18 Diamondback Syncr

Mentioned: 85 Post(s)
Tagged: 0 Thread(s)
Quoted: 3453 Post(s)
Liked 447 Times in 308 Posts
Originally Posted by Nyah View Post
This question is in regards to conventional crank design. I don't ride bicycles regularly anymore and have not done much distance cycling. The most recent cycling trip of considerable distance that I took was somewhere around 52 miles total over two days. Afterwards, I could feel that my right leg was considerably more fatigued than my left. I narrowed the cause of this discrepancy down to the fact that the crank arm of the right side of the bike has a bar (or pin) that drives the spider/chainring. I would like to know if this phenomena has a name or, if this bar/pin crank design has a name or, if there are any alternative crank designs which attempt to spread the driving force evenly between both of the rider's legs. Thanks!

Edit: The bike is a Trek 520 touring bike, which I bought new from a bike shop. The frame size is appropriate for my physiology.
Take a picture of the bar/pin that you are referring to. I have no idea what you are trying to describe. A crank flexes on both sides. The bottom bracket attaches to each arm at the same location and if anything, the arm on the drive side is thicker(and therefore stiffer).
mstateglfr is offline  
Old 10-31-19, 01:43 PM
  #13  
livedarklions
Cyclesomatic
 
livedarklions's Avatar
 
Join Date: Jun 2018
Location: New England
Posts: 5,264

Bikes: Trek FX 3; 1994 Specialized Allez Pro; Motobecane Fantom CX; Giant OCR A1

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 2708 Post(s)
Liked 1,072 Times in 655 Posts
Originally Posted by mstateglfr View Post
Take a picture of the bar/pin that you are referring to. I have no idea what you are trying to describe. A crank flexes on both sides. The bottom bracket attaches to each arm at the same location and if anything, the arm on the drive side is thicker(and therefore stiffer).
The link I posted in # 10 is the crank that comes standard with the Trek he identified.
livedarklions is online now  
Old 10-31-19, 02:18 PM
  #14  
shelbyfv
Senior Member
 
shelbyfv's Avatar
 
Join Date: Jun 2007
Posts: 5,784
Mentioned: 25 Post(s)
Tagged: 0 Thread(s)
Quoted: 1290 Post(s)
Liked 318 Times in 203 Posts
Has anyone figured out what the "bar/pin" is?
shelbyfv is offline  
Old 10-31-19, 02:44 PM
  #15  
livedarklions
Cyclesomatic
 
livedarklions's Avatar
 
Join Date: Jun 2018
Location: New England
Posts: 5,264

Bikes: Trek FX 3; 1994 Specialized Allez Pro; Motobecane Fantom CX; Giant OCR A1

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 2708 Post(s)
Liked 1,072 Times in 655 Posts
Originally Posted by shelbyfv View Post
Has anyone figured out what the "bar/pin" is?
I think it's the bolt on the front of the non-drive side crank arm:

livedarklions is online now  
Old 10-31-19, 03:29 PM
  #16  
ThermionicScott 
hungry
 
ThermionicScott's Avatar
 
Join Date: Aug 2011
Location: CID
Posts: 19,382

Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers)

Mentioned: 81 Post(s)
Tagged: 0 Thread(s)
Quoted: 2463 Post(s)
Liked 361 Times in 263 Posts
The ideal crank wouldn't flex at all, so I'm leaning way harder in the direction of a fit issue here.
__________________
Originally Posted by chandltp View Post
There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
RUSA #7498
ThermionicScott is offline  
Old 10-31-19, 03:47 PM
  #17  
mr_bill
Senior Member
 
Join Date: Sep 2013
Location: Massachusetts
Posts: 3,792
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 1640 Post(s)
Liked 139 Times in 119 Posts
On the drive side, there is a pin that keeps the chain from jamming between the largest chainwheel and the crank. It transmits no torque.

On the non-drive side there is a safety-plate. Some people call it a pin. It serves two purposes. It is a gauge to aid in proper assembly of the two piece crank, and, if the crank arm bolts are not torqued correctly, to serve as a fail-safe for a few turns of the crank. It transmits no torque under normal operations.

So, double check:

Crank arm lengths. (Unlikely.)
Centerline of frame to cranks. (Unlikely.)
YOU.

We are asymmetric creatures, think lobster claws.

(For most people the duh moment is put your right hand over your right shoulder at the top of your spine behind your back. Then put your left hand behind your back above the bottom of your spine and reach up and grab your right hand. Then visa-versa.)

-mr. bill

Last edited by mr_bill; 10-31-19 at 04:01 PM.
mr_bill is offline  
Old 10-31-19, 05:28 PM
  #18  
Elvo
Senior Member
 
Join Date: Oct 2006
Location: Orange County, CA
Posts: 4,175
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 380 Post(s)
Likes: 0
Liked 34 Times in 26 Posts
Elvo is offline  
Old 11-01-19, 07:14 AM
  #19  
livedarklions
Cyclesomatic
 
livedarklions's Avatar
 
Join Date: Jun 2018
Location: New England
Posts: 5,264

Bikes: Trek FX 3; 1994 Specialized Allez Pro; Motobecane Fantom CX; Giant OCR A1

Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 2708 Post(s)
Liked 1,072 Times in 655 Posts
Originally Posted by mr_bill View Post
On the drive side, there is a pin that keeps the chain from jamming between the largest chainwheel and the crank. It transmits no torque.

On the non-drive side there is a safety-plate. Some people call it a pin. It serves two purposes. It is a gauge to aid in proper assembly of the two piece crank, and, if the crank arm bolts are not torqued correctly, to serve as a fail-safe for a few turns of the crank. It transmits no torque under normal operations.

So, double check:

Crank arm lengths. (Unlikely.)
Centerline of frame to cranks. (Unlikely.)
YOU.

We are asymmetric creatures, think lobster claws.

(For most people the duh moment is put your right hand over your right shoulder at the top of your spine behind your back. Then put your left hand behind your back above the bottom of your spine and reach up and grab your right hand. Then visa-versa.)

-mr. bill
Honest question--if the issue is rider asymmetry, what can be done to address it? Is it a conditioning issue or are there mechanical fixes?

I've never experienced this, so I'm wondering if anyone has had to deal with it and what they did.
livedarklions is online now  
Old 11-01-19, 08:10 AM
  #20  
MoAlpha
 
MoAlpha's Avatar
 
Join Date: Jun 2015
Location: Land of Pleasant Living
Posts: 3,586

Bikes: Occasionally

Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 2157 Post(s)
Liked 365 Times in 223 Posts
The left front tire on my car went flat and I've narrowed down the cause to the extra weight of the driver and controls, which are on that side. Can anyone recommend a car without this obvious design flaw?
MoAlpha is offline  
Old 11-01-19, 08:40 AM
  #21  
cgates66
Junior Member
 
Join Date: Oct 2014
Posts: 15
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I've been following this thread for a couple of days, and I feel compelled to weigh in. FairWheel bikes did a study a while back comparing crank stiffness, using a 200 pound load (I think the bar graph above is from that study, or maybe an earlier one). The range for deflection on the DS was between 4 - 6mm, and on the NDS was 5 - 7mm or so, depending on the model. An ideal 175mm beam, with a 5x25mm section would deflect ~4mm under a similar load. Anyway, the DS / NDS difference is ~1 - 1.5mm under a 200 pounds. It is highly improbable that anyone could do 200 pounds per pedal stroke for any extended period of time - think 30 - 60 pounds as more typical, and the deflection is linear with the load for these small values. That means 1mm under a 200 pound load would be more like 0.15 - 0.3mm under a "typical" load.

It is highly unlikely that a 1mm deflection difference would have any physiological effect, and even less likely that a 0.15 - 0.3mm deflection would have any effect.
cgates66 is offline  
Old 11-01-19, 08:46 AM
  #22  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,284

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 887 Post(s)
Liked 116 Times in 95 Posts
Originally Posted by Nyah View Post
This question is in regards to conventional crank design. I don't ride bicycles regularly anymore and have not done much distance cycling. The most recent cycling trip of considerable distance that I took was somewhere around 52 miles total over two days. Afterwards, I could feel that my right leg was considerably more fatigued than my left. I narrowed the cause of this discrepancy down to the fact that the crank arm of the right side of the bike has a bar (or pin) that drives the spider/chainring. I would like to know if this phenomena has a name or, if this bar/pin crank design has a name or, if there are any alternative crank designs which attempt to spread the driving force evenly between both of the rider's legs. Thanks!

Edit: The bike is a Trek 520 touring bike, which I bought new from a bike shop. The frame size is appropriate for my physiology.
It's not plausible that a minuscule difference in crank stiffness caused injury/pain to 1 leg.
Plenty of more likely causes.
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: http://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 11-01-19, 09:09 AM
  #23  
DrIsotope
Non omnino gravis
 
DrIsotope's Avatar
 
Join Date: Feb 2015
Location: SoCal, USA!
Posts: 7,392

Bikes: Nekobasu, Pandicorn

Mentioned: 113 Post(s)
Tagged: 0 Thread(s)
Quoted: 4073 Post(s)
Liked 545 Times in 340 Posts
On a Trek 520, frame flex at the bottom bracket is significantly more likely than crankarm flex.

For the arms to deflect, the OP would either need to be putting down a whole bunch of power, or have a really off-balance pedal stroke.

I think the simple answer here is the OP doesn't ride much, then did 26 miles a day on back-to-back days.

Conditioning most likely, with bike fit a close second. Frame/crank material not even in the running.
__________________
DrIsotope is offline  
Likes For DrIsotope:
Old 11-01-19, 09:36 AM
  #24  
Caliper
Senior Member
 
Join Date: May 2014
Location: Michigan
Posts: 910

Bikes: Many

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 331 Post(s)
Liked 25 Times in 21 Posts
Originally Posted by MoAlpha View Post
The left front tire on my car went flat and I've narrowed down the cause to the extra weight of the driver and controls, which are on that side. Can anyone recommend a car without this obvious design flaw?
A Formula 1 car avoids this design flaw, I suggest you upgrade!


To the OP... Yes, as an engineer, I am sure that I could calculate slightly more flex on the left side crank arm due to having to transmit torque through the crank axle to the drive side. However, that difference in flex is going to be minuscule, something best measured with tools a machinist would use. If you are riding in regular street shoes, I would expect the flex in the sole of your shoe to be larger than in the crank. I would agree with those above that this is a setup or bike fit issue. Our bodies are often fairly asymmetrical whether it is noticed or not.
Caliper is offline  
Old 11-01-19, 10:08 AM
  #25  
mr_bill
Senior Member
 
Join Date: Sep 2013
Location: Massachusetts
Posts: 3,792
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 1640 Post(s)
Liked 139 Times in 119 Posts
Originally Posted by livedarklions View Post
Honest question--if the issue is rider asymmetry, what can be done to address it? Is it a conditioning issue or are there mechanical fixes?

I've never experienced this, so I'm wondering if anyone has had to deal with it and what they did.
About a year ago first time putting any weight on my leg:



Anyhow, most people are not that extreme obviously. Just keep riding is usually all that needs to be done.

But yes, in some cases you adapt the bike. See adaptive cycling forum here.


But in atrophy cases like mine, pros help. I miss my physical therapist honestly. I had to mindfully make sure that I wasn't cheating with my right leg.


Many crank power meters assume rider symmetry. We aren't. But you don't need a power meter.

The easiest real world way to find out is to ride on a quiet bike path or quiet road. Slight uphill useful, and nobbies help but road tires work too.

WAAAaaahWAAAaaahWAAAaaahWAAAaaah. (Symmetric power application.)
WAAAaaahWAAAaaahWAAAaaahWAAAaaah. (Asymmetric power application.)
WAAAaaahwaaaaaahWAAAaaahwaaaaaah. (Physical therapy to work that left leg.)
WAAAaaaaaaaaaaaahWAAAaaaaaaaaaaaah. (Single-leg training.)

And of course:

WAAAWAAAWAAAWAAAWAAAWAAAWAAAWAAA. (Spin class.)
BOOMBOOMBOOMBOOMBOOMBOOMBOOMBOOM. (Spin class bass line.)
KEEP IT QUICK COME ON. STARTING TO BURN A LITTLE? (Spin class instructor.)

Finally, some asymmetry is perfectly normal. Effects runners too. Before you think symmetric is obvioulsy better, Usain Bolt has an asymmetric stride.

-mr. bill

Last edited by mr_bill; 11-01-19 at 10:53 AM.
mr_bill is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.