Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Fifty Plus (50+) Share the victories, challenges, successes and special concerns of bicyclists 50 and older. Especially useful for those entering or reentering bicycling.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 11-17-12, 08:34 AM   #1
jim p
Senior Member
Thread Starter
 
Join Date: Apr 2006
Bikes:
Posts: 1,024
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
How does crank arm length affect bike fit?

I am 6 feet tall and I am riding a 57 cm bike with 170mm cranks. I have played around with the kops method of seat placement and my knee is forward of the pedal axle. I have a nitto high extention quill stem for the bike but I think that it would feel a little better if I could raise the bars just a little higher.

So the though came to me that longer cranks would require me to lower my seat and would put the pedal axle under my knee. By lowering the seat, the relative position of the bars will be higher.

Has anyone tried using longer cranks to aid in fit or is this just ridiculous?
jim p is offline   Reply With Quote
Old 11-17-12, 08:39 AM   #2
10 Wheels
Galveston County Texas
 
10 Wheels's Avatar
 
Join Date: Nov 2007
Location: In The Wind
Bikes: 2010 Expedition, 03 GTO
Posts: 29,294
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 67 Post(s)
Yep, there is a happy size for you.

I am 6 ft with a 34 inch bike Inseam and love 175 crank arms.

http://veloweb.ca/bike-fit/
__________________
[SIZE=1][B]What I like about Texas[/B]
http://www.youtube.com/watch?v=PGukLuXzH1E

Set F1re To The Ra1n ( NY Night Rain Ride)
http://www.youtube.com/watch?v=W7jfcWEkSrI
10 Wheels is offline   Reply With Quote
Old 11-17-12, 08:43 AM   #3
LesterOfPuppets
cowboy, steel horse, etc
 
LesterOfPuppets's Avatar
 
Join Date: Sep 2008
Location: Rock Springs, WY
Bikes: My War
Posts: 26,477
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 57 Post(s)
Probably 6 of one half dozen of the other. As you lower the saddle it moves forward if left in the same spot on the rails, negating a bit of the 5mm forward shift fom 175s. I just pick the cranks that feel comfiest to spin circles with.

Curious how your saddle is positioned in relation to the bottom braket.
LesterOfPuppets is offline   Reply With Quote
Old 11-17-12, 08:52 AM   #4
LesterOfPuppets
cowboy, steel horse, etc
 
LesterOfPuppets's Avatar
 
Join Date: Sep 2008
Location: Rock Springs, WY
Bikes: My War
Posts: 26,477
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 57 Post(s)
Guess i should add that kops is generally used as a starting point for fore/aft saddle position. If you feel too far forward and your seat is pushed all the way back on the rails, then it'll move forward as you lower it.
LesterOfPuppets is offline   Reply With Quote
Old 11-17-12, 09:32 AM   #5
Rowan
Has opinion, will express
 
Join Date: Jun 2003
Bikes:
Posts: 14,650
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 50 Post(s)
I move between 170 and 175 cranks on my various bikes. The 170s evolved on my long--distance bikes and my fixie because of the reduced circles I had to pedal.

Longer cranks mean a lower seat, and a very slight shift forward in the seat.

I like being able to remain seated when my bikes come to a stop. It helps getting started again, especially on hills. If the crank length is too short, it means the seat might be too high to do this. It's a problem for women with long inseams, but who want a small frame... bike manufacturers usually put short cranks on (165) so they have to move off the saddle when putting their foot down on the ground.
Rowan is offline   Reply With Quote
Old 11-17-12, 09:54 AM   #6
ericm979
Senior Member
 
ericm979's Avatar
 
Join Date: May 2007
Location: Santa Cruz Mountains
Bikes:
Posts: 6,170
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Pick the crank length you want for your pedaling/riding style. Then fit the saddle position relative to the crank, and then the distance to the bars relative to the saddle. Last the bar height, which depends mostly on your flexibility. Changing crank length to make a bike fit is the wrong way to go about it.

I'm 6' with a 35" cycling inseam and like 175mm cranks. Since I do long road races and a lot of climbing I prefer a position to the rear of KOPS. That engages the glutes more and quads less. It also means there is less weight on my hands, making long distance riding more comfortable. Most rec riders would be best served by a similar position. The only riders I'd have on or ahead of KOPS would be crit racers or track sprinters. (not counting TT/tri position, that's a whole different setup).

From your description it sounds like your position could be greatly improved. Sitting forwards means there is more weight on your hands and may be the reason why you feel you need to raise your bars. You might consider a fitting from a knowledgable fitter.
ericm979 is offline   Reply With Quote
Old 11-17-12, 11:41 AM   #7
Don in Austin
Don from Austin Texas
 
Join Date: Jul 2009
Location: Austin, Texas
Bikes: Schwinn S25 "department store crap" FS MTB, home-made CF 26" hybrid, CF road bike with straight bar, various wierd frankenbikes
Posts: 1,181
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Seat/pedal position should be done first and then bars afterwards.

Don in Austin
Don in Austin is offline   Reply With Quote
Old 11-17-12, 03:25 PM   #8
AzTallRider 
I need speed
 
AzTallRider's Avatar
 
Join Date: Sep 2009
Location: Phoenix, AZ
Bikes: Giant Propel, Cervelo P2
Posts: 5,550
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by ericm979 View Post
Sitting forwards means there is more weight on your hands and may be the reason why you feel you need to raise your bars.
It also means you are much more aero, without being as bent over at the waist, so you maximize the possible drop for a given degree of flexibility. And, especially for taller riders, it gets you to a more balanced position (tall bike geometry pushes you back), which helps cornering and bike handling in general. Granted these have a greater effect when racing crit's, on the track, and for TT's, which is no doubt why you mentioned them, but even in a road race, if you are to win, then at some point you will expose yourself to the wind. If you are in a more aero position, and have trained to pump out the power in that position, it helps.
__________________
"If you're riding less than 18 MPH up a 2% grade please tell people Coggan is coaching you."
AzTallRider is offline   Reply With Quote
Old 11-17-12, 04:47 PM   #9
FrenchFit 
The Left Coast, USA
 
FrenchFit's Avatar
 
Join Date: Feb 2008
Bikes:
Posts: 3,015
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
If you're at the point of fine tuning your fit, and pedal stroke, it makes a big difference. Even 2.5mm will probably change your saddle position and the arc of the power stroke.
FrenchFit is offline   Reply With Quote
Old 11-17-12, 06:57 PM   #10
howsteepisit
Senior Member
 
howsteepisit's Avatar
 
Join Date: Oct 2005
Location: Eugene, OR
Bikes: Mecian
Posts: 3,634
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 20 Post(s)
5 mm is .19 inch, I don't really think it makes that much difference.
howsteepisit is offline   Reply With Quote
Old 11-17-12, 07:30 PM   #11
MikeWMass
Senior Member
 
Join Date: May 2012
Location: western Massachusetts (greater Springfield area)
Bikes: Velosolex St. Tropez, LeMond Zurich (spine bike), Rotator swb recumbent, Cignal tandem
Posts: 503
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Have you considered a seatpost with more setback?
MikeWMass is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:21 AM.