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-   -   Frame Dimension, Size And Knees (http://www.bikeforums.net/fifty-plus-50/851090-frame-dimension-size-knees.html)

Crankykentucky 10-07-12 09:09 PM

Frame Dimension, Size And Knees
 
Ok, sorry if this has been tackled before, but a local bike shop owner told me that frame design can affect the health of your knees. His theory is that the knee that is on the upstroke of your peddling circle can compress too much before continuing the rotation to a more extended position. This guy tends to recommend a bigger frame size to protect your knees.


Has anyone ever heard of this?

Fred

NCbiker 10-07-12 09:20 PM

I don't see where the frame size has any effect on your knee as long as you're able to set the correct height and fore/aft position of the seat. The length of the crank arm would be the determining factor in the shop owner's scenario.

rdtompki 10-07-12 09:47 PM

bogus. You can achieve an acceptable relationship of seat and bottom bracket/pedal spindles in a range of frame sizes. The overall geometry of the bike will certainly come into play when attempting to achieve an overall fit including reach and seat to handlebar drop.

Crankykentucky 10-07-12 09:48 PM

Ok, I see what you mean. I didn't know if he was saying the location of the crank hanger could be different or not. So, this might be one reason that people talk about changing crank sets?

The reason his commentary caught my ear is that I know of several people who complain that biking hurts their knee or knees when running or hiking doesn't. I know there are a lot of causes of knee issues in our world, but I was kind of brought up to believe biking was good for your knees.

Foldable Two 10-07-12 10:25 PM

Pedal forward geometry (like on the Electra cruiser I just sold) was harder on my knees than a standard set-up.

I would agree that proper seat height and proper fore and aft position of seat are very important to knee health. At 6'3", I need a 39" seat-to-pedal distance to be comfortable, as well as to put power into the pedals. That, and the needed arm reach, dictates a larger sized frame.

What you can accommodate in "stand-over height" is also a factor in determining how large a standard bike frame you can/should ride.

Lou

maddmaxx 10-08-12 04:48 AM

Quote:

Originally Posted by Crankykentucky (Post 14817242)
Ok, I see what you mean. I didn't know if he was saying the location of the crank hanger could be different or not. So, this might be one reason that people talk about changing crank sets?

The reason his commentary caught my ear is that I know of several people who complain that biking hurts their knee or knees when running or hiking doesn't. I know there are a lot of causes of knee issues in our world, but I was kind of brought up to believe biking was good for your knees.

If you observe a lot of bikers you will see that many who haven't been given good advice sit too low. Many do so because they believe that they want to be able to put both feet on the ground when stopped. The too low position puts the knees in a bad position at the top of the pedal stroke.

Proper position goes something like this........If, while sitting normally on the seat, you adjust the seat hight so that your leg is straight while you put your heel on the pedal, you will find that when you pedal with the ball of your foot that the knee will have a slight bend at the bottom of the stroke. You will have to lean over when stopped with only one foot on the ground, but you will save your knees ............... and................. you will probably find that you have a more powerful peddling stroke.

Foldable Two 10-08-12 10:13 AM

Quote:

Originally Posted by maddmaxx (Post 14817608)
If you observe a lot of bikers you will see that many who haven't been given good advice sit too low. Many do so because they believe that they want to be able to put both feet on the ground when stopped. The too low position puts the knees in a bad position at the top of the pedal stroke.

Proper position goes something like this........If, while sitting normally on the seat, you adjust the seat hight so that your leg is straight while you put your heel on the pedal, you will find that when you pedal with the ball of your foot that the knee will have a slight bend at the bottom of the stroke. You will have to lean over when stopped with only one foot on the ground, but you will save your knees ............... and................. you will probably find that you have a more powerful peddling stroke.

+1

Crankykentucky 10-08-12 10:27 AM

Quote:

Originally Posted by maddmaxx (Post 14817608)
If you observe a lot of bikers you will see that many who haven't been given good advice sit too low. Many do so because they believe that they want to be able to put both feet on the ground when stopped. The too low position puts the knees in a bad position at the top of the pedal stroke.

Proper position goes something like this........If, while sitting normally on the seat, you adjust the seat hight so that your leg is straight while you put your heel on the pedal, you will find that when you pedal with the ball of your foot that the knee will have a slight bend at the bottom of the stroke. You will have to lean over when stopped with only one foot on the ground, but you will save your knees ............... and................. you will probably find that you have a more powerful peddling stroke.

This makes a lot of sense. I remember the old bike dealers I grew up with always looked for a slight bend in the bottom pedal leg. I also have had different advice from local dealers regarding seat height.

My nephew rode competitively in college and now gets knee pain on the "up stroke" while riding. It's all very fascinating and I appreciate the info from you all.

BikeWNC 10-08-12 05:50 PM

Saddle height, crank arm length and fore/aft position will dictate knee angles at the top and bottom of the pedal circle. The frame is only there to help connect the dots of your position. Some frames will make getting your desired position easier some harder and some will make it impossible when combined with where the bars need to be.

oldbobcat 10-08-12 08:58 PM

Quote:

Originally Posted by BikeWNC (Post 14820288)
Saddle height, crank arm length and fore/aft position will dictate knee angles at the top and bottom of the pedal circle.

And proper pedaling technique. Before learning to spin, I set my saddle to the 108% formula as mandated by Eugene Sloane's Complete Book of Bicycling and mashed my knees into oblivion. I thought it was because my bike was too small.

After a break from the bike I started training with a racing club. The saddle came down and back, gearing came down and the feet turned faster. Forty years later, when I injure my knees, doing things like running too much, skiing, or peeling off climbing walls, cycling is part of the therapy. And I'm still riding the same size bike.

howsteepisit 10-08-12 11:22 PM

Sloan's 108% always was a good stating point for me, I end slightly higher. Key thing is no mashing, not now not ever (at least for long periods of time, sometimes you have to mash u-p a short hill, just to get to the top.

flan48 10-09-12 06:48 AM

Quote:

Originally Posted by Foldable Two (Post 14818512)
+1

+1 - A couple of LBS' looked at me, and my 5'5" height and said I need a small, generally 15 or 15.5" frame. Turns out that on both a Jamis Coda and the Trek 7.4FX that I purchased, a 17.5" frame is actually perfect.
Best regards

Cleave 10-09-12 08:20 AM

Quote:

Originally Posted by BikeWNC (Post 14820288)
Saddle height, crank arm length and fore/aft position will dictate knee angles at the top and bottom of the pedal circle. The frame is only there to help connect the dots of your position. Some frames will make getting your desired position easier some harder and some will make it impossible when combined with where the bars need to be.

IF you are riding a standard road bike, then +1. The most important thing about fit is getting your saddle in the correct position relative to the bottom bracket. Do not move your saddle to adjust your reach to the handlebars, change your stem length. If you plan to ride a lot then a professional fit ($200) is well worth the money assuming there is a highly qualified fitter in your area.

Fit is the most critical thing for good pedaling mechanics and good joint health. If you are using cycling shoes with cleats, cleat position is almost as important. I say almost because most cleat have lateral float which lets you get away with a ballpark location. Learning to pedal correctly -- pedaling technique and appropriate gearing -- is that last big piece of the puzzle.

Quote:

Originally Posted by maddmaxx (Post 14817608)
If you observe a lot of bikers you will see that many who haven't been given good advice sit too low. Many do so because they believe that they want to be able to put both feet on the ground when stopped. The too low position puts the knees in a bad position at the top of the pedal stroke.

Proper position goes something like this........If, while sitting normally on the seat, you adjust the seat hight so that your leg is straight while you put your heel on the pedal, you will find that when you pedal with the ball of your foot that the knee will have a slight bend at the bottom of the stroke. You will have to lean over when stopped with only one foot on the ground, but you will save your knees ............... and................. you will probably find that you have a more powerful peddling stroke.

I agree that many people want to be able to stay on the saddle when stopped. For a standard road bike, you can't stay on the saddle while stopped if your seat height is correct. Maybe it's because I've been doing it for 40 years, but it's not hard for me or any of the new riders in my club to unclip one foot and slide off the saddle when stopping.


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