Shimming guidelines

Discuss light weight issues concerning road bikes & parts.
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HUMP DIESEL
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by HUMP DIESEL

For those who believe in shimming for a shorter leg, what is the general rule for the amount? I have heard half of the actual difference in leg length, but wanted to get the WW opinions.

HUMP
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fdegrove
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by fdegrove

Hi,

Difference divided by two is what I heard as well.

There's a big market out there for these kind of corrections. Surprisingly little product is available....

Ciao, ;)
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eric
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by eric

Wouldn't the WW perspective be to shorten the longer leg?

system787
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by system787

:lol:

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HammerTime2
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by HammerTime2

I have heard no guidelines, other than in this thread. However, leaving aside that you might want to make the shim (initially) half the difference, so as to gradually ease into any change, why wouldn't you want to make the shim equal to the difference, so that the length of both legs to the bottom of the cleat are equalized? That equalization will be in play throughout the pedal stroke, so I fail to see a logic in going half the difference.

Edit: O.k., ignore the above.
Last edited by HammerTime2 on Wed Jun 19, 2013 12:58 pm, edited 1 time in total.

thisisatest
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by thisisatest

It's complicated. Is the discrepancy in the femur or tibia? Do you use correction when standing, walking, in general? if so, for how long?
If you have a small leg length discrepancy and don't correct for it in daily life, your body has compensated for it to some degree. For walking n standing, it's just a heel lift, but that would do nothing for on the bike. Your body will "lift the heel" (aka drop the toe) somewhat out of habit.
So after that, and many other variables, most people perform well with a correction of about 1/2 the actual difference. So it's a good starting place.

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ghisallo2003
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by ghisallo2003

Hump, my only advice is caution and have it done properly, if at all. Some leg length discrepancy is apparent, rather than real, with a cause that lies in the way the hips are rotated at the pelvis.

My own attempts at resolving small discrepencies have not been happy, with my body basically saying that it has been doing it this way for 20 years, why change? I can see the point for elite athletes looking for marginal gains, but for the older athlete with a total body system that works with various in-built compensations, I think the risks need to be weighed up.

HUMP DIESEL
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by HUMP DIESEL

For those who ask.
1. I do not compensate in daily shoes, but I dont walk alot, I sit behind a desk. This past week I was in DC for vacation and we walked a large amount every day, averaging about 10 miles a day. It became apparent that something is wrong during this time with my left outside of foot hurting and showing bruising. I did get an over the counter arch support that did lift the heel and that seemed to help, that and Advil. I am still feeling the effects of that and have contacted my PT to discuss the leg length difference.
2. I broke my ankle before heading into my junior high years, so somewhere around 11 or 12 years of age. It was a complicated fracture and had to be set, but no screws or pins.
3. The length difference is in the lower leg. When I set my saddle height to the low leg, the long leg is cramped and my toes are being pushed into my right shoe, When I set it to the long leg, the left leg is wanting to reach, but the long leg feels solid and smooth.

I had a shim that I made of my own about three years ago, and had a really good experience, but the look of it caused me to see if I could go without it. I know, how shallow. I remember having some of the best results that year, and never feeling like I was lacking.

HUMP
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bricky21
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by bricky21

As far as I can tell the general consensus within the podiatry community is to shim half the amount of the measured difference in leg length. A lot of the reasons have already been mentioned. The problem is that walking and pedaling are two very different actions. When fixed to a bicycle you loose most of your ability to compensate for the discrepancy. Best advise I can offer is to shim slowly, and methodically adding and subtracting shims only if it improves your pedaling action. I wouldn't pay too much attention to leg length measuring since it isn't highly accurate.

sigismond0
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by sigismond0

If the difference is profound enough (2.5mm or more, that is), you could be a true Weight Weenie and put a shorter crankarm on that side. This has the added upside of not having to shim all of your shoes and is a permanent fix. Only worth pursuing if you do the shimming and determine that's the correct difference for you though.

HUMP DIESEL
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by HUMP DIESEL

That question was asked of me from a friend who does not cycle. I have thought of that, but has anyone done that successfully?
Why are the best things in life always the ones you start last?

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