Grank arm lengths

[BADGER.BRAD]

Hello All,

My misses had a serious motorcycle crash some years back which has resulted in one leg being 2 inches shorter than the other. In order to try to combat the rocking motion caused by this. I thought about using a longer pedal arm on the left side of the bike (her left leg being the longest). The fitted pedal arms are 170mm I wondered if you could get longer than this ? My only other option is to cut the pedal arm (steel) and weld a section in. Any ideas anyone.

Thanks for your help and thoughts.

Brad l

 

[jpb]

I know that you can get 172.5 and 175s quite easily.

 

[gaz]

It's not a good idea to mix crank lengths.
A shorter crank length results in a larger gear ratio. This means that her shorter leg will have to work harder to keep a constant cadence.
A better idea is to build up the shoe or pedal to make up the difference.

 

[albion]

Two inches is 50mm.I'm surprised she does not have an extension piece for her shoes though either methods achieve almost exactly the same result.

 

[GrasB]

Go see a sports physio to see exactly what is needed to correct her problem. I know it seems expensive but after you've messed about with different things you'll probably end up saving money getting it right first time.

 

[RecordAceFromNew]

Sheldon offered a couple of suggestions.

 

[albion]

Useful though even his thoughts also go a bit skewiff.With an extension cleat/platform shoe the shorter leg rotates in the same size arc as the longer leg.The total amount of work on each can ve the very same for each leg. Of course that is up to the rider.Badger, if it is an 8 speed cassette or less junior cranksets are very cheap on ebay. (£10 or so)A cheap experiment if so. I was to try it out for my knee but as yet have not ascertained if they would fit my bottom bracket.

 

[RecordAceFromNew]

Useful though even his thoughts also go a bit skewiff.With an extension cleat/platform shoe the shorter leg rotates in the same size arc as the longer leg.The total amount of work on each can ve the very same for each leg. Of course that is up to the rider.Badger, if it is an 8 speed cassette or less junior cranksets are very cheap on ebay. (£10 or so)A cheap experiment if so. I was to try it out for my knee but as yet have not ascertained if they would fit my bottom bracket.

I think the late great Sheldon was not talking about the amount of work done by each leg, which perhaps to some extent one is always free to differentiate somewhat (as is using the up stroke or not with clips/cleats).

Since one's feet are always more or less on top of the end of the cranks, at 3 or 9 o'clock e.g. when effort is most significant the leverage or mechanical advantage will be greater with a longer crank, which is desirable for the weaker leg. In other words, for the same work done by each leg the force necessary to be exerted on the pedal by the shorter leg will need to be correspondingly higher if that crank is shorter.

 

[albion]

It's always going to be 'different' with a platform shoe/cleat.
A shorter leg will need more bend at the knee and thus more force will be used at these points.

The knees are also likely to be further out too in that it is only the lower leg that gets the extension.
There is no way around round it though total work can be the same.
I certainly think different crank lengths is the slightly more balanced approach.

 

[BADGER.BRAD]

Hello again all,

Thanks for all the fantastic info and ideas your imput is very much appreciated.As she will only ever do a max of 5/6 miles on an occasional afternoon with kids and dogs I'm going to go initially with building up the pedal if this does help her without hurting her knee (she has no kneecap) then I will give the junior pedal arm ago. She is way too proud to wear built up shoes or admit that she is semi disabled in anyway. Hitting a van head on which was on the wrong side of the road on a motorcycle at 100mph+ impact speed tends to do some damage to the body, a near same accident on the same bend put my two best friends 6 foot under. Considering the original injuries she is doing quite well and has been riding my cheap folder which she finds a little skittish (it is !) But yesterday I found a cheap mountain bike. Having done a quick service I sent her up and down the road and noticed the rocking motion her leg created.

I will report back on my findings once I have sorted the pedal I just hope the problem is caused just by the shorter leg and not her knee.

Thanks again all.

 

[GrasB]

I will report back on my findings once I have sorted the pedal I just hope the problem is caused just by the shorter leg and not her knee.

This is why I said go see a physio, a sports specialist if you can. They are in a much better position to work out what the exact problem is & suggest solutions which are particular to your other half.

 

[RecordAceFromNew]

A mtb is a great idea to provide better stability than a small wheel folder. If everything works out well and she seldom goes "offroad" you might want to consider replacing knobbly tyres, if they are currently present, with a pair of light slicks (e.g. Schwalbe Kojak 26x1.35 or Continential Sport Contact 26x1.3). They will make the journeys quite a bit easier.

 

[BADGER.BRAD]

Thanks again everyone for the replies,The bike at the moment is fitted with cheap square off road tyres that flex like hell when you corner on a hardish surface so it is my intention to change them to my winter road tyres (cheap ones) and get my self some new ones, as long as you inflate them to the top end of their limit they work well. 99% of her riding is off road on either canal towpaths or a local disused railway route which is about as much as she can manage., Hills would be way too much for her. She is under the physio at the moment for a problem with her good foot ( related to over using it to compensate for her bad leg) So I will get her to have a word with them. Wether she will listen or not is another thing ! She was told after the accident at 16 she will never run, walk more than a few hundred yards or climb a ladder and would be in a wheel chair by the time she was 30, she paid no attention to this and at 47 is still able to get about relativity well and run for short distances without any aids. As far as the sport physio goes one I don't think she would go and two our house hold budget is so stressed at the moment and about to get a lot worse ( I work for the local council thanks Mr Cameron) that I dout we could afford it. The point your making is of course quite correct!

Thanks again all

Brad