Smaller Cranks and Fitting Chainsets

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531colin
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Re: Smaller Cranks and Fitting Chainsets

Postby 531colin » 4 Apr 2016, 1:33pm

TraceyW wrote:.....Colin: It feels like you are criticising me for wanting shorter cranks.....


Well, it was you that came on here asking for free advice; presumably you thought there might be people using this site who have more experience than you do?
My experience suggests you will be perfectly OK with standard length cranks, and my advice is that you should look elsewhere for a solution to your aches and pains. If you choose to interpret advice as criticism, that is your problem, not mine.

Bottom bracket bearing units come with a wide range of axle lengths....the length of axle you need is determined by what crankset you are using, and whether you want a road or an MTB chainline, so its pretty unlikely that any random chainset that you buy will need the same axle length as the unit fitted to your bike.

bobc
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Re: Smaller Cranks and Fitting Chainsets

Postby bobc » 4 Apr 2016, 1:53pm

TracyW
if you're in Cheshire (Congleton or Knutsford) I'll probably be able to help you try a set of 150s - I bought a cheap set ages ago for a trike & have used a diferent solution. PM me if you're local (Sandbach or Macc (just) counts as local :)
Bob

TraceyW
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Re: Smaller Cranks and Fitting Chainsets

Postby TraceyW » 4 Apr 2016, 2:34pm

Hi All

Thanks very much for your responses and yes, I include you Colin. I didn't say you WERE criticising me I said it just FELT like it. Nevertheless I apologise unreservedly for any offense I may have caused - it was unintended. Anyway if we can move forward please.

I have now had a chance to check the chain and it looks to be in very good condition no slackness in any of the links around the cogs at all and by measuring with a ruler no apparently stretching at all either. I'm therefore going to limit what I change to the chainset only and see how we go. Colin I take the point you made about the BB and will be keeping an eye open for that. What may need sorting out is the derailleur setting up at the rear.

I've also checked my riding position according to the document I was pointed to by Colin and have suitably made any necessary adjustments. I'm sorry to say though that the piccy he posted shows his friend with a noticeable downward slant on the thighs at near top of the pedal stroke my thighs at the top of the stroke are horizontal. Not exactly a good riding position. So what the hell is going on with me I'm unsure - and this is whilst the bike is on a turbo. Perhaps I'll get the bike to a dealers and ask them to check out my riding position.

Bob: unfortuneately I'm in Essex.

All the best
Tracey

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Re: Smaller Cranks and Fitting Chainsets

Postby Vorpal » 4 Apr 2016, 2:58pm

TraceyW wrote:my thighs at the top of the stroke are horizontal. Not exactly a good riding position.

I would suggest that your saddle is probably too low. Can you raise you saddle until your leg is *almost* straight at the bottom of the pedal stroke?

Some people use: when the ball of you foot is just over the pedal spindle, and you straighten your leg completely, your heel will be slightly lower than your toes.

Raising your saddle may result in your not being to put your feet down when sat on the saddle. That's okay (even if it isn't ideal).
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531colin
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Re: Smaller Cranks and Fitting Chainsets

Postby 531colin » 4 Apr 2016, 3:27pm

Saddle too low is the first thing I would look at. May also be too far forward. Some pictures of you on the turbo would be useful.

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Re: Smaller Cranks and Fitting Chainsets

Postby TraceyW » 4 Apr 2016, 4:52pm

Hi

To be honest I have adjusted the seat considerably higher but it leaves me lacking confidence since it is difficult to set my feet on the ground when stationary. I should perhaps also add that I am 71 as well as somewhat overweight. When I learnt to ride a bike I was advised to have the saddle height set such that you could put your feet on the ground, preferably the balls of the feet. This is how I've always set my bikes up since and its only now that I'm having any problems and unfortunately I have no way of knowing how long the cranks were on my previous bikes. Suffice it to say that it feels very different. Anyway I'm still playing with the riding position to see if I can get it any better and I'll certainly take your comments to heart. Before I post this, let me ask: what do you do when you have to stop? Do you get off the saddle and place yourselves between saddle and handlebars or are you able to put your feet on the ground? What doesn't actually help is that I think the derailleurs, front and rear, could both do with setting up properly.

Tracey

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georgew
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Re: Smaller Cranks and Fitting Chainsets

Postby georgew » 4 Apr 2016, 5:12pm

If you can place your feet on the ground when sitting on the saddle then your saddle is too low which of course will have an effect upon everything else. Usually it's possible to touch the ground with your toe when seated but one should not expect to have ones feet on the ground when stopped. Th usual method when stopping is to move from the saddle forward over the top tube while braking, and then come to a stop with one foot remaining on the pedal. This is then also the position for starting, and following a strong push on the pedal one then moves backwards to sit on the saddle.

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Re: Smaller Cranks and Fitting Chainsets

Postby TraceyW » 4 Apr 2016, 5:24pm

Hi fellas

Its Tracey again. I've just this minute taken my saddle up by a total of some two to two and a quarter inches but still my thighs seem to be horizontal at the top of the pedal stroke and I have no chance of touching the ground whilst sat on the saddle. The saddle is set such that with the bike on the turbo it is just about level with my waist or even a little above it and taking it off the turbo would lower it by no more than an inch. Does that really sound right? What I will say is that pedalling seems to be a bit easier than it was.

Tracey

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531colin
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Re: Smaller Cranks and Fitting Chainsets

Postby 531colin » 4 Apr 2016, 5:29pm

Its fair to say that the bottom bracket on a recent hybrid bike will be much higher than the bottom bracket of a roadster bike of 50 years ago.
Crank length hasn't changed much....used to be 6 1/2", was it?

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Re: Smaller Cranks and Fitting Chainsets

Postby georgew » 4 Apr 2016, 5:48pm

TraceyW wrote:Hi fellas

Its Tracey again. I've just this minute taken my saddle up by a total of some two to two and a quarter inches but still my thighs seem to be horizontal at the top of the pedal stroke and I have no chance of touching the ground whilst sat on the saddle. The saddle is set such that with the bike on the turbo it is just about level with my waist or even a little above it and taking it off the turbo would lower it by no more than an inch. Does that really sound right? What I will say is that pedalling seems to be a bit easier than it was.

Tracey



Two and a quarter inches is a massive amount to have to raise a saddle.

It really would be better to consult an experienced cyclist and let them see you mounted and pedalling. It's absolutely impossible to give a useful opinion relying on your written reports whereas someone with experience would probably see the problem straight off. Again photos would be a help if you don't know anyone with some experience.

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Re: Smaller Cranks and Fitting Chainsets

Postby Vorpal » 4 Apr 2016, 8:50pm

TraceyW wrote:Hi

To be honest I have adjusted the seat considerably higher but it leaves me lacking confidence since it is difficult to set my feet on the ground when stationary. I should perhaps also add that I am 71 as well as somewhat overweight. When I learnt to ride a bike I was advised to have the saddle height set such that you could put your feet on the ground, preferably the balls of the feet. This is how I've always set my bikes up since and its only now that I'm having any problems and unfortunately I have no way of knowing how long the cranks were on my previous bikes. Suffice it to say that it feels very different. Anyway I'm still playing with the riding position to see if I can get it any better and I'll certainly take your comments to heart. Before I post this, let me ask: what do you do when you have to stop? Do you get off the saddle and place yourselves between saddle and handlebars or are you able to put your feet on the ground? What doesn't actually help is that I think the derailleurs, front and rear, could both do with setting up properly.

Tracey

Although I'm a bit taller than you, I cannot put my feet down on the ground from the saddle on most of my bikes. I cannot even touch the ground on one of them. I hop down each time I stop. Colin is right that bike designs have changed somewhat over the years (more than crank lengths!). Town bikes still tend to be designed so that it is easier to set a foot down; they don't need the higher bottom brackets on hybrids.
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Re: Smaller Cranks and Fitting Chainsets

Postby seph » 4 Apr 2016, 11:32pm

I'm about 5' 10'' and run 160mm cranks. I started using them as an experiment to see if had any effect on (right) knee pain I got on 170 cranks. I don't get that pain anymore, except when I use the one bike I have left with longer cranks. I think that my knee is particularly affected by the sharpness of the angle it has to adopt at the top of the pedal stroke, and this can be lessened using shorter cranks.

I use the spa cranks, well made, cheap and look good.

But I did want to add to the discussion (unless I missed it up post) that crank shortening is possible, by this chap http://www.bhpc.org.uk/short-and-sweet- ... rrows.aspx amongst others . It would allow you more choice of both crank make and length. ( though I'm not sure about shortening hollow cranks like these http://ropeandcanvas.blogspot.co.uk/201 ... ranky.html :shock: )

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531colin
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Re: Smaller Cranks and Fitting Chainsets

Postby 531colin » 5 Apr 2016, 8:11am

If you go ahead and fit cranks 20mm shorter, this would mean the distance from the top pedal to the bottom pedal would be 40mm less, because the bottom pedal is 20mm higher, and the top pedal is 20mm lower.
However, unless you raise the saddle the extra 20mm, there is no benefit from the bottom pedal being 20mm higher.

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squeaker
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Re: Smaller Cranks and Fitting Chainsets

Postby squeaker » 5 Apr 2016, 8:16am

seph wrote:But I did want to add to the discussion (unless I missed it up post) that crank shortening is possible, by this chap http://www.bhpc.org.uk/short-and-sweet- ... rrows.aspx amongst others . It would allow you more choice of both crank make and length.
IIRC, 20mm is the minimum shortening that can be achieved, although looking at some photos of a Pioneer I'm not sure that those particular cranks could be shortened due to the tapered section.

Regarding saddle height, I usually start with straight leg, heel on pedal and pelvis level side to side, then take it from there.
"42"

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531colin
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Re: Smaller Cranks and Fitting Chainsets

Postby 531colin » 5 Apr 2016, 8:48am

crank shortening is pretty well explained here http://highpath.co.uk/crank-shortening/