help with crank arm shorteners

Roose said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

Without going into an extended critique of the other proposed
approaches to your situation, might I suggest that it would probably
be worthwhile to look into recumbent bikes as an alternative? Many of
them have a seating position that greaty reduces the amount of knee
flex required, and while they aren't cheap when new, you might be able
to scare up a used one for a reasonable amount.
--
Typoes are a feature, not a bug.
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Roose said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

We had a bike in the shop recently which was set up for someone with a
disability. The cranks were lever arms with perhaps 45degrees of
restricted motion. They were chained to independant (singlespeed)
freewheels on both sides of the hub, and wired so that depressing one
crank lifted the other. There were three speeds, but you had to get off
the bike and move a lever arm to another peg to shift speeds.

This bike converted pedalling into a linear motion, like using a
stepper. It was quite a thrill to ride, actually. The bike was old and
had changed owners a few times, so we werent able to establish who made
it. Sorry I can't be more helpfull than that, but you might consider
searching something like this, it felt like quite a good mechanism to me.

Hi Andy,

I would go for a cheap used bike and some of the less expensive
shorteners you found. Ride around for a while to see if cycling will
work for you. If it does, maybe look into a custom set-up. These guys
http://www.hscycle.com make custom sized cranks and also things for
folks with leg length mismatches and other special circumstances. Maybe
they can help.

But first I'd just try the shorteners. They should work on just about
any bike. Pedal threads are pretty standard on adult size bikes.

Good luck!

Joseph

Jacobe Hazzard said:

We had a bike in the shop recently which was set up for someone with a
disability. The cranks were lever arms with perhaps 45degrees of
restricted motion. They were chained to independant (singlespeed)
freewheels on both sides of the hub, and wired so that depressing one
crank lifted the other. There were three speeds, but you had to get off
the bike and move a lever arm to another peg to shift speeds.

This bike converted pedalling into a linear motion, like using a
stepper. It was quite a thrill to ride, actually. The bike was old and
had changed owners a few times, so we werent able to establish who made
it. Sorry I can't be more helpfull than that, but you might consider
searching something like this, it felt like quite a good mechanism to me.

Actually, that one's probably just one of the 'stepping is better
therefore I'll reinvent the bicycle. Again.' manufacturers, not
specifically for disabled people. There was a famous one in the late
eighties.

Jasper

Quoted message said:

But first I'd just try the shorteners. They should work on just about
any bike. Pedal threads are pretty standard on adult size bikes.

However, the shape of the cranks could interfere with the shorteners. I'd
buy the shorteners myself, first, and then take them with me while fitting
bikes at the bike shops. Once you've found one or more bikes that fits you
properly, make sure that the crank arms that are on there work with the
shorteners, or get them to install a different set of cranks for you (the
latter they probably won't do unless you promise to buy the bike
afterwards, though).

Jasper

Quoted message said:

1) Is one device better than the other or do they have different uses?

They are different - one just shortens the crank length (but instead,
you could just buy a bike with short cranks). The other allows one leg
(or both, if you buy two) to move in a non-circular path. There are
other systems, such as the Rotor cranks.

I'd suggest you go and visit a decent bike shop, preferably one with a
Serotta or similar fitting service. This is a stationary bike with
virtually everything adjustable; you get on and pedal, and they tweak
everything until you are comfortable. Your limited range of motion can
be compensated for in many ways (seat height is another variable you
can play with). The fitting cycle has huge advantages - you can adjust
things far more easily than on a real bike, and you can gauge your own
comfort better when you don't have to concentrate on traffic.

You don't say exactly where in the Bay area you are, but check here

http://serotta.com/pages/west.html

for some recommendations on where to go.

Hi Andy,

Before we go off into the world of custom cranks and special adaptors that cost
more than I pay for brand new cranks.....

A properly fit bike does not require that you bend your knees "fully." Have you
tried riding a real, grown-up bike with a real bike mechanic on hand to see if a
standard bike could be made to fit. Something like 83% of everyone who rides a
bike has the seat set way too low which puts needless strain on even healthy
knees and hips. * This is especially common in childrens and cheap department
store bikes, perhaps like the ones you used to ride when you came to the
conclusion that you had problems with a standard crank. I'd try a decent bike
store comfort bike with cranks on the shortish side of standard ((165 - 170mm)
typical on that type bike) the saddle set properly and then see.

Maybe you've followed through on all that and have still decided that you need
special cranks. But since you don't mention it I've gotta ask.

Ron
*63% of all statistics are just made up

Roose said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

I searched around on the net, and I found that there are 2 kinds of devices
that you can put on a bike to solve this problem.

The first are so called crank arm shorteners:

http://www.hostelshoppe.com/cgi-bin/readitem.pl?Accessory=1033761548
http://www.tandemseast.com/parts/cranks.html

The second is basically an extra piece in the crank that rotates
independently:

http://www.hostelshoppe.com/cgi-bin/readitem.pl?Accessory=1026425305

I found some other links to similar devices, but they were from the UK and
other foreign sites (to the USA).

So the situation I'm in is that I don't even own a bike, but I want to buy
one and use one of these devices with it. So essentially I think I can
choose a bike based around this constraint.

I don't know too much about bike hardware other than what I found out
surfing around yesterday and finding these links. So I'm wondering a few
things:

1) Is one device better than the other or do they have different uses? The
main difference I see is that the first shortens the diameter symmetrically,
while the other one does it asymmetrically, but that doesn't seem to be a
huge deal if you just change the height of the seat.

e.g. see diagrams here:
http://www.highpath.co.uk/cycles/products/swingcrank.html

2) How should I go about choosing a bike that will work the best, given that
I don't own a bike yet? How do I make sure they fit? I presume if I just
go out and buy some random bike and some random crank arm device, they will
vary considerably in "compatibility".

3) Any downside to using these? Is the bike adversely affected as compared
to just having a shorter crank? I've seen some that cost $1000, like here:
http://www.powercranks.com/estore/information.php?info_id=3 . What are you
paying for if you get something expensive like that?

4) Also if anyone knows any shops in the SF bay area that might do this kind
of thing... from what I see on the Internet, it's a fairly specialized
thing, and there's not a lot of selection from different manufacturers. Do
I need someone to get the devices to fit or can I just buy them myself and
make it work? (Given that I don't really know much about bikes.)

My budget is flexible, but I'd like to start out reasonably cheap and if I
find that I'm really into it, I can upgrade later. Thanks for any help.

Andy

Quoted message said:

They are different - one just shortens the crank length (but instead,
you could just buy a bike with short cranks). The other allows one leg
(or both, if you buy two) to move in a non-circular path. There are
other systems, such as the Rotor cranks.

I think it's still circular, just with a center that's lower. Essentially
that one seems to move the pedal in toward the BB first (in the regular
shortener that's included), and then that hanging thing moves the pedal
downwards to the ground by an inch or so -- but that still makes a circle.

Jasper

Werehatrack said:

Roose said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

Without going into an extended critique of the other proposed
approaches to your situation, might I suggest that it would probably
be worthwhile to look into recumbent bikes as an alternative? Many of
them have a seating position that greaty reduces the amount of knee
flex required, and while they aren't cheap when new, you might be able
to scare up a used one for a reasonable amount.

Werehatrack's comment about reducing knee flex by using a recumbent is a
startling detour from his usually well considered writings.

The hips are fixed in place, the feet travel in circles defined by the
crank lengths. That describes both standard bikes and recumbents. Knee
flex is identical, just rotated about an axis through the hips.

--
Ted Bennett

Thanks for the advice... I wasn't sure how many variables to consider, but
it sounds like it will be enough to just get one of the cheaper ones and
bring it a bike store. I want to keep it simple at first, and if I keep up
with it, then I can tweak the setup if necessary.

To a couple of the other posters, I did run across recumbents in my
Googling, but I don't think it would work well, because there seems to be
less room for error. On a normal bike at least I can sort of stand up to
compensate, and the gravity helps bend the knees. And if I could just raise
the seat, I would, but I don't have the full range. I would end up trying to
bob up and down or side to side, if you can picture that...

Also, if I could just buy a new bike with short cranks that would be nice,
but it doesn't seem like that's really an option.

thanks,
Andy

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Hi Andy,

I would go for a cheap used bike and some of the less expensive
shorteners you found. Ride around for a while to see if cycling will
work for you. If it does, maybe look into a custom set-up. These guys
http://www.hscycle.com make custom sized cranks and also things for
folks with leg length mismatches and other special circumstances. Maybe
they can help.

But first I'd just try the shorteners. They should work on just about
any bike. Pedal threads are pretty standard on adult size bikes.

Good luck!

Joseph

Roose said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

I searched around on the net, and I found that there are 2 kinds of devices
that you can put on a bike to solve this problem.

Steel cranks takes to welding like a duck to water, particularly the single piece ones. And since they're often found on cheap bikes this might be the place to start experimenting if you know someone with a stick or wire feed welder. Simply get a second hand bike, cut a piece out of the crank arm and weld it back up.

Do note that the crank arm is a highly stressed piece, so I don't recommend it for regular riding. But if joined by a half-decent welder it should hold up well enough for some closely monitored and limited experimenting.
It's not a perfect fix but it might be the cheapest way to find out if cycling will fit you.
Later if/when you go for the real deal you might want to pay attention to the gearing ratio to get one that's compatible with the shorter cranks.

Quoted message said:

Quoted message said:

Hi,

I'm looking to get back into biking. I biked a fair bit as a kid and
teenager, but I stopped because I have a disability which prevents me from
bending my knees fully.

Werehatrack said:

Without going into an extended critique of the other proposed
approaches to your situation, might I suggest that it would probably
be worthwhile to look into recumbent bikes as an alternative? Many of
them have a seating position that greaty reduces the amount of knee
flex required, and while they aren't cheap when new, you might be able
to scare up a used one for a reasonable amount.

Huh? That doesn't make any sense. The amount of knee flex required is
strictly determined by the crank length and the seat/saddle to crank
distance.

In my own experience, recumbent riding tends to make my knees hurt while
upright riding generally doesn't.

It has gotten better since I switched to 160 mm cranks on my recumbent
though.

Sheldon "Goes Both Ways" Brown
+---------------------------------------------------------------+
| There are 10 kinds of people in this world: |
| Those who understand the binary system, and those who don't |
+---------------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

A shy person said:

Steel cranks takes to welding like a duck to water, particularly the
single piece ones. And since they're often found on cheap bikes this
might be the place to start experimenting if you know someone with a
stick or wire feed welder. Simply get a second hand bike, cut a piece
out of the crank arm and weld it back up.

Do note that the crank arm is a highly stressed piece, so I don't
recommend it for regular riding. But if joined by a half-decent welder
it should hold up well enough for some closely monitored and limited
experimenting.
It's not a perfect fix but it might be the cheapest way to find out if
cycling will fit you.

Actually, one-piece "Ashtabula" type cranks such as you describe are
dirt cheap, typically $15 or less, and come ready made in lengths as
short as 3 1/2", since this style is most often used for children's
bikes these days. It would make much more sense than cutting and
welding in most instances.

Quoted message said:

Later if/when you go for the real deal you might want to pay attention
to the gearing ratio to get one that's compatible with the shorter
cranks.

That's correct.

See: http://sheldonbrown.com/gain

and: http://sheldonbrown.com/gears

Sheldon "Gain Ratio" Brown
+--------------------------------------------------+
| If you find yourself standing to accelerate, |
| on level ground, it is a sign that your gear |
| is too high, or that your saddle is too low. |
| See: http://sheldonbrown.com/standing.html |
+--------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com