help with crank arm shorteners

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/...ory=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/...ory=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 he
http://www.highpath.co.uk/cycles/pro...wingcrank.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 he
http://www.powercranks.com/estore/in....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

On Mon, 14 Nov 2005 21:49:04 -0800, "Roose" wrote:

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.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Roose wrote:
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

On Tue, 15 Nov 2005 03:39:49 -0500, Jacobe Hazzard
wrote:

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

On 15 Nov 2005 03:06:59 -0800, wrote:

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

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





On Mon, 14 Nov 2005 21:49:04 -0800, "Roose" wrote:

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/...ory=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/...ory=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 he
http://www.highpath.co.uk/cycles/pro...wingcrank.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 he
http://www.powercranks.com/estore/in....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

On 15 Nov 2005 05:27:09 -0800, wrote:

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 wrote:

On Mon, 14 Nov 2005 21:49:04 -0800, "Roose" wrote:

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