Short cranks for limited knee movement?
tom adams
degree bend.
When she rides a bike, she has to put the seat overly high and still
kind of raises off the seat a bit to get around the top of the crank.
I think shorter cranks would solve the problem. But are they
available?
Any other ideas?
Chalo
Yes. BMX racing equipment is designed for kids from ankle-biting size
on up, and it is usually good strong stuff that doesn't cost too
much.
Here are cranks from 115mm to 180mm in 5mm increments:
http://www.maximumbmx.com/catalog.php?item=129
The above cranks will accept a ring as small as 34 teeth. Because the
crank is short, her gear ratio should also be short in comparison to
someone riding on normal length cranks. The short cranks will allow
her to spin faster than normal, but she should not have to push the
pedals harder than normal.
Because of this relationship between pedal force, lever length, and
cadence, it is probably a good idea if both crank arms are the same
length. But if her leg with limited range of motion is particularly
weak or slow, it may make sense to have a short crank for that leg and
a long crank for the other leg so it can do most of the work.
Chalo
Marcus Coles
BMX "eurostyle" cranks are 110mm bolt circle, square taper and come in
shorter arm lengths.
Several other approaches are available from http://highpath.net/cycles/
including crank shortening, crank shorteners, and swing cranks
specifically designed for reduced leg motion.
HTH
Marcus
andre...@aol.com
Also, a triathlon bike with a 78 degree angle and moving the saddle
forward will help her. Triathlon bikes are designed to reduce knee
bend in order not to over excert the hamstrings and lower back so that
athletes can run fast after a grueling bike ride.
With your current bike, start by pushing the saddle all the way
forward. This should allow the saddle to be higher. She can also turn
the seapost around so that the clamp will face forward, allowing the
saddle to go further forward. There are also seaposts that move the
saddle forward.
Keiron
Don't know any short cranks specifically but wondering what kind of bike
it is she rides? If it's an option it might be best to go for a different
style of bike? Hybrid maybe: choice of crank lengths, upright position so
she sits higher anyway, lower bottom bracket so legs more outstretched
(both up and down, and forward - suggests more limited range of movement
to me?)?
I suggest this only because with my knee problem, although it sounds
completely different, I sometimes find the downward stroke uncomfortable
(stability issue for me) and I guess a shorter crank would not be
friendly due to the lower leverage. Only guessing.
Keiron
Slight hijack i'm afraid but possibly useful: What advantages do road
bikes offer over triathlons bikes then? I'd like to take all my rides on
a more efficient machine with less possibility of aches.
Keiron
<http://ezinearticles.com/?In-Depth---Road-Bikes-Vs-Triathlon-
Bikes&id=2453879>
Or
Particularly paragraph 5. Ok so the lady in question probably isn't going
to run straight away after but the added knee stress (if true) may be a
factor?
RonSonic
Tri bikes are less efficient and less comfortable than road bikes. They simply
spare running muscles more than a normal road bike positioning would. Tri's are
looking for the lowest combined time so losing some time on the bike stage to
leave themselves fresher for the run makes sense. This is pretty specialist
stuff that may not even apply to a sprint tri.
Bicyclic Blogging: http://dumbbikeblog.blogspot.com
RonSonic
A others have said, lots of options in the crank department.
>Any other ideas?
Yeah, a question mostly and please understand I can't know what you know or your
background or knowledge so please none of this should cause offense.
When you say "she has to put the seat overly high" do you mean overly high by
the standards of serious cyclists or overly high for a cruiser sort of bike on
which a lot of people expect to be able to touch the ground while seated?
Bike position is variable according to the style of riding and individual needs.
It isn't overly high if she's comfortable and it isn't causing strain at the
back of the knee. That she has room to raise off the saddle without outright
standing on the pedals tells me that while her position may be a bit too high it
isn't outrageously so.
So I'm not arguing that shorter cranks isn't a good idea. But I will point out
that damn near every recreational cyclist I see out on the paths has the seat
set way too low. Everybody's knees hurt when the seat's too low.
Anyway, a bit of context would help. What kind of bike, what kind of riding in
what kind of area?
Bicyclic Blogging: http://dumbbikeblog.blogspot.com
Tim McNamara
<4eccc562-7a0e-41a4...@k6g2000yqn.googlegroups.com>,
tom adams <tada...@yahoo.com> wrote:
Well, if only one knee is the problem then it would be possible to use a
normal length crank on one side and a short crank on the other. That
might feel awkward, though- I've never tried it.
A trend among recumbentists is to use very short cranks- 150 mm. There
are several people who will machine down a crank and drill and tap new
pedal eyes. For standard bikes there may be some risk to this, given
that the weight of the rider can be placed on the pedal whereas this
doesn't happen with recumbents.
A local-guy-to-me has offered this service for recumbents, and has an
interest in adaptive approaches for bicycles. He has several options
for short cranks:
someone
> In article
> <4eccc562-7a0e-41a4-82a1-96883a146...@k6g2000yqn.googlegroups.com>,
Stronglight have a crank design which incorporates a multiple choice
pedal mounting through choice of insert, although I think they are for
long cranks. It could be worth using for someone who needs to
temporarily have one crank shorter. If you use 175mm cranks, the
alternative position with the insert reversed is 170mm and there is
another insert for 172mm
Jay Beattie
Apart from all the ideas below, you can use crank adaptors -- which I
used on my tandem when my son was small. See
http://www.bikeparts.com/search_results.asp?ID=BPC313333 I'd sell you
mine for a lot less than the listed price in that ad. -- Jay Beattie.
M-gineering
Other possibility: a crank with a pivot in the middle, so the TDC for
the pedal is at BB height
--
/Marten
info(apestaartje)m-gineering(punt)nl
andre...@aol.com
> On Tue, 21 Jul 2009 16:39:57 GMT, Keiron <po...@NOSPAMsheffield.ac.uk> wrote:
>
> - Show quoted text -
I am not suggesting a full TT bike. I was suggesting a TT frame
geometry which is essentially a road bike with a steeper seat angle. I
have short legs, a long torso and get a sore lower back after over two
hours on the saddle. I had a frame made with a 76 degree angle. I used
it as a road bike for a long time. I never had any lower back pain
with that setup. I could easily ride foru or five hours without
getting of the bike and my back fresh as a cucumber.
I have been riding a specilized road frame with 73.5 seat angle. I
moved the saddle pretty far forward. I get lower bakc pain within the
first three hours and have to do a lot of stretching on the bike if I
don't want to dismount and stretch on hte ground. The reason I ride
this frame is because it is an old lugged steel frame which I like a
lot and feels great.
Tom Adams
It was pretty high when we tested a while back. I am not sure it was
completely out of the range of a serious cyclist. Her comfort was
certainly part of the issue, since she is not a serious cyclist.
I am a regular commuter cyclist and I am aware good seat adjustment,
and I see cyclist with there seats too low all the time, as you said.
Anyway I don't think she will ride with the seat at or a little about
the proper height, even if it is possible.
RonSonic
Just checking, getting her comfortable is the thing. I just wanted to make sure
that expectations of how low a bicycle seat can go are reasonable.
You got a lot of info on alternative cranks, hope it helps.
Ron
Mom, he's still blogging: http://dumbbikeblog.blogspot.com
RonSonic
Old thread, but maybe this will help.
http://www.bikesmithdesign.com/Short_Cranks/shorten.html
He warns of possibly weakening the crank, but a petite woman with bad knees is
probably no threat to the crank even if there is less meat around the eye.
--
Oh damn. There's that annoying blog. Again. http://dumbbikeblog.blogspot.com
someone
> On Tue, 21 Jul 2009 08:27:23 -0700 (PDT), tom adams <tadams...@yahoo.com> wrote:
> >My wife want to ride a bike but one of her knees is limited to >90ish
> >degree bend.
>
> >When she rides a bike, she has to put the seat overly high and still
> >kind of raises off the seat a bit to get around the top of the crank.
>
> >I think shorter cranks would solve the problem. But are they
> >available?
>
> >Any other ideas?
>
> Old thread, but maybe this will help.
>
> http://www.bikesmithdesign.com/Short_Cranks/shorten.html
>
> He warns of possibly weakening the crank, but a petite woman with bad knees is
> probably no threat to the crank even if there is less meat around the eye.
>
Drill and thread for 1/2" pedal axle.
John Thompson
> On Tue, 21 Jul 2009 08:27:23 -0700 (PDT), tom adams <tada...@yahoo.com> wrote:
>
>>My wife want to ride a bike but one of her knees is limited to >90ish
>>degree bend.
>>
>>When she rides a bike, she has to put the seat overly high and still
>>kind of raises off the seat a bit to get around the top of the crank.
>>
>>I think shorter cranks would solve the problem. But are they
>>available?
>>
>>Any other ideas?
>
> Old thread, but maybe this will help.
>
> http://www.bikesmithdesign.com/Short_Cranks/shorten.html
>
> He warns of possibly weakening the crank, but a petite woman with bad knees is
> probably no threat to the crank even if there is less meat around the eye.
Or, non-destructively:
http://www.jensonusa.com/store/product/CR309E00-Ride2+Crank+Arm+Shorteners.aspx
Phil Wood used to make a similar product, but I don't know if it's still
available. I used a set on my tandem kid-back when my kids were little.
Alas, I sold them many years ago after they outgrew the kid-back.
--
-John (jo...@os2.dhs.org)
russell...@yahoo.com
> On 2009-08-17, RonSonic <ronso...@tampabay.rr.com> wrote:
>
>
>
>
>
> > On Tue, 21 Jul 2009 08:27:23 -0700 (PDT), tom adams <tadams...@yahoo.com> wrote:
>
> >>My wife want to ride a bike but one of her knees is limited to >90ish
> >>degree bend.
>
> >>When she rides a bike, she has to put the seat overly high and still
> >>kind of raises off the seat a bit to get around the top of the crank.
>
> >>I think shorter cranks would solve the problem. But are they
> >>available?
>
> >>Any other ideas?
>
> > Old thread, but maybe this will help.
>
> >http://www.bikesmithdesign.com/Short_Cranks/shorten.html
>
> > He warns of possibly weakening the crank, but a petite woman with bad knees is
> > probably no threat to the crank even if there is less meat around the eye.
>
>
> Phil Wood used to make a similar product, but I don't know if it's still
> available. I used a set on my tandem kid-back when my kids were little.
> Alas, I sold them many years ago after they outgrew the kid-back.
>
> --
>
>
> - Show quoted text -
The problem with these things is they spread the legs another 2 inches
wider. I'm not one of these Grant Petersen Q factor whackos, but
increasing the width that much might be bad. Particularly for a short
small person with short legs. One would think a short small person
with short legs might want the Q factor even less than normal.
RonSonic
While the guy modifying cranks is very clear and open about possibly
compromising the strength of the crank arm and pedal eye, I trust those with my
weight a lot more than a bolt on thing.
Q on bikes has been getting pretty bad in recent years anyway. Don't want to
make that any worse.
AMuzi
>>>> My wife want to ride a bike but one of her knees is limited to >90ish
>>>> degree bend.
>>>> When she rides a bike, she has to put the seat overly high and still
>>>> kind of raises off the seat a bit to get around the top of the crank.
>>>> I think shorter cranks would solve the problem. But are they
>>>> available?
>>>> Any other ideas?
>> RonSonic <ronso...@tampabay.rr.com> wrote:
>>> Old thread, but maybe this will help.
>>> http://www.bikesmithdesign.com/Short_Cranks/shorten.html
>>> He warns of possibly weakening the crank, but a petite woman with bad knees is
>>> probably no threat to the crank even if there is less meat around the eye.
> John Thompson <j...@vector.os2.dhs.org> wrote:
>> Or, non-destructively:http://www.jensonusa.com/store/product/CR309E00-Ride2+Crank+Arm+Short...
>> Phil Wood used to make a similar product, but I don't know if it's still
>> available. I used a set on my tandem kid-back when my kids were little.
>> Alas, I sold them many years ago after they outgrew the kid-back.
russell...@yahoo.com wrote:
> The problem with these things is they spread the legs another 2 inches
> wider. I'm not one of these Grant Petersen Q factor whackos, but
> increasing the width that much might be bad. Particularly for a short
> small person with short legs. One would think a short small person
> with short legs might want the Q factor even less than normal.
Phil Wood crank shorteners move pedals out 5mm each side.
Something, yes, but not 50mm.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
Mark J.
Yes, that was my estimate. I also had them for the kid-back and sold
them on ebay when no longer needed. I'm pretty sure they are no longer
in production.
Before the O.P. starts hunting them, note that Phil Wood shorteners
won't fit on modern angled-arms cranksets (sorry, I'm missing the right
term here). They only fit on straight-sided cranks (e.g. original Campy
Record, Sugino Mighty, and those of like era). Most (all?) modern
cranks from about 1985 onward angle the arm outward to afford more ankle
clearance (among other reasons), and the Phil shortener couldn't hold
the pedal spindle parallel to the crank spindle on such cranks.
Mark J.
russell...@yahoo.com
> >>> tom adams <tadams...@yahoo.com> wrote:
> >>>> My wife want to ride a bike but one of her knees is limited to >90ish
> >>>> degree bend.
> >>>> When she rides a bike, she has to put the seat overly high and still
> >>>> kind of raises off the seat a bit to get around the top of the crank.
> >>>> I think shorter cranks would solve the problem. But are they
> >>>> available?
> >>>> Any other ideas?
> >> RonSonic <ronso...@tampabay.rr.com> wrote:
> >>> Old thread, but maybe this will help.
> >>>http://www.bikesmithdesign.com/Short_Cranks/shorten.html
> >>> He warns of possibly weakening the crank, but a petite woman with bad knees is
> >>> probably no threat to the crank even if there is less meat around the eye.
> > John Thompson <j...@vector.os2.dhs.org> wrote:
> >> Or, non-destructively:http://www.jensonusa.com/store/product/CR309E00-Ride2+Crank+Arm+Short...
> >> Phil Wood used to make a similar product, but I don't know if it's still
> >> available. I used a set on my tandem kid-back when my kids were little.
> >> Alas, I sold them many years ago after they outgrew the kid-back.
> > The problem with these things is they spread the legs another 2 inches
> > wider. I'm not one of these Grant Petersen Q factor whackos, but
> > increasing the width that much might be bad. Particularly for a short
> > small person with short legs. One would think a short small person
> > with short legs might want the Q factor even less than normal.
>
> Phil Wood crank shorteners move pedals out 5mm each side.
> Something, yes, but not 50mm.
I'm guessing the Phil Wood shorteners were positioned differently than
the ones in the link above. The ones above put the new threaded hole
and pedal on the outside of the crankarm. Same place the pedal goes.
Pedal threads are about 3/4" long. So the piece has to be at least
3/4" thick. 1.5" x 25.4mm = 38mm wider. I suspect you have sold the
crank shorteners pictured in the link above and know they move the
pedals out much wider. I would guess the Phil Wood model puts the new
threaded pedal holes in front of the crank arm, not out to the side.
The pedals on the Phil Wood model are not directly above the original
pedal hole and in line with the bottom bracket. They are out in front
of the crank arm forming a triangle between the new pedal hole, the
existing pedal hole, and the bottom bracket bolt.
>
> --
> Andrew Muzi
> <www.yellowjersey.org/>
> Open every day since 1 April, 1971- Hide quoted text -
Chalo
>
> RonSonic wrote:
> >
> > http://www.bikesmithdesign.com/Short_Cranks/shorten.html
> >
> > He warns of possibly weakening the crank, but a petite woman with bad knees is
> > probably no threat to the crank even if there is less meat around the eye.
>
> Drill and thread for 1/2" pedal axle.
1/2"-20 is standard UNF threading, with taps available in RH and LH at
fastener and tool sellers in the USA.
9/16"-20 is nonstandard threading and taps are generally only
available through bicycle suppliers.
Chalo
Nate Nagel
Well, the LHT might be hard to find, but McMaster-Carr probably has it.
nate
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
markafo...@gmail.com
> My wife want to ride a bike but one of her knees is limited to >90ish
> degree bend.
>
> When she rides a bike, she has to put the seat overly high and still
> kind of raises off the seat a bit to get around the top of the crank.
>
> I think shorter cranks would solve the problem. But are they
> available?
>
> Any other ideas?
datakoll
datakoll
> My wife want to ride a bike but one of her knees is limited to >90ish
> degree bend.
>
> When she rides a bike, she has to put the seat overly high and still
> kind of raises off the seat a bit to get around the top of the crank.
>
> I think shorter cranks would solve the problem. But are they
> available?
>
> Any other ideas?
Tom $herman (-_-)
> On Monday, 10 Sep 2012 at 11:03:31 -0700 (PDT),
> markafo...@gmail.com raised the following post from the dead to
> reply to:
> Engineering (6th item down on this page):
> http://www.icetrikes.co/explore-our-trikes/sprint/accessories
>
> You can also get cranks shortened in a few places, but what is most
> accessible to you depends on where you are.
>
> Short cranks are most popular in the recumbent community, so that's a
> good place to search. Do bear in mind that cranks for a 'bent never
> need to take full bodyweight, so some shortening methods may be
> insufficiently robust for use on an upright.
>
I know that several velomobile riders in the UK have gone to cranks as
short as 110-mm, with most running 140-mm or less.
--
Tºm Shermªn - 42.435731°N, 83.985007°W
Post Free or Die!
Andy Morris
>
> Short cranks are most popular in the recumbent community, so that's a
> good place to search. Do bear in mind that cranks for a 'bent never
> need to take full bodyweight, so some shortening methods may be
> insufficiently robust for use on an upright.
>
--
Andy Morris
Andy dot Jinkas at Googlemail