Finding a bike that fits.

[Peter Clinch]

Nick Maclaren wrote:

> The 50% was a guesstimate, based on the experiences of people I have
> spoken to (including a manager of a recumbent 'school') and those that
> I have read. Please note that I was referring to riding in traffic.
> If you can't signal for a period of 10 seconds while turning a shallow
> curve over a normally rough road, and start on the flat without
> wobbling significantly, you are in considerable danger.

I would imagine most people at the "school" were not very experienced.
As with my first use of an upright bike I wasn't tremendously steady
within 10 minutes of getting on, but with a little persistence riding
round a low traffic block at home I rapidly moved to being completely
happy in traffic. Again, as with the upright, this was something that
took finite time, rather more time than a quick try-out might reasonably
allow.

> My recollection is that the school manager said that about half their
> customers had significant problems with a short wheelbase recumbent

As I pointed out before, there are quite a lot of SWB 'bents and they
are variously difficult to ride. IME of seeing people try them out the
limiting factor for getting on easily is /not/ balance but failing to
relax and putting far too much force through the handlebars, which has a
very different effect to the one they're *very* used to (as with riding
a trike, some "unlearning" needs to be done, rather than it being a
fundamental problem of the design). This opinion is reinforced by
seeing people who couldn't ride one /at all/ on several tries on first
acquaintance, but who subsequently go on to own and love SWB 'bents
[waves to Jo...].

> No, not really serious - just minor.

"extremely difficult and dangerous" is not serious, just minor? hmmmmm...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[Nick Maclaren]

In article <[email protected]>,
M-gineering <[email protected]> writes:
|> >
|> Flex is called compliance, and should not be confused with free play.
|> If a steering system is stiff enough, it's not automatically going to be
|> improved by increasing stiffness.

"Compliance" is so much cosier a word than "flex", isn't it? Flex
is bad, compliance is good

But, yes, I was definitely talking about flex, not free play, and I
quite agree that there is no point in increasing stiffness beyond
need. But, in the light of what David Martin said, it is possible
that the "mountain bicycle" fad has FINALLY got this myth kicked
into the long grass - after many decades!

Until fairly recently, and perhaps even now, most 'cycling experts'
claimed that a good lightweight frame should flex sideways when you
prod the bottom bracket with your foot, and that the design criterion
for front forks should be just heavy enough to avoid breakage. That
is, after all, why forks were/are tapered with a vertical oval cross-
section.

The desirability of flex flies in the face of all engineering theory
and practice.

> ??? I don't know of any. I know of one which are tapered, and those
> which are straight, but no vertical ovals.

Boggle. Well, until recently, most forks had a vertical oval section.
Even my Batavus has tapered forks with a slightly vertical oval section,
but lightweight and flexible it is not.

> How about it being a design compromise. Being in Dundee I am somewhat
> familiar with the concept of a hill which to those in Cambridge must be
> somewhat alien..

Well, I assert that real engineers take design compromises deliberately
and accept responsibility for the deficiencies that they introduce.
Simon Brooke clearly disagrees.


Regards,
Nick Maclaren.

 

[Ben C]

On 2006-09-26, Nick Maclaren <[email protected]> wrote:
[...]
> The desirability of flex flies in the face of all engineering theory
> and practice.

I thought the reason flex/compliance was avoided on things like cars was
just to make the maths easier.

If only the bits move that are supposed to move, then what a simple
simulation predicts for the way the tyres sit on the road as the
suspension moves is more likely to be borne out in practice. If the
chassis itself wobbles everywhere at the same time then your careful
design of everything else goes out of the window.

But if you understood the wobble precisely and took it into account, you
could probably build a lighter car.

But a bicycle is simple enough that you can just build one and see how
it feels. There's no suspension (well, not on a "normal" bike anyway)
and only two wheels. If you make the frame out of thinner and thinner
steel so it's lighter and it still seems to ride OK (better even
perhaps), and doesn't break, then why not?

 

[Rolando]

My first, innocent plea for help on this subject certainly seems to
have caused a bit of a stir. I write from a position of ignorance on
the technicalities of bike design. I mention 700 mm wheel size, because
that's what I thought I had heard quoted by the experts, it seems it
should have been 700C (?), I know nothing of biscuits, chocolate or
otherwise, except that one can eat them, and much of the "in crowd
jargon" and technical terms are like a foreign language to me. I'm just
a simple bloke with a problem. I've looked into the possibility of
fitting a shorter crank arm (as another contributor suggested) but even
the shortest available would not have solved the problem, nor would
thinner tyres, (although both these things together would help) because
it's NOT just a question of distance from the ground. On modern bikes
the seat is too far forward, probably because the tube into which the
seat post fits has been brought to a more verticle angle, I have
confirmed this angle difference by comparing the tube angle of a bike
made in the 50s (or thereabouts) with a large number of current
machines. One writer tells me it isn't really necessary to reach the
ground anyway. Well, as far as I am concerned, it is. If both your feet
are normally about three inches off the ground and you have to make an
emergence stop on a steep camber, and you are no longer agile enough to
slide off the saddle quickly, you could be in trouble. I really do
apologise to all those dear folk, yourself included, for not knowing
the technical terms, and not realising that "bottom bracket" was
something that everyone else in the whole world knew about. Well, I
didn't, so I wanted to make sure I got it right. To all who seek to
suggest that it is MY fault for having difficulty finding a bike that
fits to MY satisfaction, I apologise, but I am the one who's going to
ride it. Recumbents are out, uni-cycles are out, penny-farthings are
out, folding bikes are out (because I've tried them with no success),
and I don't know what an ATB is (I said I was ignorant), chocolate
bicuits are out because they get soggy in the rain. I just want
something I can ride comfortably and safely without having to fall off
every time I have to stop suddenly.

Rob Morley wrote:
> In article <[email protected]>
> Rolando <[email protected]> wrote:
> > I have, so far , had no luck finding a bike that I can safely and
> > comfortably ride. All modern bikes, it seems, are made to a geometry
> > adopted some years ago to cater for the new breed of "off road" and
> > "cross country" machines. Sadly, instead of restricting these changes
> > to those bikes for which they were originally introduced, they were
> > applied universally to ALL bikes, including those intended for "comfort
> > commuting". The most noticeable changes that I am aware of are the
> > raising of the bottom bracket (the cylindrical box through which the
> > crankwheel spindle passes) and the sloping rear tube into which the
> > seatpost fits, this has been brought forward to a more vertical angle.
>
> I think we know what a bottom bracket is Frame angles haven't
> changed much since the sixties, in fact ATBs are closer to the old-style
> 'roadster' than the 'racers' of the seventies.
>
> > These changes, exacerbated by my upper leg bones being short relative
> > to my lower leg bones (equally on both legs) means that when I adjust
> > the seat post so that I can just reach the ground with my toes, I
> > cannot get the balls of my feet onto the pedals, if, alternatively, I
> > still further raise the seat post so that I can pedal through a full
> > 360 degrees, I cannot then reach the ground.
>
> That's OK - you don't need to touch the ground while you're pedalling,
> and you don't need to sit on the saddle while you're stationary.
>
> > I should point out here
> > that I am not noticeably deformed, I look like a fairly normal elderly
> > man of about 5' 7", also it goes without saying that I have tried all
> > the different frame sizes, but the problem has not been solved.
>
> I suggest you'll have more luck trying shorter cranks - it's the cranks
> that determine how far your knees go up and down, and many modern bikes
> have longer cranks than was common in days of yore.
>
> > I
> > recently paid a visit to a cycle retailer in York who imports bikes
> > from Holland, where they still make their machines pretty much the same
> > as we used to make ours. I came close to success with the Dutch bike I
> > tried, which was a ladies bike with, I think, a 20" frame,
> > unfortunately, I understand all the Dutch bikes come with 700mm wheels,
> > which is just over 27.5" in "old money".
>
> 700C, not 700mm - that's the standard size for road bikes these days,
> and is actually 622mm rim diameter.
>
> > In the days when I had no
> > problem finding a bike I could ride, wheel sizes were, I think, 28" for
> > tall
>
> 700B (635mm) = 28 x 1 1/2" and was used on some old British roadsters,
> 700A (642mm) = 26 x 1 3/8" on others and 28 x 1 1/4" (647mm) on Dutch
> bikes.
>
> > riders, and 26 7/8" for "shorties" like me.
>
> 26 x 1 3/8" (590mm) - the standard 3-speed utility size.
>
> > I am now looking into
> > the possibility of buying an elderly, renovated British bicycle,
> > preferable a man's with 26 7/8" wheels and built to the old geometry,
> > but such machines appear to be in very short supply. Has anyone else
> > had this problem, and solved it?
> >
> As I said, shorter cranks is probably the main thing to look for unless
> you really don't think you can manage getting on and off a high saddle.
> The problem is that these days shorter cranks are generally only fitted
> as standard to kids' bikes, and those are going to be a bit small for
> someone of your height. Short cranks are easy enough to buy and
> retrofit though. If you also want a low seat then one option might be
> to get a suspension bike and remove the suspension - there must be
> plenty of cheap ATBs on the tip with knackered suspension.

 

[Nigel Cliffe]

Rolando wrote:
> My first, innocent plea for help on this subject certainly seems to
> have caused a bit of a stir. I write from a position of ignorance on
> the technicalities of bike design.

I think a few people have wandered off down alleys.


> I mention 700 mm wheel size,
> because that's what I thought I had heard quoted by the experts, it
> seems it should have been 700C (?),

I don't think its a big issue. You were clear.

The reason 700C and 26in (mountain bike) come up is they are the really
common sizes which all bike shops know about. Everything else is unusual to
a greater or lesser extent.


> I'm just a simple bloke with a problem. I've looked into the
> possibility of fitting a shorter crank arm (as another contributor
> suggested) but even the shortest available would not have solved the
> problem, nor would thinner tyres, (although both these things
> together would help) because it's NOT just a question of distance
> from the ground. On modern bikes the seat is too far forward,
> probably because the tube into which the seat post fits has been
> brought to a more verticle angle, I have confirmed this angle
> difference by comparing the tube angle of a bike made in the 50s (or
> thereabouts) with a large number of current machines.

To an extent, the more vertical seatpost has been compensated for by the
"lay back" in the seatpost. A 50's machine has the saddle directly on a post
sticking out of the frame. A modern design has a seatpost with a bend at
the top which moves the saddle back a couple of inches.


> To all who seek to suggest that
> it is MY fault for having difficulty finding a bike that fits to MY
> satisfaction, I apologise, but I am the one who's going to ride it.

If your requirement is a 1950's style of bike, then you may find it in one
of the following:

Some "sensible urban" bikes, particularly those sold into Germany/Holland.
I've seen some Giant models which might suit, and there are some German and
Dutch brands at higher prices.
Pashley; UK maker of traditional bikes.
Pedersons; fairly expensive (over £1000 I think), look a bit wierd, upright
comfortable ride (I used the term "regal" when I handed back the one I
borrowed)

Rebuild an old bike. But that can be very expensive if you lack a parts
pile and knowledge to know which modern bits will fit and which won't. If
using older wheel sizes, check tyre availability before starting.

Custom built bike. Budget £1200 upwards for a complete bike. There are
custom frame builders around, and I think that some would be prepared to
build to your requirements.

Don't dismiss folders and some of the other options without trying. Just
because one folding bike was rubbish doesn't mean all others are the same.



- Nigel









--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/

 

[Brendan Halpin]

"Rolando" <[email protected]> writes:

> My first, innocent plea for help on this subject certainly seems to
> have caused a bit of a stir.

You can talk about helmets all you like on this group, but if you
want to see real blood start a physics war!

Brendan
--
Brendan Halpin, Department of Sociology, University of Limerick, Ireland
Tel: w +353-61-213147 f +353-61-202569 h +353-61-338562; Room F2-025 x 3147
mailto:[email protected] http://www.ul.ie/sociology/brendan.halpin.html

 

[wafflycat]

Hmm...

Honest, you really don't need to be able to put your feet flat on the
ground. If you do, then you'll end up having a bad position for your knees.
Knee pain is horrible. You simply don't see oodles of cyclists all falling
off everytime they stop just because their feet don't touch the ground. It
really isn't a problem, except, perhaps, one of confidence? Suggestion - but
it is one that would cost you some dosh. Go to a bike shop that has a proper
bike-fitting jig and get fitted up by an expert. Ask questions - tell the
person you aren't a bike expert and that you'd like answers with as little
jargon in as possible. Any expert fitter worth his or her salt should be
able to do this for you.

The last time I fell off my bike was a 'clipless moment' I use pedals that
your foot clips into by means of a cleat on the sole of my shoe which holds
fast to the pedal. A sort of skiboot fitting to ski fitting but on a bike of
shoe to pedal. I simply forgot to unclip before the bike came to a full
halt - so I was still attached. Would have looked funny on video. But I've
never fallen over because my foot isn't on the ground as I'm on the saddle.
Not once, in all my (mumble... mumble... of advancing age) years. Come to
think of it, I can't remember seeing anyone do that and I cycle with folks
from very young age to old (in their 70s)

By the way, I wouldn't recommend using chocolate biscuits as bicycle wheels
;-)

Cheers, helen s

 

[Mark Thompson]

Nick Maclaren wrote in news:[email protected]:
> I agree that, in a recumbent, you could probably rig up a decent
> mirror, so don't need to look over your shoulder.

Eeek!

 

[Nick Maclaren]

In article <[email protected]>, Ben C <[email protected]> writes:
|> On 2006-09-26, Nick Maclaren <[email protected]> wrote:
|> [...]
|> > The desirability of flex flies in the face of all engineering theory
|> > and practice.
|>
|> I thought the reason flex/compliance was avoided on things like cars was
|> just to make the maths easier.

Nope. It is grounds for failing the construction test (for new designs)
and the MOT (for old cars).

|> If only the bits move that are supposed to move, then what a simple
|> simulation predicts for the way the tyres sit on the road as the
|> suspension moves is more likely to be borne out in practice. If the
|> chassis itself wobbles everywhere at the same time then your careful
|> design of everything else goes out of the window.

Precisely.

|> But if you understood the wobble precisely and took it into account, you
|> could probably build a lighter car.

Grrk. No. If you know control theory, you will know why that ain't
so. If you don't, it is tricky to explain. The problem is delay.
Basically, when it wobbles left, you have to correct right in a much
shorter time than the natural period of the system; if you don't, you
are likely to introduce positive feedback and destructive oscillations
(and end up falling off).

Now, the natural period of a stiff steering linkage depends on the
geometry, and is least for a track bicycle and greatest for a long
wheelbase recumbent or traditional roadster. But the natural period
of flex in the forks is very fast indeed - and, if the flex-induced
(and human-enhanced) oscillations build up enough to start causing
steering/balance oscillations, few cyclists will be able to handle
the bicycle.

|> But a bicycle is simple enough that you can just build one and see how
|> it feels. There's no suspension (well, not on a "normal" bike anyway)
|> and only two wheels. If you make the frame out of thinner and thinner
|> steel so it's lighter and it still seems to ride OK (better even
|> perhaps), and doesn't break, then why not?

But they DON'T ride OK! That is the point.

The issue is that the rider is a major part of the control linkage.
Riders with good middle-ear balance, fairly fast reactions and well-
trained reflexes have a fast response time. Those without any of
those (and I lack ONLY the first) have slower or very much slower
ones. I could explain why, but that gets into neurology.

In the case of riders with significantly impaired middle-ear balance,
there is a second problem in that significant flex-induced wobble
interferes with the touch feedback through the hands that we depend
on for balance. That certainly applies to about 20% of the population,
and probably to another 30% or so to a lesser degree.

This is why it is so wrong to say that "I have no problem; therefore
there isn't a problem." Almost all such speakers are among the 5%
most "bicycle adapted" people in the country. God help me, even I
may be :-(


Regards,
Nick Maclaren.

 

[Nick Maclaren]

In article <[email protected]>,
"Rolando" <[email protected]> writes:
|>
|> ... because
|> it's NOT just a question of distance from the ground.

Right. Spot on.

|> On modern bikes
|> the seat is too far forward, probably because the tube into which the
|> seat post fits has been brought to a more verticle angle, I have
|> confirmed this angle difference by comparing the tube angle of a bike
|> made in the 50s (or thereabouts) with a large number of current
|> machines.

Yup. Very much so. I used to ride one with a 60 degree angle.

|> One writer tells me it isn't really necessary to reach the
|> ground anyway. Well, as far as I am concerned, it is. If both your feet
|> are normally about three inches off the ground and you have to make an
|> emergence stop on a steep camber, and you are no longer agile enough to
|> slide off the saddle quickly, you could be in trouble.

This is where the trained reflexes come in. I am no longer agile, but
can do that. However, it takes a fair amount of learning, especially
as you get older.

|> folding bikes are out (because I've tried them with no success),

My experience, too.

|> I just want
|> something I can ride comfortably and safely without having to fall off
|> every time I have to stop suddenly.

I strongly recommend getting a Dutch or Danish traditional bicycle.
A Pashley traditional or similar would do, too. Go for the oldest
appearing design that you can find, with raised, swept-back
handlebars.

My advice is to get the largest frame where you can get your feet
down to your satisfaction with the saddle right down on the frame.
As you get accustomed to riding (and sliding off the saddle), you
can then raise the saddle and reduce the stress on your knees.


Regards,
Nick Maclaren.

 

[Tom]

Rob Morley <[email protected]> wrote:
>
> I suggest you'll have more luck trying shorter cranks - it's the
> cranks that determine how far your knees go up and down, and many
> modern bikes have longer cranks than was common in days of yore.
>

Shorter cranks would mean having to set the seat higher too, making it less
likely that the OP could touch the floor while seated (not that he needs to,
I know)

Tom
--
Return address is dead. Real address is at
http://www.box.net/public/0n493oa6y7

 

[Rob Morley]

In article <[email protected]>
Ben C <[email protected]> wrote:
<snip>
> But a bicycle is simple enough that you can just build one and see how
> it feels. There's no suspension (well, not on a "normal" bike anyway)
> and only two wheels. If you make the frame out of thinner and thinner
> steel so it's lighter and it still seems to ride OK (better even
> perhaps), and doesn't break, then why not?
>
Because it flies in the face of good engineering practice, apparently.
The fact that bicycles have been successfully built this way for quite a
while now with only the occasional failure doesn't seem to come into it.
I suspect not all the cranks in this group are of the bicycle variety.
While we're on the subject, has anyone else noticed how the wings on a
Boeing 747 wobble up and down a bit? I expect we should ground them all
until they've been sorted out by a proper engineer.

 

[Peter Clinch]

Rolando wrote:

> folding bikes are out (because I've tried them with no success)

*All* of them? There are quite a lot of different designs with
significantly different geometries.

Since you've tried out /some/ *non*-folding bikes with no success, does
that lead you to a conclusion that they're *all* unsuitable? Apparently
not, so why should a different standard by brought to folders?

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[Rob Morley]

In article <[email protected]>
Nick Maclaren <[email protected]> wrote:
>
> In article <[email protected]>, Ben C <[email protected]> writes:
> |> On 2006-09-26, Nick Maclaren <[email protected]> wrote:
> |> [...]
> |> > The desirability of flex flies in the face of all engineering theory
> |> > and practice.
> |>
> |> I thought the reason flex/compliance was avoided on things like cars was
> |> just to make the maths easier.
>
> Nope. It is grounds for failing the construction test (for new designs)
> and the MOT (for old cars).

That's because they're designed to be rigid, and excessive flex points
to structural weakness. Except some long wheelbase non-articulated load
carriers that are designed to have torsional flex in the chassis so they
keep all wheels on the ground. Also, have you noticed the negative
camber on F1 cars when they're in the pits? If their suspension didn't
flex when loaded in a fast corner the tyre contact would be far from
optimal, but according to you that means that they're badly engineered
and undriveable.
>
> |> If only the bits move that are supposed to move, then what a simple
> |> simulation predicts for the way the tyres sit on the road as the
> |> suspension moves is more likely to be borne out in practice. If the
> |> chassis itself wobbles everywhere at the same time then your careful
> |> design of everything else goes out of the window.
>
> Precisely.
>
> |> But if you understood the wobble precisely and took it into account, you
> |> could probably build a lighter car.
>
> Grrk. No. If you know control theory, you will know why that ain't
> so. If you don't, it is tricky to explain. The problem is delay.
> Basically, when it wobbles left, you have to correct right in a much
> shorter time than the natural period of the system; if you don't, you
> are likely to introduce positive feedback and destructive oscillations
> (and end up falling off).

Consider how much work Honda put into building their walking robots, and
how little effort it takes for most of us to ambulate bipedally.
>
> Now, the natural period of a stiff steering linkage depends on the
> geometry, and is least for a track bicycle and greatest for a long
> wheelbase recumbent or traditional roadster. But the natural period
> of flex in the forks is very fast indeed - and, if the flex-induced
> (and human-enhanced) oscillations build up enough to start causing
> steering/balance oscillations, few cyclists will be able to handle
> the bicycle.

You can spout theory all you want - the real world says that bicycles
perform adequately.
>
> |> But a bicycle is simple enough that you can just build one and see how
> |> it feels. There's no suspension (well, not on a "normal" bike anyway)
> |> and only two wheels. If you make the frame out of thinner and thinner
> |> steel so it's lighter and it still seems to ride OK (better even
> |> perhaps), and doesn't break, then why not?
>
> But they DON'T ride OK! That is the point.

That's funny, I've never had a problem.
>
> The issue is that the rider is a major part of the control linkage.
> Riders with good middle-ear balance, fairly fast reactions and well-
> trained reflexes have a fast response time. Those without any of
> those (and I lack ONLY the first) have slower or very much slower
> ones. I could explain why, but that gets into neurology.

If you're physically incapable of balancing then you're not going to get
on well with single-track vehicles - convert to recumbent trikes or find
another newsgroup to pester.
>
> In the case of riders with significantly impaired middle-ear balance,
> there is a second problem in that significant flex-induced wobble
> interferes with the touch feedback through the hands that we depend
> on for balance. That certainly applies to about 20% of the population,
> and probably to another 30% or so to a lesser degree.

They're just not going to get on with bikes. Are you going to redesign
swimming pools for people who can't swim?
>
> This is why it is so wrong to say that "I have no problem; therefore
> there isn't a problem." Almost all such speakers are among the 5%
> most "bicycle adapted" people in the country. God help me, even I
> may be :-(
>
Maybe everyone should ride fixed wheel to make one-legged people happier
about cycling. Perhaps we should all have little engines attached as a
concession to those who can't get up steep hills. If I wanted to run
any distance I'd need a specialised knee brace (I used to have one, very
clever thing with sliding titanium tubes and things) and orthopaedic
shoe inserts - you could get a sidecar or a trike conversion.

 

[Rob Morley]

In article <[email protected]>
Peter Clinch <[email protected]> wrote:
> Rolando wrote:
>
> > folding bikes are out (because I've tried them with no success)
>
> *All* of them? There are quite a lot of different designs with
> significantly different geometries.
>
> Since you've tried out /some/ *non*-folding bikes with no success, does
> that lead you to a conclusion that they're *all* unsuitable? Apparently
> not, so why should a different standard by brought to folders?
>
Don't spoil the discussion with reason and logic.

 

[Marcus Red]

Helen Deborah Vecht wrote:
> Marcus Red <[email protected]>typed
>
>
>> Rob Morley wrote:
>> (snipped)
>
>>> 700C, not 700mm - that's the standard size for road bikes these days,
>>> and is actually 622mm rim diameter.
>>>
>>>> In the days when I had no
>>>> problem finding a bike I could ride, wheel sizes were, I think, 28" for
>>>> tall
>>> 700B (635mm) = 28 x 1 1/2" and was used on some old British roadsters,
>>> 700A (642mm) = 26 x 1 3/8" on others and 28 x 1 1/4" (647mm) on Dutch
>>> bikes.
>> (snipped)
>
>> So what does the "700" refer to?
>> Genuine Q from a mere bicycle user.
>
> The wheel diameter when you use a certain tyre. (39mm with a 700c frexample)
>
> Wheel rims can tolerate all manner of tyre widths. This will change the
> overall wheel diameter.
>
> The wheel rim has a critical dimension called the bead seat diameter.
> This is 622mm for a 700c wheel, which is a popular touring/road size.
> Put 18mm racing tyres on such a wheel and your wheel diameter is less
> than 26"...
>
Thankyou both. I Should have JFGI, sorry.

 

[Nick Maclaren]

In article <[email protected]>,
Peter Clinch <[email protected]> writes:
|> Rolando wrote:
|>
|> > folding bikes are out (because I've tried them with no success)
|>
|> *All* of them? There are quite a lot of different designs with
|> significantly different geometries.
|>
|> Since you've tried out /some/ *non*-folding bikes with no success, does
|> that lead you to a conclusion that they're *all* unsuitable? Apparently
|> not, so why should a different standard by brought to folders?

When I last looked at them, I investigated every one on the market,
and none of them were even plausible enough to be worth trying out.
But, as I have pointed out, my requirements are close to one boundary
of the normal cycling requirements. If you can mention even one
that meets my requirements, I should be most interested

I did once own one that was adequate, but it was a 1930s model, and
needed a spanner and 15 minutes to fold or unfold.


Regards,
Nick Maclaren.

 

[Simon Brooke]

in message <[email protected]>, Nick Maclaren
('[email protected]') wrote:

> In article <[email protected]>, Ben C
> <[email protected]> writes:
> |> On 2006-09-26, Nick Maclaren <[email protected]> wrote:
> |> [...]
> |> > The desirability of flex flies in the face of all engineering theory
> |> > and practice.
> |>
> |> I thought the reason flex/compliance was avoided on things like cars
> |> was just to make the maths easier.
>
> Nope. It is grounds for failing the construction test (for new designs)
> and the MOT (for old cars).

This explains, for example, why Morris and Renault cars for many years used
torsion bar suspension, and why some Citroen, Subaru and Alfa Romeo models
use deliberately flexible rear swing arms to induce a controlled degree of
high speed rear steering, and so on. All these cars, according to you,
must fail the construction test. I think you'd better tell their
manufacturers - they don't seem to know. All car bodyshells and chassis
flex to one degree or another; the marked (and generally undesirable)
flexing of many convertible models is widely known as 'scuttle shake', but
not all convertibles fail their MOTs either, surprisingly.

> Now, the natural period of a stiff steering linkage depends on the
> geometry, and is least for a track bicycle and greatest for a long
> wheelbase recumbent or traditional roadster. But the natural period
> of flex in the forks is very fast indeed - and, if the flex-induced
> (and human-enhanced) oscillations build up enough to start causing
> steering/balance oscillations, few cyclists will be able to handle
> the bicycle.

In an earlier post in this thread, you said that this was a common - almost
universal - fault in modern bicycles. Now you're saying it causes an
oscillation which 'few cyclists will be able to handle'. If almost every
bike has the problem, and few cyclists can handle it, then the
overwhelming majority of cyclists must crash every single time they take a
bike out on the road. Evidence?

> |> But a bicycle is simple enough that you can just build one and see how
> |> it feels. There's no suspension (well, not on a "normal" bike anyway)
> |> and only two wheels. If you make the frame out of thinner and thinner
> |> steel so it's lighter and it still seems to ride OK (better even
> |> perhaps), and doesn't break, then why not?
>
> But they DON'T ride OK! That is the point.

So, again: the majority of bicycles, you claim, don't ride acceptably. Very
well, where are all the crashes caused by people riding unridable
bicycles?

> The issue is that the rider is a major part of the control linkage.
> Riders with good middle-ear balance, fairly fast reactions and well-
> trained reflexes have a fast response time. Those without any of
> those (and I lack ONLY the first) have slower or very much slower
> ones. I could explain why, but that gets into neurology.
>
> In the case of riders with significantly impaired middle-ear balance,
> there is a second problem in that significant flex-induced wobble
> interferes with the touch feedback through the hands that we depend
> on for balance. That certainly applies to about 20% of the population,
> and probably to another 30% or so to a lesser degree.

As it happens, I have virtually no middle-ear balance - I cannot balance at
all with my eyes closed, or walk though my own house in the dark without
falling over. I can't track-stand any more, but apart from that my ability
to ride a bike seems unaffected.

> This is why it is so wrong to say that "I have no problem; therefore
> there isn't a problem."

If there were a problem, I would be one of the people who would have a
problem. I have very poor balance and poor co-ordination. If I don't have
a problem, there isn't one.

Earlier in this thread I challenged you - twice - to name just one model of
bicycle in current production which exhibits the faults you claim are
universal, to whit that is 'made to enhance... flex in a control linkage'.
You've still failed to name one. If you weren't talking total bollocks,
you would be able to name ten off the top of your head, but just one will
satisfy me. Now's your opportunity.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

Morning had broken, and there was nothing left for us to do
but pick up the pieces.

 

[Simon Brooke]

in message <[email protected]>, Rob Morley
('[email protected]') wrote:

> In article <[email protected]>
> Ben C <[email protected]> wrote:
> <snip>
>> But a bicycle is simple enough that you can just build one and see how
>> it feels. There's no suspension (well, not on a "normal" bike anyway)
>> and only two wheels. If you make the frame out of thinner and thinner
>> steel so it's lighter and it still seems to ride OK (better even
>> perhaps), and doesn't break, then why not?
>>
> Because it flies in the face of good engineering practice, apparently.
> The fact that bicycles have been successfully built this way for quite a
> while now with only the occasional failure doesn't seem to come into it.
> I suspect not all the cranks in this group are of the bicycle variety.
> While we're on the subject, has anyone else noticed how the wings on a
> Boeing 747 wobble up and down a bit? I expect we should ground them all
> until they've been sorted out by a proper engineer.

What about the Airbus A380, which has wings which are deliberately curved
downwards at rest, and relies on the flex imposed by carrying 560 tonnes
to straighten them in flight. Clearly not airworthy. Ban it.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/
,/| _.--''^``-...___.._.,;
/, \'. _-' ,--,,,--'''
{ \ `_-'' ' /
`;;' ; ; ;
._..--'' ._,,, _..' .;.'
(,_....----''' (,..--''

 

[Dave Larrington]

Simon Brooke wrote:

> This explains, for example, why Morris and Renault cars for many
> years used torsion bar suspension, and why some Citroen, Subaru and
> Alfa Romeo models use deliberately flexible rear swing arms to induce
> a controlled degree of high speed rear steering, and so on.

Not to mention the "rubber" bushes in the suspension. One of the first
things one does when converting a motorcar for track use is to throw away
all the rubbery bits and replace 'em with rose joints...

--
Dave Larrington
<http://www.legslarry.beerdrinkers.co.uk>
It is impossible to eat a banana without looking like a tw*t.