Braking Distance of Cycles

On 17 Aug, 12:57, (Alan Braggins) wrote:
In article , Roland Perry wrote:
In message , at 09:32:56
on Tue, 17 Aug 2010, chris French
remarked:

IME, it doesn't make a lot of difference, if anything, a child in a
rear mounted seat improves matters as you have more weight where you
want it over the rear wheel. Yes, it is high up, but it's also further
back, which makes *a big difference. Even just moving your weight back
by slipping off the back of the saddle helps.

I wasn't really asking about the physics - more the psychology.

But presumably the physics of a child sat between the saddle and the
handlebars is worse than if they weren't there?

I'll bet you've never seen a cyclist with an occupied child seat doing
anywhere close to the 20mph under discussion, which will have a more
significant effect on the braking distance than the weight shift.

How about a four point harness, a rollover cage and side bars?

On 17 Aug, 13:43, (Nick Maclaren) wrote:
In article ,
Paul - xxx wrote:

On 17/08/2010 09:32, chris French wrote:
Even just moving your weight back by
slipping off the back of the saddle helps.

Actually that's a well known technique for stopping more quickly than
'normal'. *Used a lot in off-road mountain biking .. the sudden weight
transfer to the rear helps maintain balance and control and
significantly shortens the braking distance.

If you learn to use the technique correctly and quickly, it also
delivers benefits on-road too.

Well, yes and no. *It's hard to do unless you have your saddle
low,

More suitable shorter cranks easily give the clearance when you ues
Knee Over Pedal Spindle fit. Got it! At last a reason for KOPS,
although I'm not fond of such a forward position it does mean I can
get my hips behind the saddle. Shorter cranks on my #2 mean I do
sit further back anyway and I do find I can lock up the front wheel in
the wet.

which has other problems - that's not a problem for off-road
'mountain biking', as people do use low saddles for that.

There is also the point that, while you are doing it, you are
accelerating the bicycle hard forward, and so have to delay braking
or risk losing control. *Even at 0.5 seconds, that's 5 yards at
20 MPH.

A more serious problem is that, if you crash, you will be rammed
hard in the abdomen by the saddle, with the consequent risk of
rupturing your spleen or doing similar damage. *That could turn a
survivable accident into a fatality.

Regards,
Nick Maclaren.

On 17 Aug, 13:43, (Nick Maclaren) wrote:
In article ,
Paul - xxx wrote:

On 17/08/2010 09:32, chris French wrote:
Even just moving your weight back by
slipping off the back of the saddle helps.

Actually that's a well known technique for stopping more quickly than
'normal'. *Used a lot in off-road mountain biking .. the sudden weight
transfer to the rear helps maintain balance and control and
significantly shortens the braking distance.

If you learn to use the technique correctly and quickly, it also
delivers benefits on-road too.

Well, yes and no. *It's hard to do unless you have your saddle
low, which has other problems - that's not a problem for off-road
'mountain biking', as people do use low saddles for that.

There is also the point that, while you are doing it, you are
accelerating the bicycle hard forward, and so have to delay braking
or risk losing control. *Even at 0.5 seconds, that's 5 yards at
20 MPH.

No. Brake hard and move back together, there is a slight delay before
maximum braking takes its toll on the machine as everything compresses
up and the rubber starts biting the rim as it heats. Dont know how
disc brakes respond though, but even if they bite straight away they
are usually on fat tyres with added suspension units so the time delay
is probably longer.


A more serious problem is that, if you crash, you will be rammed
hard in the abdomen by the saddle, with the consequent risk of
rupturing your spleen or doing similar damage. *That could turn a
survivable accident into a fatality.

I dont drop my backside behind the saddle when braking from the tops,
there never seems to be the need. I'll need to experiment with this,
although I feel it's ingrained not to hang low when braking from the
tops for me.

On 17 Aug, 14:31, chris French
wrote:
In message , Nick Maclaren
writes



In article ,
Paul - xxx wrote:
On 17/08/2010 09:32, chris French wrote:
Even just moving your weight back by
slipping off the back of the saddle helps.

Actually that's a well known technique for stopping more quickly than
'normal'. *Used a lot in off-road mountain biking .. the sudden weight
transfer to the rear helps maintain balance and control and
significantly shortens the braking distance.

If you learn to use the technique correctly and quickly, it also
delivers benefits on-road too.

Well, yes and no. *It's hard to do unless you have your saddle
low, which has other problems - that's not a problem for off-road
'mountain biking', as people do use low saddles for that.

I do it on most of my bikes, which ave the saddle set at the appropriate
height. With the cranks horizontal standing up gives plenty of clearance

There is also the point that, while you are doing it, you are
accelerating the bicycle hard forward, and so have to delay braking
or risk losing control. *Even at 0.5 seconds, that's 5 yards at
20 MPH.

Well yes, for really emergency braking it's probably not of much use as
there would be the time. But useful in of other situations.

If you need to stop in the shortest distance then it is better to move
back. I've been doing this for over twenty years after it was shown
to be the quickest way in a group of riders. Full on braking down a
hill, four went forward by about six to ten lengths and me and one
other where within a wheel of each other. I had my back wheel just
off the ground so wasn't quite so good, but this made the steering
highly resposive, so making it easier to pick a line.

A more serious problem is that, if you crash, you will be rammed
hard in the abdomen by the saddle, with the consequent risk of
rupturing your spleen or doing similar damage. *That could turn a
survivable accident into a fatality.

Probably depends on the extent to which you do it. *On road I generally
just move back, and maybe down a *bit, but so much so as to be in a
positron

Wasn't that the eunuchiser, stem shifter?

to *ram the saddle into my abdomen.

Off road people do sometimes take it to more extremes, but in those
situation, probably just more likely to fall off in heap than ram front
first into something

Yep, back wheel slides, muddy arse.

On 17 Aug, 23:59, "DavidR" wrote:
"Nick Maclaren" wrote

In article ,
DavidR wrote:

The cyclist "thinking distance" must be the same so that gives 11m
braking.
That makes Cyclecraft's brakes just 34%. They have picked a rubbish bike
(a
level well below what I tolerate on any bike of mine) then credited it
with
41m to stop in the wet. 10%. Very, very scary. I think not. It would be
quicker to dispense with the brakes and just go Flintstone style.

As I have just posted, the 34% figure is due to loss of control, and
is accurate for many (or even most) cyclists.

As I said previously, I have a bike that came with Weinman side pulls. I
still use the back brake which gives about 15kgf maximum so I would have had
30-40% at best on this set up. This is only adequate for routine braking
with absolutely nothing in reserve. So much so I pulled several cables
through the nipples.

You aren't going to
reduce that, HOWEVER efficient your brakes are.

I have progressed through centre pull to dual pivot for the front of this
frame. Getting a new bike with V brakes was a marvel. All these calipers are
not improvements merely because they're kinder to cables. So I beg to
differ.

The 10% is probably fair, too, for rim brakes.
While a lot of people claim that THEIR rim brakes are fully effective in
the wet,

I don't claim they remain fully effective. I do suggest 10% is ridiculous..

I have
never seen a cyclist with rim brakes manage to decelerate hard in the
wet, in many decades of living in Cambridge. *I haven't investigated
why the claimed efficiency of modern brakes and blocks on aluminium
in the wet isn't delivered in practice, but it assuredly isn't.

Not many hills in Cambridge. Where I am there are a number of 6-8%-ers. Wet
brakes still provide noticeable enough retardation.

There is a comparable claim by motorists, too. *Modern cars amd tyres
can stop at about 1 g under good conditions, but a lot of people claim
that they can achieve that under most circumstances. *Well, it ain't
so ....

Actually many people think their cars can stop from 30mph in distances that
would require several g.

It is possible to go over parity using cadence braking, everything
must be tied down though, this is not going to be much fun with a
toolbox through your seat back. Yep, I knew guys who left their
toolcase on the rear seat, and they locked up and slid off the road,
luckily no injuries.

On Wed, 18 Aug 2010 01:24:41 +0100, The Medway Handyman garbled:

Mike Causer wrote:
On Tue, 17 Aug 2010 19:28:24 +0000 (UTC) Mike P wrote:

Stoppies are a piece of cake. I used to do rolling stoppies on my
Fireblade

Did you ever progress to stationary stoppies? Enquiring minds ...

Oh look. The immature cyclo****s are taliking about doing tricks to
impress girls. How cute. They even have neat little names for the
tricks. Even cuter.

What a bunch of ****ing *******.

Since when has a 900cc crotch-rocket been a pushbike, you stupid ****wit?

--

Mike P

In article , Mike P wrote:
On Wed, 18 Aug 2010 01:24:41 +0100, The Medway Handyman garbled:
Mike Causer wrote:
On Tue, 17 Aug 2010 19:28:24 +0000 (UTC) Mike P wrote:

Stoppies are a piece of cake. I used to do rolling stoppies on my
Fireblade

Did you ever progress to stationary stoppies? Enquiring minds ...

Oh look. The immature cyclo****s are taliking about doing tricks to
impress girls. How cute. They even have neat little names for the
tricks. Even cuter.

What a bunch of ****ing *******.

Since when has a 900cc crotch-rocket been a pushbike, you stupid ****wit?

Maybe the sight of men in leather upsets him as much as men in lycra,
and so he's opposed to motorcyclo****s too?

"David" wrote in message
...
snip

OUCH!

--
Brian
"Fight like the Devil, die like a gentleman."
www.imagebus.co.uk/shop

In message , at 17:43:43 on Tue, 17 Aug
2010, Tony Raven remarked:
But presumably the physics of a child sat between the saddle and
the handlebars is worse than if they weren't there?

Probably about the same difference as if you were/weren't wearing a
rucksack.
Do you wear rucksacks on your belly?

No but the difference between having one on your back and not on your
back is probably about the same as having or not having a child sat on
the crossbar.

And what of the non-Physics considerations. Like your violent braking
being likely to throw the child out of their seat?
--
Roland Perry

In message
, at
17:59:15 on Tue, 17 Aug 2010, thirty-six
remarked:
Using custom polythene single use handlebar bags tends to slow a
cyclist for fear of the spokes rubbing holes in the bags.

Do you think using other kinds of bag should be made illegal as a
result? And would cyclists just add this to their extensive list of
"laws I don't feel like obeying"?
--
Roland Perry