Riding on ice

Well, it's not why off-road riders do it coming out of corners - on
straights where you want as much grip at the rear, however, they stand
up then lean back 'cos that works beautifully...

--
Veggie Dave
UKRMHRC#2 BOTAFOF#08
IQ 18 FILMS http://www.iq18films.com
V&S Extreme Photography http://www.bikehouse.demon.co.uk
Extreme Racing http://www.veggie-dave.co.uk
Put Out The Lights On The Age Of Reason

 

This I can see, but I was initially talking about the guy falling off his
bike while riding on ice/snow. He was standing up on his bike and he fell
off 'cos the whole plot was more unstable due to a raised CofG.

 

Yebbut, they can only lean back a limited amount because they still have
to keep hold of the bars. It doesn't seem like they're going to get much
weight transferred onto the back wheel because of that.

 

[snip]

You need an iSkidoo, suit you sir.
--
Tim two#21, YGL#3 & BOTAFOT#84

Due to the limitations of current email, the lip movements may be
out of synchronisation as you move your finger under the text while reading.

tim dot ukrm2 at dsl dot pipex dot com

 

Just arrived this morning, mine did. Straight across the fields to
Tesco, picked up imilk and a couple of ipapers, took the long iroute
home. Cool as ****, it is - so cool that me imilk was frozen solid by
the time I got home.

 

Didn't you pick-up any iice cream ?
--
Tim two#21, YGL#3 & BOTAFOT#84

Due to the limitations of current email, the lip movements may be
out of synchronisation as you move your finger under the text while reading.

tim dot ukrm2 at dsl dot pipex dot com

 

Bollox. "Instability" is not what causes you to crash at lowish
speeds.

 

[1] "Motorcycle Tuning : Chassis" by John Robinson.
ISBN:0-7506-1840-X

<sigh. I suppose you want me to type in the equations from the book,
don't you.

 

mb said...

He probably fell off cos he wasn't doing it properly. When I ride off-
road I spend most of my time standing up, that way I can shift weight
about much more easily to stabilise the bike.

You only have to watch a bit of motocross or trials to see Veggie's
right and you're wrong. Those blokes hardly ever put their bum on the
seat and it's for a good reason.

 

Niice.

No, it's colder than a witch's tit here and I'm not prejudicing my
core temperature for any bugger's raspberry ripples. The frozen imilk
will do as a substitute on me leftover deep-fried Christmas pudding.

 

Lozzo wrote

Unsprung masses and inertia and shit is it?
With yer arse on the seat you have to do more work on the bike to keep
from falling off but with yer legs acting as shocks supporting your body
weight this makes the work easier. Also possibly to do with the point
at which the forces you exert are actually transferred to the bike?
Summat on those lines?

Nothing to do with them stupid little seats being rammed right up your
arse every time you go over a bump then?

 

Body weight plus the weight transfer of a machine under acceleration is
quite a lot - plus it's an 'every little bit helps' situation

--
Veggie Dave
UKRMHRC#2 BOTAFOF#08
IQ 18 FILMS http://www.iq18films.com
V&S Extreme Photography http://www.bikehouse.demon.co.uk
Extreme Racing http://www.veggie-dave.co.uk
Put Out The Lights On The Age Of Reason

 

"Under acceleration" being quite an important phrase here.
FFS I started off making a simple observation and I get into a long winded
argument about the physics of trial bike riding. How the **** did that
happen?

 

Naah, that's the sound of slush freezing.

 

? I agreed with what Veggie said.
I'll say this again for the hard of hearing. The guy was riding on
ice/snow.

Yes I know that you have more control on a trials bike if you stand up,
this is because you can move around more, as you have stated above - I
don't have any argument with that.
I don't think the same applies to an extremely slippery surface like ice,
or compacted snow.

The thing I have been saying is; if you stand up, then you raise the CofG
and you become more unstable.
Some of you seem to be disagreeing with that.

 

NAHAY?

 

There are lots of reasons for standing up when riding off-road:

1. You can use your legs for extra suspension.

2. You can lean back to either get more weight over the rear wheel,
lighten the front end so you can 'blip' it over bumps, or to stop you
going over the bars on steep downhills

3. You can lean forward when going up hills

4. You can lean the bike to either side underneath you - can be useful
when riding across steep slopes

5. You can weight a footpeg more easily to help steer in ruts, or when
crossing slopes.

MX/Enduro/Trail riders will generally stand up on the straight bits
(until they're too knackered), but cornering depends on the track. If
there's a big berm to ride round, they may stay standing as the wheels
are unlikely to wash out. However if it's a flat slippery surface, you
sit down, as far forward as you can, & stick your 'inside' leg out in
front of you with your foot by the front wheel. This helps keep the
weight forward, and also leaves your foot in the right place to kick the
bike up if a wheel slides.

Standing up whilst riding on a slippery road is a very bad idea imho. It
just ensures you've got no chance of 'kicking out' of a slide should one
happen.

 

Equations don't prove much:

a = x [true for some a's and x's]
a+a = a+x [add a to both sides]
2a = a+x [a+a = 2a]
2a-2x = a+x-2x [subtract 2x from both sides]
2(a-x) = a+x-2x [2a-2x = 2(a-x)]
2(a-x) = a-x [x-2x = -x]
2 = 1

 

At this point the LHS = 0, hence all you are "proving" is that 2*0 = 1*0

 

'Cos you're missing the fundamental point of standing up. By doing so,
you're not simply raising the CoG of a fixed object, but making a
pivot in the middle, such that the body weight is effectively removed
from the bike's stability equation and forms a second mass which can
move independently to counter the moment of the bike's mass and cause
the whole system to be inherently more stable.