Stopping distance Bike Vs Car

<waves>

 

TOG@toil, ,

Well, not really. The first to do it, obviously, was the instructor, and
most people managed to come quite close to his stopping distance. 50kph
in a straight line on a dry road isn't all that fast, after all, once
you've done it a few times.

I was on a bike with ABS (F650) and after a few goes I was happily
slamming on the brakes and letting the ABS look after the consequences.
The most surprising bit at first was the way the front end bounded up
when the ABS released the brake, presumably more marked because the F650
has fairly long suspension travel.

I have an RT now, and I have to admit I've not dared to push it that
hard. I will, but maybe not until next year now.

 

Please elaborate. If you don't make a coherent statement
then we won't be able to point out where you are going wrong.

 

Ignoring the contact patch area of four round squared-off rubbery things
v. two pointy ones. You only have to watch quite 'standard' cars braking
for 'triangle' at Loton Park compared with the best bikes (that includes
an R1 BTW). TBF if you mean coming to a complete stop without any care
as to ability to then immediately proceed in a brisk fashion round a
bend your point is perhaps more valid.
--

+-------------------------------------------------------------+
| Pete Fisher at Home: |
| Voxan Roadster Gilera Nordwest Yamaha WR250Z |
| Gilera GFR Moto Morini 2C/375 |
+-------------------------------------------------------------+

 

I have vivid memories of Alex Ferrier going flat out in the rain
towards the Creg then turning round to face me and saying "isn't ABS
great".

Do you want me to test it in France?

 

Indeed. The CofG makes a difference to the behaviour, as well. High
CofG = stoppie. Low CofG = wheel lock-up.

 

TOG@toil, ,

On the R-GS, the only time that the ABS has cut in during normal riding[1]
is whilst riding down very steep Alpine roads. This is more to do with
weight transfer than slippery tarmac though.

[1] where normal riding includes the occasional emergency stop

 

<fondles misshapen collar-bone>

 

I really hope that's not a euphemism.

 

<Feels imprint of crash barrier on spine>

--
_______
..'_/_|_\_'. Ace (brucedotrogers a.t rochedotcom)
\`\ | /`/ GSX-R1000K3 (slightly broken, currently missing)
`\\ | //' BOTAFOT#3, SbS#2, UKRMMA#13, DFV#8, SKA#2, IBB#10
`\|/`
`

 

snip>

Where the **** did you get the gem from? If it's straight out of a
book then that's fine because I read fiction too but if it's from real
time experience I need you to give me some lessons on how to out brake
other riders.

 

But mass balances out in the equations:

F=m*a; F_max=m*g*CoF => a_max=g*CoF where F is force of braking, a is
deceleration, g is gravitational acceleration "constant" and CoF is
coeeficient of friction. i.e. maximum braking force is a function only
of the CoF of the tyres, not the mass.

What Eiron is arguing is that it's more likely that a bike's rear
wheel will start to lift before a_max is achieved. If the CofG is distance
r away from the front axle, at an angle th from the horizontal, the potential
torque backward along r is m*g*cos(th)*r. The torque forward from the
braking force is F*(horizontal distance of CofG above axle) = F*r*sin(th).
Note that because of the behaviour of sin and cos around zero, the torque
from the mass is always backward while the torque from braking is forward for
th>0 (CofG above axle) and backward for CofG below axle -- obviously if
the CofG is below the axle the vehicle dips rather than rises under braking.

The rear wheel will start to lift when the two torques balance
(assuming CogG above axle) i.e. m*g*cos(th)*r = F*r*sin(th) = m*a*r*sin(th)
or g*cos(th) = a*sin(th) i.e. a=g/tan(th); Since tan(th) is monotonic with
th, the larger th, the larger tan(th) and the lower the value of deceleration
a which will cause the CofG and thus the rear wheel(s) (assuming a rigid
chassis...) to lift.

Now I've got to get back to my Boosted Decision Trees and Gene
Expression Programming. Play nicely, kids.

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
KotPT -- "for stupidity above and beyond the call of duty".

 

Pull harder on the front brake lever.
If you find yourself sliding down the road you pulled too hard
so fix your bike and body and take it a bit easier next time.

HTH.

 

I seem to remember a CBR600RR (with a good rider apparantly) sailing
past a Atom under braking, on Top Gear a few years ago. Now I fully
admit that an Atom is hardly representative, but it was SO much better
on the brakes, that I'd put my money on an avgerage car/driver over an
average bike/rider any day.

Also agree with the point abouut ho whard you can brake in the rain if
you know ABS is going to stop the front locking up!!

Cheers

SS

 

<folds>

 

It didn't. I fully understand about how to brake hard but I need to
know how I can brake harder with the back wheel in the air than with
it on the floor.

 

Andy Bonwick wrote

Chain driven or shaftie are we talking here?

 

Of course you can't.
"The hardest you can brake is just before the rear wheel leaves the ground."
Is that better?

 

On a very, very good day at a hill climb, when the blood is up, I can
sometimes brake hard enough on the Tart that the front tyre 'chirrups'.
On the Nordie, being nose heavy to start with, I can feel the rear unit
topping out and the back a bit skippy. We are talking braking for a
hairpin here, not to a standstill. I suspect that my technique is poor
and that I don't provide enough rear brake pedal pressure.

 

Ask the OP who made the statement.