> >> If you do lock up the front wheel in slippy conditions, you can still > >> balance a bike with normal steering geometry but you wont be able to > >> effect front wheel steering. The balance corrections need to be > >> exagerated for you are unable to use wheel momentum to move the front > >> of the bike sideways.
> >If you lock the front wheel of any single-track bicycle or motorbike > >for anything but a small fraction of a second you'll be on the ground > >using your clothing or skin as retardation friction material. Just > >maybe Valentino Rossi could get away with it occasionaly, but mere > >humans cannot.
> A long time ago, when I was an RAC/ACU motorcycle training instructor, > we used to demonstrate to the students the relative benefits of the > front and rear brakes. > This involved riding at speed across the training area and applying > only one brake. > The rear only demonstration inevitably left a long black mark on the > tarmac, whichever instructor demonstrated it. > The front only demo was always much less than half the stopping > distance, and the demonstrator seemed to make more difference than the > use (or not) of the rear brake in combination with the front. > One instructor was particularly good on the front only, and laid down > a 25yd black stripe with the front tyre, while holding the rear about > 2" in the air. It was a truly impressive display of machine control > (front tyre smoking and rear elevated), but more significantly, it was > the shortest stop we ever measured.
> So locking the front under control can be done. > I understand from a couple of police motorcyclists I've spoken with > that their training included front wheel lockup recovery. > But then they wear leathers!
I'd heard about front wheel lockup on a suspended machine but was unable to imagine how it was done in the dry until now. I think the front suspension requires compression and with the front brake released and the suspension rising fast the brake is snatched on initiating the skid. With the front sliding freely, more retardation is caused by easing the brake, so when the rear starts to rise the lever is pulled tighter and braking at the road is reduced because of heat build up melting the tyre tread. I have locked up in the dry on the road, but it was steep and dusty so was similar to the wet weather experiences I have had. I did not maintain the locked wheel in the dry. It may be pertinent to note that I was using short arm single pivot side pull racing brakes ('monoplaner') with Campy blocks and cables (stout wire) or Weinmann 405 (Carrera type) for most of my experience with sustained front wheel lock. And, I had worked out the tricks of bowden wire installation.
> On 2009-11-02, Andre Jute <fiult...@yahoo.com> wrote:
> > On Nov 2, 8:56 am, Ben C <spams...@spam.eggs> wrote: > >> On 2009-11-01, Neal <N...@hotmail.com> wrote:
> >> > I've been reading about the road rage trial in L.A. The case where the car > >> > driver slammed on his brakes and two cyclists were injured when they hit the > >> > car.The defense had a accident specialist testify that the bikes could have > >> > stopped before hitting the car. He stated that the cyclists were traveling > >> > at 30 mph which was taken from their GPS computer. He states the bikes could > >> > have stopped in 2 seconds. This seems more than optimist to me.
> >> 30mph is 13m/s. So to go from 30 to to 0 in 2s would require > >> deceleration of 6.5m/s^2, or 0.66g, so it should be possible.
> > I think, Ben, that unless that's a veeeery long wheelbase cruiser and > > you're sitting real close to the ground, you'll be doing a face-plant > > at 0.66g.
> Agreed, or at least fall off in some kind of painful and > collarbone-breaking way.
> > Anyway, that isn't 2s available, it's 2s less reaction time which is > > generally a minimum of 0.75s. So, to stop in 1.25s from 30mph is 1.1g. > > (If this weren't such a serious matter, I would ask you where you > > bought these magic tyres...)
> > The only place and time a cyclist decelerates at 1.1g is the moment > > after his face hits the tarmac.
> Well certainly I don't think I would be able to control the thing if I > tried to brake as hard as possible at 30mph.
> It's not like a car which has 4 wheels, is very stable, and has an > idiot-proof pedal that you just stomp on.
> But you can see where the lawyer gets this from-- he ignores thinking > time and uses the theoretically possible figure of 0.66g. You might pull > that when coming to a stop from a low speed, but no way from 30mph.
As someone else pointed out already, that lawyer and so-called "expert" were only doing what they were paid to do. According to a URL Jobst posted in a related thread, the jury saw through the pseudo- technical bullshit to the driver's intention of causing harm to the cyclists, and voted the perpetrator guilty.
It does make you wonder though if in law everyone is assumed to be a superman -- and especially cyclists. We've seen in this thread reaction times of 0.3s thrown about; possible for extremely paranoid athletes in military training with live ammunition but hardly likely on our streets. I think that even the 0.75 often accepted as some kind of an average is too low for Joe Blow unless he has been alerted to expect some event to react to. It is a level of readiness one cannot maintain permanently, even when riding a bike in traffic. It seems to me that we should build in 2s of observation and reaction time into safe distances behind other vehicles.
Andre Jute "The brain of an engineer is a delicate instrument which must be protected against the unevenness of the ground." -- Wifredo-Pelayo Ricart Medina
On Nov 4, 5:11 pm, Norman <invasivenor...@gmail.com> wrote:
> On Nov 4, 4:32 am, Andre Jute <fiult...@yahoo.com> wrote:
> > As someone else pointed out already, that lawyer and so-called > > "expert" were only doing what they were paid to do.
> They _would_ say that, wouldn't they? Well, it's a good > thing that being paid to do something instantly absolves > them for being lying pricks.
Psst, Norman, RBT is a community of cyclists. It's the wrong place for you to absolve a greedy, lying shyster and a greedy, lying "expert" of anything, never mind of trying to exonerate a driver who deliberately put two cyclists in hospital. Unless you're a masochist looking for a good kicking, of course.
Alas! Satire, irony and even sarcasm does poorly on the net, what with so many mindless morons running around. I know what you meant, but you shouldn't count on the majority catching your drift.
Andre Jute "What Chairman Mao really meant to say"
On Wed, 4 Nov 2009 09:11:26 -0800 (PST), Norman <invasivenor...@gmail.com> wrote:
>On Nov 4, 4:32 am, Andre Jute <fiult...@yahoo.com> wrote:
>> As someone else pointed out already, that lawyer and so-called >> "expert" were only doing what they were paid to do.
>They _would_ say that, wouldn't they? Well, it's a good >thing that being paid to do something instantly absolves >them for being lying pricks.
Actually it does. It's weird and almost counter-intuitive but it works. We've created a system where the liar does not have an advantage in court. Part of that is that the defense attorney is expected to do whatever is possible within the broad rules to defend his client, no matter how guilty and culpable the bastard is. Goes back to John Adams defending the British soldiers after the Boston massacre.
> And if _I_ had been driving behind the _doctor_ in _that_, I > wouldn't have even _touched_ my brakes when he jammed his on.
Of course space and time has little to do with tractor wheelies.
He could have offered a video of a Bobcat mini-wheel dozer showing the fantastic acrobatics these tractors can perform... wheelies and spins-in-place. There is a reason why they have sturdy enclosures and safety belts for drivers. Besides, it isn't occurring at the speed in question for the "teach them a lesson" sudden stop.
> > And if _I_ had been driving behind the _doctor_ in _that_, I wouldn't > > have even _touched_ my brakes when he jammed his on.
> Yes, but you might have to take into account the reaction time > necessary to drop the bucket to the appropriate height.
Bucket height is usually low when driving on public roads. If it is high, when braking hard, the cab topples forward and falls sideways. Most drivers will run a machine flat out and raise the bucket height after it skims the road rather than slow down. The bucket may end up 30" or more above the road.
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