Slightly OT: one for the anti 4x4s?

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"Ian Rawlings" <[email protected]> wrote in message
news:[email protected]...
> On 2006-10-19, Austin Shackles <[email protected]> wrote:
>
> > ferfexache. it's 'cos the ****in' thing weighs about 30 times as
much....
>
> I don't think it was that simple. The technology for HGVs hasn't come
> on much, many use drum brakes and the pneumatic actuators add about
> 0.2 seconds to the response time.
>
> However I think that the weight is more likely to be the cause, but
> Richard seems to think that an HGV can out-brake a car, which I didn't
> think he'd go for but now he has, I'm trying to winkle out of him just
> exactly why that is.

Just depends if he calls his series Landrover a car. ;-)

Martin

>
> > but yes - someone staged it on telly, cooking VW glof compared with 38T
> > artic (note that 44T is only allowed on certain routes in the UK, AFAIK)
> > and from 40 the artic takes about twice the distance to stop.
>
> I'd read that it takes up to 3 times longer for a truck to stop than
> it does for a car, but no idea on what conditions that "test" was done
> so the 3x figure is a bit up in the air really.
>
> --
> Blast off and strike the evil Bydo empire!


 
On or around Thu, 19 Oct 2006 22:08:14 +0100, Ian Rawlings
<[email protected]> enlightened us thusly:

>On 2006-10-19, Austin Shackles <[email protected]> wrote:
>
>> ferfexache. it's 'cos the ****in' thing weighs about 30 times as much....
>
>I don't think it was that simple. The technology for HGVs hasn't come
>on much, many use drum brakes and the pneumatic actuators add about
>0.2 seconds to the response time.

modern ones have discs, and ABS. But you have 30 times the mass (roughly)
and thus have to dissipate 30 times the energy, at the same speed. The
brakes slow the vehicle by, for the most part, converting the kinetic energy
to heat. Based on the test I saw, the brakes on the truck might well be 15
times as good at that as the car was. Now, if the truck's unladen, it only
weighs about 10 times what the car does, then it's got effectively better
brakes, provided the limiting factor isn't tyre grip.

>
>However I think that the weight is more likely to be the cause, but
>Richard seems to think that an HGV can out-brake a car, which I didn't
>think he'd go for but now he has, I'm trying to winkle out of him just
>exactly why that is.
>
>> but yes - someone staged it on telly, cooking VW glof compared with 38T
>> artic (note that 44T is only allowed on certain routes in the UK, AFAIK)
>> and from 40 the artic takes about twice the distance to stop.
>
>I'd read that it takes up to 3 times longer for a truck to stop than
>it does for a car, but no idea on what conditions that "test" was done
>so the 3x figure is a bit up in the air really.

probably depends on load and so forth - mind you, braking distance is very
dependant on technique. I demonstrated this in a friend's car - she'd
scared herself by standing on the anchors on a damp road and getting not
much response. Took it out up a dry road and demonstrated: hit the brake
pedal very hard very fast (as you tend to if you get a sudden panic-stop
moment), the front tyres lock up and skid, with little transfer of weight.
hit the brakes more progressively, so the weight transfer happens before you
apply full braking force, and you can stop it a LOT quicker, and it takes a
lot more deceleration to hit the point where the fronts lock up.

'course, with ABS, this doesn't apply in the same way, as it doesn't lock up
and slide.

--
Austin Shackles. www.ddol-las.net my opinions are just that
"The breezy call of incense-breathing Morn, The swallow twittering
from the strawbuilt shed, The cock's shrill clarion, or the echoing
horn, No more shall rouse them from their lowly bed."
Thomas Gray, Elegy Written in a Country Churchyard.
 
On 2006-10-19, Austin Shackles <[email protected]> wrote:

> Took it out up a dry road and demonstrated: hit the brake pedal very
> hard very fast (as you tend to if you get a sudden panic-stop
> moment), the front tyres lock up and skid, with little transfer of
> weight.

Heh. Trying to stop my Defender with a stuck piston on one front
caliper, in the wet, with an unladen rear, on cheap mud pattern tyres,
when a deer jumped out in the road... It's amazing what you can learn
when you need to ;-)

I certainly learned though, the next animal that jumped out on me got
flattened :p

As for ABS versus non-ABS, I keep hearing conflicting reports of
whether ABS stops you faster or not, but one concrete advantage
certainly seems to be that you can generally keep control of the car
much more easily, barring weight transfer unsettling the rear of course.

--
Blast off and strike the evil Bydo empire!
 
On or around Thu, 19 Oct 2006 23:15:24 +0100, Ian Rawlings
<[email protected]> enlightened us thusly:
>
>As for ABS versus non-ABS, I keep hearing conflicting reports of
>whether ABS stops you faster or not, but one concrete advantage
>certainly seems to be that you can generally keep control of the car
>much more easily, barring weight transfer unsettling the rear of course.

depends on the conditions - on loose gravel and dry snow, a locked wheel
gives maximum braking, for example.

Weight transfer seems to work better with ABS, presumably because the front
wheels don't lock too early and then not provide any more retardation.

Having said that, when the sierra had working ABS, I think I only invoked it
twice without trying - it did stop PDQ on those occasions, mind. It also
failed to stop noticeably on more-or-less ice (shiny packed snow) when I
went out testing it, but then it'd have done that without the ABS as well.
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Any man's death diminishes me, because I am involved in Mankind; and
therefore never send to know for whom the bell tolls, it tolls for thee"
John Donne (1571? - 1631) Devotions, XVII
 
In message <[email protected]>
Austin Shackles <[email protected]> wrote:

> On or around Thu, 19 Oct 2006 18:02:09 +0100, Ian Rawlings
> <[email protected]> enlightened us thusly:
>
> >Naah. HGV braking systems are ****e compared to cars, the government
> >even paid shedloads of loot some time ago to investigate why this is,
> >URL below (it's a summary);
>
> ferfexache. it's 'cos the ****in' thing weighs about 30 times as much....
>
> duhhh!
>
> but yes - someone staged it on telly, cooking VW glof compared with 38T
> artic (note that 44T is only allowed on certain routes in the UK, AFAIK)
> and from 40 the artic takes about twice the distance to stop.

But was the test vehicle patrially loaded, or fully loaded? There's
a significant difference. "Tests" staged on TV programs are notable
only for their lack of rigour (in the scientific sense), as indeed
are most auto magazine tests (they usually don't compare like with
like, e.g. was the Golf loaded to it's maximum capacity, and was
the truck). The one they almost always fall for is at vehicle
launches, where the "new" vehicles is given the best possible tyres
and the "rivals" the worst ones they can get away with.

Richard
--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
In message <[email protected]>
Ian Rawlings <[email protected]> wrote:

> On 2006-10-19, beamendsltd <[email protected]> wrote:
>
> > It's highly probable that some can, since off-road oriented tyres are
> > usually a softer compound than car tyres,
>
> They don't have stipes, they have solid blocks instead, which grip the
> road less as the blocks have much less give in them. This of course
> refers to mud tyres, not road tyres like ATs. Most ATs will put less
> rubber down than a proper road tyre of course, which will lessen grip.
>
> > and, of course, the braking system is designed (on proper 4x4's)
> > with towing in mind. The braking ability is designed in, not an
> > accidental outcome.
>
> The same is true of cars, which on average are lighter, more
> dynamically stable and have a lower centre of gravity so I doubt that
> the average car would be out-stopped by the average 4x4.
>
> > A partly loaded 44 ton truck (i.e. loaded enough to stop the
> > trailer wheels locking up) will out-stop most cars. Easily.
>
> Naah. HGV braking systems are ****e compared to cars, the government
> even paid shedloads of loot some time ago to investigate why this is,
> URL below (it's a summary);
>
> http://www.rmd.dft.gov.uk/project.asp?intProjectID=7944
>
> Accidents involving lorries smacking into the back of queues are
> pretty common too because of the long stopping distances of lorries,
> coupled with lorry drivers not paying attention.
>
> Given however that you've stated that lorries can stop faster than
> cars, can you provide any figures? I tried to find some but can't
> find anything which was surprising as I thought driver training
> information would have something, although it's going to change so
> much from one vehicle to the next.
>
> However a dynamically unstable vehicle like a lorry isn't going to
> like stopping, the rear tyres for a start are going to lose most of
> their grip due to the high centre of gravity shifting the weight so
> far forwards. Then there's the load moving, and the ****E tyres
> lorries use!
>
> > I'm fooling no one, it's the driver and the pedestrian that makes
> > a vehicle dangerous or not,
>
> That's not what I was talking about, it was the bit about being hit by
> a car being worse than being hit by a 4x4. On average that's not the
> case, although you could of course compare a volvo V90 or whatever
> versus an old Jag XJS. Like for like though it's better to be hit as
> low as possible.
>
> > The drive train configuration has nothing to do with it (well,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > actually if probably does, but in the 4x4's favour).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Ah yes, having four-wheel drive gives the tyres more grip eh! Hmm....
>

No, having a 4x4 drive drive train gives (or can give, depending
on the design) more control - which is why I said what I've
underined above.
Anyway, going by your comments about truck tyres, and the stuff
about tread patterns (if you mentioned wet conditions you'd have
a point) I think I'll give up. The info I have comes from Tedley,
who was the vehicle dynamasist at Rolls-Royce Motor Cars when I
worked there, and Marky-Mark who was tyre technician for a Word
Rally Champoinship Team (they won) and is currently preparing
to go to Brazil for his current job as tyre technician for a
Formula One team, gaining these posts on secondment from
Michelin (Stoke) - which specialises in truck and, until
recently, 4x4 tyres (of which I have a set development OR's
on my 110 at the moment for evaluation).

Richard

--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
In message <[email protected]>
Tom Woods <[email protected]> wrote:

> On Thu, 19 Oct 2006 17:26:11 +0100, beamendsltd
> <[email protected]> wrote:
>
> >It's highly probable that some can, since off-road oriented tyres are
> >usually a softer compound than car tyres, and therefore have a
> >higher friction coeficient - and, of course, the braking system
> >is designed (on proper 4x4's) with towing in mind. The braking
> >ability is designed in, not an accidental outcome.
>
> There is a big tyre test in one of the old landy mags currently in my
> excremeditation chamber.
>
> I'm pretty sure it shows that the best offroad tyres had the longest
> stopping distance. I think there was quite a bit in it and the
> knobbliest one was close to double the distance of the most 'road'
> one.
>
>

It depends on the conditions - knobbly tyres can be fantastic in the
dry, but leathal in the wet, and to an extent the reverse can be true.
My first bike was a Suzuki TS100 which came with knobbly tyres which
where factastic in he dry but hopeless in the wet - the same goes
for the XCL's I had on Knobby. Yet the OR's I had on the 90 were
great in the wet but somewhat iffy in the dry. It's impossible to
generalise.

Richard

--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
In message <[email protected]>
Austin Shackles <[email protected]> wrote:

> On or around Thu, 19 Oct 2006 23:15:24 +0100, Ian Rawlings
> <[email protected]> enlightened us thusly:
> >
> >As for ABS versus non-ABS, I keep hearing conflicting reports of
> >whether ABS stops you faster or not, but one concrete advantage
> >certainly seems to be that you can generally keep control of the car
> >much more easily, barring weight transfer unsettling the rear of course.
>
> depends on the conditions - on loose gravel and dry snow, a locked wheel
> gives maximum braking, for example.
>
> Weight transfer seems to work better with ABS, presumably because the front
> wheels don't lock too early and then not provide any more retardation.
>
> Having said that, when the sierra had working ABS, I think I only invoked it
> twice without trying - it did stop PDQ on those occasions, mind. It also
> failed to stop noticeably on more-or-less ice (shiny packed snow) when I
> went out testing it, but then it'd have done that without the ABS as well.

ABS just looks for a wheel rotating at a different speed to the avarage
of the rest, and applies/releases the brake to get it back in sync.
Most systems will realise that since the car is moving all the
wheels should be rotating, and does the same to avoid skidding. It will
cetrainly provide the best possible braking in almost all conditions
(though some systems cannot cope with loose gravel under all 4 wheels
- LR's can - another LR world first at the time) - however, it can't
perform mircles (despite Audi/BMW owners seeming to think so). There are,
as Austin says, some circumstances where a skid may be desirable,
just what those are is a subject of some debate.

Richard
--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
On 2006-10-20, beamendsltd <[email protected]> wrote:

> No, having a 4x4 drive drive train gives (or can give, depending
> on the design) more control - which is why I said what I've
> underined above.

Not really, if you've got the brakes on then the only way a 4x4
drivetrain can affect things is if it locks all the diffs giving you a
form of traction control, but only one vehicle that I know of does
that, the Volvo C303.

We are talking about stopping distances remember, so throwing in stuff
about getting more grip going round corners is a whole different argument.

> Anyway, going by your comments about truck tyres, and the stuff
> about tread patterns (if you mentioned wet conditions you'd have
> a point) I think I'll give up.

Why mention wet conditions? Tyres aren't equal in the dry.

--
Blast off and strike the evil Bydo empire!
 
In message <[email protected]>
Ian Rawlings <[email protected]> wrote:

> On 2006-10-20, beamendsltd <[email protected]> wrote:
>
> > No, having a 4x4 drive drive train gives (or can give, depending
> > on the design) more control - which is why I said what I've
> > underined above.
>
> Not really, if you've got the brakes on then the only way a 4x4
> drivetrain can affect things is if it locks all the diffs giving you a
> form of traction control, but only one vehicle that I know of does
> that, the Volvo C303.

Er, so what about the engine? It has no effect of braking control?
A center diff (unlocked) has no impact on braking? Brakes don't
operate in isolation from the rest of the vehicle. Try taking
a shock absorber off and see what happens to your brakes!

>
> We are talking about stopping distances remember, so throwing in stuff
> about getting more grip going round corners is a whole different argument.

Who said anything about corners? Not me....

>
> > Anyway, going by your comments about truck tyres, and the stuff
> > about tread patterns (if you mentioned wet conditions you'd have
> > a point) I think I'll give up.
>
> Why mention wet conditions? Tyres aren't equal in the dry.

No I really do give up!

>

Richard

--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
JD wrote:

>(Australia) there has been a lot of bad press about suburban 4x4s backing
>over small children in the driveway (usually the driver's kids). And
>"everyone knows that 4x4s have worse rear vision than ordinary cars". This
>has now pretty much gone quiet after a local motoring organisation carried
>out some scientific testing - and showed that (as you would expect) rear
>visibility has nothing to do with how many wheels are driving
>
Some cars have absolutely appalling rear visibility. In the US most
drivers don't seem to reverse unless there is no option, and given the
view out of the rear of the last car I hired over there (a chevolet of
some flavour) I can see why. Being a saloon it had a relatively high
rear window, at a very flat angle which would have been hard enough to
see out of to start with (couldn't have seen a bollard when reversing,
for example), then they put a spoiler across it! Talk about a tool not
fit for the job. I have much better visibility out of the back of the 101.

Lizzy
 
On 2006-10-20, beamendsltd <[email protected]> wrote:

> Er, so what about the engine? It has no effect of braking control?

Not as much as the brakes!! And if you're stopping hard then engine
braking isn't of much interest unless of course your brakes are so
screwed that they can't slow you down enough.

> Try taking a shock absorber off and see what happens to your brakes!

That's very different to the engine, the shock absorbers help keep the
wheels on the ground, but when the brakes are on hard, a 4x4
drivetrain isn't going to be affecting things much, if at all.

--
Blast off and strike the evil Bydo empire!
 
Ian Rawlings wrote:

> On 2006-10-20, beamendsltd <[email protected]> wrote:
>
>> Er, so what about the engine? It has no effect of braking control?
>
> Not as much as the brakes!! And if you're stopping hard then engine
> braking isn't of much interest unless of course your brakes are so
> screwed that they can't slow you down enough.
>
>> Try taking a shock absorber off and see what happens to your brakes!
>
> That's very different to the engine, the shock absorbers help keep the
> wheels on the ground, but when the brakes are on hard, a 4x4
> drivetrain isn't going to be affecting things much, if at all.
>
The only effect I can see for a four wheel drive drive train (and then only
for constant four wheel drive and in gear)is to even out braking effort to
some extent - if one wheel locks it increases the braking on the other
three through the drive train, but I would not expect the effect to be
noticeable.
JD
 
In message <[email protected]>
JD <[email protected]> wrote:

> Ian Rawlings wrote:
>
> > On 2006-10-20, beamendsltd <[email protected]> wrote:
> >
> >> Er, so what about the engine? It has no effect of braking control?
> >
> > Not as much as the brakes!! And if you're stopping hard then engine
> > braking isn't of much interest unless of course your brakes are so
> > screwed that they can't slow you down enough.
> >
> >> Try taking a shock absorber off and see what happens to your brakes!
> >
> > That's very different to the engine, the shock absorbers help keep the
> > wheels on the ground, but when the brakes are on hard, a 4x4
> > drivetrain isn't going to be affecting things much, if at all.
> >
> The only effect I can see for a four wheel drive drive train (and then only
> for constant four wheel drive and in gear)is to even out braking effort to
> some extent - if one wheel locks it increases the braking on the other
> three through the drive train, but I would not expect the effect to be
> noticeable.
> JD

Ten Jolly Junior points and a Gold Star to that man! Only the
effect is quite (relatively speaking) marked - the inertia
in a (particularly steel) wheel and tyre can be quite significant,
as the diffs etc all count and provide something of a damping effect
when a wheel is thinking about locking up.

Richard
--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
On 2006-10-20, JD <[email protected]> wrote:

> three through the drive train, but I would not expect the effect to be
> noticeable.

Especially not with the clutch in, which most would have in an
emergency stop situation.

The Volvo C303 has a nice system, when you whack the brakes on it
engages drive to the front axle, which is the Defender equivalent of
locking the centre diff. This helps to prevent the rear wheels
locking which is a problem in an empty load-carrying vehicle,
especially a forward control like the C303. There are more modern
systems which are better of course, but for a 1960's truck it was a
good idea. That's a situation where a 4x4 drivetrain has been
designed explicitly to help under braking, but it's the only one that
I'm aware of.

--
Blast off and strike the evil Bydo empire!
 
On 2006-10-20, beamendsltd <[email protected]> wrote:

> Ten Jolly Junior points and a Gold Star to that man! Only the effect
> is quite (relatively speaking) marked - the inertia in a
> (particularly steel) wheel and tyre can be quite significant, as the
> diffs etc all count and provide something of a damping effect when a
> wheel is thinking about locking up.

With the effect, if any, being even more marginal at low speeds of
course due to the reduced inertia.. Plus of course if a car has ABS
it's not relevant at all, and if it doesn't have ABS it's only
relevant if the driver has managed to get the braking into a zone in
which such a marginal effect comes into play - close enough to the
tyres unsticking that it makes a difference. Not even F1 drivers can
always prevent a wheel locking during a race when they're expecting to
brake hard and they've practiced like mad on that same bit of track so
your average driver wrangling kids won't manage it. They're going to
either brake less than they could, or to just mash the pedal and lock
up, not get it to a point at which inertia of drive shafts becomes
relevant!

All in all, no a 4x4 drivetrain has no noticeable effect on braking,
certainly not enough to compensate for things like the additional
weight transfer to the front due to higher centre of gravity, and all
the other stuff that the average 4x4 has to put up with that the
average saloon car doesn't.

I'm perfectly happy to know that my vehicle is more hazardous to a
pedestrian than the average saloon car, given the chances of me
hitting someone it's not something I can be bothered to worry about.
There are far more lorries on my tiny local roads than 4x4s and they
come round the corners on the wrong side of the road, which is rather
scary....

--
Blast off and strike the evil Bydo empire!
 
On or around Fri, 20 Oct 2006 11:21:56 +0100, Ian Rawlings
<[email protected]> enlightened us thusly:

>That's very different to the engine, the shock absorbers help keep the
>wheels on the ground, but when the brakes are on hard, a 4x4
>drivetrain isn't going to be affecting things much, if at all.

the viscous diff on the classic RR T-boxes probably transfers some torque
under braking, in a situation where one or more wheel would otherwise
lock...
--
Austin Shackles. www.ddol-las.net my opinions are just that
"Brevis esse laboro, Obscurus fio" (it is when I struggle to be
brief that I become obscure) Horace (65 - 8 BC) Ars Poetica, 25
 
In message <[email protected]>
Ian Rawlings <[email protected]> wrote:

> On 2006-10-20, beamendsltd <[email protected]> wrote:
>
> > Ten Jolly Junior points and a Gold Star to that man! Only the effect
> > is quite (relatively speaking) marked - the inertia in a
> > (particularly steel) wheel and tyre can be quite significant, as the
> > diffs etc all count and provide something of a damping effect when a
> > wheel is thinking about locking up.
>
> With the effect, if any, being even more marginal at low speeds of
> course due to the reduced inertia.. Plus of course if a car has ABS
> it's not relevant at all, and if it doesn't have ABS it's only
> relevant if the driver has managed to get the braking into a zone in
> which such a marginal effect comes into play - close enough to the
> tyres unsticking that it makes a difference. Not even F1 drivers can
> always prevent a wheel locking during a race when they're expecting to
> brake hard and they've practiced like mad on that same bit of track so
> your average driver wrangling kids won't manage it. They're going to
> either brake less than they could, or to just mash the pedal and lock
> up, not get it to a point at which inertia of drive shafts becomes
> relevant!
>
> All in all, no a 4x4 drivetrain has no noticeable effect on braking,
> certainly not enough to compensate for things like the additional
> weight transfer to the front due to higher centre of gravity, and all
> the other stuff that the average 4x4 has to put up with that the
> average saloon car doesn't.
>
> I'm perfectly happy to know that my vehicle is more hazardous to a
> pedestrian than the average saloon car, given the chances of me
> hitting someone it's not something I can be bothered to worry about.
> There are far more lorries on my tiny local roads than 4x4s and they
> come round the corners on the wrong side of the road, which is rather
> scary....
>

I'll let Marky-Mark know they've got it all wrong. He's going to
be very disappointed!

Richard
--
www.beamends-lrspares.co.uk [email protected]
www.radioparadise.com - Good Music, No Vine
Lib Dems - Townies keeping comedy alive
 
On 2006-10-20, beamendsltd <[email protected]> wrote:

> I'll let Marky-Mark know they've got it all wrong. He's going to
> be very disappointed!

OK, my consultancy rates are reasonable ;-)

Bear in mind though that at the level of a racing outfit, small
differences count but they don't at the level we were talking about,
and I've been saying that any differences are going to mean bugger all
on the school run!

--
Blast off and strike the evil Bydo empire!
 
On Fri, 20 Oct 2006 15:04:56 +0100, Ian Rawlings <[email protected]>
wrote:

> ...
> and I've been saying that any differences are going to mean bugger all
> on the school run!

Make the little buggers walk - or if they're too far then give Austin the
work.

School run indeed - whatever next?

--
William Tasso

Land Rover - 110 V8
Discovery - V8
 
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