On Sun, Oct 26, 2014 at 05:15:20PM +0000, Roland Perry wrote:

Not permanently locked ones, but a brake in the diff (rather that at the
wheel).

Why go to the expense, weight, bulk, and maintenance cost of adding
another brake?

--
David Cantrell | A machine for turning tea into grumpiness

All principles of gravity are negated by fear
-- Cartoon Law IV

On Sun, 26 Oct 2014 12:32:48 +0000, Mizter T
wrote:


On 26/10/2014 11:32, Recliner wrote:

On Sun, 26 Oct 2014 05:07:58 -0600, Arthur Conan Doyle
wrote:

Recliner wrote:

It's only a matter of time before all cars are automatics: with more
ratios, they're more fuel efficient and perform better than manual
transmissions. In fact, many high performance and almost all Eco cars are
now auto-only. The manual gearbox is going the way of the manual choke,
carburettor, starting handle, etc. It's almost 30 years since I switched to
automatics, and I wouldn't dream of going back.

Finding a US rental car with a manual transmission in the US is near impossible
outside of certain specialist vehicles. This also reflects the private vehicle
market as even cars offered with supposed "manual" transmissions are really
automatics with paddle shift switches.

Isn't it still possible to buy at least some sporty cars with
traditional stick shifts in the US? But, certainly, the mainstream
and rental markets abandoned the stick shift a long time ago. I wonder
how many American drivers would be able to use a clutch pedal?


In the UK, it seems to be quite different and I'm not sure why.

Autos are usually more expensive, and traditionally had higher fuel
consumption. As cars and fuel are already much more expensive in the
UK than the US, I suppose this is a significant factor with the small
cars that are more popular here than in the US. But with the pressure
for cleaner, more economical cars, auto transmissions will become the
norm here, too, as computers can control the (larger number of) ratios
better.


The issue highlighted upthread of the potentially astronomical cost of
fixing an automatic if it goes wrong is also a consideration.

In my experience, it's clutches in manual transmission cars that most
often need attention, and that takes a lot of labour. Auto gearboxes
have a very long life.

On 2014-10-27 12:40:05 +0000, Recliner said:

In my experience, it's clutches in manual transmission cars that most
often need attention, and that takes a lot of labour. Auto gearboxes
have a very long life.

Though that's one of the many cases where car manufacturers don't
design for easy maintenance, as they can gain from it being more
expensive. Otherwise an easier to replace clutch might have been
designed.

That said, your point is correct - you have to drive a car more
carefully to avoid wearing the clutch out if it's a manual. An auto
will look after itself.

Neil
--
Neil Williams
Put my first name before the @ to reply.

On 27/10/2014 12:40, Recliner wrote:
[...]
Autos are usually more expensive, and traditionally had higher fuel
consumption. As cars and fuel are already much more expensive in the
UK than the US, I suppose this is a significant factor with the small
cars that are more popular here than in the US. But with the pressure
for cleaner, more economical cars, auto transmissions will become the
norm here, too, as computers can control the (larger number of) ratios
better.

The issue highlighted upthread of the potentially astronomical cost of
fixing an automatic if it goes wrong is also a consideration.

In my experience, it's clutches in manual transmission cars that most
often need attention, and that takes a lot of labour. Auto gearboxes
have a very long life.

Perhaps (?) that's because your experience over the years has been with
higher end automatics?

I'm by no means an expert on any of this - a quick google brings up all
sorts of differing 'expert' opinion (of which the world of motoring has
a particular surfeit of), including varying views on fuel consumption
(though plenty sticking with the traditional 'autos drink more fuel'
line), but the potential expense of repairs to automatics does seem to
feature significantly.

The other significant thing of course being the higher initial purchase
price.

Note that I've no particular dog in this race! Ultimately I'd say
whatever is most economical with fuel consumption is the way to go, and
if autos are now starting to better manuals then that's all good.

Mizter T wrote:
On 27/10/2014 12:40, Recliner wrote:
[...]
Autos are usually more expensive, and traditionally had higher fuel
consumption. As cars and fuel are already much more expensive in the
UK than the US, I suppose this is a significant factor with the small
cars that are more popular here than in the US. But with the pressure
for cleaner, more economical cars, auto transmissions will become the
norm here, too, as computers can control the (larger number of) ratios
better.

The issue highlighted upthread of the potentially astronomical cost of
fixing an automatic if it goes wrong is also a consideration.

In my experience, it's clutches in manual transmission cars that most
often need attention, and that takes a lot of labour. Auto gearboxes
have a very long life.

Perhaps (?) that's because your experience over the years has been with
higher end automatics?

Yes, that's true. In fact, with my current car, there wasn't even a manual
option, as there would be no demand for one. And with with one of my
previous cars, there was no manual option because they didn't have one that
could handle the torque.


I'm by no means an expert on any of this - a quick google brings up all
sorts of differing 'expert' opinion (of which the world of motoring has a
particular surfeit of), including varying views on fuel consumption
(though plenty sticking with the traditional 'autos drink more fuel'
line), but the potential expense of repairs to automatics does seem to
feature significantly.

Yes, if you're unlucky enough to have an auto box fail outside the guaranty
period, it's very expensive. Fortunately, they tend to last a long, long
time if they didn't have any manufacturing faults which normally show up
early.

The other significant thing of course being the higher initial purchase price.

Yes, that's certainly true, though with higher end cars, the resale value
is much worse with a manual box, so they actually work out more expensive
to own. But it's certainly a factor with cheaper cars.


Note that I've no particular dog in this race! Ultimately I'd say
whatever is most economical with fuel consumption is the way to go, and
if autos are now starting to better manuals then that's all good.

I don't think torque converter gear boxes are more economical than manuals,
though the extra gear ratios of the latest boxes probably mean they
approximately equal them. But dual clutch autos are certainly more
economical than manuals as well as torque converter autos, though they're
not quite as nice to drive as a classic slush box auto.

I've always had the latter, and just love the smooth, seamless gear
changes (you can only detect a gear change if you watch the tach) and easy
driving in stop-start traffic. Mine only has six speeds, but the latest
model of my car has eight, and the next will probably have nine and I
suppose ten won't be far away. That certainly helps the fuel consumption,
which is the main factor behind the increase in the number of ratios. I
don't think car manual gear boxes are likely to go beyond six speeds, so
there's less chance of being in the optimum ratio.

In message , at 09:52:31 on Mon, 27
Oct 2014, Neil Williams remarked:
On 2014-10-27 09:44:36 +0000, Neil Williams said:

On 2014-10-27 09:22:46 +0000, Roland Perry said:

That sounds fine if you aren't attempting to put any power on the
road through the 'spinning' wheel. I'm looking at the case where you
want about half the power that would otherwise be sent through the
rubber to remain.
Then you apply partial braking, the effect of which is to send it to
the other wheel (with a small loss via friction).

Imagine, say, you have a mains-pressure water tap with a Y piece added
to it. The Y piece is large enough to take the maximum flow from the
tap on either side (the cross-section of each side of the Y piece being
the same as or greater than that of the pipe feeding the tap). You
place your hand over one side of the Y piece completely - all the water
goes out the other way (this is the effect of braking one wheel fully
with a non-locked diff). You release the hand a bit and some water can
flow out of the "blocked" side - this is the effect of partially
braking the wheel. You will note that in neither case is significant
force applied to your hand.

You partially block both sides - such that the "engine" is having to do
some work. In that case, there is force applied to both sides (on one
side the road, on the other side the balancing effect of the brakes),
though. This is what it would be like when the system applied partial
braking. I guess what you have is that the brake on the "spinning"
side is having to apply the same force as the wheel is applying to the
road on the other side,

The concept I've having difficulty with is that braking a wheel causes
that wheel to transmit more power to the road. Let's say it's a long
uphill slippery road with 100HP from the engine; does this braking
activity swap the 100HP from one driven wheel to the other and back as
each one encounters a slipperier side of the road?

which as it can stop the vehicle it's probably more than capable of.

So I suppose a bit of both. But the fact is (a) it works and (b) it's
simpler and cheaper than locking or limited slip diffs.

Neil

--
Roland Perry

In message

, at 04:47:11 on Mon, 27 Oct 2014, Recliner
remarked:
If you want 75% of the power put on the road through the left wheel,
and 25% through the right wheel, how does braking the right wheel
achieve that without absorbing some of the engine power?

It will need to apply a small force to the wheel, but I can't see why
it would absorb any significant power as that would just go to the
other wheel via the diff.

That sounds fine if you aren't attempting to put any power on the road
through the 'spinning' wheel. I'm looking at the case where you want
about half the power that would otherwise be sent through the rubber to remain.

With ASC, you would be putting some power through the wheel that would
wastefully spin with a locking diff.

If the diff is locked both driving wheels rotate at the same speed. If
one is spinning, very little power is "lost" - the only place it can be
dissipated is warming up the tyre/road surface and if slippery/icy
that'll be very little. The rest of the power inevitably goes to the
wheel with grip.
--
Roland Perry

In message , at 09:43:58 on Mon, 27
Oct 2014, Neil Williams remarked:

It can only do that if the controlling element is in the
differential. Otherwise all the torque is still going to the wheel,
but the brakes are stopping the wheel from rotating too fast, which
means those brakes are absorbing the power, which is thus not
(purposely it seems) available at the road surface.

You clearly *don't* understand how a (non-locking) differential works.

Don't be ridiculous.

The bit about the brakes absorbing the power is in the situation where
the 'slipping' wheel is *both* being braked (in your scheme) and *also*
applying power to the road surface.
--
Roland Perry

In message

, at 04:47:11 on Mon, 27 Oct 2014, Recliner
remarked:
A locked diff is providing traction via the non-slipping wheel, except
the "slipping" one isn't - because it's rotating at the same speed as the
"non-slipping" one - and is therefore well placed to start providing
traction as soon as road adhesion returns to that side.

With ASC, each wheel is provided with just enough traction to stop it
spinning,

Is ASC also controlling the throttle? If I'm driving a car with both
wheels *just* about to start spinning and I floor the accelerator, what
prevents them starting to spin? Or is this the scenario I'm trying to
explain to Neil where the brakes will have to be burning off the excess.

Having the brakes absorbing the excess power for a few seconds if the
objective is to stop a skid on a roundabout (which is the sort of
scenario the video clip posted earlier is simulating), but I'm wondering
about how long they'd survive if the car was being driven
enthusiastically up an Alpine pass with power applied for very long
periods.

so *both* wheels are providing whatever traction they can, and
neither is either spinning or locked. That's much better than a locked diff
which is, at best, optimising traction for just one wheel.

--
Roland Perry

On 2014-10-28 09:20:43 +0000, Roland Perry said:

The concept I've having difficulty with is that braking a wheel causes
that wheel to transmit more power to the road. Let's say it's a long
uphill slippery road with 100HP from the engine; does this braking
activity swap the 100HP from one driven wheel to the other and back as
each one encounters a slipperier side of the road?

Ah, I see. Essentially, yes, that's how it works, using a side-effect
of how a diff functions.

With a normal diff, if one wheel spins all power is lost via that
wheel, none goes to the one with traction (like my water example, all
the power goes the easiest way it can, which is a free-spinning wheel).
Braking therefore allows the power to be passed to the *other* wheel,
with the aim that when the brake is released that wheel might have had
chance to gain some grip and try again.

I *think* it's also the case that maximum traction is gained at the
point *just before* a wheelslip, which stopping the spin to try again
from that point will help, though I admit I find that quite hard to get
my head around. (ABS mainly prevents wheels locking up for another
reason - to allow them to keep their ability to steer).

Neil
--
Neil Williams
Put my first name before the @ to reply.