Orchid XP v8 wrote:
> 
> Power is nothing without control, 'tis true. But most cars (and animals)
> don't really have much of a problem with traction. The glaringly obvious
> thing about fast animals (including the cheetah) is that they weigh
> approximately nothing. Hell, fast cars tend to have the exact same
> property! Except they're made of metal, which is strong, but quite heavy.
> 

Have you ever actually driven anything more powerful than the 1.6i? With
the traditional 1-wheel drive grip practically somewhere around 150hp
starts to make an effect (depending on the car, of course), even on
clean asphalt. Around 250-300hp you'll really start missing 4wd when
accelerating from standing position. Remember that the cheetah can take
practically ~full power to its legs right from the start (and to the
ground also). On nature films I've never seen a cheetah to "sping the
feet". Now, if the cheetah would be on clear ice, it would be a bit
different...

Yes. Even when you have the power-to-weight -ratio, to accelerate a car
like a cheetah you'll need enormous traction, an amount that actually is
incredible.

-Aero

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Eero Ahonen wrote:
> Now, if the cheetah would be on clear ice, it would be a bit
> different...

I must thank you for one of the most amusing mental images I've seen all week.

-- 
Darren New, San Diego CA, USA (PST)
   Forget "focus follows mouse." When do
   I get "focus follows gaze"?

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> Power is nothing without control, 'tis true. But most cars (and animals) 
> don't really have much of a problem with traction.

Have you seen cats on hardwood floors? (they slip a lot)

Or someone flooring it in a car from a standstill? (the wheels spin a lot)

I suspect the cheetah is so fast at accelerating because its claws can dig 
into the ground to get traction.

If you got a vehicle with spiked tyres and drove it on grass it would 
probably accelerate quicker too.  IIRC snow-mobiles have a similar drive 
system that digs into the ice and they can get phenomenal acceleration.

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> Nope. The 123d has two turbochargers. The 120d has a bigger
> turbocharger, different injectors, IIRC different crankshaft and some
> other differencies compared to 118d. 118d and 116d may possibly be the
> same engine, I haven't found theier differencies, but I'd guess that
> they too have different turbos.

I stand corrected! I assumed that as there seemed to be software upgrades 
available that the hardware was actually the same.

> I'd say that if it's done correctly, the reliability shouldn't be a
> major problem on that engine (especially 123d). But the software I
> referred to is a official software (by Hirch), so it won't trash the
> warranty of the car.

Yeh I saw that a lot of the more reputable companies will pay for anything 
if the OEM refuses to pay out.  It seems though that (at least for BMW) you 
do not automatically invalidate your warranty by changing the software, just 
that they reserve the right to refuse to pay out if they think it's because 
of you changing the software.

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scott wrote:
>> Power is nothing without control, 'tis true. But most cars (and 
>> animals) don't really have much of a problem with traction.
> 
> Have you seen cats on hardwood floors? (they slip a lot)

Or lino.

But then, domestic cats didn't evolve for that environment. There *are* 
in fact animals which regularly hunt on sheets of ice, and they have 
special adaptations to increase traction. (That said, none of them is 
anywhere near as fast as a cheetah. But you might argue that's due to 
lack of available fuel...)

> Or someone flooring it in a car from a standstill? (the wheels spin a lot)
> 
> I suspect the cheetah is so fast at accelerating because its claws can 
> dig into the ground to get traction.

And not because, oh, I don't know, it's 100x smaller mass has 
significantly lower inertia to overcome in the first place?

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> And not because, oh, I don't know, it's 100x smaller mass has 
> significantly lower inertia to overcome in the first place?

That's only important once you get up to a high enough speed that you can't 
overcome friction (about 10-20 mph in road cars, 60 mph in fast cars, up to 
100 mph in racing cars).  Before that coefficient of friction is the only 
thing that matters.

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scott wrote:
>> And not because, oh, I don't know, it's 100x smaller mass has 
>> significantly lower inertia to overcome in the first place?
> 
> That's only important once you get up to a high enough speed that you 
> can't overcome friction (about 10-20 mph in road cars, 60 mph in fast 
> cars, up to 100 mph in racing cars).  Before that coefficient of 
> friction is the only thing that matters.

My point being that a smaller mass requires a smaller force to 
accelerate it, and thus less traction.

A cheetah's legs don't need to generate 500 BPH to get it from 0 to 60 
in 4 seconds. Because a cheetah doesn't weigh a quarter of a ton...

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> My point being that a smaller mass requires a smaller force to accelerate 
> it, and thus less traction.

Actually exactly the same traction.  If you accelerate an object at 10 m/s^2 
then it will need a coeffcient of friction of about 1.0 no matter what the 
mass is.  This is the point I was trying to make.

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scott wrote:
>> My point being that a smaller mass requires a smaller force to 
>> accelerate it, and thus less traction.
> 
> Actually exactly the same traction.  If you accelerate an object at 10 
> m/s^2 then it will need a coeffcient of friction of about 1.0 no matter 
> what the mass is.  This is the point I was trying to make.

So a force of 1N and a force of 1,000N both require the same amount of 
traction?

How does *that* work?!

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> So a force of 1N and a force of 1,000N both require the same amount of 
> traction?
>
> How does *that* work?!

If the 1000 N force is on an object weighing 1000 kg, and the 1 N force is 
on an object weighting 1 kg, then yes, they both require the same amount of 
friction and will result in the same acceleration.

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