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Old 25th June 2003, 10:29 AM   #21 (permalink)
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more unsubstantiated drivvel

I don't agree the heavier car will win every time. The parameters are vague and wide open to interpretation.

look at me, i wasted time on another post...

paul
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Old 25th June 2003, 01:35 PM   #22 (permalink)
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You could go on for hours talking about the different variables to come to a solution that proves it one way or another, but lets just look at some real examples.

What corners better :

a Dodge Viper or a Catherham Super 7.

a bentley or a ford focus

a ferrari 355 or a lotus elise.


The best tyres possible will have been chosen for the power/weight in each case so we can ignore that variable.

Anyone know the cornering forces that can be generated by these cars. I would have thought the light ones can do it better, the heavy ones catch up on the straight.
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Old 25th June 2003, 04:33 PM   #23 (permalink)
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My 14yo son walked in a few moments ago and I asked him to think about which car would be faster... about a minute of silence... then he said 'obvious!!!' the heavier car... 'Why, do you think that?
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Well they would have the same driver right? and he would weight the same right? so in the 2 ton car he will have less of an effect!!!

How old are you Pavlo?
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Old 25th June 2003, 04:48 PM   #24 (permalink)
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ahem mycroft

Quote:
posted by mycroft earlier
they are perfectly matched... even down to the 'G' force each can generate in any given curve...
If they are perfectly matched then the driver will need to be of a differing weight also
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Old 25th June 2003, 05:40 PM   #25 (permalink)
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Quote:
2 cars... 1 weighs 1 tonne the other 2 tonnes they both have equal power-to weight ratios and torque curve/gearing coincide exactly for each... they are perfectly matched... even down to the 'G' force each can generate in any given curve...

In a race the 2 tonne car will eat the 1 tonner... quite easily....

Well, the cars are perfectly matched aren't they?

Each has the same 12stone driver...

I find it amusing that none of you saw this... yet my 14yo did... in less than 5 minutes...

Anyway... back to the search for the full answer...

Any more 'ideas'
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Old 25th June 2003, 06:30 PM   #26 (permalink)
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Ooh you ARE a card mycroft, making it into a little puzzle

back to the original thoughts though, and I still haven't found a thread on this board I don't have the physics knowledge or motoring experience but my opinion is currently that a lighter car can outmaneouvre a larger one in cornering, and uses less force to brake - therefore at the same force will brake better.

If you do say a heavier car has an advantage, I will search some more after tea.
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Old 25th June 2003, 06:59 PM   #27 (permalink)
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I think pavlo may think I am something beginning with 'C' but I'm sure that is the spelling that he is thinking of...

I am getting bored with this so a good part of the answer is in the 17" rims thread, it was posted by a fellow 200SX driver and is entirely correct... if anyone here wishes to read Milliken Brothers books then in the section on Comparable Dynamics a fuller and also entirely accurate explanation is shown...

On a track the heavier car will be 3% quicker on a give and take track... the greatest advantage coming on the exit from bends and the manner of the adhesive transition...

I f you can run the correct program then go here and download even more on this and put in the parameters yourself...

http://www.racer.nl/reference/carphys.htm
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Old 25th June 2003, 07:02 PM   #28 (permalink)
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Hah wow I'd forgotten all about Racer ...

I'll try and obtain that book for a read too, cheers
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Old 25th June 2003, 10:48 PM   #29 (permalink)
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Quote:
Originally posted by Mycroft
I think pavlo may think I am something beginning with 'C' but I'm sure that is the spelling that he is thinking of...
Not at all.

It's my mistake for always calculating the power to weight ratio including the driver. You did not state the power, only the power to weight ratio was equal.

Your assumption that the heavier car will 3% quicker is flawed, unless you further define the "parameters", especially those that really are perfectly matched, compared to those which you set to suit your argument.

Paul
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Old 25th June 2003, 11:08 PM   #30 (permalink)
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Could you post a single instance of power-to-weight ratio[s] being calculated as you say... I'm sure we would all be interested in that... never seen it myself... would very much like to see that...
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Old 25th June 2003, 11:18 PM   #31 (permalink)
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Somewhere near the bottom on this page
http://www.scoobynet.co.uk/bbs/threa...=122925&Page=4

Paul
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Old 25th June 2003, 11:28 PM   #32 (permalink)
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Yes, we know YOU do it... the question is does anyone else?

I have certainly never seen it quoted... because i suppose the guy at Ford may have been on a High fibre diet the previous few weeks whilst the Gm driver has bloated out on MacDonalds and pints of Newcastle Brown Ale...

I won't labour the point.

------
Have you read Milliken on this matter?

Or do you have the 'Performance' program i posted a download link to?

Both agree with me, can you find anyone [apart from yourself ] who agrees with you?
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Old 25th June 2003, 11:47 PM   #33 (permalink)
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I am glad you wont labour the point. I don't see the point of comparing power/weight ratios without fuel and driver, especially on lightweight cars (ie under 500kg) as the results are distorted. Given your claimed background in motor racing I would have thought this was second nature to you.

No I haven't read Milliken on the subject.

I am sure the "parameters" can be set to make the heavier car faster. Since you haven't defined what "perfectly matched" is it's impossible to say. Is that matched spring rates or suspension frequency (which I hate anyway)? Is it matched steady state g-force, peak or both? Matched drag or matched power/drag ratio? Matched steering weight or steering weight/driver strength ratio? Four wheel drive? Front, rear wheel drive?

I am referring to the real world, not an approximation.

Paul
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Old 26th June 2003, 12:00 AM   #34 (permalink)
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The parameters are simple and as posted, these cars are as per my post... the only difference between the cars on all singular tests is weight... you can perform any singular test and get identical readings... yet when that weight and those identical singularities are put together on the track the heavier car will be the faster car... by about 3% around a track...
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Old 26th June 2003, 09:54 AM   #35 (permalink)
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Meanwhile, back in the real world rather than Planet Mycroft or some theoretical computer generated race track:

Given 2 cars with identical PWR (calculated however you like) the lighter one will be faster round a circuit because the heavier car will not have some magical and theoretical tyre/suspension/geometry set-up to allow the heavier car to put it's power down more effectively on the way out of corners and neither will it have an adequate brake set-up.

I'd be willing to bet that a 230-ish hp 200SX would beat a 300-ish hp Soarer round any race track (unless there is a straight long enough for the Soarer's power/aero advantage to become a factor) assuming equal drivers.
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Old 26th June 2003, 12:39 PM   #36 (permalink)
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Mycroft,

Quote:
the only difference between the cars on all singular tests is weight...
Not possible.

The only difference is the weight? So they have the same wheels and tyres?

Is it a race of so many laps? The heavier car will get tyre up to temperature faster, but they will also go off faster.

Are the cars limited by lateral grip or traction?

Can the driver actually drive the heavier car as effectively as the the light one? Does the heavier car have assisted steering to help counteract the heavier steering loads?

Do the cars have the same body shape, overall width etc?

How does does the heavier car recover the loss in friction that would be encountered using the same tyres? Are they wider tyres of the same compound? That will decrease front track, adversely affecting weight transfer in the corners.

What about the racetrack? Is it an oval, or a series of tight 30-40mph alternatiing bends?

Paul
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Old 26th June 2003, 12:43 PM   #37 (permalink)
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OK I was bored while eating my lunch, so I decided to use Car Test and play with some settings. I created 2 identical cars (Light an Heavy). The only difference between them was weight and power. Light weighs 2000lbs and has 100bhp, Heavy weighs 4000lbs and has 200bhp.

According to Car Test:

Light

0-60 8.8
0-100 27.8
1/4 mile 16.6 @ 82mph

Heavy
0-60 8.4
0-100 22.52
1/4 mile 16.3 @ 85mph

So the heavier car is faster in a straight line (probably more due to gearing and power than PWR)

So then I put them on a virtual Brands Hatch circuit.

Light managed a 2:25.2, heavy 2:27.9, so the slower car in a straight line is theoretically the faster car on th circuit.

Next time I get bored, I'll start playing with Heavy to see if I can get it round Brands as quik as light by only adjusting the tyre sizes and vehicle dimensions (leaving drag, gearing and PWR identical to Light).

God I'm bored
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Old 26th June 2003, 12:50 PM   #38 (permalink)
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And this is what the sane people have said all along.
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Old 26th June 2003, 01:44 PM   #39 (permalink)
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And like a dog stupidly clinging to a stick he won't let go of:

To get the heavy car to lap about the same as the Light car, it needed tyres that are approx. 20% wider (195/55x15 vs 235/45x15). In fact the heavy car is 0.1 sec quicker.

Interestingly, the Heavy car only pulls an advantage towards the middle of the back straight, where it's greater engine power is overcoming air resitance more easily than the light car. The Light car makes up most of that advantage on the brakes into the corner at the end of the straight.

The Heavy car's ability to lap quicker is down to the fact it now has more grip available to it, and not because it's weight gives any advantage.

Anyone care to genuinely prove me wrong, because so far all I'm hearing is "the answer is out there" rather than proof of the point.
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Old 26th June 2003, 05:02 PM   #40 (permalink)
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You are almost there Rev, but now, if you can, put in the cornering G force at 1 'G' to both... you may have to increase the tyres to 265s' to get equal cornering 'capture' speeds... and the bigger car eats the smaller one...

Because the heavy car will have a greater 'over burden' of power during any incremental speed it will almost always accelerate quicker for the same PtW ratio...

To corner a bigger car at 1G will mean that it will have huge reserves when in transition to the straight [I did mention this earlier] something like 80% greater adhesion in that transition...

For the heavier car to be slower in any corner would mean that the 'G' forces cannot be equal...

You must also ensure that the 2 tonne car can brake equally quickly, that means the singular factorial number must be upped to compensate... both cars must be able to generate equal 'G' in the braking too... do all of that and the 2 tonne car positively swamps the lightweight...

###
2 cars... 1 weighs 1 tonne the other 2 tonnes they both have equal power-to weight ratios and torque curve/gearing coincide exactly for each... they are perfectly matched... even down to the 'G' force each can generate in any given curve...

In a race the 2 tonne car will eat the 1 tonner... quite easily....
###
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