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Old 1st August 2003, 08:40 AM   #201 (permalink)
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Quote:
Originally posted by Mycroft
Andyf, I would like to hear how you view that graph in Simons link.
If you are referring to this graph:

http://autozine.kyul.net/technical_s...g/friction.jpg
(the server this image is hosted on doesn't like people linking to it. You'll need to copy/paste the URL into your browser and get to it that way.)

then personally I don't know what to make of it. The main problem is, the x and y axis have no units. I can't form a mental image properly without some form of units. The x-axis 'vertical load' could be measured in grams for all I know.

Simon's graph:

<img src="http://www.scoobynet.co.uk/images/graph.gif">

is a little bit more useful, but again a lack of units prevents me from thinking how this affects a real-world car.




PS. I think the topic of this thread needs changing now
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Old 1st August 2003, 08:42 AM   #202 (permalink)
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Apologies andy

That second graph was purely to disprove that an angle of greater than 45 degrees does NOT mean that the y axis more than doubles with each doubling of the x axis.

It has no real relevance to cars.

Cheers

Simon
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Old 1st August 2003, 08:45 AM   #203 (permalink)
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Quote:
Originally posted by SDB
That second graph was purely to disprove that an angle of greater than 45 degrees does NOT mean that the y axis more than doubles with each doubling of the x axis.
I'd agree with that based on what I'm seeing.

Mycroft, what is it you wish Simon to explain? is it the purpose of the graph, or the section he has chosen to label points 1 and 2, or other?
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Old 1st August 2003, 08:49 AM   #204 (permalink)
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The first graph shows a concept (which was explained underneath it on the page it came from) that as load increases, the amount of additional grip gain reduces.

Obviously at low loads, these reductions are small, and the reductions increase exponentially as load increases.

What this means is (as you are requesting the information, this is no longer futile), that at small loads, the amount of grip you loose (as a proportion of the load) is much smaller than the amount of grip you loose at large loads.

Obviously, the graph is not completely accurate, in the same way that the other graph (that mr mycroft contiunually requests confirmation on) is not accurate. But both are used by their seperate authors (as can be clearly seen by the text underneath them) to illustrate a staple and basic principle of vehicle dynamics that doubling the load on a tyre, less than doubles the grip it produces.

All the best

Simon
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Old 1st August 2003, 08:52 AM   #205 (permalink)
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Quote:
PS. I think the topic of this thread needs changing now
I'd have to agree andy.

If there are no more questions on what we've been discussing, perhaps there are other questions on issues broadly around the topic?

All the best

Simon
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Old 1st August 2003, 08:53 AM   #206 (permalink)
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Thanks Simon, I comprehend.

* andy throws the ball into Mycroft's court
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Old 1st August 2003, 09:12 AM   #207 (permalink)
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Well I was thinking of asking a downforce-related question, as the effect of downforce on a car can be thought of in some ways as extra mass... but I think I will leave it for just now as it's another complicated subject.
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Old 1st August 2003, 09:19 AM   #208 (permalink)
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Hi Andy

It may be that your question has been answered (or partly answered) earlier in this thread, or actually, I think it was the previous one, that you started...

Let me take a look.

Cheers

Simon
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Old 1st August 2003, 09:27 AM   #209 (permalink)
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Hi Andy..

This *may* be related to the question you were thinking of...

https://www.gtr.co.uk/forum/upload/sh...5&pagenumber=7

The "interlude" part of my 6th post on this page

If not, apologies.

All the best

Simon
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Old 1st August 2003, 09:36 AM   #210 (permalink)
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real world "simple" question

on track I take the spare wheel out of the boot because I kid myself that losing this weight helps with

a - top speed
b - cornering
c - braking

true or not?
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Old 1st August 2003, 10:26 AM   #211 (permalink)
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It will almost certainly help to a small degree on cornering, low speed acceleration and braking...

But probably not at all on top speed.

The only proviso to this, is if the chassis has been set-up specifically requiring the spare wheel to be there, but it's almost inconceivable that it would be this accurate on a road car due to the fact you can have any number of passengers, of different heights, c/g, weights, and different levels of fuel, etc, etc.

So in short. removing the weight of the spare wheel is likely to slightly improve the performance of your car (probably not enough to worry about though)

All the best

Simon
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Old 1st August 2003, 10:33 AM   #212 (permalink)
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Thanks Simon

"But probably not at all on top speed."

on the basis that aerodynamics would be the limiting factor rather than weight?
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Old 1st August 2003, 10:53 AM   #213 (permalink)
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Is there a simple 'rule of thumb' way to calculate an ideal tyre width for a particular car, perhaps based on weight, and obviosuly practical considerations? I use my car for track days, and have a spare set of wheels for this, I have been contemplating trying a wider tyre, but from reading here, that may not actually provide more grip? I appreciate that the actual tyre invloved will have a big effect here, but assuming a quality road / track day type tyre (not a slick) is there a simple way to predict whether it's worthwhile or not?
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Old 1st August 2003, 10:54 AM   #214 (permalink)
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Hold on now I'm confused!

I quote Simon as saying:

Quote:
Originally posted by SDB
Build two cars from scratch. One has to weight 1000Kg, and the other 2000Kg. You are allowed to spend 10 trillion dollars on each, and have the entire world of vehicle dynamics experts working on the project.

You will always be able to make the 1000Kg car go immeasurably faster round a circuit.
But Mycroft quotes him as saying:

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...."
These are contradictory?

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Old 1st August 2003, 11:13 AM   #215 (permalink)
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the first quote is from this thread , the second is actually mycroft himself from the earlier "with bickering" thread.
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Old 1st August 2003, 11:24 AM   #216 (permalink)
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Hi Harry

That was indeed the basis of my statement, plus the fact that mass is only important when it is required to be accelerated (accelerated meaning, resisted in corners, resisted under braking, and (what we usually think of as acceleration) when "accelerating" ).

So once you get close to top speed, you are only (if you exclude things like rolling resistance of the tyres, and other such things) reducing the amount of acceleration you get rather than the terminal speed.

323GT-R

Quote:
Is there a simple 'rule of thumb' way to calculate an ideal tyre width for a particular car
My answer to the specific question is "I don't actually know to be honest". I can ask though, and will do. My gut feeling says no, as there are too many other parameters that affect the idea of an ideal tyre.

Without question, the only way to be sure what works is to test it.

For instance. I remember doing some winter testing in a group a legacy many moon ago in holand on their glorious snow covered forest roads.

We got what we need to do done early and decided (almost for a laugh) to see how much slower forest tyres were than the studs.

Obviously there was little comparrison between the two and the forest tyres were WAY off the pace - not even in the same ball park.

So, again, (definitely) just for a laugh, we decided to test some intermediate slicks (maybe they didn't want to have to pay for my flight home??? ). To everyones amazement, the slicks were FASTER than the forest tyres.

Nobody could have guessed that would be the case, but we all learnt something that day.

I have, ever since, been hoping for more winter testing work so I could convince them to allow us to repeat the test, as I have no doubt it would be different.

All the best

Simon
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Old 1st August 2003, 11:25 AM   #217 (permalink)
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Cem

Apologies, I wasn't ignoring you. You're absolutely right, they are completely contradictory.

All the best

Simon
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Old 1st August 2003, 12:03 PM   #218 (permalink)
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Quote:
Originally posted by Mycroft
There is no arguement to win now, the statement made by Simon is manifestly wrong, we experience it in the real World every day.

To be honest this has become a matter of 'personality choice' as soon as I see that I am debating with people such as yourself and other MKIV forum members I will only be a facing an irritating claque of nay sayers.

Can we now move on and try really hard to move this thread too fertile pastures Peter and others here would like to gain from this thread not be regailed with yet another 'Mycroft vs MKIV/Scooby/Tormented souls'

I will say it again, I do not believe we have the right to impinge on Cems goodwill and bandwidth to continue some sad, petty vendetta.
Hmmm could have continued to have been a good debate if things had have moved on after this obvious admission of defeat.

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Old 1st August 2003, 12:29 PM   #219 (permalink)
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Interesting stuff about the winter testing Simon - why were the slicks quicker anyway?


PS Throughout the course of this thread I have wondered what real-world experience Mycroft has in this particular field - he certainly never refers to any...
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Old 1st August 2003, 01:01 PM   #220 (permalink)
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Quote:
Originally posted by SDB
Cem

Apologies, I wasn't ignoring you. You're absolutely right, they are completely contradictory.

All the best

Simon
So was Mycroft misquoting you?

Cem
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