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Discussion Starter #261
Keith_C said:
Cool - cheers Simon. Would be interesting to know :)
As would your answer to my questions... this one would be a good start...

''So I ask you simply this, your 'not doubling' isn't in that little grey area into which we Engineers put all our little 'instrument and 'inconvenient' little failures to 'close' all the calculations is it?

I certainly hope not Simon as that would be at best disingenuous and at worst the most dreadful deceit imagineable and would certainly destroy any credibility you may yet retieve from this thread.

So give me the simple assurance in your next post that you are not playing fast and loose with the truth like that.''



In white!...
 

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Oops!!

Just remembered, I forgot to talk about slicks, then someone reminded me, then I forgot again :D

It's not really worth the wait I'm afraid...

The reason slick behave in the same way (as the description of treaded tyres) even though they don't have tread blocks is that different areas of the contact patch have different loads, different skew, etc, etc. The reason I chose to talk about treaded tyres in the example is that it's much easier to imagine.

All the best

Simon
 

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Discussion Starter #263
Simon it seems that you are more concerned with not losing face than telling the truth, in the absence of any answer from you I will have to continue to de-bunk your posts.

You have been caught out.
 

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SDB said:
The reason slick behave in the same way (as the description of treaded tyres) even though they don't have tread blocks is that different areas of the contact patch have different loads, different skew, etc, etc. The reason I chose to talk about treaded tyres in the example is that it's much easier to imagine.
Simon,

Are you saying that even though a slick is "smooth", that there is actually kind of tread to it, i.e. the contact patch is not consistent? I hope you understand what I mean, excuse the ignorantly non-technical description!

Cheers,

Mark.
 

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Hi Mark

I *think* i get what you're saying...

it's easy to imagine the contact patch as a static object which just sits there. Then you move on to thinking of it as something that stretches and skews - but is still fixed in one place as an entity of it's own.

But the contact patch isn't a fixed entity, it is constantly "evolving" as new rubber meets the ground, forces act on it, imperfections in the tarmac, etc, etc. So it's almost (although please don't picture this as what a contact patch might be like) you got a sheet of thin rubber and screwed it up in a ball, then twisted it around (like draining a cloth) and then pressed it in to the ground. The amount of pressure each part of it exerts on the ground would be different. Then twist it even further whilst still pressing it in the ground and the bits that were "sticking" most would stay where they were, and the rest would stretch and skew around it, then changing which bits are exerting the most pressure, etc. This kind of thing is happening continuously at the contact patch.

That's probably a crap explanation, so let me know if it's not clear.

Cheers

Simon
 

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Discussion Starter #266 (Edited)
The Velcro analogy I posted is closer to the truth, just imagine an 'male' piece of Velcro shaped like the contact patch and slap it onto a larger patch of 'female' material... the faster you do it the less 'grip' [that dreadful word] you attain.






You won't forget this will you Simon... still waiting.

''So I ask you simply this, your 'not doubling' isn't in that little grey area into which we Engineers put all our little 'instrument and 'inconvenient' little failures to 'close' all the calculations is it?

I certainly hope not Simon as that would be at best disingenuous and at worst the most dreadful deceit imagineable and would certainly destroy any credibility you may yet retieve from this thread.

So give me the simple assurance in your next post that you are not playing fast and loose with the truth like that.''
 

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I'm still on the grip vs load thing and it seems graphs are easier to understand the the level of maths needed here. so
http://phors.locost7.info/phors21.htm
has a graph using some "Magic Formula" maths which shows the increase in cornering forces for an increase in vertical load

The horizontal axis measures slip in percent. The deep axis, going into the page, measures Fz thats vertical force from 5 KiloNewtons, nearest us, to zero in the back. The vertical axis measures the result of applying the formula to our model tyre, so it's longitudinal force-force of launching or braking ie accceleration and deceleration in Newtons
 

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Discussion Starter #270
Excellent...

So this makes my question even more relevent...

''So I ask you simply this, your 'not doubling' isn't in that little grey area into which we Engineers put all our little 'instrument and 'inconvenient' little failures to 'close' all the calculations is it?

I certainly hope not Simon as that would be at best disingenuous and at worst the most dreadful deceit imagineable and would certainly destroy any credibility you may yet retieve from this thread.

So give me the simple assurance in your next post that you are not playing fast and loose with the truth like that.''
 

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Discussion Starter #271
Simon, isn't 'ground pressure' bloody irritating!?!

ROFLMAO :D:D:D

Oh dear, oh dear, oh dear!

Quote from Mycroft [regularly]

''It's just a ground pressure thing''

So please now Simon... answer my question:-

''So I ask you simply this, your 'not doubling' isn't in that little grey area into which we Engineers put all our little 'instrument and 'inconvenient' little failures to 'close' all the calculations is it?

I certainly hope not Simon as that would be at best disingenuous and at worst the most dreadful deceit imagineable and would certainly destroy any credibility you may yet retieve from this thread.

So give me the simple assurance in your next post that you are not playing fast and loose with the truth like that.''
 

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Ok I'm prepared to admit that even with a HND in Electrical engineering which is roughly equivalent to A level maths I do not understand all the formula's in the link and can't fully see how this translates into the relationship in the 3D graph.

What I do understand is what the Prodrive engineer is saying.
The tyre may or may not behave as a proportional Newtonian device at very low load levels - a few tens of kg - but I don't care; by the times the loads have got that low they are not influencing the car any more and my attention has transferred to a more heavily loaded wheel. Because of the (surprisingly complex) wriggling about in the contact patch then the non-linearity sets in early, especially on road tyres.
I find that quote straight forward.

Lets dwell on this bit.
the non-linearity sets in early, especially on road tyres
So the relationship between load and"grip" is not linear then and its not lnear from very low levels, levels so low that it does not matter on road cars even to one of the worlds top motorsport companies.

So if that's the case the lighter the better for the car then surely or am I just being thick?

Perhaps Peugeot know different and that's why Subaru are loosing ground this year? ;) But then again its perhaps the Peugeots are smaller, more agile, change direction quicker.

Right or wrong that's just my take on whats been posted.

Lee.

PS.

Thanks for the Welcome Cem. I'll have to blag a ride in your new Skyline the next time we run into each other, I rather enjoyed my laps in your old one. :D
 

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Discussion Starter #273
Originally posted by logiclee
Ok I'm prepared to admit that even with a HND in Electrical engineering which is roughly equivalent to A level maths I do not understand all the formula's in the link and can't fully see how this translates into the relationship in the 3D graph.
Don't worry, you are in good company, Simon has been doing quite well with his Gold, Junior Backstroke Proficiency Medal from the Orpington Public Baths... and see how far he's got in the last few days... :D ROFL

Originally posted by logiclee
So the relationship between load and"grip" is not linear then and its not lnear from very low levels, levels so low that it does not matter on road cars even to one of the worlds top motorsport companies.
That is his rather watered down version of the truth, in reality when you put this into a Cray or a Fujitsu Goliath, all those little bits i have referred to make up the difference, someone asked a good question a little while back, it is the question that on page one or two of this now hopelessly ragg-ed thread would have been answered.

Originally posted by logiclee
So if that's the case the lighter the better for the car then surely or am I just being thick?
The same money spent on the lighter car will get you a faster car than if that money was spent on the heavier one, that has never been in doubt at anytime.

Originally posted by logiclee
Right or wrong that's just my take on whats been posted.
An honest and clear post and that is like a breath of fresh air in here.

Good on'yer

----------------

Don't let the joke at the front of this answer rile you, it is just my posting style.
 

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Hi Lee :)

Right or wrong that's just my take on whats been posted.
Absolutely, and I think you're in the company of all but one of the people reading this thread :)

Shall we take this in a new direction now? (question, not a demand!! :D)

The cool thing is, that almost all areas of vehicle dynamics can stem from this very subject (grip less than doubles, when ..... - I've typed that too many times in this thread :D), so we could go on to any number of different subjects to expand the topic.. or tell me to shut up and continue if there's still more to be discussed on this one :D

Some fun ideas might be (some may be obvious to some, but not others, etc)...

- What would you change on a race car set-up if you were caught out on a dry set-up when it started to poor down? (apart from your underpants!! :D)

- How could you get a car to lean INTO the corners rather than away from?

- Why does tramlining happen? - Only my personal theory on this, and by tramlining I mean the tyres wandering due to contours in the road.

- Bump Steer

- Whatever you like - Fingers crossed I'll know SOMETHING about it :D

All the best

Simon
 

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If there's something I've gained from this thread ...


it's that I REALLY want to drive both a Merc SL55, and a Caterham R500 :D:D
 

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Discussion Starter #276
Simon,

I think you are a spent force here, you are only enthralling the MKIV guys, why don't you go there and and be feted as a hero, they like faulted logic there.

Damned by faint praise by even you own mate 'Damian Harty'
 

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Discussion Starter #277
Originally posted by SDB
What would you change on a race car set-up if you were caught out on a dry set-up when it started to poor down? (apart from your underpants!! :D)
[yawn, no relevence to raod cars, never mind 4WD]

- How could you get a car to lean INTO the corners rather than away from?
[We've done active, I have an Active car, have worked on them, know more in real terms than you ever will]

- Why does tramlining happen? - Only my personal theory on this, and by tramlining I mean the tyres wandering due to contours in the road.
[A good idea]

- Bump Steer
[A Subaru fault, nuch more than a Skylines]

 

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Simon,

Thanks for the (slick) explanation earlier (I know it was a bit of an aside anyway), I understand what you mean - I appreciate the "Early Learning Centre" example, that's just about my level :D - basically I'm the other end of the "know it all" scale to claiming to know more than the chief engineer of Prodrive ;)

Cheers,

Mark.
 

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Discussion Starter #280
I think for the sake of clarity and ease of future searches that any thread on tramlining etc should really go in the Brakes/susp/ wheel/ tyres section.
 
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