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Old 27th July 2003, 05:15 PM   #1 (permalink)
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Mass of car, cornering and braking, without the bickering.

So, hopefully we move forward.

Without pointless bickering.

A vehicles' wheels on the move will have some distinct types of weight/forces acting upon them, the first is the 'natural' weight shared by each wheel, at a constant speed this remains [if aerodynamically neutral] this is basically the weight of the car when stationary, you will have seen this on some tests as figures presented like these... F/R 55/45.

That figure really only 'works' on a staionary car.

Another force is the aerodynamic one, I hate the term aerodynamic as it is so 'wrong thinking' and causes, by its use, much misunderstanding.

For example many people have an immediate image when they hear or see this word, many will see the section of a wing with little flow lines around it... I bet that is indeed what many of you saw in your minds eye, now do me and yourself a favour, try to entirely remove that image from your thinking here.

I'll help you a little and at the same time destroy perhaps one of your most cherished pillars of wisdom.

Get in your car and go for a drive, wind the window down and ensuring it is safe to do so at about 50mph, stick you hand out, fingers out-stretched [but closed] now rotate it... yep it behaves just like you would imagine a wing would do... but your fingers and palm are not really much of a copy of that image in your minds eye is it!

The only benefit that the wing section provides is to be more efficient at pushing air downwards providing lift, that along with the fact that that shape can also be modified by further 'little wings' called flaps.

All vehicles even carbunculate warts like Subarus' [sorry Simon, couldn't resist ] will have a tendency to try to behave like a wing.

The front will be forced up just a touch, the rear will take more weight, the rear spings depress and the air at the front acts on even more of the underside of the car... keep going and you will flip.

To understand the force that does this go to the 'Ekranoplane' thread from a while back.

But despite this it is possible to force an apparent weight to be placed on the car wheels.

The third major aspect is very much forgotten by the many.

As this thread has shown by the numerous 'incredulous' posts to my simple and correct statement that I hope we have in the back of our minds.

This third aspect is weight transfer, successful use of any cars power means that the power has to be put to good use, now if you put 1000lbs of real torque through a huge tyre that has only enough weight to take 300lbs of torque before spinning then your power has been neutered, by applying weight [by whatever means] to that tyre you gain traction, this is simply a ground pressure phenomenon.

Now, too much weight transfer in a turn will also be detrimental to the performance as it will force the tyre to use much of its quotient of adhesion in just keeping to the line chosen, leaving little for the forward motion, so again the applied power overcomes the limit.

If there is one attribute that makes the best of weight transfer it is this... SMOOTHNESS.

This is one of the least broadcast but the most important attribute that any suspension can acquire.

That's a start.
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Old 27th July 2003, 05:17 PM   #2 (permalink)
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SMOOTHNESS = ROADHOLDING

On the face of it this seems such an odd thing to say, we all believe our suspension operates smoothly we 'feel' the wheel move up and down absorbing the road contours and with that big spring and damper acting against the weight of the car itself it appears entirely counter intuitive that there could any real real jarring and judder during its operation.

Every respect this 'belief' is wrong... in fact I will go so far to say that you would be hard pushed to be more wrong.

We'll take a look at some of the components that cause this lack of smoothness.

We start with one of the biggest components in the suspension, the Coil spring, remember that a Coil spring is just effectively a wound Torsion bar and that is its downfall, many manufacturers do not treat these springs to a final piece of 'tempering', when we wind a piece of steel so that it behaves as a spring the process will cause stresses within the material itself these will mean that in places both the incremental rate and displacement are uneven, this happens on every coil spring without a single exception.

To have springs like that on any car will reduce its performance and worse still if the springs are not re-tempered they will over time sag.

This final tempering has a name well known to many of us, for all the wrong reasons... they are said to have been 'PRANG'D' and that is pretty close to what happens to them, the manufacturer at the last will strike them with the full anticipated load that they will ever have to endure for just a moment, like they had been struck with a huge sledge-hammer.

This single trick re-stresses the springs perfectly, but not all evenly, after being prang'd the springs will all be slightly different in height and have slightly differing rates now the manufacturer can go 2 ways after this.

First he can match them all in pairs for height, this is the most common approach, it is cheap and easy but not perfect, these springs may be that same height and will not sag but will almost certainly of different rates!

The better and much more expensive way is for the manufacturer to match the springs for rate [another labour intensive operation] and then supply a shim to sort the mismatch in height.

If you pay about £200/250 for a set of 4 springs then you will almost certainly getting the former or even un-prang'd units, if you are paying £400/500 then you are getting the real Mc Coy.

The difference is that properly 'matched for rate' springs will give you far greater cornering speeds. [providing you do all the other things that such wonderful pieces of metal need]

That is enough this morning, I am off for a drive in my Soarer, the only car that ever came from Toyota with properly prang'd and 'matched for rate' springs as standard.
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Old 27th July 2003, 05:18 PM   #3 (permalink)
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So, we are now aware that although most springs are created equal they do not necessarily remain that way.

In response to SDBs concerns I am sure that you won’t rush out and change your springs tomorrow for Prang’d ones

Let’s look down the scale of things and the next item to attract our attention is the ARB [anti-roll bar]

The ARB is frankly a damned nuisance for the suspension designer as far as fundamentals go, its effects can be less than helpful sometimes and a real boon at others.

We all should know its’ function so we won’t dwell there but to my mind on fast road cars the only place where rose jointing would be of benefit is in its connection to the lower arms.

I couldn’t be bothered to go that far myself so just bought some metalastic bushes for my car from Oz.

Along with new bushes where the ARBs fix to the bodyshell this made a huge difference to the manner of their operation, they remain supple but everything is now working ‘earlier’ [less compliance] and again it all works as a piece, there is smoothness to its operation, you don’t have quite so much slack which can cause a slight slap as it ‘catches up’.

Tightening up the operation of the ARB may just be one of those cheap mods that make a difference, the state of some that come off a 5 year old car!

Go for the cheap and hardest polybushes they’ll cost you 20/30 nicker and a Saturday of cursing and swearing Try to use the factory body fixes/bushes, they will cost a bit more.

Grease, get yourself off to a Chandler, if you live near the coast or an inland waterway/canal you will have one nearby, you ask for a tub of Propellor grease, this is the stuff that is smeared on to any thing that is subject to ‘wash’ this stuff is tenacious and can easily last at least one Winter in the wettest of places, when re-assembling any thing with that has a rubber/ metal interface and is subject to water splash then this is the only stuff to use. Try to get the Evinrude Multi-Purpose with Lithium… not cheap!

If your suspension has grease points you can also buy a ‘wash-proof’ equivalent of the one you would normally use, do it!
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Old 27th July 2003, 06:47 PM   #4 (permalink)
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Mycroft

Quote:
by applying weight [by whatever means] to that tyre you gain traction, this is simply a ground pressure phenomenon.
One thing to make clear here is that there is not a performance gain if weight (mass) is added that the added demand on the tyres will be greater than the increase in grip they are provided. Adding load through downforce is very different and creates a direct benefit with only the negative of drag - which can be directly countered with horse power alone.

Quote:
Now, too much weight transfer in a turn will also be detrimental to the performance as it will force the tyre to use much of its quotient of adhesion in just keeping to the line chosen, leaving little for the forward motion, so again the applied power overcomes the limit.
Mycroft, I don't want to insult you by mis-understanding what you mean by this and replying, so I think it would be worth you explaining exactly what you mean by "it will force the tyre to use much of its quotient of adhesion in just keeping to the line chosen". I also think this is a very valuable and interesting part of the topic.

One final thing.

It is important - in my humble opinion - to clear up the actual subject of this thread.

Does adding weight to a car increase or decrease its potential cornering performance.

The answer is that it decreases it.

The reasons are (simply put). Doubling the weight on a tyre, does not double it's grip. So any extra mass that needs to be accelerated will not add enough grip to the tyres to cope with it.

Downforce is different in that it does not add mass that needs to be accelerated, merely increases the force almost free of charge. The only real cost is drag.

All the best

Simon
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Old 27th July 2003, 06:49 PM   #5 (permalink)
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PS..
(sorry forgot).

Any increase in performance by using (as near as possible) perfectly match springs will be negligible, rather than "far higher cornering speeds" suggested.
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Old 27th July 2003, 07:23 PM   #6 (permalink)
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I think you may have missed the point.

Simply Matched springs are good, but as you say ALONE they will not really give any noticeable advantage.

Hence the further proviso in the text.

To quote the passage as intended:-

''The difference is that properly 'matched for rate' springs will give you far greater cornering speeds. [providing you do all the other things that such wonderful pieces of metal need]''
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Old 27th July 2003, 08:21 PM   #7 (permalink)
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''Mycroft


quote:
--------------------------------------------------------------------------------
by applying weight [by whatever means] to that tyre you gain traction, this is simply a ground pressure phenomenon.
--------------------------------------------------------------------------------



One thing to make clear here is that there is not a performance gain if weight (mass) is added that the added demand on the tyres will be greater than the increase in grip they are provided. Adding load through downforce is very different and creates a direct benefit with only the negative of drag - which can be directly countered with horse power alone.''


Why take only part of the sentence? Removing the context is as bad as mis-quoting me. the whole passage reads:-
''This third aspect is weight transfer, successful use of any cars power means that the power has to be put to good use, now if you put 1000lbs of real torque through a huge tyre that has only enough weight to take 300lbs of torque before spinning then your power has been neutered, by applying weight [by whatever means] to that tyre you gain traction, this is simply a ground pressure phenomenon.''

The passage read as a whole points out quite clearly what you say only more succinctly.


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

quote:
--------------------------------------------------------------------------------
Now, too much weight transfer in a turn will also be detrimental to the performance as it will force the tyre to use much of its quotient of adhesion in just keeping to the line chosen, leaving little for the forward motion, so again the applied power overcomes the limit.
--------------------------------------------------------------------------------



Mycroft, I don't want to insult you by mis-understanding what you mean by this and replying, so I think it would be worth you explaining exactly what you mean by "it will force the tyre to use much of its quotient of adhesion in just keeping to the line chosen". I also think this is a very valuable and interesting part of the topic.


We have 'done' slip angles, adhesion, static friction and a good few others before, may I suggest the search button?
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Old 29th July 2003, 12:38 AM   #8 (permalink)
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Quote:
Originally posted by SDB
Doubling the weight on a tyre, does not double it's grip. So any extra mass that needs to be accelerated will not add enough grip to the tyres to cope with it.
Hi Simon,

Nice to have you posting here, especially on a thread like this. You have undoubted levels of experience and expertise on this field, so I'm very interested to hear of your opinions.

(for those who don't know, SDB is the webmaster of Scoobynet and holds the current world record for the longest ever powerslide)

I've quoted the above. Does this mean that for maximum grip efficiency, a tyre must require a minimum weight upon it? I ask this when thinking especially of cars like the Caterham which (correct me if I'm wrong) rely mostly on rudementary aerodynamics. It's grip on the road is determined by it's overall weight which, by common estimations, must be minimal? Does this in effect create a negative effect?

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Old 29th July 2003, 11:31 AM   #9 (permalink)
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Hi Cem

Thank you for the kind words.

Tricky one to answer in a short reply, but I'll give it a go.

A tyre produces more grip, the more load you put on it (up to a point - but a point way beyond anything a car will produce in normal circumstances).

Every bit of mass in a car (whilst it is cornering) has to be accelerated towards the inside of the turn (pompus way of saying "stopping it from just shooting off the outside of the bend") by the tyres. So in effect, the laws of physics are pushing the mass of the car outwards, and the tyres are pushing it back inwards.

Now...

If you have a car which is set up so that it's mass can be resisted in a turn to the point where you'll be pulling 1G, then the tyres have enough load on them to resist all of the mass up to that lateral acceleration.

If you then add mass to the car, the tyres will produce more grip, but not enough extra grip to resist the extra mass. So the car now grips more, but it has more mass as a relation between it and the grip.

Not sure if that's covered it... If not, ask me again and I'll try to think of it from another direction.

All the best

Simon

PS. Sorry for the delay in responding, I was travelling back to blighty
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Old 29th July 2003, 12:17 PM   #10 (permalink)
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Sorry... just realised that's not clear at all!!

OK.. With more mass on the car... the TYRES grip (not that car - as I stated above) more, but not enough to resist the extra mass, so the car as a whole grips less.

So with the Westfields, etc... One of the main things they rely on in order to produce their performance is the lack of weight. They are then able to use decent suspension and tyres to exploit that further.

Cheers

Simon
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Old 29th July 2003, 04:13 PM   #11 (permalink)
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Just had another thought as to what you may be asking...

Quote:
Does this mean that for maximum grip efficiency, a tyre must require a minimum weight upon it?
What I think you may be asking here is this.. "When a car corners, is the idea to get as little of the cars weight on to the tyres as possible?" or "Does the tyre with the least weight on it perform the most efficiently".

In which case, no. The more weight you can get on a tyre the more grip it will produce, so in a bend, the outside tyres are the ones producing the most grip.

But... Because "when you double the load on a tyre, you less than double the grip", the idea is the *share* the weight of the car as evenly as possible.

When stationary (taking one axle), the inside and outside tyres support 50% of the load (let's say).

When you corner, some of the load on the inside tyre is transfered to the outside tyre. So in effect, the inside tyre will produce less grip, and the outside tyre produce more.

Due to the fact that grip increases at a lesser rate the more load you add, you end up losing more grip from the inside tyre than you gain from the outside tyre.

This is why the "roll-couple-distribution" is such a vital part of the handling of a car. This is the ratio of roll resistance between the front and the rear and is affected (by a dramatic degree) by the roll bars (almost every other part of the suspension also, but directly by bars).

Imagine a car with no roll resistance (otherwise termed as roll rate - high rate being high resistance) in the front and absolutely solid (effectively 100% roll rate) at the back.

When you went round a corner, the car would roll at the front, and in doing so, left the inside rear wheel as it toppled, like a table with one leg shorter than the other 3.

What has happened here is that 100% of the load on the inside rear tyre has been transfered to the outside rear tyre (actually, some to the outside front, but it's not important to this) which means you have greatly reduced the grip on the rear end of the car.

So.. by altering the roll-couple-distribution by tiny amounts you can alter the ratio of grip between the front and rear during cornering.

All the best

Simon
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Old 29th July 2003, 06:29 PM   #12 (permalink)
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Quote:
Originally posted by SDB
...."when you double the load on a tyre, you less than double the grip"
That is not correct! That only applies after the tyre has reached its' optimum load/adhesion break point!

Until that point the exact opposite is the case!

Cem, there is indeed an ideal and what you say is correct.

But in reality the vehicles weight remains largely constant and for this weight there is an ideal 'size for function' tyre choice.
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Old 29th July 2003, 06:46 PM   #13 (permalink)
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Quote:
Originally posted by Mycroft

------------------
Doubling the weight on a tyre, does not double it's grip. So any extra mass that needs to be accelerated will not add enough grip to the tyres to cope with it.
------------------

That is not correct! That only applies after the tyre has reached its' optimum load/adhesion break point!

Until that point the exact opposite is the case!
Mycroft

Do you have ANY evidence as to this being the case as the world of vehicle dynamics engineering relies on quite the oposite?

Could you also explain exactly what you mean by "optimum load/adhesion break point!"?

Cheers

Simon
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Old 29th July 2003, 06:50 PM   #14 (permalink)
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Read this:-

http://www.millikenresearch.com/rcvd.html
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Old 29th July 2003, 06:54 PM   #15 (permalink)
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Oh come on Mycroft, don't be like that.

Surely you have this knowledge at your fingertips and would like to share it with us?

Otherwise there is no way to have a discussion with you.

Instead you might as well reply as you have done above to every other thread asking for information.

All the best

Simon
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Old 29th July 2003, 07:02 PM   #16 (permalink)
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Well, those books and papers will provide all the 'evidence' you ask.

I know of a few others but those are the most accessable.

Would you be able to point me to any original published work that confirms your proclamation?
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Old 29th July 2003, 07:10 PM   #17 (permalink)
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Mycroft. It was (as I understood it) your intention for this thread to be a more helpful one than the last. I am trying to produce just that with information and input. If you are able to provide this forum (and me) with some information, then please carry on. It may well be that I have mis-understood what you meant by your last post, in which case, the insights you would provide would aid everyone.

In the absence of the above, if anyone requires more detail information on tyre producing less than double the grip when you double the load, please let me know. There are BOUND to be a number of graphs / technical works on the net somewhere that would provide data, etc.

Perhaps Mycroft you would be good enough to answer the second part of my question on what you meant by the phrase you used?

If not, I'll assume you are unwilling to contribute.

All the best

Simon

ACBSFTC,IANITSBSTYHSCTTMWBSADDFTWG.NOTTIIUIIDTPOTC AIATC(ABAA).BGAWAIWBATDTIMTCFPBTT.
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Old 29th July 2003, 07:14 PM   #18 (permalink)
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brief search on google "tyre load grip graph" produced the following page (about third one down)...

http://autozine.kyul.net/technical_s...handling_3.htm

All the best

Simon
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Old 29th July 2003, 07:19 PM   #19 (permalink)
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Sigh. I was interested in this thread.

Mycroft if you do have the proof of your claims at hand (and I'm not saying that you don't, I'm just interested in finding out), could you actually direct us to the actual bit on the link you posted (or in the books you mention)?

When pressed you do seem to often just respond with "well its all there if you can be bothered to look" type statements, and then just try and ridicule people when they cannot find the information. Would it not be better just to provide the information from the start?

Intrigued.
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Old 29th July 2003, 07:19 PM   #20 (permalink)
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SDB

Which confirms exactly what I have said!

Any graph that shows an angle of greater than 45deg. supports my statement.

Thank you.
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