DrEvil

Interesting thread..

But Simon DB - you haven't answered Jerry B's question about greasing eels.. I'm intrigued

KF

rovo: Your quote "bigger tire for the same load --> bigger contact area --> lower contact pressure --> higher coefficient of friction" has piqued my interest.

The link is not logical. Why does a lower contact pressure create a higher coefficient of friction?

Let me be clear. You are stating that the coefficient of friction (not the frictional rection itself) is inversly preportional to the reaction force between the surfaces?

One would have thought that the harder the tyre was pushed into the road the more it keyed into the surface, and the higher the coefficient?

Just to show that I know nothing. I preferred the RE010's in the dry, and the Goodyear Eagles in the wet.
KF.

Stef

Just out of interest, but I've not seen any Bridgestone marketing that states the S0-3 is the new high perfromance flagship replacement for the S0-2. Is it? Or is it just a new decent all-round tyre?
Did we just presume it was a step up because of it's name?

Stef.

Lambo

After starting this thread with a fairly simple question it seems that S02's are the tyres for 16" rims, and my local tyre place ( Chiltern Tyres in Hazlemere ) can do S02 Pole Positions for 97 quid fitted which is a very good price.

So what have I bought ?

A set of 17" P1 wheels with Pirelli P-Zeros !! They look fantastic, the car drives much better with hardly any of the tyre roar I got with the RE101's and they only cost me a bit more that the 4 new tyres I was going to buy.

I am soooo happy.

Lambo


PS Just a quick question, do I need a new set of wheel nuts for the OZ rims or are the std MY99 nuts OK ?

Interloper

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Lambo:
<B>Is anyone using these ? I would be grateful for any feedback owners have.[/quote]

Ben Lovejoy from the ringers list here - using the handle 'cos I don't drive a Scooby. :-O

Just a quick word of warning: on an MX-5 at least, S02s and S03s don't mix well. Although experiences seem to differ, on my car at the Ring the S03s are grippier - when I had S02 front/S03 rear I was getting understeer for the first time ever. With the wheels swapped, I was getting unprovoked oversteer instead of four-wheel drifts.

This definitely appeared to be down to the tyres as the S02s were also very new. I wanted S02s again but nobody seemed to have them any more - only S03s.

Ben

SDB

**IMPORTANT** - I am editing this post as I have just realised I put in a "less" when I meant "greater", apologies.
----------------------------------

rovo...

come to the front of the class, and bend over, because you're about to get a thorough whipping sonny!!!!

I'm affraid your comments are a classic example of inexperience filling in the gaps between accurate data being taken out of context.

I will explain..

(first of all, let re-iterate AGAIN, that the weight / tyre pressure formula is NOT an EXACT science, and that tyre construction come into it as well as tread layout, etc.)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
The basic principle is that if a tire is relatively lightly loaded the friction coefficient is a bit higher (so you can take for example corners at a higher speed).
[/quote]

First of all, this is not relevant to the argument, but secondly (and way more importantly) you have mis-understood this.

The coefficient of friction is NOT higher with less weight, but it is RELATIVELY greater *per unit of weight* than with heavier loads.

This means that if you put 20Kg on a tyre it will produce more grip than if you put 10Kg on it, but not as much as double.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
The bigger tires (diameter and/or width) are able to withstand a higher load (see the tables of the tire manufactures).
[/quote]

This is ABSOLUTELY true (in most cases), but that does not state anything about pressures or weight. It may occur to you, that you are able to run lower pressures on some wider tyres, which means that the contact patch will be increased in area. This does not mean that the width of the tyre increases the area, it means that the lower pressure does.


<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
And for the same (vertical) load therefore are able to generate higher cornering forces.
[/quote]

The only thing that affects a car (in normal circumstances), excluding aerodynamics is the road/tyre interface... so a wider tyre alone does not produce more of anything, a larger contact patch DOES. So we are still not into any information about contact patches relating to wider tyres.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
The link being: bigger tire for the same load --&gt; bigger contact area --&gt; lower contact pressure --&gt; higher coefficient of friction.
[/quote]

This is all true, except for the "--&gt; bigger contact area" as there is nothing in this post to say that wider tyres = bigger contact area. The reason for this is because it is not true!

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
Tyres, suspension and handling
John C. Dixon
"An increase in contact area gives a higher limiting force - this has contributed to the trend to very wide racing tyres with some tendency in the same direction for passenger cars."
[/quote]

This is the main thing you have taken out of context. If you had a narrow tyre and wanted to increase the contact patch area, you would need to lower the pressure. You can only lower it so far until the tyre distorts to the point where it is useless. Before you get to this point, you need to opt for a wider tyre constructed to cope with lower pressures.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
Race car engineering & mechanics
P. van Valkenburgh
"Tire size is the most apparent criterion in selection. It's obvious that with all other factors such as tire compound and pressure being equal, the more rubber on the ground, the greater the traction. But another advantage is that the greater contact area permits the use of softer or stickier compounds. Not only is there more rubber to wear away for the same tire mileage in a race, but there is a larger surface area to dissipate the greater heat generated. There appears to be no basic physical limit to the overall width of a tire tread."
[/quote]

Again, this tells us NOTHING about the way you calculate a contact patch area. In fact, it only says that the more rubber you get on the ground, the more the tyres can cope with.. which is ABSOLUTELY accurate.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR><B>
The next time you want to say "nice try", you better back it up with some substantial information .
[/quote]

LOL

Either that or I could do what you did and quote a load of irrelevant information from well known sources and then just make wild statements about the subject we were originally discussing!!!

Bare in mind, that I have never said that a wider tyre does not increase grip. Merely that it's width does not feature in the calculation of it's contact patch *area*.

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

I'll give you some quotes now... (and mine will directly relate to the subject, not be something that sounds similar)..

Car Suspension at Work (kindly lent to me by Mike Nunan, and received on Thursday)
Jeffrey Daniels
“<B>Tyre: is wider really better</B>
….
What actually happens is that, beyond the optimum size, the contact patch becomes shorter and wider. The total contact patch area is, more or less, the weight of the car divided by the tyre pressure, so there is no more ‘rubber on the road’, ….”

--

I would also draw your attention to the following explanation with all the formulas which CLEARLY states that the formula for calculating a tyres contact patch is..

area = force / pressure

rovo

KF, you are right, if you increase the vertical load on the tire the absolute cornering/braking force will increase. But if you increase for example the vertical force by 20% the cornering/braking force is increase by a little less, lets say appr. 18%. The coefficient of friction is the cornering/braking force divided by the vertical force, so for the increased vertical load the coefficient of friction is actually a little less. This aspect is for example important when cornering. When cornering the weight is being transfer to the outside wheels and the inside wheels loose the same weight. But the outside wheels gain lesser cornering/braking force than the inside wheels are loosing. Therefore it is very important to have as little as possible weight transfer --&gt; low centre of gravity and wide track.

Simon, damn now I have to start reading your answer .

Robert

Dave T-S

SdB
Very impressive - so calculate the pressure on your kitchen floor when your lunch is on the table LOL

PS - i'm bored with this one now. I did email Bridgestone (twice) for their comments but they can't be ar5ed to respond....

[This message has been edited by Dave T-S (edited 07 July 2001).]

Ian Cook

Im not getting involved in all this technical jiggery pokery !

Stef ! I think that may be the case, remember the S-02 wasnt a very good tyre, the S-02 Pole Position was the flagship model, 2 completely different tyres !

Also Bridgestone do/did NOT recommend the S-02 PP in 16" sizes on Imprezas because of the higher levels of stress put on the sidewalls (just to throw that old one back in the works )

SDB

Dave LOL!

The pressure of my kitchen floor has to be HUGE to support the weight of my lunch!

"I'm bored of this now"...
transalted using bablefish.com "DaveTS --&gt; English" =

"I'm sorry.. I seem to be COMPLETLY wrong. Please accept my humble apologies, I'll go back to the muppet show and start a thread on the contact patch of egg when pressed onto my face!!" Sorry.. couldn't resist!

All the best

Simon

SDB

apologies... just realised I'd made a couple of typo errors, so I've edited my post above (the long one)

Dave T-S

SdB

LOL

Translated with Davelfish &gt; SdBspeak:

I'm a Gemini, I get bored easily, just cos you are the bloody webmaster doesn't mean I have to kiss your **** mate

Dave T-S

Err.....my logon appears to be locked - wonder why that is...

bren simpson

Just thought someone maybe interested to know that Ive one set of new Goodyear Eagle F1 205 50 16s for sale for Ł240.

Id advise you to be quick if your interested!

Bren

Dave T-S

SDB

LOL @ dave

rovo

Simon,

I have read your answer (the long one), but the information you provided also leaves room for discussion. The best thing I can do is to send an e-mail to the tire manufacturers to see if they want to answer the question. I believe Dave T-S already tried this, perhaps if more of us do they are inclined to answer.

And perhaps this is the wisest thing I can do before my logon is locked too (somebody has got to be the wisest .

As soon as I receive an answer I will place it on the bulletin board.

Robert

rovo

Simon,

I have read your answer (the long one), but the information you provided also leaves room for discussion. The best thing I can do is to send an e-mail to the tire manufacturers to see if they want to answer the question. I believe Dave T-S already tried this, perhaps if more of us do they are inclined to answer.

And perhaps this is the wisest thing I can do before my logon is locked too (somebody has got to be the wisest .

As soon as I receive an answer I will place it on the bulletin board.

Robert

SDB

Nice one rovo, good idea.

It does seem strange however, that in the face of all this evidence and expert opinion, you still need further confirmation.

I've thoroughly enjoyed this thread, but I probably won't check back on it as often now as I feel it's run it's course..

however, maybe someone would email me if they find anything earth shattering that disputes the weight / pressure formula as I would *genuinely* be very interested indeed.

All the best

Simon

Jza

Reminds me of bleedin physics classes!!!

So - in summary

a) Some of you have way too much time on your hands - to be searching the web for tread/contact patch equation thingys is a definate sign of this!!

b) the S03 isn't a direct replacement for the S02 i take it - and theres an S04 tyre coming out that will be the successor to the much loved S02.

Is that right? When will the tyre be released??

Sorry to break off from the Albert Einstine wannabees thread stuff....

Jza

MatthewC

I'd like to say thanks to everyone here for providing me with some good info on a subject I have long fretted about

FWIW....
SimonDB has all the right equations. Noone has actually proved him wrong yet through rational debate (or perhaps as WM he has deleted those posts...). Pressure=weight/area is about as simple a physics equation as you can get. HOWEVER he hasn't convinced me that his answer is the most relevant to optimum tyre performance on a car.
Sure, adding width only changes the SHAPE of the contact patch at CONSTANT pressure. But as you say, you can run them at lower pressures. All tyres have an optimum (warm) pressure to give maximum grip on a smooth road - we need to know in what way this pressure varies with profile of tyre. NOBODY has given that info yet...

My intuition would be that the lower profile gives stiffness =&gt; should win. There's no equation to back this up here, but it seems the most likely reason that all experimental data of simply putting wider rubber on otherwise identical wheels tends to give you more grip.

COEFFICIENT of Friction:
This has been an interesting distraction! I think rovo summed it up best i.e. CoF drops as load goes up. This is a property of rubber tyres and the complicated way they distort to create grip. The side-effects are that, as rovo said, weight transfer reduces your overall grip, but ALSO that lighter cars WILL corner faster (all things being equal ). People often try to deny this, but it's true. However, I think you won't often notice the difference in most tests, as the other things are never equal!

Cheers all for the entertainment - I never expected this sort of thing on ScoobyNet

Mr Lovejoy:
As a fellow Mazda owner I was interested in your comments. Was your 'Ring lapping in the dry?

tut

They also don't go off as easily as SO2's when heated up.


Rich

That is the first mention I have seen of them not going off as soon as the SO2s. This is a problem, even on our much lighter Elises, and 12-14 laps of Knockhill is as many as you can do, before the handling starts to go off.

tut

tut

Stef

Good point. I just assumed that SO3s were naturally an improvement and replacement for SO2s. Maybe that is not the case. I had a full set on order for my Elise, but I could not wait any longer, so had SO2s fitted on Friday. My replacement car had POs on, and if the Scooby is anything like as bad as the Elise in the wet with these things on, then users have my sympathy.

For us they are bloody lethal, as anybody using them at a very wet Knockhill last week found out.

tut

bigmac

recently got S03's fitted on STi V4 4 door (tyre size 205/50 on standard sti 16 inch alloys)

Ł83 per corner.

200 miles done.

Very pleased with them.

Previously had the Pzeros. Performed OK, but the new SO3's are a lot better. Never had SO2's so can't comment on these.

regards, Mark.

Mickle

hey bigmac, I've just been quoted Ł116 per corner for the same size, am I getting ripped off or what! Anybody know a tyre place in Warwickshire that's cheaper?

rovo

I asked the questions below to several tire manufacturers and Vredestein were the first to answer.

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

Dear Sirs,

on the scoobynet bulletin board we are having an interesting technical discussion concerning the contact patch of a tyre with the road. The scoobynet bulletin board (http://bbs.scoobynet.co.uk/) is a meeting place for Subaru Impreza owners to exchange information. This bulletin board is based in England but has contributors from all over the world. The topic (http://bbs.scoobynet.co.uk/Forum11/HTML/001548.html) we are interested in is if the tyre size (diameter and/or width) influences the contact patch with the road, keeping all other parameters (tyre pressure, vertical load, etc.) constant. Some think the contact patch will stay (exactly) the same, others think the contact patch will increase.

Using the Hertzian contact stresses formulas (for lack of a better formula) the contact patch would increase when the diameter and/or width of the tyre increases, question is if these formulas within limitations can be applied for a tyre. All other documentation or books are not conclusive concerning this subject. I even went through all my study material from professor Pacejka, but unfortunately this also did not provide the answer.

Therefore my question to you as a tyre manufacturer does the tyre size (diameter and/or width) influence the contact patch with the road, keeping all other parameters (tyre pressure, vertical load, etc.) constant. I would imagine that with test results and/or finite element calculations you would be able to provide us with the answer to our question.

There is also another question I would like to ask you. In general the Bridgestone S02 Pole Position tyre is at the moment rated by most of the contributors to the bulletin board as the best tyre for the Subaru Impreza. At the moment the Bridgestone S03 Pole Position is also available, but practical information is still very limited. The tread pattern of the S03 PP tyre is completely different from the S02 PP. The S03 PP having the more classical tread pattern and the S02 PP having the "V-shaped" tread pattern. From your professional opinion how do the tread patterns influence the wet weather behaviour and the cornering in dry and wet weather?

On forehand I would like to thank you for answering these questions.

Kind regards,

Robert Vogels MSc

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

Dear Mr. Vogels,

Please find here the answer our Tyre Information Centre gave
to your question:


&gt; As a tyre manufacturer we are always glad to notice
&gt; that there are people who are looking very seriously to tyres. One of the
&gt; reasons for you is off course that the Subaru is a performance car for
&gt; which Vredestein by the way has perfect performance tyres.
&gt;
&gt; To answer your question, we assumed it is a size for
&gt; a Subaru Impreza and the outside diameter of the tyre has to remain the
&gt; same dimensions. When you fit a wider tyre than original, the contact
&gt; patch will hardly increase. The shape of the patch however will change
&gt; from long-small to short-wide. So the shape will change, an increase in
&gt; contact patch is hardly noticeable. So no winners in this discussion I am
&gt; afraid.
&gt;
&gt; A wider tyre does have a wider steelbelt and
&gt; therefore generate more lateral forces.
&gt;
&gt; Regarding the tread pattern, we can tell you the
&gt; following:
&gt; A "V" shaped tread pattern has a lot of advantages
&gt; to prevent aquaplaning and on wet surfaces but the same advantages you can
&gt; get with a lot of circumferential groves. On dry roads you like to have as
&gt; much as possible contact patch on the road. Therefore a low air ratio
&gt; (slicks) of the tread would be the best. Vredesteins own R&D department
&gt; has chosen for many products the "V" shaped pattern, because the relation
&gt; between water disposal and drift forces.
&gt;
&gt; Of course we have no insight as to how our
&gt; competitiors as Bridgestone choose their patterns. It is better to contact
&gt; them yourselves.
&gt;
&gt;
&gt; The best way to experience the effect of V shaped
&gt; patterns off course is to use Vredestein Sportrac W for your Impreza. You
&gt; will notice that it is a perfect Summer tyre that performs excellent under
&gt; the Subaru Impreza. We are very curious to your opinion while driving on
&gt; them. So let us know.
&gt;
&gt;
I hope to have served you with this
information and if you have any further questions please do not hesitate to
contact us.

With kind regards,
VREDESTEIN BANDEN B.V.

Jeanet van Kooi

millband

What an excellent thread! I've got S02PP's on original 15" rims ( ), and am v.happy with them, but they'll be due for replacement soon so I too am interested in opinions on the S03's.

However, I feel the technical discussion misses the important point that "V" treads on the S02's *LOOK* much better than other tyres!

A good performance tyre should make you want to park with full lock on so others can admire them - S03's don't seem to have the *wow* factor I'm afraid...

Steve

SDB

rovo

VERY well done! and VERY VERY well done to Vredestein for taking the time to answer.

Dave
I will accept apologies in cheque, master card or american express!!

Rovo
A final clarification would be to ask what factors *do* make a difference to contact patch area.

As the "hardly noticeable difference" is the "it's not an exact science as tyre construction does come into it" part of my argument, so it would be nice to clarify if indeed the contact patch area is a predominantly a function of load / pressure.

All the best

Simon

SDB

I've just read your post again rovo...

For a start off you have not stated clearly that it is the *area* that I am saying stays the same... and you have also said that "some think the patch will stay (<B>exactly</B>) the same.

This was never the case. If you read my posts, I was always very careful to state that this was not an exact science.

In addition, you have said that other references have not been conclusive on the subject. What was inconclusive about the two references I brought forward which clearly stated the EXACT information we were trying to achieve and the way in which it is derived?

Just thought I would point this out, as it's a slight bending of the truth, not that it really matters.

All the best

Simon

rovo

I received another answer to my questions. I take it it's from Pirelli. It seems that Simon is right for the radial tires and I am right for the bias ply tires. So again no winner Simon.

But at least I am happy that we are receiving some respons to the questions. Some tire manufacturers seem to take the scoobynet bulletin board serious.

-------------------------------------------
(The table is in Excel, if someone could tell me how to put it on this bulletin board?)

Good morning Mr Vogels.
I received your question and passed it to my colleagues in R&D.
Please find attached a small summary table I received from R&D; they
summarized the following data for some sizes (actual measurement data):
* Contact area (mm˛): it is the surface of rubber in contact with the
ground
* Total area (mm˛): it includes the parts in the footprint not in
contact with the ground (grooves, slots, etc.)
For each tire we measured the contact patch in two points at 180° from each
other.
As you can verify yourself, the first two sizes have different width and
aspect ratio but the same i.p. and basically the same load; please be
informed that the specs included (A1, A2, etc., B1, B2, etc.) can be very
different in terms of tire construction and materials. Yet the contact patch
area is more or less the same for both sizes. The same situation is found
for the second two sizes. The fifth size shows an inferior contact patch,
but its i.p. is slightly higher than the previous two, so maybe if we reduce
its pressure we would find a result in line with the previous (this datum we
don't have.)
From these figures we can infer that the extent of the contact patch seems
to depend only on load and inflation pressure, and does not directly depend
on tire dimensions; anyhow we don't have the formula calculating this
dependance.
Please bear in mind that this is surely true for the radial tire, which has
a steel belt package re-distributing the stress on the whole carcass; on the
other hand we expect the bias (crossply) tire to behave more in line with
the hertzian model, since the deformation is concentrated in the contact
area only.
I hope this answer is satisfactory for you, anyhow we remain available for
any doubts or questions you might have.
I wish you a nice weekend.

&lt;&lt;CONTACT AREA VS TIRE SIZE.xls&gt;&gt;

Vittorio Lanciaprima
Field Engineer, BFE-Consumer Products