rovo

Uhhhhhh Simon,

I have to agree with Dave T-S (is this a bad thing? ) on the tire size. On agricultural vehicles they put big tires (the diameter has the largest influence, not the width) to have a bigger contact patch and consequently lower surface pressure so they won't sink away in the ground. For the realitively small width increase of the tires for our cars, the effect will be very small. The parameters you described will influence the contact patch more.

But basicly Dave T-S is right.

SDB

LOL

Agreeing with Dave is never a good thing!! LOL.. but you are right about the agricultural vehicles..

and if you read up to one of my previous posts it says something along the lines of "this formula does not apply to mud / surfaces the tyre can sink into."

cheers

Simon

SDB

hmmm... difficult to know what to do for the best to be honest.

I'm just going to put up with them until they wear out, then fit something else.

I have a feeling they're going to get a lot better a they wear though as most of the squirm seems to be coming from the tread rather than the sidewalls. Althought the sidewalls *are* softer than S02s.

I think it's a case of putting up with them I'm affraid

Cheers

Simon

Dave T-S

SdB
Moi? Stubborn? Surely not!! You know me better than that. Actually, as it's you, i'm being generous and not too cantankerous.....

Re new S03's in the wet, I was surprised by how good they were out of the mould. I know they use silicone mould release agent or similar on them, but even so they were pretty good - but then i'm an ace in the wet hehe

As it's got my interest, I'm now doing some research on this myself....be in touch

MartinM

OK , a bit off topic, but get your head round this...

Go out to your car and put a chalk mark on the outide wall of a tyre where it touches the ground. Mark that point on the ground too. Push the car ( ) so that the wheel rotates once until the chalk mark on the sidewall is again on the ground. Measure the distance on the ground between the marks.

Now, take the wheel off ( ), put it at the first mark on the floor and, again, rotate it once. Make a mark on the ground again.

Are the second marks for each experiment in the same place?

Yes - 'cos the circumference of the tyre is the same ie the same amount of rubber has had to be contact with the ground for one rotation
No - 'cos the radius of the tyre when on the car is different to the radius when its not, due to the distortion/flattening of the tyre due to the weight of the car...so the circumference must be different for one rotation, so the marks are in different places!

...try thinking about a tyre with 2psi in it - it'll be very flat on the car, but very round when not on it. So what's the answer in that case????

PS Theoretical answers please, don't try this at home!!!

Triggaaar

Yes, will be the same. Radius may be different, but wheel is no longer round, so irrelevant. Now go and tell me what pads to use on my APs.

Jerry B

Ah, interesting, I thought....just take a look and see what people make of S-02s and 3s as I'm about to change out the RE010s - and then I found all this mental stuff about width having no effect on contact patch area!

All that aside, don't you guys always find new tyres squirm about a lot more than the old balder ones you just got rid of? I mean there's quite a bit of flex in a block of tread rubber 6mm long compared to 2-3mm (or less)on the old well-worn ones. I'm nearly always disappointed with the dry grip/handling of new tyres. Anyway, think I'll get the S-02s to be safe!...

Hoppy

At what speed does centrifugal force begin to interfere with the contact patch or rolling radius?

Richard.

PS Keep at 'im, Dave

MartinM

Trigaaaar

Definitely brake, definitely not brillo

Dave T-S

Jerry B
Ah - RE010's - the tyre with the friction coefficient of a heavily vaselined eel on polythene.....

Optimum tread depth for most tyres - dry grip -v- tendency to aquaplane is around 3-4mm.

Hoppy
Speed/centrifugal force DOES reduce the contact patch....extreme case, top fuel dragster - watch the tyres grow!

Hoppy

Dave, yes I've seen that on dragsters. I think they actually use that characteristic to increase gearing when on the move.

But is it a significant factor on a road car at, say up to 130/140mph?

Richard.

Dave T-S

I'm still researching......but, a further thought regarding the original question i.e. that of using S03 in 16".....

There is a vast difference in sidewall HEIGHT of different size tyres - see below:

205/50x16 = 102.5mm
215/40x17 = 86mm
225/40x18 = 90mm
225/35x18 = 78.75mm

As you will see the standard tyre 16" size has a VERY tall sidewall in comparison to the other sizes listed (which are the closest to the standard rolling diameters, with the exception of the last one, which see below. Sidewall height MUST influence sidewall flex.

Pete Croney is running 225/35x18 on his MY01 which has an exceptionally low sidewall depth, which will be a part factor in why it handles so well on track (plus Leda, and the fact that it is a MY01 - better geometry, stiffer shell etc...).

I elected to go for 225/40x18 rather than 225/35 because it is the closest to the MY01 standard tyre rolling diameter of 626mm (at 637mm).

I think the sidewall HEIGHT of the 205/50x16 MUST be a factor in why the S03 feels very squirmy to SdB in 16" and not to me in 18".

Incidentally, Bridgestone say the tread pattern of the S03 was developed from their F1 rain tyre - probably why it feels so good in the wet.

[This message has been edited by Dave T-S (edited 03 July 2001).]

Lambo

Thanks eveyone for their input to this thread, ( especially Dave and Simon ) but I'm still no where near the answer to my question about S03's being a better choice that S02's.
Can I take a quick straw pole, and I'll go with the majority, I need tyres this week as all 4 are baldies.
So for my 16" rims will it be ;

S02 or S03 ?

Cheers
Lambo

Dave T-S

OK
I would say then, in 16", go with Mark/Simon's advice i.e. S02....

SdB
Please do not for one minute think this means I agree with you.....

I can't honestly say S03 DO work in 16", because I have not tried them. I CAN say they DO work in 18", because I have. Maybe the sidewall height as indicated in my earlier post is the key.....

But I am still going to do some further research on the subject also

BugEyed

Lambo

I think that you'll find the SO2's to be better on your 16" wheels given the profile of the tyre. The jury is out for bigger sizes such as the 18".

SDB

Hi Chaps

Dave
You're absolutely right... the sidewall height does indeed play a huge part in the squirmyness (technical term ) and the sidewall movement on he s03 is greater than that of the S02..

But in addition, the tread flex is also substantial. Isolating the flex in the tread alone there is a definite movement there as the tread bends and rolls in addition to the tyre body / sidewall movement.

In terms of the tread being born out of their research carried out in F1. They all say this, and technically they are probably all correct as they learn things at every wet race, and at every wet test session (things even *they* didn't know. so what chance do we have!! ), but this does not mean that the tread has been designed to work as well as possible in the wet.

The wet grip of S03's *is* good... but on 16" it is not as good as the S02...

Like I said, I totally expect the S03 to be much better in larger size wheels, but I would be surprised if the wet grip ever matches that of the S02. I would *love* to be pleasantly surprised.

Cheers

Simon

Airmiles

Blimey! Thread of the year?

Despite my sadly direct experience of RE010s lack of grip, I've so far resisted the Siren Song of Mark at TN re S02s (I do plenty of motorway miles, so rarely need the grip, and had vague hopes of wearing the flipping things out soon).

But if SO2s are going to be discontinued - how long have we got? And does the criticism of S03s move Eagle F1s or Toyo Proxes ahead in the 16" recommendation stakes?

(As an aside, when I took the SnowProxes off and put the RE010s back on, I couldn't BELIEVE the amount of tramlining. Crap!)

Cheers

Miles

Jza

Jeez,

I dont have any problems with the re011 whatsits! They slide nicely if im a bit too hot into the corner. Cheap too.. cost £21499 inc VAT from my dealer.

Am i still not cornering quick enough? Have to go out for another "spin" then.

How can you tell (explain the feeling to me) if a tyre is good or bad.

Or am i just a slow coach?

Jza

Robertio

iTrader: (1)

Jza, the fact the car has very little grip, the front end goes straight on as soon as a rain cloud makes an appearance, you can't hear the streo, even though it is at full volume, over the road noise, the slightest road imperfection drags the car towards a ditch/wall (delete where appropriate), you get no feedback from the steering at all. If the above are true, then your tyres are not very good

Jerry B

Very interesting all this. Haven't had cause to try greasing eels, I'll assume there's a genuine reason behind your experience of this practice....

But there is another question I wanted to ask about S02s or indeed 3s from the vast pool of motoring experience here. Ultimate grip etc apart, are they predictable on the limit? Like the man says, 010's slide quite nicely - and controllably at least (amongst other 'features'like tram-lining etc).

rovo

Simon,

just to get back to the contact patch area (you're not thinking we were letting you go this easily ).

You asked for a formula:
"I've trawled the net trying to find a formula for calculating contact patches and can't find one.. (maybe someone else knows of one) ..but the size of tyre does *at no point* come into the calculation of the *area* of the contact patch, only the shape."

If you take the Hertzian contact stresses (they are used to calculate the contact stresses of metals into contact) you get the following formulas:

for a ball on a flat surface:
radius of contact patch = (1.5*(1-v^2)*F*r/E)^(1/3)

for a cilinder on a flat surface:
width of contact patch = 2*(8*F*r*(1-v^2)/pi/E/l)^(1/2)

v = Poisson's ratio
E = elasticity modulus (could compare this with tire pressure)
F = force (~ weight resting on the tire)
l = length of cylinder (~ width of tire)
r = radius of sphere/cylinder (~ radius of tire)

As you can see if you increase the radius of the sphere/cylinder (~ radius of the tire) the contact patch increases and the other formulas (not shown) for the contact stresses decrease similarly. Just like Dave T-S mentioned earlier. So I still have to agree with Dave T-S .

rovo

Jerry B,

currently I have got the S02's (16") and find them very predictable near the limit, far more than the Goodyear Eagle F1 I had before. You find yourself going to the limit more and more, the S02's are a joy to drive. Hmmm, one of these days I've got to be very carefull .

SDB

Rovo..

AWESOME formula!!!

Elasticity is NOT the same as air pressure in any way at all.

This formula does not (IMHO) represent tyres in any way.

In addition, a cylinder bares no resemblance to a tyre except in conceptual shape. It is not a close cell of air pressure supported by a solid centre, so think about it..

Of COURSE making the cylinder winder would increase the contact patch as there are no other forces to take into account, you are simply increasing the amount of material to be included into the formula and not changing anything else..

Nice try!!

BTW.. if you find a formula which disproves the statements I've made, some of the leading tyre engineers at Ford, Daimler Chrysler, and many motorsport teams would probably be very interested as it will mean they've been doing it all wrong for all these years!!!

Cheers

Simon

Dave T-S

jza
The RE011's are a big improvement on the RE010's. At 96.75mm sidewall height, assuming similar construction, they are almost certainly stiffer laterally/in torsion than the RE010's which helps them give more grip - or less *squirminess*.

"Feel" of a tyre is very much a seat of the pants thing and driving experience (i've been around a long time LOL ).

I also drive on snow in the Alps four or five weeks a year which is great practice.

Tyres are the primary things that keep you on the road, and i've used the best available for the job for a number of years - one of the first performance radials I had was the Pirelli Cinturato CN36 back in the 70's...

Sideways de Banke
I'm not done with this thread yet....research continues

ian_sadler

Guys this has to be up for the thread of year award.

What should we award? Are there any awards?

Answers on a post card to.....

Ian
Terzo 33

ps Lambo Hope to see you at the Royal Standard on Wed.

[This message has been edited by ian_sadler (edited 03 July 2001).]

Rich_R

I had 215/40/17 SO3's fitted at Bedford - for the first 500 miles they were VERY bad - squirming all over the place and very erratic. Very different to the slippy characteristics of SO2's for the same first 500 miles.

I have now done a couple of thousand miles including 12 laps of the Ring and they are certainly as good if not better as the SO2's I used there at Easter. The main factors that impressed me is the wear rate on the shoulder - after some hard sideways stuff the SO2's would wear badly - the SO3's hardly show any signs of wear. They also don't go off as easily as SO2's when heated up.

To sum up SO3's in 17's IMO - as good grip as SO2's (braking, cornering), less shoulder wear and better grip when really hot. Not really tested much on the limit in the wet so no comment there. I also think that I get less understeer than before.

Rich.

Dave T-S

Rich
One of the advances of the S03 over the S02 is that it has a dual compound - harder on the shoulders - to counteract the shoulders rolling off with *energetic* use as you describe - so it sounds like it works.

Jerry B

Rovo

Thanks for the info.

rovo

Dear Simon,

the basic principles for the contact pressure and area as part of the formulas is also applicable to tires. In all the books I have got about car handling and tires (and I've got a lot of them!) no direct formulas for contact area are mentioned. Almost all of the research is direct towards understanding the (vertical) load on the tire and the forces generated by the tire. 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). The bigger tires (diameter and/or width) are able to withstand a higher load (see the tables of the tire manufactures). And for the same (vertical) load therefore are able to generate higher cornering forces. The link being: bigger tire for the same load --> bigger contact area --> lower contact pressure --> higher coefficient of friction. (And the "big boys" do understand this. )

To support my statements above, I have some statements copied from two books. These books are internationally well known books on the subjects of tires and handling.

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."

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."

So Simon it seems to me that the statement "a bigger tire means a bigger contact area" is certainly valid. And I believe it's being backed up by applicable information. The next time you want to say "nice try", you better back it up with some substantial information .

Kind regards

Robert Vogels

rovo

When going through the books to educate Simon a bit , I also came across some information concerning the influence of the centrifugal forces (= speed) on the loaded radius of the tire. For tires suited for high(er) speeds the increase in diameter is approximately 2%.