What some people do not realize is that the contact patch area does not change that much when going to a wider tyre. In fact, if tyres did not have any stifness, that is, if they were elastic like a party balloon, the contact patch area would only depend on the tyre pressure and vehicle weight and would be the same regardless of tyre size.

In reality, tyres do have some inherent stiffness, and the tyre patch area does change somewhat with tyre size. Albeit, the basic principle still applies.

What does change is the contact patch shape: with a wider tyre the contact patch is wider but shorter in length. Another reason why hydroplanning is easier with wider tyres!

I think that what I am trying to say, is that there is no substitute for experimentation when it comes to real world conditions.

Theory let's you hone quickly on what works and what doesn't but if you really want the best setup you need to try it.

Now, the billion dollar question is whether Honda did select the "killer" setup with its tyre design & choice or whether we common mortals can improve upon it. The jury is still out.

 

AMEN Luis, Thats how I feel. My experience now tells me that these PP tires do better in the wet and I cant tell any difference on dry. I'm not a professional driver who might notice a difference and I dont drive over aggressively on dry so I'm not going to beat this dead horse any longer and belabor this issue. I think we are getting a little too technical and I'll be happy to comment on what happens when I put the PP's on the front in the spring unless I drive off a mountain pass.

 

Thanks. I was going to post the same thing.

To add to what Luis said, while the size of the contact patch may not change much with tread width, its shape has real importance. All things being equal (i.e., sidewall stiffness, air pressure, tread design, and rubber compound) a short, wide patch will be more resistant to lateral slippage, and therefore deliver higher g's in a corner. A long, narrow patch will be more resistant to fore-aft slippage and therefore deliver better traction under acceleration and braking. And it will also be better in rain and snow.

In the dry, wider tires are best for the S2000 because we don't need better traction in the fore-aft dimension. Braking is best-in-class, and it's already devilishly hard to break the tires loose from a standing start. IMO, S02 PPs will cost you a little in corners and also make standing starts even harder, though braking may improve a bit. This may be a good trade if PPs perform that much better in the wet, which they may.

Changing tire brands means you get a different compound and tread pattern, which changes everything. There may be a tire out there that's as good as the OEM S02s in the dry and better in the wet (and lasts longer to boot). Or you may find some that are as poor in the wet but much worse in the dry. IMO the second possibility is the most likely if you're thinking of paying half what the Bridgestones cost.

I'll be reading posts on other tires with great interest while I'm using up my second set of S02 rears.

 

Luis and Tox,
I am totally confused, you guys say that a narrower tire will have the same contact patch size as a wider tire, only it will be narrower and longer? Isn't the "length" of contact dependent on the circumference and amount of deformation under load of the tire? Tox then supports this idea by saying a narrow tire will accelerate and brake better then a wide tire. Does this mean that my car will launch harder, accelerate faster and brake in a shorter distance if I use 185/60 tires?? And if I was to use 255/45 tires the reverse is true?

STL : ALL W and Y tires are known as "ZR", you will not find any 225/50WR16 93, you WILL find it's 225/50/ZR16 93W. Over 15 years ago, a better tire then the VR was created, it was given a 149+ mph rating. Over time this rating has been expanded to W for 168mph and Y for 186mph but manufacturers kept the Z in their designations.

 

Assume, in round figures, a 2900-lb car with 50:50 weight distribution and 32 psi in the tires. Each tire supports 725 lb. If the tires are totally flexible, like a balloon, each one will have a contact patch of 22.7 square inches. Tire stiffness changes this somewhat, but I see no reason to think a fat tire would have a different-sized contact patch than a thin one at the same pressure.

As for the 185/60 tires, if you can find a set made with the Bridgestone S02 compound (which I'm sure don't exist), they would improve fore-aft traction. Hard to believe? Consider the ultimate acceleration machine, a top-fuel dragster. The contact patch is VERY long and thin, and the sidewalls are very tall. Of course, those tires are huge in every dimension, and run at low pressures, but that's all to make the contact patch bigger. Proportionally, I bet dragster tires are taller than 70-series Camry rubber.

Conversely, mounting wider tires should increase lateral stick at the price of more wheelspin under throttle and longer braking distances. That's why fat tires are used in any racing series that involves turning, where cornering speed trumps braking and acceleration.

Finally, I never suggested the S2000 would launch harder with a narrower tire. From a standing start there's already plenty of traction and it's hard to get enough wheelspin to get into the power band. More traction would make this worse.

 

Take a look at http://www.tirerack.com/tires/Spec.jsp?mak...el=Potenza+S-02

You'll see a list that includes xxx/xxWR16 -- but I agree that I don't see WR too often. Most often I usually find W-rated tires are listed as "xxx/xxRxx xxW" while Z-rated are shown as "xxx/xxZRxx". I have not seen a W-rated tire listed as "xxx/xxZRxx xxW" -- probably becuase that looks confusing.

 

Actually now that I look at little more, I notice that Dunlop's specs (at Tirerack) are listed like that!! But the Yoko specs matched what I saw for Bridgestone.

It seems the Z rating doesn't really tell the consumer much. It does say the tire is good at speeds of 149mph+ but without an upper limit that doesn't really give much guidance!! The lettering convention implies that a Z tire is rated for higher speeds than a Y (or W) rated tire -- but how much higher?? (Or is that even true?)

[This message has been edited by STL (edited December 20, 2000).]

 

Does anyone know what the SL means in "xxx/xx/ZRxx SL"?? What about MFS or RF in place of SL?

Wonder where I'm see these...checkout: http://www.tirerack.com/tires/Spec.jsp?mak...l=SP+Sport+8000

 

STL,
Just wanted to point out that a W or Y rated tire is ALSO considered a Z rated tire.. A tire that is rated 168mph is obviously also rated 149+mph. The lettering convention is outdated. As for your other questions click on "tire specs key" on the bottom of the page you linked for answers.

Tox,
22.7 square inche contact patch?!?!? How did you get that? 725lbs divided by 32 psi? Does that mean if I only put in 10psi I have a 72.5 square inch contact patch? A contact patch that is 3 times as large as running 32 psi? You can not measure contact patch with algerbra. If the contact patch stays the same as you say, the amount of friction between the road and the car is the same and therefore wouldn't braking and acceleration "grip" be the same? There would be NO DIFFERENCE in going to a wider or narrower tire
Without going into deformable bodies and calculus to make life a little easier. let's agree with your assumption of everything being equal "i.e., sidewall stiffness, air pressure, tread design, and rubber compound" Let's further assume that any tire you put in 185/60 205/55 225/50 255/45 has the EXACT same sidewall height. Therefore deformation of the sidewall is the same under the same amount of weight. Contact patch LENGTH is determined by the deformation of the tire (circle) where it meets the ground (line). As it's the same deformation it is the same length.

Top fuel dragsters have a large sidewall and low pressure so that they can get a larger deformation and hence a longer length on the contact patch.

 

[QUOTE]Originally posted by Nick T:
[B]STL,
...
As for your other questions click on "tire specs key" on the bottom of the page