GTRPower

cdelena-

I think your statement sums up my conclusions fairly well...

pfb-

I still don't understand what your point is, but I'm sure we'll talk it over a drink at S2KDays...

Reverend-

It's hard to "stay on topic" when the question asked is affected by more than the one variable assumed in the response...

[Edited by GTRPower on 02-20-2001 at 02:14 PM]

ultimate lurker

Top fuel dragsters use big slicks for several reasons. But one of the most important is the dynamic change in tire diameter as speed increases. If you ever watch a Top Fuel car go through a burnout, notice how the slicks grow. And as they do, the contact patch gets narrower and longer (longitudinally). When they slow back down, the only part of the slicks that is really heated up is the center third or so of the "tread". It tends to hold that you want the contact patch elongated in the direction of acceleration. A laterally biased contact patch for cornering, a longitudinally biased one for straight line acceleration. The growth in slicks also acts like a sort of variable gear ratio since TF cars don't run trannies.

On the subject of radial tire contact patches, I think we need to be very careful about making assumptions here. There are so many factors involved that I know I can't fully explain.

For example, If you take a 205/55 tire vs. a 245/45 tire and put them both on the same corner of the same car and inflate them to the same pressure, what happens? Well, theoretically (according to this thread), you'd have identically sized contact patches, but the one on the 245/45 tire would be wider.

Assume for a second that is true. What benefits does that have besides orienting the patch for maximum lateral acceleration? Well, for one thing, I think it provides you with a less deformed tire. Think about it. For a tire to actually have a contact patch on a flat surface, it must deform from a circular shape. The more deformation you have, the more tire drag and heating you get. For a narrower tire to have the same contact patch as a wider tire, it must flatten more longitudinally.

But let's assume for a second that we're going to set up the tires for similar levels of deformation. That means we can run the larger tire with a lower pressure. This should theoretically increase the contact patch (more on that in a second). That also means that each square inch of contact patch carries less weight, and it has been shown that with tires, overall friction (normal force x Cf) doesn't rise quite linearly with weight. Therefore, there should be more grip.

However, we're talking about radial tires here, and that adds a lot of elements into determining contact patch. When I place one of drag racing slicks next to my street tires and deflate them both (off the car), the street tire doesn't look too different, but the drag slick gets flatter and flatter till it actually caves in the center, the sidewalls only being propped up by the rim beads. The radial tire has an internal supporting structure and that's key.

Think of it this way. I have a perfectly rigid flat plate that I place on the ground. It has an area of X. I stand on it, all Y lbs of me. There is now a certain ground pressure of Y lbs/X sq. inches. I put my friend on the plate with me, she weighs Z. Now we have Y+Z lbs/X sq. inches. But have we increased the surface area? No. The other extreme is a balloon with perfect elasticity. I put a certain amount of air in the balloon and stand on it. It deforms to create a surface area appropriate to the internal pressure. I add more air, the surface area goes down proportionally.

A radial tire lies somewhere between these two extremes, and thus I don't think contact patch can truly be modeled by a simple pressure calculation. Additionally, tire grip is not solely Cf x normal force. Mechanical interaction between the tire material and the road surface also plays a significant role (which is one reason why you can corner at more than 1g without downforce - something that every beginning physics student will tell you is impossible). A wider tire, with a sufficient internal stiffness, may allow more of that mechanical interaction to take place.

Kind of off topic, but probably worth thinking about.

UL

Barry in Wyoming

I cannot think of a better thread than this one since I started on the old board in April and this one in October!

You guys amaze me. It's been ages since I studied physics but this is definitely a keeper.

My background before medicine was in experimental psychology. I would guess the next step would be to experiment, but that would be complicated because once you go from the stock setup, there are so many variables: wheel size, tire size, cambor.

Let me ask Prolene's question again really. For my situation, aggressive but legal-limit summer driving on public two lane twisty roads in Wyoming's mountains, is there a clearly better choice for the corners than stock SO2s on stock wheels, JDM BBS forged stock wheels in my case?

Enjoying these roads requires both great lateral grip and ample acceleration to make use of the occasional passing zones. These roads switchback and twist from the prairie up into the Big Horns, a front range of the Rockies, and end at my favorite fly fishing spot. How sweet!

Thanks in advance to UL, GTRPower, pfb, cdelena, The Reverend and the rocketman. Especially thanks to Prolene for starting this thread.

Barry in Wyoming...
Enjoying the car and its community!

Prolene

In a way, I'm with you, Barry. Again on the fence between 16" and 17". 17"s look better, and there are a lot of tires of the 245/40/17. I suppose if I found a light enough 17" rim, I'd go with that. Since I might have a 16" coming my way, I think the performance of 17 won't be too significant over a good 16" tire, and I'll be staying with the 16".

I saw the PR6 rim in MGRacing under "Js Racing" in MG site. These 17"ers weigh 13.2/13.64 lbs fr/back. Lighter than Volks 17". Not sure how they compare with Mugen. They look good.

turbo_pwr

[QUOTE]Originally posted by Prolene
[B]I saw the PR6 rim in MGRacing under "Js Racing" in MG site.

cdelena

[QUOTE]Originally posted by Prolene
[B] I saw the PR6 rim in MGRacing under "Js Racing" in MG site.

Prolene

Those PR6s are too expensivo for me.

I think an advantage of an other than stock or JDM 16" rim is lighter weight and 8" wide at back as opposed to 7" wide stock. The sidewall of a 245/45/16 should act stiffer on the wider nonstock/JDM rim, leading to better handling. Of course for stock autox, one must stay with JDM at this time.

[Edited by Prolene on 02-21-2001 at 07:44 AM]

pfb

For your application, I don't think so. You've already shed some weight with the JDM wheels, S02's are arguably one of the best dry weather non-race tires available, and Honda has custom speced them to match the S2K's handling. Maybe play with the pressure a bit. My experience is that higher pressures really makes a positive difference, due to less roll in the tire.

Once someone goes through the effort of sourcing a perfect offset, perfect width, lightweight 17" wheel with tires matched to the S2000's handling, likely through a process of trial and error, it might be a better option.

P.S. Let me know if come warmer weather you want to take a S2000 trip to somewhere in Southern Wyoming... I'll head north from Colorado.

Prolene

That answer helps, thanks, Pfb.

The Reverend

Umm, don't mean to rain on the JDM parade, but the JDM BBS rims are exactly the same size as the USDM Enkei rims. Both are 16x6.5 +55 front and 16x7.5 +65 rear. Only difference is the appearance, the JDM rim is slightly lighter, and the JDM rim is forged while the USDM rim is cast.