RyanEJ8

I need traction, so I'm trying to come up with a new tire/wheel combo for my 00 Civic coupe. I think I'm going to go with a 15x7 rim, most likely the Rota Circuit 8's. The car is mostly used as a weekend drag car and will hardly see 2000 miles a year so treadlife is not a concern, nor is wet traction. Because of this I was thinking of using BFG g-Force T/A. I would like to use 225/50-15, if they would fit.

According to this tire calculator, http://www.powerdog.com/tiresize.cgi the stock Civic tires (185/65-14) are 23.5" in diameter and 225/50-15 are 23.9" in diameter. This should be fine right? According to the calcuator my speedometer would be only 1 MPH off and the odometer will be off by 166 miles every 10,000 miles. Is this correct? Also, what offset would I need to fit these tires? The car has H&R Sport Springs which I believe is about a 1.7" drop in the front and about 1.5" in the rear. Should I use the same tires in the rear for better handling and ride or should I just use cheaper tires in the rear?

Thanks for helping me with my long winded question.
Ryan

Neo79Si

What if I told you that I've got a 205/50R15 DOT drag radial that's hooking up on 12 sec & 13 sec SRT-4's at a local drag strip??

The Dunlop SP Sport Inferno is the premier drag radial on the market right now. Yes, I'm an engineer for Dunlop, so I might be biased. However, I've taken these tires to the local drag strip for 'tuner night' and let 9 different drivers demo the tires. Every single one of them has been amazed with the traction and results, and I have driver's comments and times recorded to prove it. Just last week, an SRT-4 went from 13.96 on BFG g-force T/A's to 13.73 on the Inferno's.


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

Here is a copy + paste from another post I'd made...

The Dunlop SP Sport Inferno is our latest DOT-legal drag radial. I acutally had four sets of them out at the local drag strip last night (Norwalk Raceway Park, in Ohio) for people to try out. Here are some unedited comments from the evening...

"Awesome radial tire - a must have - had Mickey Thompson ET Drag and went 13.52...no other mods, just the Dunlops, and it went 13.40"

"...by far the best feeling tire I have ever run...They virtually removed all wheel hop and allowed for a launch I didn't think was possible"

People were running anywhere from 0.5 to 1.5 seconds faster than on street tires, and everyone was very happy with how well they hooked up.



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

I also have this tire on the front of my 2000 Si, with normal summer tires in the rear. I was surprised with how quiet they are, and how well they ride and handle. They are even good in the wet. Initial turn-in response is sick (probably because tread depth is only 6/32"), but overall the lateral grip isn't as good as my normal summer tires. The car is very controlable, you really can't tell that you have "drag radials" on there at all. I've only got about 500 mi on them so I can't comment about wear.

At the moment, the tires are available in a 205/50R15. They can be had from Harlow Specialty Tire (419.663.8473) for $115/ea. Jim is awesome, and ships UPS daily. Make sure you tell him that Matt from Dunlop sent you, should you decide to order. The 225/50R15 is the next size due to be released, but the 205/50R15 is available now.

Please let me know if you have any other questions...sorry for the long-winded reply!



Matt

nsxtasy

Hi Ryan,

You have two different (but related) questions here. One is which tire to use, and one is which size to use.

As for size...

The best size would be tires with the same outer diameter, if they're available for the tire you're looking for. The 195/55-15 size has the same outer diameter as stock and would be best, if they're available in the tire you want. (So does 215/50-15, but there aren't many tires available in that size.) 205/50-15 is 1.7 percent smaller in outer diameter than stock, and 225/50-15 is 1.7 percent larger than stock - not as good, but not way off, either. The problem you run into with a tire size like the 225/50-15 is that it is both larger in diameter than stock, and much wider than stock; as a result, there is a very good chance that the tires will rub on the wheel well liners and/or suspension components. So you start looking at rolling the fenders and other measures to compensate for the tire size, and you're basically creating one problem after another. So my suggestion would be NOT to use 225/50-15, but rather, to use 195/55-15 if it's available in the tires you select, and otherwise, to use 205/50-15.

Regarding which tire...

I'm not sure which BFG tire you mean, because they make a lot of different tires with the name "g-Force T/A" - everything from their top-of-the-line g-Force T/A KD, to their budget g-Force T/A KDW and g-Force T/A KDW 2, to the all-season g-Force T/A KDWS. But let's go back a step. I'm not even sure why you are thinking about BFG tires to begin with. [EDIT - I didn't realize you were talking about BFG drag radial tires, sorry for the confusion.] Because it sounds like your main concern, perhaps your only concern, is dry traction. Then why not get the Falken Azenis RT-615? They are a super-sticky tire, great for your needs (and the downsides, like relatively rapid wear, don't affect you). They are available in 205/50-15 now, and will be available in 225/50-15 later this year (see discussion below regarding sizes). A similar tire that is also available in 205/50-15 is the Hankook R-S2 Z212, which is slightly less expensive than the Azenis. Both these tires are available from Discount Tire.

Another alternative might be to get an R compound track tire, either a drag radial or a conventional (road racing) R compound track tire. They're not generally used on the street because of rapid wear and poor wet traction, but again, those downsides don't affect you, and besides, your use is largely for the dragstrip anyway. Have you thought about getting track tires instead of street tires?

EDIT (adding this paragraph): I see that Matt has posted about the Dunlop SP Sport Inferno drag radials while I was writing this post. Great minds thinking alike at the same time! That's exactly the kind of tire that I'm talking about, when I suggest track tires. Plus, it's available in 205/50-15, which ought to work fine on your car. That sounds just about perfect for you.

If you cared about handling rather than pure traction, and if you were interested in a street tire that lasted longer than these tires, then I would suggest considering the Bridgestone RE010 in 195/55-15 (stock tire on the Integra Type R) and/or top-of-the-line tires like the Goodyear F1 GS-D3, Bridgestone S-03, Dunlop SP Sport Maxx, etc. But it sounds like the stickier tires I mentioned earlier might be a better fit for your stated needs.

Use the same tires. (They will also give you the ability to rotate your tires to even out the wear.)



Modified by nsxtasy at 4:02 PM 8/25/2005

RyanEJ8

Neo79Si, thank you for suggesting the Dunlop drag radials, I will definately look into those.

nsxtasy, I should have specified that I was looking into the BFG g-Force T/A KD, I have heard from many that they are super sticky. For daily driving right now I am using Yokohama Parada 205/40-17 and the minute I hit full boost I smoke the hell out of them, first-second and usually part of third. I tried throwing on a set of Nitto 555r drag radials that I have on the 14" steelies and those hook up alot better, but still get smoked in first. This is why I don't think a 195 tire would work at all and I was looking into a 225 width. These tires won't be used for the drag strip too much, maybe once in a while, as I also have a set of 22x8x13 M&H slicks.

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">I should have specified that I was looking into the BFG g-Force T/A KD, I have heard from many that they are super sticky.</TD></TR></TABLE>

That's their top-of-the-line street tire. It's a very good tire - but not as good as the other top-of-the-line tires I mentioned, which are the best street tires out there (leaving aside specialty tires like the Azenis), and will give you better traction and better handling. In particular, the Bridgestone S-03 is a better tire than the BFG, for about the same price. And the Azenis and Hankook I mentioned are even stickier, for less money.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">For daily driving right now I am using Yokohama Parada 205/40-17 and the minute I hit full boost I smoke the hell out of them, first-second and usually part of third.</TD></TR></TABLE>

The Yokohama Parada is an inexpensive budget performance tire. It's not even the best budget performance tire, not even close; for example, Yokohama's own ES100 is a much better tire, and with the ES100 we're still talking about "budget" tires that people get as much for their inexpensive price as for their performance. So it's no surprise that the Parada isn't up to your needs.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">This is why I don't think a 195 tire would work at all and I was looking into a 225 width.</TD></TR></TABLE>

The reason the tires aren't gripping is because of the tire, not because of the width. The advantage people claim for wider tires is handling, not straight-line traction. A wider tire (e.g. 225) doesn't put any more rubber on the road than a narrower tire; it just changes the shape of the rubber it puts on the road (as noted here). So a 225 isn't going to give you any greater straight-line traction than a 195 tire. But again, it may cause rubbing problems. The 225 series will also hurt your acceleration due to their larger outer diameter; it's called "effective gearing" and it's the same concept as using taller gears.

You will experience a much, much greater variations in performance from different models of tires than you will from different widths of tires. For example, you'll get a lot more traction from a 205 series drag radial than you will from a 225 series street tire.

Bottom line: If you want better performance get better tires, not wider tires.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">These tires won't be used for the drag strip too much, maybe once in a while, as I also have a set of 22x8x13 M&H slicks.</TD></TR></TABLE>

Basically, you have a choice between three categories of tires:

<u>i) Track tires</u>
Dunlop SP Sport Inferno 205/50-15
Hoosier R3S04 205/50-15
etc

<u>ii) Super-sticky street tires</u>
Falken Azenis RT-615 205/50-15
Hankook R-S2 Z212 205/50-15

<u>iii) Top-of-the-line street tires</u>
Bridgestone Potenza S-03 205/50-15

Each category will give you greater traction than the one below it. But each category will wear quicker than the one below it.

RyanEJ8

I am a little confused now. I thought that the BFG g-Force T/A KD I was referencing were R compound drag radials that would be much stickier than a normal street tire?

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">I am a little confused now. I thought that the BFG g-Force T/A KD I was referencing were R compound drag radials that would be much stickier than a normal street tire?</TD></TR></TABLE>

This is why I mentioned that BFG makes a lot of different tires with the "g-Force T/A" name. Sorry if I helped confuse things.

The g-Force T/A KD is BFG's top-of-the-line street tire.

BFG also makes two R compound drag radials, the g-Force T/A Drag Radial (which comes in 205/50-15 and 225/50-15, for $108 and $112 per tire, respectively, at the Tire Rack) and the g-Force T/A Drag Radial 2 (which only comes in bigger, wider sizes that won't fit).

Yes, I agree, the BFG g-Force T/A Drag Radial would be a great choice for your needs (just like the Dunlop would).

Thanks for asking - I was getting confused too!

RyanEJ8

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

This is why I mentioned that BFG makes a lot of different tires with the "g-Force T/A" name. Sorry if I helped confuse things.

The g-Force T/A KD is BFG's top-of-the-line street tire.

BFG also makes two R compound drag radials, the g-Force T/A Drag Radial (which comes in 205/50-15 and 225/50-15, for $108 and $112 per tire, respectively, at the Tire Rack) and the g-Force T/A Drag Radial 2 (which only comes in bigger, wider sizes that won't fit).

Yes, I agree, the BFG g-Force T/A Drag Radial would be a great choice for your needs (just like the Dunlop would).

Thanks for asking - I was getting confused too!
</TD></TR></TABLE>

Yes, those are the ones I was talking about. So many different tires....

Okay so the BFG drag radials or Dunlops would be better for my needs than the other street tires mentioned like the Falken and Hankooks?

I read the article you posted about the tire width, but how come high performance cars and muscle cars come with wider tires then? Just strictly for handling, it has nothing to do with straight line traction? I understand how tire pressure and weight can affect the traction, but I can't seem to understand how the width of the tire wouldn't?

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">Okay so the BFG drag radials or Dunlops would be better for my needs than the other street tires mentioned like the Falken and Hankooks?</TD></TR></TABLE>

Well, they're stickier, and they will stand up to heat better. So that's why I think they're better for your needs. But the Falken Azenis and the Hankook Z212 are both very sticky street tires; it just depends on whether you want tires that are even stickier, and designed specifically for drag racing. Which it sounds like you do.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">I read the article you posted about the tire width, but how come high performance cars and muscle cars come with wider tires then? Just strictly for handling, it has nothing to do with straight line traction?</TD></TR></TABLE>

Yes, that's correct.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">I understand how tire pressure and weight can affect the traction, but I can't seem to understand how the width of the tire wouldn't?</TD></TR></TABLE>

Straight-line traction is primarily a function of how much rubber you have on the ground (the size of your contact patch) and the coefficient of friction (how sticky the rubber compound is), and how much force you have on it (the weight of the car, which transfers to the rear during acceleration). As well as your forward force (torque from your drivetrain, measured at the wheels), of course. None of those factors is affected by the width of the tire.

RyanEJ8

So it sounds like the best option for me then would be to get the 205/50-15's drag radials.

I don't doubt that your pointing me in the right direction by recommending the 195's or 205's, I'm just trying to understand this a little better (I haven't researched tires too much recently). If traction isn't affected by width of the tire, how come top fuel dragsters don't use skinnier slicks in the back instead of the super wide slicks they use?

Also if I go with the 205/50-15, since it is 1.7% smaller, my gearing would be shorter and therefore I would be faster correct?

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">If traction isn't affected by width of the tire, how come top fuel dragsters don't use skinnier slicks in the back instead of the super wide slicks they use?</TD></TR></TABLE>



<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">if I go with the 205/50-15, since it is 1.7% smaller, my gearing would be shorter and therefore I would be faster correct?</TD></TR></TABLE>

You will accelerate faster within any particular gear, and at most but not all road speeds; for speeds where it forces you into a higher gear, you will accelerate slower. Overall, it should improve acceleration in the 1/4 mile unless it forces you to make an additional shift.

Neo79Si

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">
If traction isn't affected by width of the tire, how come top fuel dragsters don't use skinnier slicks in the back instead of the super wide slicks they use?
</TD></TR></TABLE>

I don't 100% agree with that article regarding tire width and contact patch size. The overall net contact area grows with tire width. Yes, the shape changes (a 225/50R15 will have a wider & shorter footprint than a 205/50R15), but I have seen the net contact area increase as well.

A tire's footprint shape is influenced by many design factors (cord angles, rubber stiffnesses, etc) on top of the load, inflation, and friction. For instance, the Dunlop drag radial was designed with one thing in mind...to go fast in a straight line. This means, the footprint was optimized to be longer in the center of the contact patch than on the shoulders. While this isn't an ideal design for low noise levels and global wear, it is ideal for applying power to the ground. Most of the forces in the contact patch during linear acceleration are generated in the centerline. THIS is where the Dunlop is different than a really sticky street tire...not only is it sticky but it was designed to go to the drag strip.

Hope this helps

Matt

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Neo79Si &raquo;</TD></TR><TR><TD CLASS="quote">I don't 100% agree with that article regarding tire width and contact patch size. The overall net contact area grows with tire width.</TD></TR></TABLE>

No, usually it doesn't.

In fact, the technical director at the Tire Rack told me that they proved this by measuring the sizes of contact patches, using the same car and inflation pressures, but tires with widely varying widths. They found that the size of the contact patch was exactly the same, within the measurement error of the process they used to measure the area (which he said was about 2 percent).

Neo79Si

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

No, usually it doesn't.

In fact, the technical director at the Tire Rack told me that they proved this by measuring the sizes of contact patches, using the same car and inflation pressures, but tires with widely varying widths. They found that the size of the contact patch was exactly the same, within the measurement error of the process they used to measure the area (which he said was about 2 percent).
</TD></TR></TABLE>

There are a lot of things a tire designer can do to tweak a tire construction, and in turn - the footprint characteristics. Cord (belts, plys, overlay) angles, rubber stiffnesses, mold shapes...all of these will change the shape and size of the contact patch. At Dunlop, I peform finite-element analyses to predict footprint properties, so I have seen a lot of variations in contact area, even within the same size, depending on what we put into a tire, and how we contour the mold.

I can't show you any data to prove it (confidentiality, etc), but I can tell you there is a difference (greater than the tire rack's margin of error) in the gross contact area between the 205/50R15 & 225/50R15 sizes of the inferno at equal load & inflation conditions.

I'm not familiar with the tire rack's experiment, but there are a lot of factors that could've influenced the results. How much did rim width change from size to size?? Were tires that were "broken-in" compared to tires that were brand new...or were they all new?? Did they use a test rig to apply the load, or was this mounted on a vehicle??

I'm not arguing with the Tire Rack's results or your statements...rather saying that this isn't always the case, footprint area can be affected by a tire designer.

If I've learned anything working with tires, it is that the words "never" and "always" do not apply I've adopted the expression, "well...it depends..."

Thanks
Matt


Modified by Neo79Si at 12:53 PM 8/26/2005

RyanEJ8

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">No, usually it doesn't.

In fact, the technical director at the Tire Rack told me that they proved this by measuring the sizes of contact patches, using the same car and inflation pressures, but tires with widely varying widths. They found that the size of the contact patch was exactly the same, within the measurement error of the process they used to measure the area (which he said was about 2 percent).
</TD></TR></TABLE>


I still don't understand this. That would be like saying a bicycle tire has as much contact patch as a 13" wide drag slick. Maybe if the vehicle isn't heavy enough to accomodate the wider tire......? I am so confused...


Modified by RyanCivic2000 at 12:08 PM 8/26/2005

RyanEJ8

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Neo79Si &raquo;</TD></TR><TR><TD CLASS="quote">
I can't show you any data to prove it (confidentiality, etc), but I can tell you there is a difference (greater than the tire rack's margin of error) in the gross contact area between the 205/50R15 & 225/50R15 sizes of the inferno at equal load & inflation conditions.</TD></TR></TABLE>

I understand you can't give up your secrets, but can you tell me, would I receive worthwhile benefits from using the 225 over the 205 tractionwise and would it be more beneficial than the shorter gearing the 205 would give me? Also, when will your Dunlop Infernos be available in 225?

Both of you have been very helpful. Thanks.
Ryan

nsxtasy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">I still don't understand this.</TD></TR></TABLE>

Then think of it this way. Let's take a vehicle that weighs 2640 pounds (e.g. Integra Type R), and we'll inflate all the tires to 33 psi (pounds per square inch). The size of the four contact patches will total 2640/33 = 80 square inches. Regardless of whether the tires are skinny 165/80-15 or steamroller 225/50-15, they will total 80 square inches. It's simple physics.

When you put wider tires onto a car, the contact patch becomes wider from side to side, but it also becomes narrower from front to back, so that the area remains the same. This is shown in the following illustration of contact patches on the Tire Rack website:



<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">That would be like saying a bicycle tire has as much contact patch as a 13" wide drag slick.</TD></TR></TABLE>

A bicycle weighs a lot less than a car, which is why its tires can be smaller. But in both cases, as long as the tires are inflated to support the weight of the vehicle (car or bicycle), if you take the weight of the vehicle and divide it by the pressure in the tires, you will find the area of the contact patches. And neither the weight nor the pressure depend on the size of the tires.

Incidentally, this equation (weight divided by pressure equals area) is why drag racers reduce the inflation in their tires - because doing so increases the area of the contact patches.



Modified by nsxtasy at 11:59 AM 8/26/2005

Neo79Si

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 &raquo;</TD></TR><TR><TD CLASS="quote">

I understand you can't give up your secrets, but can you tell me, would I receive worthwhile benefits from using the 225 over the 205 tractionwise and would it be more beneficial than the shorter gearing the 205 would give me? Also, when will your Dunlop Infernos be available in 225?

Both of you have been very helpful. Thanks.
Ryan</TD></TR></TABLE>

The 225's in the Inferno will be available as soon as they can be built, basically. The engineering work is done. My friend in the race tires dept is @ a race this weekend or I'd give him a call to ask. The engineering work is done, just a matter of production. I would say before the end of the year for sure, but I'm not 100%

It's tough to say if you'd be better off w/the 225's when you take gearing into acct. I would say go w/the 205's available now. I know you're putting down 300hp, but I've seen a fwd-turbo'd talon & a SRT-4 click off mid-13's on this tire and sing nothing but praises to me at the end of their runs...they were both on 205's and loved them.



Matt

Neo79Si

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

Then think of it this way. Let's take a vehicle that weighs 2640 pounds (e.g. Integra Type R), and we'll inflate all the tires to 33 psi (pounds per square inch). The size of the four contact patches will total 2640/33 = 80 square inches. Regardless of whether the tires are skinny 165/80-15 or steamroller 225/50-15, they will total 80 square inches. It's simple physics.
[/i]</TD></TR></TABLE>

I agree that physics tells us Pressure = Force / Area, and so Area = Force / Pressure.

I think we're talking about 2 different pressures. You're referring to inflation pressure, I'm referring to footprint pressure in the contact patch (tire/road interface). This is where our opinions differ.

Also, I'm saying I can make changes to the way a tire is designed and give you a different contact area with the same sized tire, just built different ways. I can do this by changing the stiffness of the tire itself.

For instance, lets fill an identically sized basketball and kickball with 30psi. Now put 100lbf on top of it. Will their contact patches between the ball and the ground be the same size??.....

No - the basketball has a higher structural stiffness, so it supports the load differently than the kickball. It's contact area will be smaller, but the contact pressure will be higher. The kickball hardly has any structural stiffness, so it will have a larger contact area...the same force is distributed over a larger contact area, so the contact pressure is lower. Both objects still obey P = F/Area, but the "pressure" that we're concerned with is the contact pressure, not inflation pressure.

It's the "structural stiffness" that I can design into a tire. It is possible that all of the different tires the tire rack tested had very similar structural stiffnesses...from test data I've seen most (within the same size/type of tire) are very very close. But it is possible to change that stiffness a great deal by making design changes, which changes contact area.

You're definitely thinking along the right lines, but we can't forget about the structural stiffness of the tire itself. This can be tuned and adjusted, and it has a direct impact on net contact area.

Tires are strange, which keeps my job interesting

Good discussion!!!

Matt

nsxtasy

To the extent that the structural stiffness (e.g. of the sidewalls) supports the weight of the car, they can indeed have an effect. Historically that effect has been relatively insignificant, but this is changing, particularly with the more widespread use of run-flat tires. When punctured, run-flat tires become that exception noted previously, where the inflation of the tire is not supporting the weight of the car, but the stiffness of the sidewall is (even when the pressure in the tire drops to zero - I'm sure we've all seen the demonstrations where they show a car driving with a tire that has had a hole drilled in the sidewall).

Neo79Si

You are 100% correct Ken...the inflation inside a tire does the majority of the work when it comes to supporting the load, and a tire's structural stiffness plays a smaller part.

As engineers, we can't tune inflation pressure. Whatever an OE car maker tells us they want is what we give them. So we're forced to change tire characteristics (vertical stiffness, footprint properties, contact area, etc) by changing the structure itself, and how it supports the load (ie - stiffnesses)

RyanEJ8

Wow, this is a great thread. I have a much better understanding of how tires work now.

boosted92

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Neo79Si &raquo;</TD></TR><TR><TD CLASS="quote">I know you're putting down 300hp, but I've seen a fwd-turbo'd talon & a SRT-4 click off mid-13's on this tire and sing nothing but praises to me at the end of their runs...they were both on 205's and loved them.</TD></TR></TABLE>

That doesn't really tell us much though, I'm not the greatest driver in the world and last time at the track I had no trouble knocking down 12's on Azenis, I'd hope that you can drive a 13 second car on DR's fine.

RyanEJ8

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted92 &raquo;</TD></TR><TR><TD CLASS="quote">That doesn't really tell us much though, I'm not the greatest driver in the world and last time at the track I had no trouble knocking down 12's on Azenis, I'd hope that you can drive a 13 second car on DR's fine.</TD></TR></TABLE>

If the SRT4 was stock that's fairly impressive though.

thehatchninja

this is a great post