Wheel diameter rule change Poll

[Eric Parham]

Okay, I see.

The problem here is that there are truly several motivations for this rule change (one or more applying to each competitor), and a few more against it.

The "for" are:

1. Buy new but inexpensive wheels.

2. Run larger wheels to increase performance.

3. Have a choice of wheels to change gearing.

The "against" are:

4. Giant wheels are too expensive.

5. Giant wheels are too fast.

6. Giant wheels require expensive tires.

7. ANY change will cost me money.

Did I miss any?

Considering that 15" wheels are currently both the cheapest and the most available, would many people object to the following rule?

Allow cars running anything less than 15" to run *up* to 15". Allow cars running anything more than 15" to run *down* to 15". Allow cars running exactly 15 to run +/- 1" (i.e., 14"-16").

[Eric Parham]

Oh, and did I forget to mention that 15x6 are already getting hard to find for some applications (most aftermarket are at least 6.5 or 7" wide)... so...

[Geo]

Originally posted by Eric Parham:
Okay, I see.

The problem here is that there are truly several motivations for this rule change (one or more applying to each competitor)

Not in my case because any change in this rule (diameters only, not widths) will not affect me. I can already use 15" or 16" wheels per the ITCS (BTW I will use 15").

Originally posted by Eric Parham:
2. Run larger wheels to increase performance.

I won't deny that some people will try this because they think it will increase performance. Personally, I think they should knock themselves out because it will be a futile effort and keep them chasing the wrong thing. It won't make them faster.

Originally posted by Eric Parham:
3. Have a choice of wheels to change gearing.

This is silly. Wheels don't change gearing. Tires do.

Originally posted by Eric Parham:
4. Giant wheels are too expensive.

Well, again, if my competitor decides to chase this instead of something that will make him or her faster, I don't care.

Originally posted by Eric Parham:
5. Giant wheels are too fast.

People used to think the world was flat too.

Originally posted by Eric Parham:
6. Giant wheels require expensive tires.

See number 4.

Originally posted by Eric Parham:
7. ANY change will cost me money.

Won't cost me anything. Again, I already have a choice. I only continue to point this out because I'm pushing this rule change and it does not affect me. I think it's for the good of the club.

Originally posted by Eric Parham:
Did I miss any?

Nope. Those are pretty much the perceptions out there.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[dickita15]

let's just move jake's mr2 to ITB where it belongs. I assume you cam still buy 14x6".

[Jake]

YES!! I've already got a set picked out!

[The Sleeper]

This rule can be made as complex as a lawyer`s will, or as simple as a letter to a friend. I prefer the latter. Does anybody remember the KISS principle?

Min and Max rim sizes for each class shall be based on the cars allowed in your class. If car brand X is allowed 13" wheels and car XX is allowed 14" then all cars in this class can run any rim dia from 13" to 14". Naturally this would vary from class to class.
The slip ratio of a tire is influenced by the sidwall`s flex thus a shorter aspect ratio or shorter sidewall will flex less thus reducing the tires slip ratio. True you may not be able to notice the difference because of the limited mods we are allowed to do in IT. But if you take 10 of those small limited items that seem to small to bother with or to waste your time with and put them together, humm all of a sudden you might just be quicker then you were before.
Just food for thought...Have a happy Thanksgiving......

[Geo]

Originally posted by The Sleeper:
This rule can be made as complex as a lawyer`s will, or as simple as a letter to a friend. I prefer the latter. Does anybody remember the KISS principle?

Min and Max rim sizes for each class shall be based on the cars allowed in your class. If car brand X is allowed 13" wheels and car XX is allowed 14" then all cars in this class can run any rim dia from 13" to 14". Naturally this would vary from class to class.

Doesn't sound like KISS to me. KISS would be any diameter and set a max width.

Originally posted by The Sleeper:
The slip ratio of a tire is influenced by the sidwall`s flex thus a shorter aspect ratio or shorter sidewall will flex less thus reducing the tires slip ratio.

Sorry, but that's wrong (excluding extremely tall sidewalls where the sidewall becomes part of the contact patch - this shouldn't be happening with any race cars). The flex of the sidewall will delay the set the tire takes and thus reduces some transient response, but will not increase the slip angles.

If you put the same contact patch on the ground and are using all the tread and none of the sidewall, grip will be the same.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[Jake]

Originally posted by Geo:
KISS would be any diameter and set a max width

Yup. That's basically the same conclusion on the Honda Tech Poll:

Online Poll » Results

up to a max size per class (80%, 16 votes)

allow 1 inch upsize from current rules / all classes (15%, 3 votes)

keep current rules (5%, 1 votes)

allow 2 inch upsize from current rules / all classes (0%, 0 votes)

17 inch max / all classes (0%, 0 votes)

don't care (0%, 0 votes)

other (0%, 0 votes)

[The Sleeper]

"Orginally posted by Geo"
Sorry, but that's wrong (excluding extremely tall sidewalls where the sidewall becomes part of the contact patch - this shouldn't be happening with any race cars). The flex of the sidewall will delay the set the tire takes and thus reduces some transient response, but will not increase the slip angles.

If you put the same contact patch on the ground and are using all the tread and none of the sidewall, grip will be the same.


Hummm interesting. Well since I am new here and unknown, I must prove my point. From a respected book and author.
Tire Slip Angle
"Design characteristics that affect tire slip angles are, tire compound, cord bias angle, cord material, ASPECT RATIO, SIDEWALL HEIGHT VERSUS THREAD WIDTH..etc"
What this means a tire with the same thread width with a 4" sidewall will have a larger slip ratio then a tire with a 2" sidewall. And the higher the slip ratio the slower corner entry speed and steady state corning speed will be..

[tderonne]

The less give in the sidewall, the better the camber control (of the car/suspension) must be.

Struts have inherently bad camber control. A higher aspect tire CAN help keep more tire on the ground.

Just one more thing to think about.

[Jake]

People - we're talking about wheel diameter here! Not aspect ratio. I don't care if you run a 205/50-13,14,15,16, or 17 - you are going to have the same contact patch, squirm angle, tread displacement, friction yaw, and whatever technical term you come up with! Don't forget, 45 series tires are availble in 13's as well. Yes, you do get taller gearing when you use those 17's on your 100hp IT car, but a fail to see that as an advantage.

[Knestis]

But Jake, you ruin the fun if you force people to argue about just one aspect of a change. It makes it WAY harder to push a particular agenda...

K

[The Sleeper]

OK Jake here is an example of what I am trying to explain:
P205/55ZR14 thread width 8" approx Dia 22.8" Circ 71.5"
compared to
P225/45ZR15 thread width 8.6" approx Dia 22.8" Circ 71.6"
In this example you have gained .6" thread width, Dia is the same and Circ is .1" larger and you just lost 1" of sidewall flex thus a smaller slip angle which will result in higher corner entry speed and higher steady state cornering speed. Since the Dia and Circ are withen .1" of each other your gear ratio has not been altered all you have done is increase your performance. The same thing can be done going from 15" to 16" rims, the only deterent to this is the increase in unsprung weight, but that is a steady given aspect not varieing such as turnin ratios or corner aspects, so I will gladly trade in a bit of unsprung weight for improved slip ratios. Oh and the above spec`s came from Hoosier`s web site. I am not trying to agrue with anyone just bringing forth knowledge and the facts to back it up.

[Greg Amy]

A bit disingenuous isn't it, comparing 205/55-14 to 225/45-15? Try the same study again, comparing 205/55-14 to 205/55-15...

[Geo]

Originally posted by The Sleeper:
In this example you have gained .6" thread width, Dia is the same and Circ is .1" larger and you just lost 1" of sidewall flex thus a smaller slip angle which will result in higher corner entry speed and higher steady state cornering speed.

<snip>

I am not trying to agrue with anyone just bringing forth knowledge and the facts to back it up.

I hope no one is really trying to argue here. For my part, I have no dog in this hunt. I would like to know the book and the author you are referencing.

Also, even if the slip angles are higher (slightly), that does not mean the overall grip is less. Some tires already like more slip angle than others at maximum grip. Slip angle is not necessarily an indicator of road holding.

------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[This message has been edited by Geo (edited November 28, 2003).]

[oanglade]

Originally posted by The Sleeper:
OK Jake here is an example of what I am trying to explain:
P205/55ZR14 thread width 8" approx Dia 22.8" Circ 71.5"
compared to
P225/45ZR15 thread width 8.6" approx Dia 22.8" Circ 71.6"
In this example you have gained .6" thread width, Dia is the same and Circ is .1" larger and you just lost 1" of sidewall flex thus a smaller slip angle which will result in higher corner entry speed and higher steady state cornering speed. Since the Dia and Circ are withen .1" of each other your gear ratio has not been altered all you have done is increase your performance. The same thing can be done going from 15" to 16" rims, the only deterent to this is the increase in unsprung weight, but that is a steady given aspect not varieing such as turnin ratios or corner aspects, so I will gladly trade in a bit of unsprung weight for improved slip ratios. Oh and the above spec`s came from Hoosier`s web site. I am not trying to agrue with anyone just bringing forth knowledge and the facts to back it up.

Why would you compare a 205/55-14 with a 225/45-15?

You can run any tire width/aspect ratio right now, so you should compare the 225/45-15 with a 225/50-14

Then, the only "advantage" that you get is .4 inch less sidewall (if you assume that this is not traded off by weight difference) and this means that you drive the car a little bit differently, but it would not make the 14" tire/wheel combo obsolete for those that already have them.

------------------
Ony

[The Sleeper]

Here you go Greg:
P205/55ZR14 thread width 8" approx. dia 22.8 circ. 71.5

versus

P205/50ZR15 thread width 8" approx. dia 22.8 circ. 71.6
same thread width same dia .1" difference in circ. Less sidewall flex improved slip ratio.
I did the earlier comparison to show gaining an 1/2 in thread and loosing 1" of sidewall flex was possible without any ill affects or changes in final gear ratios.

Geo> Steve smith pubs. Formula car Technology by howdy holmes and don alexander.

[oanglade]

All you are doing is changing the optimum slip angle for the tire, not increasing traction.

You change the shape of the slip angle vs. lateral acceleration curve, the angle value where the peak is, but not the level of the peak itself. The peak of the curve is a function of the tire compound.

This translates into the tire needing to be driven differently to get the most out of it. It does not mean that a tire with a lower profile will have achieve higher lateral acceleration than another tire of the same compound.


From "Performance Handling" by Don Alexander (pg.28):
"The aspect ratio has little direct effect on traction. The aspect ratio does affect the slip angle, however. A lower profile tire is usually stiffer, and operates at a lower slip angle for the same load and cornering force. Assuming the tire contact patch stays the same, the lower aspect ratio tire will operate at a lower slip angle under the same load and cornering conditions. This will affect the handling balance if the aspect ratio is changed at only one end of the vehicle."

Then, on page 34:

"As sidewall stiffness increases, the tire contact patch can generate the same cornering force at a smaller slip angle. Since it takes less time for the tire to reach a smaller slip angle, the tire than can generate a given cornering force at a lower slip angle will be more responsive...

...a lower aspect ratio almost always increases sidewall stiffness. HIGER TIRE PRESSURES ACCOMPLISH THE SAME THING (emphasis is mine). Both will improve responsiveness."


------------------
Ony

[The Sleeper]

Ony, you are confirming what I have been saying here:
"As sidewall stiffness increases, the tire contact patch can generate the same cornering force at a smaller slip angle. Since it takes less time for the tire to reach a smaller slip angle, ""the tire that can generate a given cornering force at a lower slip angle will be more responsive""...

The aspect ratio is one of the factors that affects the coefficient of friction, there are others. And while you can adjust the, let me rephrase that you can cheat the aspect ratio by running more air (to try to achieve a stiffer sidewall)but then you open another ball of wax.
If in the examples I have given both showing the same approx dia and the circ only being .1" different but loosing 1" of sidewall therefore decreasing the slip ratio without having to resort to playing the air game, use the air to adjust what it is ment to do.

[Geo]

Originally posted by The Sleeper:
Ony, you are confirming what I have been saying here:
"As sidewall stiffness increases, the tire contact patch can generate the same cornering force at a smaller slip angle. Since it takes less time for the tire to reach a smaller slip angle, ""the tire that can generate a given cornering force at a lower slip angle will be more responsive""...

The aspect ratio is one of the factors that affects the coefficient of friction, there are others.

Not exactly. I think you missed the point. I'm NOT throwing stones, but trying to get us all on the same page.

The aspect ratio does not affect the coefficient of friction. It affects the slip angle. They are decidedly not the same. Higher slip angles most certainly do not mean lower grip (in and of itself). As I said, some tires operate at higher slip angles than others. That doesn't necessarily mean more or less grip.

If you separate the two concepts you'll be on the right track.


------------------
George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com