ST Rules Clarification - Tire Type

[thorpe911]

I could use a little help with a clarification of the rules regarding tire types. It seems the rule only reads to non-DOT approved tires. Do I not get an add-on to my modification factor if I run a 245 DOT approved tire (Toyo RA-1) even though it is slower than the 245 non-DOT approved tire?

 

7.4.2 Modification Factors

Tires:
Non-DOT approved tires = -0.75
Size 275 to 250 (or 10.5” to 9.5” for non-DOT approved) = +0.4
Size 245 or smaller (or less than 9.5” for non-DOT approved) = +0.8

[rlogan]

The first line item is only an issue if you run non-DOT. So, if you run DOT it does not apply. If you did use non DOT tires you lose .8 hp/wt accordingly. (But if they were smaller than 275/245, you get some of it back, see below)

 

The rationale for the second item is that most cars run over 275 width tire, if you are under that, you get the bonus (.4 HP/WT ) whether it's DOT or not

 

If you run 245 or smaller, you can add even more HP (.8 hp/WT) whether it's DOT or not

[TexaST-1]

My understanding of your issue is clear, but may need attention from Greg.

 

Currently, if you use a "Slick" you take the .75 hit regardless.

If you run a small DOT you get the add back bonus.

 

If you run a small "Slick" is there a middle ground. Is that your question?

Edited April 17, 2008 by Guest

[thorpe911]

Texas ST-1,

 

Your understanding of the rule makes sense; you get a hit for running a slick and get a little help for running a smaller tire. However, all verbiage of the rule states "non-DOT approved" and there is no reference to "DOT Approved" tires.

 

So my concern is, if I run a 245 DOT approved tire (i.e. Toyo RA-1), I don't get any adds or hits. But, if I run a 245 non-DOT approved slick, I get a +0.8 add and it is significantly faster that the Toyo. This does not make sense to me, that is why I wanted the clarification. Maybe we will have to wait for Greg to take a look at this.

 

Thorpe.

 

Tires:
  Non-DOT approved tires = -0.75
  Size 275 to 250 (or 10.5” to 9.5” for non-DOT approved) = +0.4
  Size 245 or smaller (or less than 9.5” for non-DOT approved) = +0.8

[kbrew8991]

the adjustment "signs" aren't 100% intuitive

 

plus is bad, means you carry more weight per horsepower

minus is good, means you carry less weight per horsepower

[TexaST-1]

Yes, what Ken said.

 

Example:

 

HP to Wt = 8.7:1 (8.7 - .75=7.95)

Adding true slicks would modify HP to Wt by -.75 = 7.95 Hp to Wt. This would move you from ST-2 to ST-1. Meaning adding weight or reduce HP to stay in ST-2.

 

Example:

 

HP to Wt = 8.7:1 (8.7+.8=9.5)

Install tiny 245 DOTs increases +.8 Hp to Wt = 9.5:1. This would allow you to reduce weight or add HP or both.

 

Hope this is a little clearer.

 

PS: Most Dots are faster than the Toyos

[thorpe911]

I think we are getting a little off the subject. I understand how the factor works, my only question is how tire types (DOT vs. non-DOT) affect the modification factor.

 

And, I think I just had an epiphany. Take a look at this and tell me if I'm correct.

 

The rule for tires is a two step process.

 

Step 1) Tire type - if you run non-DOT you get a -0.75 hit. If you run a DOT tire, it is par. No points either way.

 

Step 2) Tire size - If you run 250-275 then you get +0.4. If you run 245 or smaller then you get +0.8 regardless if it is DOT approved or not.

 

Example: a 245 Kumho slick. -0.75 for non-DOT and +0.8 for 245 or smaller for a net total of +0.05 added to my factor.

 

Does this sound right? Greg G, can you comment to this ?

 

Thanks,

Thorpe

[kbrew8991]

yes, it is a two-step process

[thorpe911]

I think I found my answer.

 

Greg, can you please confirm?

 

P.S. - who is the ST director?

[Greg G.]

the adjustment "signs" aren't 100% intuitive

 

plus is bad, means you carry more weight per horsepower

minus is good, means you carry less weight per horsepower

 

 

I guess they really are not intuitive since you got it backwards

 

A modification factor with a "+" sign means that you get to add that number to your wt/hp ratio calculation. That is a "good" thing. It allows you to either add more power, or drop more weight before approaching the 8.7:1 or 5.5:1 limits.

[Greg G.]

Texas ST-1,

 

Your understanding of the rule makes sense; you get a hit for running a slick and get a little help for running a smaller tire. However, all verbiage of the rule states "non-DOT approved" and there is no reference to "DOT Approved" tires.

 

So my concern is, if I run a 245 DOT approved tire (i.e. Toyo RA-1), I don't get any adds or hits. But, if I run a 245 non-DOT approved slick, I get a +0.8 add and it is significantly faster that the Toyo. This does not make sense to me, that is why I wanted the clarification. Maybe we will have to wait for Greg to take a look at this.

 

Thorpe.

 

Tires:
  Non-DOT approved tires = -0.75
  Size 275 to 250 (or 10.5” to 9.5” for non-DOT approved) = +0.4
  Size 245 or smaller (or less than 9.5” for non-DOT approved) = +0.8

Thorpe,

 

Your quote of the rules above says "Size 245 or smaller (or less than 9.5" for non-DOT approved) = +0.8" The "Size 245 or smaller" refers to DOT approved tires, and the "or less than 9.5" for non-DOT approved" refers to non-DOT approved tires.

 

So, a Non-DOT slick that is less than 9.5" (essentially equivalent in size to a DOT 245) first gets hit with the -0.75 mod factor, then benefits from the +0.8 mod factor. The net result is going to be +0.05 added to the calculation of measured wt/power ratio--which is an almost negligible benefit compared to the "assumed standard ST tire" which would be a DOT approved tire between 285 and 345mm in size.

 

A DOT approved 245 tire gets the +0.8 mod factor added to the calculation of measured wt/power ratio, which is a significant advantage in wt/power ratio (needed to help equalize cars running 245's vs cars running 345's, etc).

 

Let's assume your 7's Only Mazda GT Spec car has a minimum comp. wt of 2125 lbs. So, if you continue to run 245 size Toyos (or other DOT approved tires), and your car made a maximum of 225 rwhp on a Dynojet, your calculations would look like this:

2125/225= 9.44

- 0.2 (dog box tranny)= 9.24

+ 0.8 (245 tire)= 10.04

- 1.1 (weight chart 2125 lbs)=8.94

- 0.2 (7's Only Mazda Spec RX-7 mod factor)= 8.74 = ST2

 

So, basically, if you wanted to max out your car, you can run up to 226 rwhp and change to Hankooks/Hoosiers/Kumhos/etc. (or start adding weight to the car if you want more power). One note, the 7's Only Spec cars were classed with the -0.2 mod factor as they were presented as a Spec car that we initially approved for PTA, but had to bump to ST when they were to the Jerrico box tranny's. As such, they are permitted to change the tires, and max out their weight/power ratios; however, they are not permitted to change their body design or make aero mods. If we were to permit additional aero mods, the -0.2 mod factor for the vehicle would be higher, which would bump the cars to a non-competitive status in ST1 as built.

 

Yes, I'm the National ST Director and the ST Director for SoCal.

[Greg G.]

I think we are getting a little off the subject. I understand how the factor works, my only question is how tire types (DOT vs. non-DOT) affect the modification factor.

 

And, I think I just had an epiphany. Take a look at this and tell me if I'm correct.

 

The rule for tires is a two step process.

 

Step 1) Tire type - if you run non-DOT you get a -0.75 hit. If you run a DOT tire, it is par. No points either way.

 

Step 2) Tire size - If you run 250-275 then you get +0.4. If you run 245 or smaller then you get +0.8 regardless if it is DOT approved or not.

 

Example: a 245 Kumho slick. -0.75 for non-DOT and +0.8 for 245 or smaller for a net total of +0.05 added to my factor.

 

Does this sound right? Greg G, can you comment to this ?

 

Thanks,

Thorpe

 

Bingo--I should have read the entire thread before answering above, but now it should be clear as mud--I mean glass.

[thorpe911]

Hi Greg,

 

I put together a spreasheet for our Mazda GT cars that mirrors the Clasification Form. Can I send it to you for validation?

 

I do not intent to replace the form, rather to make it easier to find out where our cars fit in the ST-2 class and what we can do to get us closer to the 8.7:1 mark.

 

If you are ok with this, can you give me your email address or provide me with some other way of sending it to you. It is in Excel format.

 

[email protected]

 

Thanks,

Thorpe

[thorpe911]

And, thank you for answering my question. I was writing the last post when your answer came in.

 

I will sleep much better tonight.

[Greg G.]

Hi Greg,

 

I put together a spreasheet for our Mazda GT cars that mirrors the Clasification Form. Can I send it to you for validation?

 

I do not intent to replace the form, rather to make it easier to find out where our cars fit in the ST-2 class and what we can do to get us closer to the 8.7:1 mark.

 

If you are ok with this, can you give me your email address or provide me with some other way of sending it to you. It is in Excel format.

 

[email protected]

 

Thanks,

Thorpe

 

Sure, [email protected]

[TexaST-1]

Sorry if my sig isn't clear. Greg is the man. I am the NASA Texas ST Director and School Director.