Clarification of rules for TT/ST6

[Magus2727]

 Sorry if these are newbie questions.

1.  Under 6.1.2 - 1).3 is says DOT-approved R-compound autocross tires (“A-tires”) are not permitted in ST5 and ST6.”  Is there a way to tell a difference in autocross tires?  Specifically I am looking at the RC-1's.  They are a 100 UTQG rating (so would get an advantage of the modification factor of +0.5) but on Maxxis site it specifically says "DOT-approved R-compound" but does not say autocross. 

2.  6.1.3 - 2.)3 says removal of plastic wheel well liners is fine.  If the OEM liner is a fabric does it that allso allow?  I have plastic front liners but in the rear its a fabric. 

3. 6.1.8 - Talks about transmission limitations.  It does not talk about differentials and the install of limited slip differentials.  Searching of the document I found it does not talk about differentials at all and the install of helical or disc/clutch LSD's.  Are these allowed to be installed with any limitations or restrictions in TT/ST6? 

4.  Measure of track width.  In my searching it looks like industry sets track width from center of tire to center of tire.  This type of measurement does not take into account the bulge of the tire sidewall (but don’t think that really matters?).  My weight I am allowed a 30mm bulge.  When calculating and measuring track width to make sure I comply to the less than 4" of increase in track width which is the proper way to measure?   Measure outside bulge of one side tire to inside bulge to the next tire? 

 

Thanks!!!

[Clavette]

1.  RC-1's are allowed.  A tires are specifically called out A7's, Z214, and one other I can't recall.

4.  NASA makes a tool.  It also provides a template for you to make the tool to test your tires.  It's simple...if it fits, the tire passes.  If it doesn't, the the tire fails.  Use the tool.

[Magus2727]

49 minutes ago, Clavette said:

1.  RC-1's are allowed.  A tires are specifically called out A7's, Z214, and one other I can't recall.

4.  NASA makes a tool.  It also provides a template for you to make the tool to test your tires.  It's simple...if it fits, the tire passes.  If it doesn't, the the tire fails.  Use the tool.

For #4 that tool is for the tire width, not track width.   It looks like most will either measure outside of tire to inside of the next tire.  Or measure the whole width outside to outside and subtract a wheel width since they have the measurement tools and most people are likely going to be close to the 266/257/226 tire widths.   

for #1 wanted to make sure and after more searching it looks like people call it out and found the fit guide.  looks like the 255/40R176 fits the 257mm width tool when installed on a 9" wide wheel.  

 

Thank you for your comments. 

[Clavette]

4 minutes ago, Magus2727 said:

For #4 that tool is for the tire width, not track width.   It looks like most will either measure outside of tire to inside of the next tire.  Or measure the whole width outside to outside and subtract a wheel width since they have the measurement tools and most people are likely going to be close to the 266/257/226 tire widths.   

for #1 wanted to make sure and after more searching it looks like people call it out and found the fit guide.  looks like the 255/40R176 fits the 257mm width tool when installed on a 9" wide wheel.  

 

Thank you for your comments. 

 

I never came across the bulge question myself.  I run in TT3 and have only had to demonstrate compliance with the tool.  Make sure to post what you learn.

[Magus2727]

The tool takes into account the "bulge"

 

For #4 I am making sure I am measuring the track width and reference planes for track width as I change wheel widths, offsets, and wheel spacers that the new calculated track width is the correct width.  I will likely try to write up an email to my local area with my math and confirm.  I will report. 

 

Any Ideal on #2 and #3?  I think #2 is that it does not matter that its a fabric vs a plastic wheel liner.  Both have no structural or aerodynamic impact being one material type vs the other.  for #3 I think I came across something showing (at least for the FWD case) the unlimited / open feature of the final drive gear also covers limited slip diff's.

[Clavette]

4 hours ago, Magus2727 said:

The tool takes into account the "bulge"

 

For #4 I am making sure I am measuring the track width and reference planes for track width as I change wheel widths, offsets, and wheel spacers that the new calculated track width is the correct width.  I will likely try to write up an email to my local area with my math and confirm.  I will report. 

 

Any Ideal on #2 and #3?  I think #2 is that it does not matter that its a fabric vs a plastic wheel liner.  Both have no structural or aerodynamic impact being one material type vs the other.  for #3 I think I came across something showing (at least for the FWD case) the unlimited / open feature of the final drive gear also covers limited slip diff's.

Dunno about #2 and #3.

lets go back to the tool and the bulge.  

I don't believe there is any restriction on the bulge.  The 30 mm references the depth of the tool.  As an example, I am at 3000 lbs and run 245's.  I take the the 0.6 credit so have to fit the 266  mm wide x 30 mm deep tool/template. 

Have you looked a the template?  If not take a look and will make a lot more sense.

 

[Magus2727]

On ‎7‎/‎17‎/‎2019 at 6:14 PM, Clavette said:

Dunno about #2 and #3.

lets go back to the tool and the bulge.  

I don't believe there is any restriction on the bulge.  The 30 mm references the depth of the tool.  As an example, I am at 3000 lbs and run 245's.  I take the the 0.6 credit so have to fit the 266  mm wide x 30 mm deep tool/template. 

Have you looked a the template?  If not take a look and will make a lot more sense.

 

Clavette, my issue is not the tire width, but I will discuss it and it will help me better understand that bit as well.  The measurement tool of 30mm (or 23mm) deep measures the bulge and is thus part of the tire width requirement.  This is why (to my understanding) you can sometimes get a wider tire to pass with the tool if it is installed on a wider wheel because you now have more of a "stretch" vs a bulge.  If the tire is tall enough and the tread depth deep enough I can see where a tool would fit and still have tire physically outside the tool range.  But this is not typical for NASA as the tire that comes to mind that would fit this are Drag radial or Mud-Terrain tires.  The tool is to measure the usable tread and footprint which will deform under heavy side loads.

 

But again my issue is not with tire width and limitations.  I have found a few good NASA forum pages where people have posted wheel widths and tire size combinations and if they fit the 3 different measurement tools.  It’s making sure I understand how NASA defines and measures track width, which I still have not fully found or understood.

 

I am looking at getting a set of wheels with custom offsets and want to make sure before I do the wheel and the width of wheel is not an issue. 

OEM wheel is a 16x6 with a +52.5 offset (another trim level had a 17x7 with a +42 offset).  I am looking to go to a 17x9 with a +23 offset.  If track width is center of wheel to center of wheel (or center of tire, which center of tire is center of wheel right?) then my track width (assuming all other things have not changed) would increase by 29.5mm (the difference in the offsets) on each side for a total of 59mm or 2.323". 

My over all width from outside of tire to outside of tire would have increased by more than that to be now 5.3" wider from outside of tire to outside of tire.  but my understanding of track width and how it is suppose to be measured would only be seen as a 2.3" increase and still within the less than 4" increase per the ST6/ST5 rules.

 

This is what I am trying to confirm.  I reached out to my local Co-Regional Director on this and he said that my understanding of the rule was correct.  But also said that “Just changing tires on one of my cars on the same rims altered my track width by almost 1”!” this makes me doubt that I do understand track width because the tire is centered on the wheel.  So a wider tire would increase the overall width of the car but because track width is taken at the center of wheel/tire going with a wider tire in of it self should NOT change track width. It would change over all width and contact patch and other things but not track width.  

 

 

 

 

[Clavette]

10 hours ago, Magus2727 said:

Clavette, my issue is not the tire width, but I will discuss it and it will help me better understand that bit as well.  The measurement tool of 30mm (or 23mm) deep measures the bulge and is thus part of the tire width requirement.  This is why (to my understanding) you can sometimes get a wider tire to pass with the tool if it is installed on a wider wheel because you now have more of a "stretch" vs a bulge.  If the tire is tall enough and the tread depth deep enough I can see where a tool would fit and still have tire physically outside the tool range.  But this is not typical for NASA as the tire that comes to mind that would fit this are Drag radial or Mud-Terrain tires.  The tool is to measure the usable tread and footprint which will deform under heavy side loads.

 

But again my issue is not with tire width and limitations.  I have found a few good NASA forum pages where people have posted wheel widths and tire size combinations and if they fit the 3 different measurement tools.  It’s making sure I understand how NASA defines and measures track width, which I still have not fully found or understood.

 

I am looking at getting a set of wheels with custom offsets and want to make sure before I do the wheel and the width of wheel is not an issue. 

OEM wheel is a 16x6 with a +52.5 offset (another trim level had a 17x7 with a +42 offset).  I am looking to go to a 17x9 with a +23 offset.  If track width is center of wheel to center of wheel (or center of tire, which center of tire is center of wheel right?) then my track width (assuming all other things have not changed) would increase by 29.5mm (the difference in the offsets) on each side for a total of 59mm or 2.323". 

My over all width from outside of tire to outside of tire would have increased by more than that to be now 5.3" wider from outside of tire to outside of tire.  but my understanding of track width and how it is suppose to be measured would only be seen as a 2.3" increase and still within the less than 4" increase per the ST6/ST5 rules.

 

This is what I am trying to confirm.  I reached out to my local Co-Regional Director on this and he said that my understanding of the rule was correct.  But also said that “Just changing tires on one of my cars on the same rims altered my track width by almost 1”!” this makes me doubt that I do understand track width because the tire is centered on the wheel.  So a wider tire would increase the overall width of the car but because track width is taken at the center of wheel/tire going with a wider tire in of it self should NOT change track width. It would change over all width and contact patch and other things but not track width.  

 

 

 

 

To my understanding and my experience, the way that NASA measures track width of the mounted tire is exclusively with their templates.  

I also don't see how spacer or offsets affect the track width of the mounted tire, unless there is some minimal deflection but I found that the mounted tire will provide the same measurement with it on or off the car.  In fact, I think there is a provision to allow for you to have the wheel off the car in which case offsets or spacers will have no difference at all.

I have a 3000 lb car.  I run 245/40/18's A7's on a 18 x 9.5 rim et35.  To get my +0.6, the tire has to pass the 266 x 30 mm template.  With that configuration the tool slides on; the tire makes contact with inside width of the tool and the edges of the tool have space between the sidewalls for the full 30 mm of depth on both sides.  NASA makes no other measurements and awards me the +0.6wt/hp modifier.

Now if you're trying to pre-figure out whether you want a 7 or an 8 or a 9 and how that may stretch the tire, that is best figured out by just going to the next NASA event and hanging out in the tech shed and seeing what works.

For example, in my tests, a 10 inch rim and a 9 inch rim with 245/40/18 A7's did not pass the 266 x 30 mm template.  Only the 9.5 rims worked.  Also 245/35/18 which is supposed to have narrower tread width did not pass on any rim size.

If I am you, I'd just go to the NASA tech shed and use their templates on various cars that go through to see what folks are running.

I am sure if you and I were talking face to face, you'd be able to show me exactly what you're asking so I apologize if I am still misunderstanding your question.

Good luck.

Edited July 25, 2019 by Clavette

[Magus2727]

46 minutes ago, Clavette said:

To my understanding and my experience, the way that NASA measures track width of the mounted tire is exclusively with their templates.  

I also don't see how spacer or offsets affect the track width of the mounted tire, unless there is some minimal deflection but I found that the mounted tire will provide the same measurement with it on or off the car.  In fact, I think there is a provision to allow for you to have the wheel off the car in which case offsets or spacers will have no difference at all.

I have a 3000 lb car.  I run 245/40/18's A7's on a 18 x 9.5 rim et35.  To get my +0.6, the tire has to pass the 266 x 30 mm template.  With that configuration the tool slides on; the tire makes contact with inside width of the tool and the edges of the tool have space between the sidewalls for the full 30 mm of depth on both sides.  NASA makes no other measurements and awards me the +0.6wt/hp modifier.

Now if you're trying to pre-figure out whether you want a 7 or an 8 or a 9 and how that may stretch the tire, that is best figured out by just going to the next NASA event and hanging out in the tech shed and seeing what works.

For example, in my tests, a 10 inch rim and a 9 inch rim with 245/40/18 A7's did not pass the 266 x 30 mm template.  Only the 9.5 rims worked.  Also 245/35/18 which is supposed to have narrower tread width did not pass on any rim size.

If I am you, I'd just go to the NASA tech shed and use their templates on various cars that go through to see what folks are running.

I am sure if you and I were talking face to face, you'd be able to show me exactly what you're asking so I apologize if I am still misunderstanding your question.

Good luck.

Thanks for taking the time to respond to my post.  I think there is a disconnect between track width vs wheel/tire width.  

 

I plan on making another post that asks just this question and also has some diagrams and pictures to describe.  Will be a bit before I can get those created.  But hope that will clear up what I am asking.