SDR SCCA
Results 1 to 9 of 9

Thread: Question on interpretation of Rule 13.4 Wheels for Street Category

  1. #1

    Question on interpretation of Rule 13.4 Wheels for Street Category

    I have a few questions about wheels for street class.

    I looked in the forum, and found several posts on wheels, but I couldn't find the exact answer to this. Please forgive me if this has been answered, and I wasn't able to find it in the forum.

    Rule 13.4 says (in relevant part):

    "Any type wheel may be used provided it complies with the following:
    A. It is the same width as standard and as installed it does not have an offset more than 7.00 mm (0.275) from a standard wheel for the car. The resultant change in track dimensions is allowed.
    B. Wheel (rim) diameter may be increased or decreased 1 from the standard part. This change may be applied to the front, rear, or both axles."

    How are 1" diameter and 7mm offset allowances determined when there are several different wheels sizes offered for a particular model of car?

    For example, on the Porsche website, there are 8 wheel choices in four different sizes for a base 2018 718 Cayman:
    size a - 2 choices with 8x18 ET57 (front) and 9.5x18 ET49 (rear);
    size b - 2 choices with 8x19 ET57 (front) and 10x19 ET45 (rear);
    size c - 2 choices with 8x20 ET57 (front) and 10x20 ET45 (rear); and
    size d - 2 choices with 8.5x20 ET57 (front) and 10.5x20 ET47 (rear).

    One reading of the rule would mean the base 2018 Porsche 718 Cayman could still run is A Street class with 8.5x17 ET50 (front) and 10.5x17 ET38 (rear) because these wheels are the same width as the widest [size d] and 1 inch smaller than the smallest [size a] and within 7mm of the smallest offset [sizes b or c for the rears].

    Another reading would be that the rule means you can only vary the diameter and offset relative to a particular size option. In that case, the widest, smallest diameter, and largest offset wheels would be 8.5x19 ET50 (front) and 10.5x19 ET40 (rear) based off of size d.

    Has the rule been interpreted one way or the other?

    Thanks!

    John

  2. #2
    I have a 2017 Camaro 1LE and have EOM 20X10 et20 up front, 20X11 et43 rear. I have the option to go to a 19 or 21 inch wheel. The offset can be played with and I can go to either et13 to et27 up front and et36 to et50 rear. After all that you can try any 200tw tire you can fit. Hope this helps

  3. #3
    Quote Originally Posted by booyaa56 View Post
    I have a 2017 Camaro 1LE and have EOM 20X10 et20 up front, 20X11 et43 rear. I have the option to go to a 19 or 21 inch wheel. The offset can be played with and I can go to either et13 to et27 up front and et36 to et50 rear. After all that you can try any 200tw tire you can fit. Hope this helps
    Thanks Will.

    That tells me that the dimensions (e.g. the offsets) for a front wheel can't be mixed and matched with a rear wheel, probably because it wouldn't be "as installed" to put a rear wheel on the front, or vice versa.

    What about mixing and matching dimensions for standard rear wheels when there are different available rear wheel sizes?

    Thanks again!

    John

    Sent from my SM-G955U using Tapatalk

  4. #4
    John,
    I’m not sure if you can swap your tires front to back, but I dont see why you cant? I would be more worried about the wheel fitting and not rubbing.

  5. #5
    I believe the answer you are looking for is you can go +/- for any wheelset that can come standard for the model of car. If a base trim only comes with a 17x8 and a sport trim can come with a 17x8 or 18x9 for example, in the latter case you could go +- from either optional wheelset.

  6. #6
    Reviving this. Thanks for the replies so far. But my question really goes for vehicles that have wheels with staggered widths and staggered offsets.

    If a car comes from the factory with staggered width wheels, like set d in my example above with 10.5" wide rear wheels and 8.5" wide front wheels, assuming it will fit, and not violate any other rules, does putting a 10.5" wide wheel on the front (i.e. same width as a standard rear wheel) comply with the rule?

    Similarly, if a car comes from the factory with staggered offsets, again like set d in my example above with ET47 offset rear wheels and ET57 offset front wheels, assuming it will fit, and not violate any other rules, does putting ET57 offset wheels on the front (i.e. same offset as a standard rear wheel) comply with the rule?

    Thanks!

    John

  7. #7
    No, you can not exchange front and rear dimensions for staggered offsets. The allowances are from as the wheels are provided in factory options in the positions provided as factory options.

  8. #8
    Thanks. I suspected that might be the case, but the rule isn't super clear on that issue, particularly in the offset language.

  9. #9
    Quote Originally Posted by JKinOB View Post
    I have a few questions about wheels for street class.

    For example, on the Porsche website, there are 8 wheel choices in four different sizes for a base 2018 718 Cayman:
    size a - 2 choices with 8x18 ET57 (front) and 9.5x18 ET49 (rear);
    size b - 2 choices with 8x19 ET57 (front) and 10x19 ET45 (rear);
    size c - 2 choices with 8x20 ET57 (front) and 10x20 ET45 (rear); and
    size d - 2 choices with 8.5x20 ET57 (front) and 10.5x20 ET47 (rear).

    John
    Hi John,
    I just looked at the Porsche website. Yes it lists optional wheels. But note how when you click on them they say: Cayman S wheels, or 911 Turbo wheels, etc?

    Porsche may allow you to upgrade to them... but for SCCA rule purposes, that may not make them "standard"

    It all comes down to the fine print.
    - Are they Factory options listed on the Monroney (installed at the factory or port)? If yes, then they are "standard"
    - If they are "dealer" options... no matter where installed, they are not standard wheels, and can not be the bases for your Rule 13.4 bases.

    As to the offsets, and diameters, that is per wheel. If fronts and rears are different... then each must be considered on its own.

    As you learn about SCCA rules, the overriding thing to remember is... unless it's specifically allowed... IT'S NOT.
    - So, 10.5" wheels on the front... that would be a width change. Note how that is NOT listed a change allowed by this rule.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •