Interim Rule Changes for 2021

From: Walter Fricke, PCA Club Racing Technical Coordinator

Effective immediately, the rules changes described on this page are in effect for the remainder of 2021.

Comments noting ambiguities in this announcement, typographical or other errors in the specifications, and problems with changes which may have been overlooked may be addressed to the Rules Committee via the address  Click on the address link to use your own e-mail client to compose and send the message.  Your message will be sent to all members of the Rules Committee.

Rule Book

Download your copy of the existing rule book — sans the changes summarized here — for comparison purposes.  Use this link to download a PDF copy of the 2021 rule changes listed below.


Use the links below to jump directly to specific changes:

911 CUP

    Serpentine fan/alternator belts are allowed, as are alternate pulley diameters. Crank/fan ratio is free. This was inadvertently left out of the 2021 revisions.


    2.7 liter 944s may run in SP3 as long as they follow the less restrictive rules of SP2 or SP3. This is to accommodate racers who find there are few if any SP2 cars at events they attend, and who are willing to accept a handicap, as it is understood that on paper the car will not be competitive.


    Snell 2010 helmets are acceptable until December 31, 2021. Racers are urged to be diligent in replacing their 2010 Snell helmets, but some models are yet to arrive at retailers, and some racers report helmets ordered last fall have not yet arrived. 

    GT3 LCA

    Several classes allow the substitution of the 996 GT3 lower control arm.  Existing rules allow aftermarket inner pieces (the short piece).  The longer outer arm piece appears to be NLA from Porsche.  Aftermarket outer arms of the same length and configuration as the factory piece are permitted.  Different classes have different rules for the thrust arm attachment (rubber, solid, adjustable or not).  Racers should be careful to obtain an aftermarket arm that meets the specification for their class in this regard, or obtains the insert for thrust arm attachment which is legal in their class, and install it.

    Ball Joints

    Ball joints for the outer lower control arm are available with thicker (larger diameter) shanks which connect to the strut assembly.  These are a permitted part.


    These cars may avail themselves of modifications approved for their model to race in IMSA or SHO or other PMNA sponsored or supported series. Racers with these post-factory modifications should have a copy of the series rules approving these modifications to show to the scrutineers and stewards should questions arise. The minimum weight in GTD remains at 3,100 pounds for all models and variants.


    There is a change in the allowed Pirelli rear slick tires for GTC5.  Racers may continue to use the previously allowed tires until the previously allowed rear tires they have in their trailers or shops are exhausted.

    For GTC5, the rear 275/645-18 DH is replaced with the DH or DHB 265/645-18 slick.

    The formal tire rule for GTC thus now reads as follows (subject to the grandfathering allowed):

    1. A. Tires are free in GTC1, GTC2, and GTC3. All later classes must use Pirelli Competition tires and display specified sponsor decals. Two Pirelli decals are required at a minimum: one on each side, or one front and one rear. No other tire company decals or logos may be displayed.  GTC4 shall run 245/645‐18 DHB slick or WH rain front and DHB 305/680‐18 slick or WH rain rear. GTC5 shall run DH or DHB 265/645‐18 slick or WH rain front and DHB 315/680‐18 slick or WH rain rear. GTC6 and GTC7 shall run 285/645‐18 DHD2 Slick or WH Rain front and 325/705‐18 DHDE Slick or WH Rain rear. GTC8 specs will be announced when available.

    GTC6, 7, & 8

    These classes may use the Bosch Club Sport M4 or M5 ABS. The M4 is NLA but may be found on some cars.

    GTC8 Spec Tires

    The spec tire for the 992 GTC8 Cup cars is Michelin:

    • 30/65 R 18 Cup N3 front
    • 31/71 R18 Cup N3 rear

    Rains are:

    • 30/71 R 18 Cup P2L front
    • 31/71 R 18 Cup P2L rear