Thought I would throw together some FAQ's on autocrossing the 3. If you have any to add, I will edit my post with the question and answer.
Here is the current SCCA Solo Rule Book
What class does my 3 fall into?
The classes for the Mazda 3i and 3s are:
Street Touring S
Street Touring X
F Street Prepared
The classes for the Mazdaspeed 3 are:
Street Touring Ultra
D Street Prepared (under the 4 cyl. mechanical induction catchall)
Right now, the only classes that the 3 and MS3 are competitive are in the Stock Classes.
What can I do to my car and remain in Stock?
First, you should always consult the SCCA rulebook for current rules. The Stock Class rules tend to stay consistent, but you should always check if you are thinking of a new mod.
Stock Class basically requires you to run the car the as presented from the factory. The only changes generally allowed are wear items such as tires (any DOT approved tire is allowed, including ‘R’ Compounds), brake pads (any pad can be used), exhaust can be changed after the last catalytic converter, the air filter can be changed.
While it is not a wear item, the front sway bar can be changed as well.
For wheels, you are allowed to use any wheel that is dimensionally the same (width and diameter) as the wheels that came with your model car. You can change the offset by .25”.
Can I use a smaller rim than what came on the vehicle and stay in Stock?
No, you must use the size that came on your model car.
What are R-Compound tires?
Some manufacturers make tires that are specifically designed to be driven on the track. Because many sanctioning bodies require DOT approved tires, the manufacturers design the tires to meet DOT regulations. Some of the tires that fall into this class are the Hoosier A6 an R6, Kumho V710, BFGoodrich G-Force R1, Hankook Z214 (There are more, but these are the top 4 in autocross)
I put a cold air intake in and dropped the suspension. Is this okay for Stock Class?
These mods will put you into the Street Touring classes. Street Touring S (STS) for the regular 3 and Street Touring Ultra (STU) for the Mazdaspeed3.
Okay, what can I do in Street Touring?
First, you should be aware that the Street Touring rules are still new and, as a result, are still changing. What is legal this year may be illegal next year (and visa-versa) If you are going to build a car to the Street Touring Rules you should get a rulebook and stay current with rules changes.
SOME of the things that you can do are:
Suspension mods (lowering, sway bars, struts)
Engine Mods (Cold air intake, emissions legal headers, mounts, accessory pulleys)
Alternate brake pads and rotors (ie slotted or cross drilled) may be used.
Wheels can be any diameter but may only be 7.5” wide.
Tires may have a maximum section width of 225mm. The UTQG Treadwear rating must be 140 or higher. There are some tires that are on the exclusion list, consult the rulebook.
No limited slips allowed.
There is much more that can be done, but that is the gist of it.
Street Touring X adds:
8” Wheels allowed
Maximum tire is 245mm (but the UTQTG rating is the same)
Diffs are allowed.
High Flow cats are allowed.
Alternate Rotors and Calipers are allowed (provided the rotor is the same size or larger than stock.)
Additional changes for STU are:
Maximum tire is 275mm (but the UTQTG rating is the same) on RWD and FWD
What is Street Prepared?
Street Prepared allows more engine work – you are allowed to change anything before and after the head. No cats are required.
Any wheel can be used and any DOT approved tire can be used.
The suspension allowances are a bit more free than in Street Touring.
To be competitive in Street Prepared, you should be prepared to trailer the car