Current (2024) SCCA Solo and NASA Autocross Number and Class Marking Rules

So exactly what are the requirements for autocross numbers and class letters? That's a good question, and one to which we can find an answer by referencing the SCCA Solo and NASA Autocross rule books.


The 2024 SCCA rule book has not been changed from 2023 to 2024. It states...

3.7 - Vehicle Identification

A. All vehicles must display numbers and class letters on both sides, which must be readable by Timing & Scoring, Course, and Grid workers at all times.

Both sides. Not the front, rear or top, but sides. Our sets all come as a set - one for each side, at no extra charge.

SCCA Rulebook Autocross Markking Example

B. Only one set of numbers and class letters may be visible while the vehicle is running.

This one's important. Nowhere on the car should any other class or number markings be visible while on course. We've seen at local events that the codriver's "1" will be stuck on the trunk or roof. Technically, this is not legal. The same goes with the "L" if your car is being run in the ladies class as well.

C. Class shall be represented by the upper-case abbreviated form rather than be spelled out. Ladies’ classes shall be indicated by the letter “L” following the class letters. (Example: “BSPL” instead of “B Street Prepared Ladies”).

I can't say we've seen this happen in the past, but it's good of the SCCA to clarify. Additionally, all class letters we produce are upper case, complying with this line.

D. Numbers and class letters should be positioned next to each other. All letters and numbers must be on body panels, not on windows. All numbers and class letters must use the same typeface and the same color, and this color must provide adequate contrast to the background color (see Appendix F for examples).

There are a couple of points to note here. Make sure your class is immediately next (generally to the right) of your number. Especially notable for the blue tape and shoe polish crowd - numbers go on the body panels, not on windows. This is largely due to the fact that windows tend to be a difficult surface with which to contrast, as they are so reflective. Pertaining to that point, numbers must contrast with the panel color. That's why our outlined premium magnetic numbers and outlined premium low tack numbers are a top choice - combined with another number color, the white outline almost certainly offers contrast.

E. Numbers must be a minimum of 8” (20.5 cm) high with a 1¼” (3.25 cm) stroke. Class letters must be a minimum of 4” (10.25 cm) high with a 3/4” (2 cm) stroke. In all cases, the height of the class letters must be between 25% and 75% of the height of the numbers. Stroke width must be at least 10% of the height (see Appendix F.)

Now we're to the nitty gritty - the sizes. 8" high for numbers and 4" for class letters. That's simple, but the stroke, meaning the thickness of the digits, is also specified at 1 1/4" for numbers and 3/4" for letters. This is simply to ensure markings are visible to workers, as thicker, bolder fonts are more easily readable than thinner fonts.

F. The “1” on two-driver cars and the “L” on Ladies class cars are subject to all of the above requirements with regard to placement, color, size, and stroke.

Ditto for the "1" and "L" on codriven and ladies cars.

G. Karts may use numbers and class letters of reduced size provided that the following conditions are met:
1. Numbers must be displayed on the front and rear in addition to both sides.
2. Class letters must be on both sides.
3. In no case may the numbers be smaller than 6” (15.25 cm) in height with ¾” (2 cm) stroke, using a high-contrast color and background.

Karts are given some leeway, but 6" numbers can still be a challenge; especially on an FJC kart. The most important aspect here is to use high contrast colors.

H. For National Championship and National Tour competition, current official SCCA® required decals must be displayed on each side and front of the vehicle in a prominent location. For National Championship and National Tour events, one (1) official SCCA®-approved National sponsor identification logo must be displayed in an upright position, in a prominent location on each side of the vehicle. Additional sponsor and/or event specific decals may also be required; refer to event supplemental regulations. Further information is contained in Appendix F.

We've got you covered here. Grab some magnetic sheets to affix these decals to your car in a non-permanent manner.


NASA-X's rules are a bit less wordy, stating that numbers must be 8" on both sides on their tech inspection form.

In conflict though, the NASA TT Rules state something different.

Section 12 - Car Appearance

12.1 Numbers and Class Designation
All NASA TT cars must display a three-digit number on both sides and the front and rear of the car unless a one or two digit number has been assigned to that vehicle by NASA TT administration. Numbers must be of a contrasting color to the car or otherwise clearly visible, at least 10-inches tall with a 1.5-inch stroke for the sides, and four inches high for the front and rear. NASA TT cars must also display a class designation on both sides and the front and rear of the car in a four-inch height in contrasting color to the car. Class Designations shall be TT followed by the group number. For example, a B Class competitor would display “TTB” as a class designation.

Theoretically, the NASA TT rules are the rules of record for NASA X, with the NASA X rules being supplemental. So which is correct? In all the NASA events we've attended, the 8" rule looks to stand, and numbers must only be present on the sides of the car - not on the front and rear like the TT rules suggest.


If you're like us, some visuals go a long way.


Bad (not enough contrast):



In Conclusion

Most of these rules are common sense. Putting yourself in the shoes of the Timing and Scoring folks will go a long way towards ensuring you make their job easier, and they ensure you get scored correctly.

In conclusion, to be legal for both SCCA and NASA events, the minimum height for numbers is 8", and the minimum height for class designations is 4". At Autocross Digits, we keep this in mind when designing all our sets, so you can rest assured knowing you'll be legal when running our digits.

See you at the races!