Please see the rule book at the bottom of this page for all official rules. Here’s just a quick summary to get you started:
- Front Wheel Drive production vehicles
- 4-cylinder Naturally Aspirated engine. No turbos, superchargers, nitrous, etc.
- Manual transmission (stick shift). No dog box, no sequential shifters.
- 100 or higher treadwear tires
- 200’s have proven to be competitive; use these for PPIR Time Attack events
- Some 100’s may be better suited for road course heat and conditions
- Up to 205 largest tire width, or 215 or 225 with a weight penalty (see below)
- Wheels weighing at least 11 lbs each (bare; without tire, weights, etc)
- Non-adjustable or single-adjustable shocks (ie Koni Yellow / 8041 and similar)
- No metal or spherical / “pillowball” suspension arm bushings
- Limited body and aerodynamic modifications
- Engine Output is limited to 160, as calculated by this formula:
- Engine Output = (Peak_Horsepower * 0.66) + (Peak_Torque * 0.32)
- Horsepower and Torque (ft-lbs) are at-the-wheels, as measured by a DynoJet
- Minimum race weight with driver (in lbs), is calculated as: Engine Output x 17
- If this comes out to less than 2200 lbs, then 2200 lbs is used instead
- When using 225 tires, there is an added penalty, reducing based on your Minimum Weight (as calculated above):
- 2200 lbs = 200 lb penalty for 225
- 2300 lbs = 150 lb penalty for 225
- 2400 lbs = 100 lb penalty for 225
- 2500 lbs = 50 lb penalty for 225
- 2600+ lbs = No penalty
- The 215 penalty is half that of 225; there is no penalty for 205 or lower
- Your Driver Profile / Competitor Registration form will easily calculate your total required weight for you: Competitor Registration Link
The goal here is to build cars that are reasonably competitive with each other, while allowing for some variety and choice, and without making this all about money.
The cars that fall on the lower weight / lower power end of things may be able to corner faster (depending on driver, tires, and suspension), while those with higher weight / higher power will attempt to make up for that with higher straightaway speeds, but the difference between the two shouldn’t be huge. Which approach is advantageous can vary depending on the track or course driven at each event, as well as driver preference, style, and strategy. This also helps keep the same car from winning every event.
Official Front4 Rule Book