Roadcar Modification Framework 

This is a collection of ideas from different sources that represents a framework that guides a car build that is both fun on the road and relatively capable on the track.

It is biased heavily to the former as cars that are uncomfortable and unreliable get driven less. The guide begins with Gordan Murray's six principles of road car design:

Gordon Murray Six Principles:

1. Size or perceived size, check if car is intimidating to drive.

2. Ergonomics; primary and secondary controls, pedals.

3. Luggage capacity, cabin storage.

4. Driveability, slow traffic engine characteristics, overtaking.

5. Ride and handling.

6. Ease of parking.

 Tires and Wheels:

- Choose tire size and aggressiveness suitable for both performance and daily driving.
- Tire compounds that are too sticky can reduce predictability and fun on the street. In addition lower grip levels transmit less shock to the driveline improving reliability. 

- Be mindful of wheel offset and width; excessive changes can affect handling and comfort.
- Lighter wheels and smaller diameters generally correlate with overall comfort. 

Brakes:

- Upgrade brakes with a focus on improving performance without introducing discomfort or noise issues.

- Choose brake pads that offer a good balance between performance and street usability.
- Lighter weight brakes can reduce unsprung weight 

Suspension:

- Select suspension modifications that improve handling without sacrificing ride quality.

- Avoid lowering the car to the point where suspension travel is overly restricted.

- Use quality components to maintain or improve ride comfort and handling.

Engine and Differential Mounts:

- Assess the trade-offs of stiffer mounts, such as increased vibration and noise, against performance benefits.

- Opt for mounts that offer improved performance without significantly detracting from comfort.

Interior:

- Modify the interior to enhance comfort and usability without detracting from the car's practical aspects.
- Ergonomics can make a big difference in the overall driver experience of the cars. 

Engine and Performance:

- Be cautious with aftermarket ECUs and tunes; prioritize drivability and emissions compliance.

- Consider the real-world implications of power increases, such as fuel type availability.

- Camshafts that are aggressive usually sacrifice low end torque, and affect drivability 

Aerodynamics and Body:

- Consider the practical implications of aerodynamic modifications, such as ground clearance and daily usability.

- Use aerodynamic enhancements that improve performance without creating issues in normal driving conditions.

- Consider heat management and how it is affected by aerodynamic decisions. 

Weight Reduction:

- Pursue weight reduction strategies that do not compromise the vehicle's comfort or safety features.

- Balance the desire for weight savings with the need to maintain a comfortable and practical interior environment.
- Batteries, seats, brakes and body panels tend to be the most cost effective places for weight reduction. 

 Exhaust:

- Choose exhaust modifications that enhance sound and performance without excessive noise. 

- Consider the impact of exhaust modifications on neighborhood relations and long-distance comfort.