Modified Autocross/Solo

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Autocross/Solo (Mid-Level)

Autocross (Also known as "Solo" and "Autoslalom") is a form of time-trial racing run with cars ranging from stock production cars to purpose-built race cars. Within classes that match vehicle type and horsepower to each other, racers negotiate a race course one or two at a time (not side-by-side, but at intervals) while being timed. The emphasis is placed on developing driver skill, having fun and keeping costs low.

A wide variety of production vehicle types and configurations are used at the mid-level of the sport. Almost any daily-driven vehicle qualifies for autocross with the exception of high roll-center vehicles which can easily roll over in sharp turns.

Mid-level differentiates itself mostly from entry-level by the number of changes and the knowledge required to make them work together to maximize performance.

Racing is generally on parking lots, kart tracks, road course circuits, and dirt circuits and is widespread throughout the Americas, UK and Australia. There is also a type of off-road racing called Autocross sanctioned by the FIA in Europe.

Power and Weight Stats
Horsepower (Typical Range) 150-450
Race Weight (Typical Range) 1225-1816 kg
2700-4000 lb

Design and Construction

Race Car Models of This Type

Production vehicles which are modified with racing/performance parts and are still considered "Streetable". Because each vehicle is categorized into its proper class, vehicles race on a level playing field.

Build Your Own Mid-Level Autocross/Solo Car

Knowledge Level

At the mid-level, it is useful to have a working knowledge of all aspects of the vehicle (Handling/operation, suspension, chassis, powertrain, aerodynamics, and safety). Many more modifications can be made to the vehicle and so the greater the knowledge of these systems, the better the choices you can make.

For instance, if you can identify the components which will provide the best value for your buck and purchase the ideal combinations of components, you can maximize more of your vehicle the same money.

Design Challenges

Suspension: Mid-level Autocross vehicle suspension modifications that can result in significant performance gains:

  1. Increasing tire contact patch and grip through wider wheels and wider street-legal racing tires.
  2. Lowering the ride height (with corresponding changes to the suspension geometry to ensure maximum tire contact patch on the road)
  3. Changing springs, anti-roll bars and damping to manage weight transfer and help the tires follow the surface of the road better.
  4. Increasing stopping power through bigger brakes

As with any race vehicle, consideration should be given to the unsprung weight at each corner of the vehicle (Wheels, tires).

Chassis: In mid-level Autocross, safety modifications such as a roll structure are welcomed and can provide additional chassis torsional rigidity which makes handling more consistent. Lightening of the body through replacement of body panels may be permitted. However, the core chassis/body must remain stock.

Powertrain: Powertrain modifications at the mid-level can include extensive changes to the engine components, and some driveline components. The goals of changes to the powertrain should be to increase horsepower and engine efficiency. This can be accomplished through replacing stock components for increased internal flow (Intake/exhaust), improved combustion, reducing friction and removing/replacing power robbing accessories. In terms of final drive, any modifications that increase power delivery (ie. Limited slip differentials) to the road should be considered.

Aerodynamic: Spoilers, airdams and wings may be permitted but unless the top speeds are high enough to generate real downforce, the benefits may not be significant enough to justify costs. That said, there is a benefit to be had if aero devices are large enough and are designed to generate maximum downforce in the speed ranges you will encounter.

Safety: Adding a roll cage provides a measure of safety that a stock vehicle does not provide. It will also add a measure of confidence for the driver, who will not be afraid to push as hard as they can in the knowledge they are protected. If a roll structure is not available off-the-shelf, however, it will need to be designed and fabricated, which will require some steel design and welding work (This can be done by speed or metal fabrication shops)

A racing seat with a multi-point harness should also be considered to enable the driver to feel the car more accurately, maintain seating position in cornering and secure the driver fully in the case of a rollover.

If you intend to race under a sanctioning body, always read and understand the regulations of your chosen racing class before designing or building any race vehicle.

Design Resources

Learn the basics about race cars and race car design from our free online knowledge series

Download our free race car design aids to assist you designing your race vehicle.

In-depth books and learning resources we recommend for mid-level Autocross car design.

Join our forum to ask and find answers to your mid-level Autocross car design/construction questions.

Construction Challenges

Most components permitted for mid-level Autocross are bolt-on type components and therefore are within the mechanical skills of most people. Challenges include the number of components which are changeable, and the difficulty in changing them (i.e. Things like engine removal), which may require specialized workshop tools.

For roll cages that must be custom fabricated, there is the additional requirement of fitting it into a production vehicle and of locating mounting points that do not compromise the uni-body chassis.

Build Costs

With many parts replaceable and new parts permitted, it is quite easy to spend a significant sum of money "hopping up" your new race car. However, with adequate knowledge, it is possible to select areas of modification that provide maximum value and keep costs to a minimum.

Build Effort

Build effort depends on the number of areas that are modified. If your modifications are performed a little at a time, the effort will also be manageable.

Racing Cost

Consumable costs are low, with the highest expense likely coming from the purchase of street-legal racing tires.

Transportation and Support Equipment

The vehicle can be driven to the track and support equipment can be carried in the vehicle.

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