Rally / Rallycross

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The Rally car is a unique type of road racing car that is designed to travel at the highest possible speeds over closed public roads from a start location to an end location. The timed races (Called Rallies) often combine dirt and paved roads and can include snow and ice covered conditions.

Most Rally cars are production sports cars that have been modified with upgrades throughout to increase performance and make them more durable for the punishing conditions they race under.

Racing is run on roads worldwide.

Power and Weight Stats
Horsepower (Typical Range) 120-600
Race Weight (Typical Range) 1044-1452 kg
2300-3200 lb

Design and Construction

Race Car Models of This Type

Donor production cars used for rallying have included Audi A1, Audi A3, Audi A4, Citroen C4, Citroen DS3, Ford Escort, Ford Focus, Honda Civic, Hyundai Accent, Hyundai i20, Mini, Mitsubishi Lancer, Nissan 240, Peugot 206, Peugot 307, SEAT Cordoba, Skoda Fabia, Skoda Octavia, Subaru Impreza, Toyota Corolla, VW Golf plus many more. Every major manufacturer around the world has examples of their cars in national or local level rallying.

Build Your Own Rally Car

Knowledge Level

There are two approaches to building a rally car: You acquire a rally car kit for your chosen donor car and assemble the car, or you design your own car from your base production model and purchase individual components. The knowledge level you require will depend on which approach you take.

Building a rally car from a kit will require some mechanical skills, but in addition to these you should have a working knowledge of handling, suspension, chassis, powertrain, aerodynamics and safety. Understanding how your car works is important in setup, troubleshooting and improving its performance.

Building a rally car from a basic donor car benefits from advanced knowledge of all aspects of the vehicle (Handling/operation, suspension, chassis, powertrain, aerodynamics, and safety). With a comprehensive knowledge and a study of existing rally car builds (especially top-level), you will be capable of making informed decisions on how to build your car. Component selection itself will have a more thorough understanding which gives additional confidence.

If you wish to make the learning curve more manageable, it is recommended that would-be Rally racers select an appropriate base vehicle and work their way up through competitive classes locally using that vehicle as their "development platform". Many of the available books provide basic to reasonably advanced knowledge in the aspects mentioned above, so they can provide a good reference alongside your experience.

Design Challenges

Suspension: Within the regulations of the sanctioning body class you wish to run in, you will want to design your car with the following goals:

  1. Protect the driver and co-driver
  2. Maximize durability. Aspects such as suspension mounts, suspension components, skid plates, etc. that stand a good chance of breaking if not up to the task. Metal fatigue is also an issue in cars where the suspension is subjected to repeated shock loads.
  3. Maximize grip by minimizing unsprung suspension weight to allow the tires to follow the road surface
  4. Maximize usable engine power
  5. Maximize brake stopping power
  6. Maximize ride height flexibility (with any changes to the suspension geometry taken into account to ensure maximum tire contact patch on the road).
  7. Maximize suspension setup flexibility with adjustable springs, anti-roll bars and damping to manage weight transfer and suspension compliance.
  8. Maximize visibility (For night stages)

There are many more potential goals, but ideally once the driver and co-driver are confident, giving the car durability, performance and flexibility will enable the driver to extract the maximum from it.

Chassis: The Roll cage/safety structure will likely help increase torsional rigidity. Lightening the vehicle by removing rear seating, interior panels and other components may be an option. Changes to the placement of components (i.e. Battery) in order to redistribute weight balance can often go hand-in-hand with lightening.

Powertrain: Depending on the class, powertrain modifications can include extensive changes to the engine components and driveline components. No matter what the class, the goals of changes to the powertrain should be to increase usable 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 such as limited slip differentials that increase power delivery to the road should be considered.

Aerodynamic: Depending on the class, aero devices and bodywork changes to enhance aerodynamics may be permitted. Reduction of drag should be a priority as frontal area of a production car is not changeable. Aero devices such as an underbody floor, air dam, wing (or spoiler) and diffuser are all possible depending on what is permitted by the regulations.

Designing the aero devices to work together and to balance front/rear downforce will provide optimal downforce and stability. Designing in adjustability to generate a wide range of downforce will give flexibility in setup.

Safety: A safety cell structure with racing seats/harnesses is mandatory. Other safety items such as a fuel safety cell and fire extinguisher may also be required. If an occupant safety cell structure is not available off-the-shelf, it will need to be designed and fabricated.

Communication: While not necessarily a design challenge, the Driver-to-Co-driver communication is absolutely critical. A good quality, clear, noise cancelling, fit-for-purpose rally communication system is a must.

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 Rally car design.

Join our forum to ask and find answers to your Rally car design/construction questions.

Construction Challenges

Having sufficient space around the car is important, as a cramped workshop will be difficult to work in.

The tools to modify the engine, chassis and bodywork can add considerably to the cost of your project if you don't already have a workshop, but borrowing or renting items is also an option.

Many components permitted for Rally racing can be 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 occupant safety cell structures that must be custom fabricated, there is the additional requirement of fitting it into the vehicle and of locating mounting points that do not compromise the uni-body chassis.

Build Costs

The base vehicle cost can be economical if purchasing a used donor vehicle up to 3-4 years old. Purchasing much older donor vehicles may open the possibility of corrosion damage and metal fatigue. Used donor cars will offer a lower cost entry point, especially as the car will be a "development platform" for both the builder and driver.

Racing parts will add to the cost of the base vehicle significantly. Suspension on a rally car is very important, and this is an area where race-proven parts are definitely worth the money. Beyond this, if you have adequate knowledge, it is possible to select areas of modification that provide maximum value and keep costs to a minimum.

Build Effort

The effort depends on the number of areas that are modified, which is a good reason to start in entry-level club rallying or in Autocrossing. If your modifications are performed a little at a time, the effort will also be manageable and your experience will grow along side your knowledge.

Racing Cost

Rally racing, by nature of its more punishing racing environment, can consume a larger budget through racing tires, engine rebuilds, and damage repairs. If using Autocross or club rallies as your "school", the costs can be kept much lower initially and the feel of the car can be determined without body damaging obstacles to hit. Ultimately, however, the rally course with its dependence on co-driver, and its on-road and off-road dangers must be run to gain rallying experience.

Transportation and Support Equipment

Trailering for non-street legal or race-only machines. Drive to the rally if street-legality is maintained. Support equipment is usually carried in the trailer/towing vehicle or a companion support vehicle.

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