​The baseline model required detailed CAD and component information in order to populate the various physics definition files used by rFactor. All input data is realistic; meaning that the parts exist and have data sheets, or their parameters were measured. Mass, inertia, and suspension geometry data is calculated from the detailed CAD model, aerodynamic data from CFD analysis, and tire data from trusted rFactor tire models.

Down Force

The baseline down force was increased by adding dual element wings to the front and back of the car with 60 in and 45 in spans respectively. The aerodynamic impact of the wings is summarized here:

• Drag Coeff. increased from 0.775 to 1.04
• Lift Coeff. decreased from -0.267 to -1.03
• Cl/Cd increased from 0.344 to 0.992

The effect of the wings increased both drag and lift, but the gain in lift was greater meaning  the aerodynamic efficiency improves. Read more about aerodynamic analysis here...

Baseline Model

The baseline vehicle is a two person, steel space frame, purpose build, track car. It is powered by a stock 2006 Kawasaki ZX10 engine, runs on DOT racing slicks (Hoosier A6/R6, BFG GForce R1, etc), and has basic aerodynamic features to avoid creating lift and to minimize drag. Total weight is estimated to be 924kg (2034lbm) including both driver and passenger in full gear. The engine produces a peak of 112kW (150Hp) at 12,000RPM. The final reduction is a 14:48 with the 48 tooth sprocket driving a Quaife chain drive differential. All 4 corners (unsprung wheel assemblies) are identical with Wilwood calipers, Brembo disks, custom uprights, Chevy Cobalt hubs, and V2 Competition wheels. Read more about the car here...

Human-in-the-Loop Race Car Parametric Analysis

This analysis uses human-in-the-loop racing simulation to compare the relative improvements in lap time gained by making significant adjustments to major vehicle parameters. The analysis was conducted at a stage in the car development when adequate information is available for creating a high fidelity model, but major changes will not impose major set backs or cost increase. The goal of the analysis is to determine which parameter has the most potential to improve race performance with the least amount of resources, i.e. the low hanging fruit. The parameters investigated are:

• Down Force

• Engine Power

• Weight
• Aerodynamic Drag

 The parameters were selected based what could feasibly be done with available resources. This analysis uses rFactor2,  human-in-the-loop racing simulation software for which content (tracks, vehicles, add-ons, etc) is some what open source. Read more about rFactor here. The following sections describe first the baseline vehicle model, and then the modifications made for each parameter.

Comparison

So the next question that comes is: "How does it compare with some performance cars that we already know?" To answer this, the simplest is to do some laps using well known performance cars also modeled in rFactor2. I chose the one production vehicle, the Nissan GTR, and one open-wheel car, the Renault Formula 3.5. The best lap time results, taken in similar manner as above, are as follows:

• GTR: 98.0 seconds
• Renault: 89.8 seconds

As above, the laps were completed without using any of the built in rFactor driving aids.

Lap Time Evaluation

Toban Raceway Park, a fictitious road course developed for rFactor was selected for first round of testing. I chose Toban because it resembles the type of track where I'd like to drive the real car. Using faster tracks like Montreal GP would end up in misleading results. Toban is a 4 km (2.5 miles) long, clockwise circuit with slow corners, fast corners, and hills. Click image to the right to expand.

I started with the baseline model and through the course of many laps I made the following adjustments:

• Caster reduction: 9deg to 5deg
• Final ratio increase: 13:48 to 14:48
• Brake bias: 50% rear to 45% rear

Weight

The baseline mass is divided into two parts, sprung and unsprung mass. The unsprung mass is primarily made up of purchased parts; removing weight from these parts is not considered as a reasonable option, therefore the unsprung mass and inertia was not changed. The sprung mass however offers weight saving potential since the frame and secondary structural components were designed as an educated guess. Some work with mechanism and structural analysis software could lead to a reduction in frame elements or in their cross section area. I assumed that a 15% reduction for the sprung mass was an upper limit of what might be achieved.

Engine Power

The engine power is increased by using data for the same engine with a turbo charger. The graphs to the right show the original dyno data for a turbo changed ZX10 engine, and a comparison of the stock versus turbo changed engines. The result is an increase in peak power from 112kW (150HP) to 216 kW (290HP). No other changes were made since the weight of turbo is offset by removing the stock exhaust. Available turbo kits for 2006 ZX 10 are approximately $4000+shipping and include all necessary parts.

​These adjustment were carried over to all models.

I then proceeded to complete ~10 lap outings with each model; rotating through the set twice, so ~20 laps each. In the future I would like to do more laps, and also include a second track, but for now this is what I've done.

The results show the average of the best lap for each outing; meaning for each outing, I took the best lap, and the result is the average of all best laps for a given model. As is, for the baseline in have 5 best laps, while for the others I have 2.

Note that all rFatcor driving aids (traction control, anti-lock brake, etc) are off with the exception of invulnerability since its a waste of time to exit the track each time I hit the wall. Also, fuel use and tire wear were set at zero to avoid changing conditions for each successive lap.

Drag

Drag was handled in the same way as weight. Using the knowledge from the aero work done to get to this point, I assume that a reduction in drag of 15% was an upper limit of what could be achieved without impacting the baseline down force. An example would be adding fenders over the tires, this would reduce drag and likely increase overall down force. I applied the 15% reduction to the rFactor parameter BodyBaseDrag, which has the units of N/((m/s)^2). The results was a reduction from 0.5014 to 0.4262. Read more about aero analysis here...

The video to the right shows a short replay of the low weight model completing a section of the test track. In the top left of the screen you will find indicators for the pedal actuation percentages, a four quadrant acceleration graph, and some numerical information. Note that although I have not yet modeled the pilot and passenger graphics, I am driving the model, and the model weight includes both pilot and passenger. Further, unfortunately the paint job I gave the car (click here to see it) didn't not appear in the replay, so I still have some polishing work to do.

Results

​The results show that the high down force and low weight models demonstrated the greatest improvement in lap time compared to the baseline. Although the high power model demonstrated amazing acceleration (2Gs exiting the pitlane at one point) it was very tricky to control at low speeds, especially in corners. Driver improvement, or traction control could improve the performance, and these will have to come later. As the saying goes, more power makes you faster in the straights, less weight makes you faster everywhere.

The low drag model did not show much improvement, likely since it only helps in high speed sections of the track.

For interest sake, the average and top speeds of the baseline, high down force, and low weight model are shown below.

• ​​Baseline; Ave. = 119 km/h; Top = 177km/h
  
• High Down Force; Ave. = 125 km/h; Top = 158km/h
  
• Low Weight; Ave. = 124km/h; Top = 183km/h
  

​​The top speed of the high down force model is low due to the greater drag coeff. Despite losing that time on the straight, it had massive gains in the corners, especially the high speed corners (see peak lateral below). This made the high down force model very forgiving.

The initial public release of the model will be low weight as a baseline, and include the engine power and down force upgrades, adding both engine and down force upgrades should make it pretty fun to drive.

Finally, shown below are the peak accelerations for the various models. The peaks were taken from data covering only the best lap completed by each model. I chose to take peaks from the best lap since that way I can be sure that I'm not looking at a peak that occurred during a maneuver which was not beneficial for overall lap time. For example, the car will experience a peak in lateral acceleration just before losing grip on a corner and spinning out (could also be braking), and as we all know, spinning out is not beneficial for lap time.