This guide will take you through the steps of creating a new car based on an existing Mod.
You will need V0.8.2 or later of carFactory to follow this guide.
We will use the Caterham Mod by Major Parts / Cubits, so you need to download and install that before you start. If you plan to race on-line then make a backup of your Caterham folder, because we will be changing the .pm and .hdv files.
We will create a road-spec version of the Caterham Classic mod. As downloaded this is quite racy, stiffly sprung and damped with virtually no roll. We will be creating a version as close as possible to the showroom spec as the current version of carFactory allows.
Click on the 'Open .hdv' button and browse to the \Program Files\rFactor\GameData\Vehicles\Caterham folder and choose Classic.hdv.
The Wheelbase and track dimensions will be propagated across the Car, Front Suspension and Rear Suspension tabs.
Now enter the following accurate values for the rest of the boxes on the Car tab:
Total Mass: 610kg
Front/ rear split 46%
CofG Height 365mm
We can now estimate a rough set of inertia values. Make sure that 'Behind front axle' is set for the engine location and 'Spaceframe' is chosen for the chassis configuration and click 'Estimate'.
Your screen should now look like the following:
Save your work so far; click File -> Save -> Car and save the Car as RoadClassic.car. CarFactory will automatically save the Front and Rear Suspension and Ride and Roll settings with matching filenames.
Click on the 'Front Suspension' tab and enter the following details:
Tyre spec: 185 60 R 14
Roll centre height: 21mm
Camber: -2.0 deg
Roll camber rate: 0.3 deg / deg
Ride height: 110mm
Bump travel: 80mm
Rebound travel: 80mm
Kingpin inclination: 11 deg
Castor: 5 deg
Ackerman angle 40%
These are all accurate values except for the bump/rebound travel, but +/-80mm should be fine for the smoothly surfaced tracks available in rFactor.
Here is what your Front Suspension tab should now look like:
Move on to the 'Rear suspension' tab and enter the following values:
Tyre spec: 185 60 R 14
Roll centre: 175mm
Camber: -1.3 deg
Camber rate: 0.4 deg / deg
Ride height: 110mm
Bump travel: 80mm
Droop travel: 80mm
The roll centre, at 175mm, looks quite high compared to the front axle's roll centre. The Caterham Classic in real-life has a DeDion rear axle. The roll centre of a DeDion axle is exactly where it is connected to the Watts Linkage, which is limited by ride height considerations from being any where near the ground.
Choose 'De Dion with Watts linkage' from the Arrangements list. Your 'Rear Suspension' tab should remble the following:
Now click on the 'Ride and Roll' tab. The usual way to design a car's spring rates is to work from desired ride frequencies, but we know that a Caterham Classic fitted with a 1.4 K Series engine has 150lb front springs and 170lb rear springs, which convert to 24079 N/m front and 27261 N/m rear. Also, the springs do not act directly on the wheel centres, but slightly inboard. They are also mounted at an angle to the vertical which gives us Motion ratios of approximately 1.3:1 for the front and 1.25:1 for the rear.
Click the 'Spring Rates' radio button and enter the following values:
Spring rate front: 24079 N/m
Motion ratio front: 1.3
Spring rate rear: 27261 N/m
Motion ratio rear: 1.25
You will see that the corrected Wheel rates are automatically calculated.
Now we need to set the damper settings. A K-Series Caterham Classic comes as standard with Bilstein F4 B48 1899 H0 front dampers and F4 1900 H0 rear dampers. I have absolutely no idea what valving is fitted so we will have to let carFactory work out sensible damper settings by entering Damping Ratios and letting it calculate the required low and high speed bump and rebound values. A sensible value for a road / race or track day car as sporty as the Caterham is in the 0.5 to 0.65 range. One of Colin Chapman's documented beliefs was that there is nothing wrong with a softly sprung car as long as it is well damped, so we will go to the upper end of that range:
Set the front and rear damping ration to 0.65.
Again, we have no idea what transition speed is used by those Bilstein dampers so leave the 0.127 m/s Transition Speed unchanged.
Now we will set the roll bar values. A K-Series Caterham Classic has a 900mm wide front roll bar with 200mm effective lever lengths, a motion ratio of approximately 2:1 and an outside diameter of 1/2” (12.7mm). Unfortunately without cutting one in half it is very hard to know the inside diameter! So we will specify a sensible roll gradient and TLLTD and let carFactory work out the technical details:
Enter a value of 1.5 deg / G for the roll gradient and a value of 53% for the TLLTD. 1.5 deg roll in a 1G corner is about right for a fairly racy road / track car and a value of 53% TLLTD puts the handling balance 7% in front of the centre of gravity (46%, we entered it on the 'Car' tab), to give a car that will be stable in very mild understeer unless provoked by sudden lift or application of power.
Save everything again, Click File->Save->Car. Your screen should resemble this:
Now we must build our front and rear suspension. Go to the Build tab, choose standard build quality (Low is only still there to help with rapid debugging and testing, it should never be used otherwise.) and click 'Build'. You should now be able to view and choose a front suspension solution:
The carFactory manual explains how to choose a trade-off between scrub, roll centre migration and camber rate.
Once you are happy with your solution for the front suspension, return to the 'Build' tab, select 'Rear Suspension' and click 'Build' again:
Because we chose a 'DeDion' arrangement there is only a single solution.
We can now generate our .pm and .hdv file snippets:
Go to the 'Generator' tab and click 'Generate':
You must now use Notepad to open the Classic.hdv and Narrow.pm files in the Program Files/rFactor/GameData/Vehicles/Caterham folder. If you have never worked with cars in rFactor before you will need to be exceedingly careful to copy everything to the correct location. A sigle typo can cause rFactor to crash when loading the car, with no helpful error message or error log explaining the reason :-(
The .pm file produced by carFactory is an entire replacement for the existing car's Narrow.pm file.
The .hdv snippets must carefully replace the existing settings in their respective sections ([GENERAL], [SUSPENSION], . . .).
You are now ready to load up rfactor and try your new car. The more experienced may prefer to create a new .veh file that points to new .hdv and .pm files thus preserving the existing Caterham Classic. It will certainly make side by side comparison easier.
What you should find is a softer, more forgiving Caterham, that matches the existing Classic mod's lap times very well. Despite suspension far more suited to the road than the track, the new geometry makes the tyres work harder making up for the road specification, right up until the brick-like aerodynamics cause terminal high speed understeer!