After hours of mind-numbing suspension measuring, AKA tracing vanishing points from crappy photos, I present to you this rally icon.
About:
I aimed to make this car the most historically accurate I could. I don't claim I was completely successful since there's a handful of missing data I had to make estimations about (see list down below).
There's plenty of information to be found about the DTM and BTCC versions of this car, but very little information about the Group A rally spec, built and raced by Prodrive in the late 80s. Most of the data I was able to gather came from some ancient paper magazines and nearly dead 20 year old forums. I did my best to only fill the gaps where there was missing data. In the end this turned out to be a joy to drive and I hope you all enjoy as well.
Additionally I've included the Bastos/Motul replica livery I made, along with 4 great rally skins from Mesa and Jempy (with their permission, of course - see links below).
Note: This is a physics mod, and requires the original M3 E30 Group A model files from Kunos to be used, which are not included here. Follow the installation instructions down below. Some additional "rally" parts, like passenger seat and codriver were included as CSP extensions.
SS Moulinon by @wmialil
Brief History of the car
After the fall of Group B in 1986, The legendary Prodrive team was forced to step into Group A and they chose the brand new M3 for the part.
The team started developing the rally spec as early as 1986, alongside the touring car. At first, they toyed with the idea of designing a 4WD drivetrain layout but this was binned early on. BMW didn't want to venture too seriously into rallying. They would only supply the know-how, with the rest remaining on Prodrive's shoulders. That meant they would have to build the car on top of the circuit variant, abeit with a lot of modifications for use in rally.
The iconic S14 engine was re-tuned for mid-range punch and was initially rated at 270 horsepower in 1987. It was upgraded to a six-speed gearbox and went up to 285 HP in 1988. Finally being able to produce 295 HP a year later.
Some of the changes made for the rally car included: stiffer chassis, body shell and power trains; completly different suspension geometry and tuning to deal with the rougher roads; shorter transmission and steering ratios; bigger rear brakes for more rear bias; smaller fuel tank; inclusion of reverse and auxiliary lights, heating system, passenger seat and all of the additions that have to be implemented to race with a co-driver.
Despite all these completly new additions and reinforced parts, Prodrive managed to keep the weight relatively low. Only about 100 kg heavier than the circuit variant.
The RWD layout meant that the car wasn't able to compete against its 4WD comtemporaries on loose surfaces. It was surprinsingly good on asphalt stages, though, and went on to win the Tour de Corse in '87, several national championships and selected rounds of the WRC between '87 and '89
Despite the victories, though, BMW still treated rallying with "supreme indifference", and its two-wheel drivetrain layout was beggining to take its toll. This culminated to 1989 being the last year Prodrive would race the E30, before welcoming Subaru.
Even though it was outshined by the enourmous success of its touring car counterpart, the M3 E30 still managed to become a rally icon, and is still being raced on regional rallies to this day.
List of Features
Physics:
- Front and rear suspension geometry designed from scratch, after photo analysis of the historical Prodrive parts.
- Rear suspension geometry designed to reflect actual semi trailing arm kinematics. Semi-trailing arm suspensions actually have almost no anti-squat in reality - vanilla AC doesn't portray this correctly, cphys (CSP extended physics) fixes this.
- Front strut suspension geometry designed from scratch, after photo analysis of the historical Prodrive parts.
- Corrected tie rod position to provide ~25-30 degrees of wheel turn.
- Historically accurate springrates, wheel travel and damping rates.
- Note: some exact values of certain suspension data wasn't available, so some estimations were made.
- Recomendation: make sure the "MacPhearson struct FFB adjustment" option is checked on CSP's FFB Tweaks for accurate force feedback with this geo.
- Historically accurate engine performance based on the 1989 variant - 295 WHP
- Retuned torque curve based on more current dyno graph data - historical prodrive dyno was not found.
- Corrected inertia values to reflect sprung weight inertia.
- Six-Speed gearbox ratios accurate to the 1989 variant.
- Differential lock same as the circuit variant: 75% power and coast.
- Differential preload was lower than the circuit variant, but I coudn't find the exact number. Left at 50 Nm for now.
- Steering ratio and wheel lock accurate to the 1989 variant: 14.4/1 and 720 degrees lock to lock.
- Brake bias more prominent in the rear in comparison to the circuit car - estimated 63% since the exact data is lacking.
- Added a usable hydraulic love-handle
- S/M/H Tarmac tyres modified from Kunos' 80s-90s touring cars tyres.
- Accurate dimentions with center of gravity height adjusted accordingly
- Limited cphys tyre integration: new rolling resistance slip and lower values.
- Added a combined slip factor line for a more "squarish" traction circle.
- Rain tyres and physics working (forced on, despite what you might have set on CM)
- Wipers working; RainFX working; VAO working.
- Removed the front bumper carbon fiber aero (and its downforce properties) - not present on the rally car.
- Removed the left fuel cap mesh - not present on the rally car.
- Added some rally details like a wind-animated roof antenna, tow hooks and license plate as extensions.
- Added a passanger seat, codriver and rally helmet for the driver as extensions.
- Redone exhaust pipe animation.
- Redone headlight refraction.
Installation
Requires Custom Shader's Patch - this car uses extended physics (cphys), so CSP is required - tested on version 1.79-p
Note: there's no need to activate extended physics on your content manager UI - the mod uses it automatically.
- Extract the content folder to the assetto corsa main directory
- Copy these .kn5 model files from "content\cars\bmw_m3_e30_gra" to the new "soll_bmw_m3_e30_gra_rally" folder:
- bmw_m3_e30_grA.kn5
- bmw_m3_e30_grB.kn5
- bmw_m3_e30_grC.kn5
- bmw_m3_e30_grD.kn5
- collider.kn5
- Go to Content Manager's "Content" tab, "Cars" and select the new BMW M3 E30 Gr. A Rally Spec
- Click on "Replace sound" and select the BMW M3 E30 Gr.A 92 (yes, the dtm version)
Credits
Huge thanks to:
- @wimdes for inspiring me to do this mod. If not for his awesome Rally wiki, I probably woudn't have even started.
- The guys over at the CSP discord for sharing their knowledge and helping me out along the way. Especially Stereo, JPG_18 and Arch who answered my dumb questions.
Included liveries:
Bastos/Motul - by me
FINA and Camel - by @mesa
Delage and Viaene - by @Jempy
Other livery recommendations:
Spanish Rally Pack - by @ShenonGZ
Cedico - by @Xedrox
Rothmans - by @BikeGamer
GoPro Rally - by @Rakoczi Richard
Ilmo Lario Pirelli - by @Hoksu
For rally tracks to race on, go check out the amazing AC Rally Wiki
If you did all that and it didn't work, make sure you have the latest CSP installed (version 0.1.78).