Chassis and Suspension Overhaul II

Written by Ivan Pandev, July 2021

The Battle Bimmer’s performance at Solo Nationals 2019 exposed several underdeveloped areas of it’s chassis which need to be optimized to take full advantage of the then-new Vortec supercharger and 315mm Hoosier A7s. So much potential was left in these tweaks that there was no point in racing the Battle Bimmer again until they were completed. The following suspension overhaul is focused on building a responsive and optimized platform on which power-adders and wide slicks can opperate effectively.

Front Suspension: The Ground Control eccentric lower control arm bearings are re-clocked in new Meyle Heavy-Duty control arms for increased negative camber adjustment, which was sorely needed at 2019 Nationals. The increased negative camber allows for more even use and heating of the tread, whereas the previous alignment overworked the outer tire circumference and allowed severe pickup to accumulate on the underworked inner circumference. More negative camber also increases camber thrust, and thus the front axle’s lateral force potential. The control arm bushings are rebuilt with new Delrin inserts. An additional 1/8″ is added to the roll center correction and bump steer correction studs to minimize the front roll couple.

The studs themselves are inspected for cracking with Dynaflux penatrating dye upon removal; the control arm studs showed evidence of fretting and were replaced. Finally, the studs are installed on the kingpin using flanged distorted-thread locknuts, since the old castellated nuts had loosened and were resting on their cotter pins (perhaps the cause of the fretting damage). The self-locking distorted threads and wider footprint of the flange will hopefully prevent this failure going forward.

Steering: The steering rack is replaced with a 330i purple-tag unit, dropping the steering ratio from from 15.4:1 to 13.7:1, a 12% reduction, and installed with titanium hardware. Note the reduced pitch angle of the welded pinion gear. The pinion shaft is welded to eliminate the compliance of the torsion bar, since the rack is de-powered. The rubber steering giubo is replaced with an aluminum unit.

Brakes: To improve trail-braking turn-in by moving the brake bias rearward, the rear brake calipers are mounted on higher-diamater 325/328 caliper brackets and matched to 298mm rotors, up from the standard 276mm. I reckon this is roughly a 16% increase in the rear brake force. Front brake calipers are replaced with rebuilt, powder-coated ones. On all four corners, teflon-cored, strainless-steel braided brake lines, brass caliper guide bushings, drilled-and-slotted brake rotors, and Hawk HP+ pads are installed. Unlike full-track pads, the HP+ pads have high, but consistent braking fricition from ambient-to-medium temperatures, suitable for autocross conditions.

Rear Suspension: As the Battle Bimmer gets increasingly light on the rear axle (weight distribution is 54/46% F/R), and the spring rates increase to meet the response frequency demands of the ever-larger Hoosiers, the rear ride height has been creeping further up on Ground Control coilover perches which are at the bottom of their adjustment range. Likely designed with lower spring rates and much more mass in mind, they are out of their comfortable adjustment range.

To drop the rear ride height .350,” the aluminum Ground Control perches are replaced with original asymmetric delrin ones. They measure 2.4mm and 2.7mm in perch height, to maintain the corner balancing achieved with the previous setup. As the car continues to evolve and weight continues to move around, the remaining balance can be made up with steel shims beneath these perches, and of course the conventional adjustable perches on the front coilovers.

Shakedown/ Driving Impressions: Click here to read how these changes affected the Battle Bimmer in our first-ever private test day at Thunderhill Raceway.

Addendum/ Rear Suspension II: The shakedown and test day at Thunderhill Raceway’s skid pad was overwhelmingly positive, and a powerful indicator of just how much time and driveability is left in modifications like the above. With this in mind, it was decided to address another neglected area of the Battle Bimmer’s chassis, even though it wasn’t an overt problem at 2019 Nationals; the rear suspensions’s bearings and bushings, many of them still the OE components with ~160k miles of wear.

The trailing arm bushings have previously been replaced with 85A polyurethane units, but these were a compromised design from the start. The trailing arm-to-chassis pivot doesn’t just rotate on a single axis, which causes friction in polyurethane bushings and transmits a bending moment into the trailing arm brackets. Also, upon removal, the inner aluminum sleeves had bent from the longitudinal loads transmitted through them; not quite a component failure but still unnerving. The new solution is a Turner Motorsport monoball unit, featuring an all-metal bearing set in a custom aluminum housing, wihch will allow for frictionless suspension articulation while further reducing compliance. The trailing arm brackets are replaced with DriftHQ units, which allow more toe adjustment (we hope to use a little more toe-out on the rear axle to encourage roation) and are made from thicker steel than the OE units.

Finally, the rear camber arm bushing was replaced with an M3-spec bearing. The standard bushing came apart during removal which revealed a suprising design detail; the inner metal race of the rubber bushing is not a straight cylinder. Instead, there is a spherical center section, so the bushing is much less compliant to radial forces than one would expect by looking at its exterior. This is good to know for any remaining bushings of this design throughout the car, but the M3-spec bearing is a welcome upgrade.

Oil Analysis 2: Bearings, Head Gasket Healthy

Written by Ivan Pandev, June 2022

Any race engine should regularly have its oil analyzed for indications of bearing wear resulting from oil starvation, but ours doubly so; the 170k-mile-now-6psi-supercharged M52tuB25, tossed about at 1.4 lateral Gs, puts a lot of faith in the near-stock oiling system (fortunately featuring under-piston oil jets) and the 40WT Red Line racing oil. The Battle Bimmer’s most recent oil analysis from Blackstone Laboratories comes after a testing and shakedown day at Thunderhill Raceway’s skid pad; roughly thirty 40s laps, the latter half essentially at full-aggression, with plenty of rev-limiter engagement. Below are the concentrations of various elements and contaminants found in the sample.

Lead is the most important indicator, as it comes from the crank bearings where the effects of supercharging and possible oil starvation will combine. The BB’s oil only picked up 2 PPM of lead for the whole test day, a relief compared to the 25 PPM measured after the 2019 SCCA Solo Nationals. This is evidence that 1) the initial onset of the lead concentration might’ve been from leaded race fuel and 2) the stock oiling system is roughly enough to cope with autocross duty, even with 6psi of boost. Elements like aluminum, iron, and tin indicate wear near the piston- or cylinder head-area, but are stable in their concentration; more evidence that oil pressure is suitably stable. Coolant is undetected in the oil, so the head gasket is holding up to boost fine as well.

Although we’ll continue monitoring oil composition, there’s no immediate need for oil pump baffling or pressurized systems.

Off-Season Power Upgrades

Written by Ivan Pandev, Winter 2018-19

Racing Dynamics exhaust headers, EPIC Motorsports ECU flash, Turner Motorsport racing alternator pulley, and an M3-spec fuel pump baffle were added in the winter of 2018/19.

The headers were painted with ceramic exhaust paint and wrapped in DEI Titanium exhaust wrap. The original header hardware was removed and replaced with E92-spec E-torx head studs. Rear O2 sensors were removed entirely.

The pulley is surprisingly large, but still supplies 14V to the battery at idle. Precise torque couldn’t be applied to the nut, so locking paint pen is used to check for tightness.

The M3 fuel pump baffle redirects return fuel to a reservoir right above the pump pickup.

Ergonomics Overhaul and Weight Reduciton I (Jan 2019)

The cabin of the Battle Bimmer is modified to more comfortably accommodate both drivers (one 145lb, 5″7′, the other 190lb, 5″9′).

Standard steel seat mounts are replaced with modified aluminum ones to save 2.8 lbs from the driver’s seat – exactly where corner balancing and chassis symmetry benefit the most. Domed, safety-wire-drilled aluminum seat-to-bracket bolts from Pro Bolt continue the weight savings. The seat sits slightly more upright in this configuration.



A Hyper Mu steering guibo is designed and prototyped to move the steering wheel 20mm closer to the driver. Its construction features 6061-T6 standoffs captured in a ABS FDM-printed cage, with elaborate pocketing. Meanwhile, washers angle the steering column further down to better meet the driver’s chest in the lowered seat. Domed, safety-wire-drilled aluminum seat-to-bracket bolts from Pro Bolt are used here as well.



Brake and clutch pedal bushings are replaced with bushings stiffer in shape and material (delrin, pictured left). The pedal pads, removed long ago, are re-installed to bring the pedals closer to the driver who now sits further back.



Finally, lateral bolstering is carved from foam stock and added to the seat for a tighter fit to the driver.

The net effect of all the above changes is that the driver has much better leverage on their control surfaces, especially steering, is better secured in their seat, and enjoys more precise braking motion.