Bobby’s Build: Part 1

Interior Strip Down

Bobby’s Build – Interior Strip Down

The first stage of most race car builds when starting with a road car is to strip out all of the unnecessary weight. Bobby’s build was no different as he took to the interior of the Mitsubishi Eclipse, pulling out everything in sight except for the door cards which are staying in place temporarily until they need to be removed to make way for the roll cage door bars at which point new ones can be fabricated. The OEM dash still remains but some of the heavier unwanted parts such as vents and metal brackets have been tossed in the bin to get the weight down as much as possible.

Bobby’s Build – Interior Strip Down

After the carpets had been ripped out the spare wheel well was next to go as the steel used for the wheel well recess is heavy and not needed. Therefore the angle grinder was picked up and some thin aluminium sheet was laid in its place. It’s no wonder Bobby was so keen to get to work on removing weight as he said:

“Last time I weighed it was with full interior and a full tank of gas which sat at 1340KG! It’s not a light car”

Therefore to make it as competitive as possible within Time Attack that weight figure needs to drop substantially.

Coilover Selection

With the weight removed and the car now sitting higher than ever before, it was time for Bobby to start thinking about coilovers. There are many options of coilovers in the aftermarket world so the first stage of many decisions is to decide which price bracket you would like to fall within. For Bobby, his budget allowed for mid-range coilovers and one of the best brands of coilover within the sub £1000 bracket is BC Racing. Next Bobby had to decide what features were most important to achieve from the dampers, a few of which were:

  • Adjustable Bump and Rebound
    • This is important to fine tune the dampers when the car is used out on circuit to allow the car to handle the spring correctly and hone in on the perfect damping values for different conditions and circuits.
  • Damper Body Length Adjustment
    • It was important to select a damper where the height could be adjusted via the damper body rather than on the spring platform. This allows the car to be corner weighted to achieve optimum balance without affecting the pre load on different springs which could potentially give each corner of the car a different effective spring rate.
  • Nitrogen Pressurised Dampers
    • When looking at mid-range dampers it is important to select one that uses nitrogen to pressurise the oil inside the damper. This helps to prevent aeration of the oil which can cause the damper oil to become foamy which alters the viscosity of the damper and therefore the effectiveness of the damper on circuit where the oil is operating at a high temperature.

With these options listed Bobby was able to head over to BC Racing to check out their range. The coilover that fell into budget and satisfied all of the above demands was the BC Racing BR Series Coilover.  With these installed the car now sits about 1 inch lower than standard for the time being. Bobby also selected the optional extra with these coilovers choosing to remove the hardened rubber top mount to install the pillow ball top mount which help to remove the flex between the coilover and the chassis helping forces to be transmitted directly into the chassis which is a much better option for a race car as it will make the ride more harsh which might not be favourable in a track car that is used on the road as well.

Front Arms and Geometry

With the car now sitting lower than standard, the angles of all of the suspension arms front and rear have been affected, increasing camber gain, bump steer and affecting all other areas of geometry. Therefore it was now time for Bobby to begin assessing the current locations of all of the front suspension pick up points and start designing his custom suspension system.

As none of the stock arms are adjustable (apart from the slight adjustment offered by the offset camber bolts) Bobby was keen to start using his fabricating skills to use to create some suspension arms with enough adjustment to achieve the optimum set up for Time Attack. The configuration of the front suspension system is a wishbone multi-link configuration meaning that it has a front upper wishbone, a lower arm and a compression rod that ties into the bottom of the hub.

The first arm to be re-imagined was the front upper wishbone. These were reconstructed from tubular steel housing rose joints at each end and offering adjustment of:

  • Caster
  • Camber
  • Anti-Dive
  • Roll Centre

The natural position of the arm in the centre of adjustment offers more caster as standard at 6.6 degrees of caster. The rose joints mounting the arm to the chassis can be made longer or shorter to move the top of the hub backwards or forwards, increasing or decreasing the amount of caster in the system. The arms allow for caster to be adjusted by +/- 3 degrees from the natural position of 6.6 degrees.

Camber is adjusted in the same place as the caster. At the rose joints that mount the wishbone to the chassis. This does slightly limit the amount of adjustment that can be done to the camber before cater becomes affected and vice versa. However, the design is dependent upon space as there are many items limiting the design freedom for the front suspension. Despite the limitations, the design offers more than enough range of adjustment for the camber as the arm now sits naturally generating -2.5 degrees of camber at the front wheels but allows for an adjustment range of +/-3.6 degrees from this position.

The design of the front upper wishbone is a clever one as it includes a spacer that can be inserted below the rose joints that move the centre point of the bearing up and own. This in turn alters the roll centre position of the front suspension geometry meaning that fine adjustments can be made to the front arm quickly by inserting or removing  washers to increase or decrease the roll centre height. This means that the car can be taken out to a circuit with adjustable anti-roll bars and have them set to the centre point of adjustment. The roll centre can then be fine-tuned to get the car operating in roll as desired which then allows further fine adjustment to be made for weather changes etc with the anti-roll bar.

Not only do the spacers allow the roll centre position to be adjusted, but they allow the anti-dive geometry to be altered as well. This is done by inserting washers at the rear rose joint than at the front, effectively angling the mounting points downhill form a side view , altering the anti-dive and anti-lift geometry; both of which will prove very useful with the front wheel drive configuration of the car.

Moving on to the lower arm, these were made by Paul Volk in the US and Bobby decided to purchase these arms as the front uppers offer the majority of the adjustment that is required  in the system and time was against him. Therefore, the tried and tested option was selected and sure enough the lower arms were installed in a matter of days offering all the adjustment that was required.  Likewise, the same ethos was applied to the front compression arm that is a simple arm in design, so the cost effective choice of a Hardrace replacement was selected offering a slightly stiffer inner rubber bush to remove flex form the system.

The final point of call for the front suspension geometry was the bump steer. Now the car was lower the bump steer had been amplified to a point where it was affecting the handling of the car out on circuit. Therefore, Bobby decided it was time to fabricate a solution to remove as much bump steer as possible. However, the solution had to be adjustable due to the fact that the car was not complete yet meaning ride heights were subject to change which would alter the bump steer characteristics further down the line.

The bump steer kit is made of two tapered spacers moving the tie rod away from the hub to improve the arc pattern of the steering arm. Washers can then be inserted between the spacers and the hub to fine tune the arm pattern which can be measured by jacking the front wheel up and down with a toe gauge on the wheel to monitor the angle changes through bump and droop. The kit has proved very effective as the bump steer is entirely removed for the system for now and can be adjusted out again if set up changes bring it back.

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