Caterham iRS

Experience the Ultimate Caterham conversion. 

What everyone has always wanted.  The comfort of the CSR in the light and nimble S3 chassis.  Alternatively, upgrade the SV chassis to the iRS.   We can now offer the conversion of your existing S3 or SV chassis to fully independent double-wishbone specification. 

This is cleverly done as we retain the standard rear suspension dampers (of course we can offer upgrades to the OE dampers additionally).  Retain the standard fuel tank, driveshafts, differential and brakes.   We can offer an improved rear calliper if wanted at an additional cost.

Although we remove a very small section of the lower chassis rail that in the standard car attaches to the lower basket this could be reversed in the future if wanted very easily.

We prefabricate a rear “basket”, wishbones and upright which is then welded onto the rear bulkhead.

Our target for the conversion is 2 weeks.

The iRS makes for vastly improved road manners, particularly over sharp high speed surfaces.  Of course, there is still a “bump” – these are small lightweight cars after all but the harsh sharp edge that we all “brace” for is removed.

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Here is some unedited text from the designer Dominik.  This will provide a little more background of the idea and perhaps explain why it works so well at the first attempt.

My goal was always to build the perfect country road Caterham for me: a light S3 that also works optimally on third-class Black Forest or Vosges roads. Undoubtedly, the DeDion rear axle works extremely well. But under such conditions, it reaches its limits due to the design-related disadvantages: Mutual influence of the wheels, large unsprung masses and a very high roll pole. It was not without reason that Caterham had Multimatic develop an independent wheel suspension for the SV-R racing cars, which was then ultimately adopted 1:1 in the CSR. The creation of the SV-R chassis is described in detail in a presentation that has fascinated and captivated me for a long time: Presentation Multimatic At the beginning of 2019, I switched internally from engine to chassis development. And suddenly it was there again, the crazy idea in the back of my head: I want to build something like that too! However, as a “lateral entrant on a probationary period”, I didn’t dare to tell my new colleagues about my project at first. After all, established luminaries who hold chassis lectures at the university or who developed LMP1 racers. But at some point it was no longer possible to hide the fact that I had a solid nail in my head, from then on it didn’t matter 😀 But instead of being scorned and ridiculed, the pros were just as happy as little children to support me in my project. So my “specifications” became more specific: – A light and simple construction – Excellent kinematics – Fully adjustable (camber, toe, toe-in curve) – Adoption of the suspension strut attachment and the S3 suspension strut – Manageable flexing and welding work and therefore theoretically (!) “retrofittable” – High dimensional accuracy thanks to welding gauges – No significant loss of trunk volume As always, the first step was the most unpleasant and time-consuming: measuring the chassis with all handlebar attachment points on the front and rear axles. For this I created an evenly aligned support surface, which later serves as a reference plane in CAD:

The point cloud generated from this was then transferred to a kinematics simulation model. This made it possible to “take stock” of the standard chassis with its kinematic properties (toe-in/camber/caster curves, roll pole height/migration, braking/starting pitch compensation, etc.), see video.https://www.youtube.com/watch?v=f9IQV3iNGSE

Funnily enough, I got in touch with the then lead engineer of the Caterham project through a colleague who developed the basic design of the 919 LMP1 with Multimatic. I was able to discuss the simulation results intensively with him – a very likeable and helpful guy – and to define the target corridor with regard to the kinematics design. After I had roughly sketched a few different concepts in CAD, I came to the unsurprising result: Multimatic has already done a damn good job. So why reinvent the wheel instead of following the CSR axis? So it was also a very classic structure: double wishbone axle with separate rear tie rod and stabilizer. A simulation model was then also created for this axle construction.

In countless iteration loops, I adjusted the CAD design and simulation to each other until an optimal result was achieved in the available package.

The individual components are manufactured in quite complex welding jigs, whereby I sometimes screw jig to jig in order to achieve high precision in the ZSB as well.

My goal was to build a fully functional axle assembly outside of the vehicle, which is then “only” welded in the vehicle with the help of a positioning gauge.

The wheel carriers are probably the most complex and unfortunately also the heaviest components. The construction is based on historical models (e.g. Formula 1). The compact wheel bearing comes from a small car and fits perfectly with the unchanged Caterham drive shafts. The bearing housing is a turned part with a corresponding press fit. In order to keep the distortion as small as possible, a steel cylinder was pressed in before the spokes were welded (–> Thanks Lars).

The tie rods are height-adjustable with spacers. In this way, toe-in curves from -3’/cm to +5’/cm can be displayed. Before the fastening straps were finally welded on, a laser was used to check whether the CAD theory also corresponded to reality.

And was all the effort worth it? Let’s start again with the bare numbers, i.e. with the weight. I could hardly believe it myself, but my axle is almost 2.5 kg lighter than the series – without the unnecessary stabilizer! In my boldest CAD projections, I hadn’t dared to dream of that and mentally prepared myself for a decent additional weight. But what is much more relevant in terms of driving dynamics: I was able to save 9.2kg (!!!) of unsprung masses”

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Please call us for more details.

The cost of this conversion is £5950.00 + vat