Home WHAT'S IN A TRIALS CAR by Grant Campbell

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The Back End on my car was one of the things that took a bit of getting right. Close inspection shows that I've used Kombi reduction gears, called in the trade 'Droppers'. My first car was essentially all Kombi, and the whole concept arose, not because I knew anything about 'torque reaction', but because I owned a 'real' Kombi and I knew how good the traction was on that car. In fact, I used to practice getting stuck in the mud before I knew anything about trials. At least the trials 'legitimised' this foolish practice.

Torque reaction is the key, and the droppers promote quite violent torque reaction which attempts to lift the car, in turn pushing the tyres down hard on the ground and thus increasing traction. This is actually a momentary thing but it lasts until the limit of travel is reached, quite often long enough to get the best of a section. Letting the car squat by applying the fiddle brakes, then using the throttle to make the car jump is a great technique to master.

A side benefit of the droppers is the 4" extra ground clearance.

It's relatively easy to adjust the back end of a VW via the splines on the torsion bars & many would do this on a lot of VW buggies, but what's really needed is springs to suit the weight of the car. Mine weighs a little less than 400kg. I know formulas exist, but trial & error lead me to machining the original down to 17mm. This works really well and means that there is always spring tension throughout the full travel of the suspension. Shiny torsion bar illustrated is a failure taken down too far at 13mm.


Note the very smooth radius, necessary to obviate stress points. I finish this part off with an angle grinder. Good mate Bob Booth used to machine these for me until I had my own lathe, but most lathe operators hate these jobs because of the springyness of the material.