Following on from what Alastair Queen stated “the Suzuki needs a lot of weight over the back end” (
http://www.themotorcyclingclub.org.uk/forum/index.php?topic=85.15 ), here's a few of my thoughts from trialling a three-wheeler in class O and a Beetle in class 4. These are just the mods I would carry out if I had an X-90 and are based on limited car trialling and no experience of this car.
The amount of work you want to put in is going to be dictated by how long you want to keep the car, but here goes:
1. Leave the suspension as standard for the Edinburgh; play around with it later once you get to pick some X-90 brains on the trial.
2. Get as much of the weight over the back end as possible. Mount the rear wheels behind the rear panel on some sort of frame, but ensure you still conform with the MSA rule '9.1.1. The body overhang of non-production cars must not exceed one-fifth of the overall car length at the front, and one-third at the rear. Overhang is measured from the line of the road wheel centres'. Load all the tools, spares, trolley jack, etc as far back in the boot as possible.
3. Strip the car of all unnecessary weight, such as door panels, front apron, carpets, bonnet lining. It'll be noisy, but as you're a biker, you'll have loads of ear plugs.
4. Install some under-guards beneath the engine and gearbox as appropriate. I've used 18 mm thick plywood with a lining of thin steel sheet to create a sandwich. The plywood gives the under-guard some spring and flexibility and the sheet steel stops the plywood getting torn. The two materials are also easier to get hold of, easier to work with and weigh less than a thick steel plate equivalent.
5. I might even toy with moving the battery into the boot.
6. I don't know how you can protect the differential, all my cars have had the diff integral with the gearbox.
Good luck.
