Choosing the Chassis

The next two steps were an agony of indecision – IRS versus Live Axle, and the various engine choices.

IRS is Independent Rear Suspension, where each wheel can move independently of each other. Live Axle is a solid rear axle, where if one wheel moves, so does the other. In theory, IRS gives better traction on rough surfaces, as each wheel can move independently to provide maximum grip. IRS will also cause the car to squat under high power loads, giving better grip off the line and when applying power through corners. By implication, IRS can also handle higher power limits, and is just less likely to spit you off the road.

Live Axle, on the other hand, is lighter and far easier to set up. IRS has all sorts of arms and linkages to get right before it handles properly. Live Axle is a simple case of bolting stuff together. You also have far fewer setup options for the rear tyres – simply bolt them on and go. If you want toe-in, bend the rear axle. With IRS would have all sorts of fiddly bits to tune and adjust each time.

It all comes down to what you want to do with the car. For track-days and smooth surfaces, Live Axle is better in that it’s lighter. If you can rely on the roads being smooth and steady, you can fling the thing around as well as an IRS. For roads, especially country roads, an IRS might one day be the difference between taking a corner and visiting the shrubbery, especially if you’re not the best driver in the world.

I’m not the best driver in the world, and I like to drive on country roads with all their pot-holes, gravel and undulations. Indeed, once you see where I’m building the thing, you’ll note that it’s probably a few hundred kays from any smooth surface.

So I went for the IRS for a couple of reasons – I’ll be on some rough roads and I want to feel that the car has the best chance of keeping me there, simple as that. The Live Axle provides more “fun” in terms of sliding the back end at lower speeds / power, which I must admit I quite enjoy. But I’ll still be able to do that with the IRS, I’m sure…..