First, the springs. Springs keep the bottom of your car from scraping along the road, and they also control body roll, both laterally and front to rear. Looking for some serious cornering ability, we fitted 15mm, 780lb springs to the front – about 50% stiffer than standard. These have worked well, with less diving under breaks and great turn in, but it’s the rear end that is the key to this car’s improvement. The rear springs have been replaced with single, tapered leafs from a Volvo 360. Single leafs have been used in rally cars for a long time, and DSRC member Horton Poulter’s ’67 Bluebird SSS was greatly improved with them. Weighing about half of a standard rear leaf, they locate the rear axle better than a traditional leaf (no slipping between springs). The Volvo springs, however, are stiffer than the standard Datsun springs – so if you’re going to do this, you do need to upgrade the fronts to balance the car. Step two for my car was shock absorbers. Like many here, I already had Koni shock absorbers in my roadster. However, the factory valving that Koni set for the Datsun roadsters seems to be much stiffer in the rears than in the fronts - which sets up that oversteer problem, and doesn’t control the heavier front end very well. So the valving was swapped, front to rear, essentially.
So, the results. It’s hard, of course, to compare fairly between a sagged out suspension and new race setup, but fortunately I was able to drive a couple of other Datsun roadsters around the same time as we finished the changes on mine. The differences are instantly obvious. The new setup, very hard on the front and more compliant at the rear, makes the car much more willing to change direction. Quick left/right snatches (as through a chicane) are much faster, with less body roll and instant turn in. The rear end only comes out when provoked, and when it does, it does it with a lovely progressive feel. In short, the rear end is much more compliant, giving good traction even on bumpier roads. What surprised me, though, is how much nicer the ride has become from what it ever was. Bumps and uneven roads are handled with aplomb and railway crossings aren’t the terror that they used to be. All in all, an excellent result. Subjectively, at least. For more objective results, Alan Field’s car has since had similar changes made, and it seems to have had good results on the track.
There's been a fair amount of input from many people and sources (Alistair, the handling guru in Queensland, Lou Mondello, a number of rally teams, and some good books, including Carol Smith's "Tune to Win"). I’d like to thank them all for the way that my car has turned out, and turns in!
I'll post some photos over the next day or two, once I've taken them!
Cheers,
Steve
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