Single leaf rear springs. (longish post)
Posted: Mon Jun 22, 2009 11:26 pm
A while back, we found that the suspension on my ‘68 Datsun 2000 Sports was seriously in need of attention. Whilst the rear springs were still semi-elliptic, the arc they described was a hill, rather than a valley! Consequently, the car was riding on the bump stops. Not particularly comfortable, though a few positive comments were made about the car’s stance on a club run! While we were looking at ride heights with a trolley jack, we also found that the front springs were sagging as well. A change had to made and while we were at it, it was decided that we take the opportunity to upgrade the suspension to something that would make it quicker around corners. It’s often noted that the Datsun Roadsters tend to oversteer, but I'd never been happy with the way that mine turned in, either (interestingly, a gentleman I met a few years back said the same thing, and he'd campaigned the ex-Doug Whiteford car here in Australia, later moving to a Lotus Elan). Whilst my car hasn’t seen any track time yet, it is certainly my intention to do so. More importantly, though, is the fact that my roadster is driven daily, on all sorts of roads, and most of my “enthusiastic†driving is on hilly back roads – not smooth race tracks. My roadster had to have some “give†in it, to absorb those nasty pot-holes and corrugations commonly found on Australian roads. If you watch a Targa style tarmac rally on those roads, you’ll soon see that circuit prepped cars tend to lift wheels mid corner, or skip around on bumpy sections. Neither is desirable when driving hard! After speaking to Lou Mondello about the experiences of various club members on tarmac rallies, I decided to try out something new on my roadster.
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
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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