The Push Rod Cantilever Front Suspension is one step further. It’s by no means complete as most of the brackets are just tack welded in place and I don’t even have the right sized bolts for some of the joints. But so far, everything is going pretty well. As you’d expect with only one bracket where there should be a pair and loose bolts all over, there is some flex in everything but the aim at this stage was purely to check that I’d got my sums and ideas right.
Luckily for me, everything works perfectly. I have about 1½” of downward movement and almost 2¾” up. More than plenty. When you move the wheel hub up and down, you can clearly see the rising spring rate in action. At normal ride height, if you move the hub up and down 1″, you get about ⅓” of shock compression. If you then repeat the exercise but close to full compression, that same 1″ of vertical wheel movement produces nearly ⅔” at the shock. That’s almost twice the movement.
This rising spring rate will give a much more comfortable ride under normal driving conditions and improves the tyres ability to remain in full contact with the tarmac. The further the car rolls, the harder the suspension becomes. Normally when a car rolls, it’s being driven harder and harder suspension is going to come into it’s own.
The push rod has a left handed thread on one end and a normal right handed one the other. This enables the push rod’s length to be changed whilst still bolted in place.
Whilst mocking everything up it was handy to use some cut down springs on the coil-over shocks. This meant I could check clearances without having to fight against a 320lb spring. One of my worries was the push rod coming too close to the chassis or the 4×4 front drive-shaft, but I shouldn’t have worried at all.
Without the weight of the shock absorber and because the arms run on my roller bearing system, the hub moves up and down very freely. The shift in weight of Inboard shock absorbers is very evident on this car, as the hubs are still remarkably light, which I hope makes up, in part, for the heavy 4×4 hubs on this car.
The above photo shows the wheel 1½” down. As I mentioned, nothing is finished and brackets are still missing but you get the idea.
The above photo shows the suspension nearly fully compressed (2¾” up). I’ve added about ⅓” of travel to the figures, as the bump stop rubber stops me squashing things by hand.
The action of moving the shocks up and down, produces flex in the crudely tack welded brackets as expected, but it also produces some twist / flex in the chassis. This chassis will require triangulation in directions and places any standard Haynes Roadster or Locost wouldn’t need. It was always the intention to add extra cross-members to the chassis, but mounting the suspension has highlighted exactly where they are needed. For now I will wait before adding them, as I haven’t mount the steering column or finished the exhaust headers. I don’t want to weld in some box section only to find that it’s is impossible to get the exhaust routed nicely. The suspension will take priority when there is a conflict but careful planning should prevent this from happening…..I hope, as I’m seriously running low on space.
In the photos the shocks look closer to the engine than they actually are. In fact they are nearly an inch clear of the rocker boxes. However, I think I will add a stabilising bar to the top of the engine somewhere to stop it from rocking around too much.
I’ve seen several Haynes Roadsters / Locosts / Kit Cars that are under construction with inboard suspension, but only 2 of them actually use bell cranks. Many of those I have seen, without wanting to sound over critical, or like an expert; which I’m not; end up with a falling suspension rate. I know that with many, the goal is simply to do something unusual or to hide those coil-overs, but I found that it is not that complicated to copy the professional Formula One boys. It doesn’t have to be expensive either, I bought four almost new coil-overs on Fleabay for £25 each, the steel cost about £2 and the rest is just time. In case you are wondering, I have used 90° Bell Cranks connected to AVO gas coil-over shocks.
If you watch the video below, you’ll see tack welded plates flexing and M8 bolts without nuts shifting around in M10 holes but you’ll get the idea.
All I have to do now is finish off all of those brackets, go bolt shopping and repeat the whole exercise on the other side. This is the sort of work I like, as the rewards far out-weigh the efforts.