Marathon post alert!
Disclaimer first; all measurements are of the set of shocks delivered to me, on my car and comments relate to what I have found. What happens on your three wheeler might be very different!
Out of the box the rear shocks had the preload wound completely off to the end stop on one and about 1mm less on the other, both were at 30 clicks from maximum damping. The front shocks were delivered with about 5mm difference between the preload settings and again both were set to 30 clicks from maximum. The overall free length of the front shocks was 2.2mm different.
I fitted the fronts first; the bushes at the bottom end were a very tight fit in the brackets which needed eased slightly to get them in. This is likely due to the brackets being spaced slightly too far apart for the standard shocks leading to them normally being bent inwards rather than parallel when the bolts are tightened, the fit with the new shocks is now really quite good.
At the top end the Suplex units have what appears to be a spherical bearing held in by circlips plus a pair of aluminium top hat bushings with O-rings. The gap between the top mounting brackets was 4.5mm greater than the top of the shocks, this is a design feature as the brackets are shared with the wishbone top mounts which have longer inner bushing tubes than the shocks. Standard these brackets are fairly severely bent inwards when tightened down on to the wishbones and more so on the shocks even though some of them have a washer or two acting as spacers – this isn’t just on my car! This leads to them being well out of parallel as standard. I fitted two heavy M12 washers on the top mount of each shock as spacers which gave a good fit. On the right the spacers went forward of the shock and on the left they went behind the shock – this was just how the shocks sat once the bottom bolt was in place.
Initially I set the preload on both shocks to 55mm lock ring to eye as suggested in the instructions. This caused both exhausts to foul on the preload adjuster rings when pushing down on the front end – I didn’t drive with it like this. Adjusting them to 57.9mm (LHS) and 58.4mm (RHS) lock ring to eye looked to just give clearance between the adjuster rings and the exhausts on maximum travel and so far this seems to be the case. At this point I had a ride height of 136mm measured on the lower chassis tubes just forward of the front lower wishbone mount on both sides – underside of tube to flat concrete floor – with the standard shocks ride height had been 150mm both sides. I went for equal ride height left and right at this stage mainly because I had to set them to something rather than any deeper reason.
The rear shocks were a seemingly straightforward fit once I had the car high enough on the axle stands to be able to drop the wheel far enough on a trolley jack to get at the lower bolts. I took a guess at a preload setting and set both shocks to it on the bench before fitting them. Interestingly though the shocks this time were the same length the distances between the mounting brackets were about 1.5mm different side to side. Once fitted I adjusted them to give the same ride height as standard as a starting point and went for a short drive.
First (short) drive; the front end seemed pretty decent but the back was terrible – very harsh and pumping down over bumps, pretty much undriveable really so I had another look at the shocks. On both sides the upper (soft) section of spring was completely coil bound and this without me aboard so I backed the preload off till I had the recommended 314.5mm eye to eye on both sides (as ever as a last resort; read the instructions) this needed slightly different preload on each side and left the right spring all but coil bound (about 0.5mm maximum gap between windings) on the soft windings, the left having some genuine space between these windings.
Second (much longer) drive; severely over damped at rear so pumping down over bumps and riding like a hard tail but front seemed to be no problem
Third drive; backed the rear damping off from 30 clicks to 40 clicks from maximum which gave a large improvement but still pumping down. Front actually pretty good
Fourth drive; backed off to 45 clicks on rears and another improvement. Front still good.
That’s it so far. My overall impressions at the moment are that the front shocks are good; they ride the bumps much better than stock and there is no longer the feeling of constantly battering off of the end stops on bumpy roads taken at fun speeds. I will no doubt try to fine tune the front in due course but wouldn’t be at all surprised if I ended up back where I've started. The rear is more complicated and I think it will need a good deal of experimentation to get it to work. I’m going to need to try less preload and then play with the damping then try more preload and again play with the damping. I have a nagging suspicion that what is required to make the back end work is a set of springs slightly lower rate than the high rate section of the supplied springs but single rate, no rising rate; I’m not sure what good a coil bound spring is even with “internal rebound assist” springs whatever they are. I may also re-fit the standard shocks to see what happens which will also give me a chance to measure the Suplex springs best as I can; might even take the springs off to see just how similar they are to each other. It is certainly possible that part of the issue with the rear is that the front is substantially improved which is highlighting any deficiencies at the rear and that refitting the Spax units might confirm this.
Incidentally since the back end of the M3W is basically a bike configuration I measured the static sag which came out at 15mm at my last pre-load settings which seems like a lot but then it is a road car not a race bike which I would normally have started at somewhere between 0 and 5mm of sag.
Other observations; the C-spanners are deep into chocolate teapot territory once the shocks are fitted, not a surprise so on-car adjustments were made the old fashioned way. Once I am more certain of my settings I will post up some easy to follow measurements in case anyone wants to trust me and set their preloads on the bench before fitting their shocks. Fitting the rears was being straightforward so when the top of the second shock was going in between the mounting brackets I did find it important to dislodge one of the top hat bushings and its O-ring which went down by the bevel box and leapt forward into the inaccessible area behind the driver’s seat so I got to take the seat and bulkhead off to retrieve them. This also of course meant that I got to find the spinning Rivnut with the part stripped thread on one of the bulkhead fasteners so I got to sort that out too. At about that point I noticed that the left fuel tank had scuff marks on it where it goes under the ash frame, so that just needed the strap tensioner tightened up and don’t start me on the fuel gauge sender bolts…
Clearance between the Suplex (left) and Spax (right) shocks and the exhausts.
Side by side of Spax and Suplex front shocks.
Top mount gap on front shocks with and without spacers.
Where the dislodged top hat bush ended up!