Rejoice! Bennett’s suspension quest is over and the fussy git is finally happy in his mission to find a ride/handling balance fit for UK roads
The latest from the 911&PW fleet including Bennett’s 996 C2, Brett Fraser’s Boxster S and Keith Seume’s hot- rod 912
Iknow this is not exactly conventional, but I feel that I should reveal the conclusion of this – my final suspension instalment – first, just so that you know that I have actually achieved my goal of 996 suspension/handling Nirvana, and that you won't have to wade through another few hundred words of chassis setup tail chasing and excuses from some sort of ride and handling nutter. My quest is over, there is a result and I'm happy. It's taken 18+ months and has cost a small fortune, but that's the price of being a fussy bugger I guess, or just questioning the off the shelf suitability of most suspension kits. So that's the long and the short of it. Here's the how.
You might recall in the last issue, that I pitched up to the temple of suspension setup known as Center Gravity, confident of an end result from my freshly fitted Ohlins kit, only to be disabused of this notion by chassis guru, Chris Franklin. He was right, of course, and so we ended up with a setup that was 90% there – that 90% being geometry, ride height and corner weights arrived at after a day on the Center Gravity chassis rig. The result was a 996 C2 – my 996 C2 – that could be driven hard, with supreme confidence, but which still had a sting in the tail.
Chris had identified it immediately on driving the car, and perhaps we would have been better off just stopping there and accepting that the spring rates of the supplied coilovers with the Ohlins R&T POZM100 kit were just too stiff, but I thought it was only fair that we should try and get the best from the off the shelf kit. And besides, the spring rates themselves had no bearing on what we achieved with all the other setup parameters, and thatinformation/experience would remain with the car and form the basis of a chassis blueprint – our very own factory settings, if you like.
That's where we left things and Chris resolved to work with Ohlins on spring rates front and rear, that would, he felt, work and would be more in keeping with what's required of a UK specific ride/handling A/B road setup. We also resolved to replace the M030 roll bars with standard Carrera C2 bars in the pursuit of compliance, which I sourced from Jasmine Porschalink and 9Apart.
Out of the box the spring rates for the Ohlins kit are 60Nm at the front and 120Nm at the rear. By way of a comparison the 996 M030 option (which I started out with) is 26Nm/53nm F/R and the 996 GT3 RS is 43Nm/80nm F/R. So it doesn't take a genius to work out that the Ohlins kit is pretty stiff and perhaps more track than road. That said, the Ohlins damper unit does feature Ohlins’ 'Dual-flow valve' technology, which effectively allows the damper to bleed off pressure when it hits a sharp bump, thus taking some of the shock out of the ride and the springs. But, whichever way you cut it, the R&T kit is at the extreme end of suspension.
The solution – worked out between Chris and Ohlins – was a reduction of spring rates to 80Nm rear and 40Nm front. A set were duly sent out and I presented myself at Center Gravity for fitting and hoping for
the best. It was another long, but worthwhile day...
First up Chris acclimatised himself with a run round the block in the car as it was and returned grimacing. “Yes, it's exactly how I remember it!” he winced. On that basis, it was only going to get better I figured. Starting at the front, the springs were teased out and the new springs offered up. Unfortunately they were of a slightly smaller diameter so some new spring cups (ironically – perhaps – these were of Bilstein origin) had to be sourced from CG'S 'odds and sods' box. Every good workshop has one!
Rear next and the whole damper spring unit is removed, which takes just 10mins per side. Well it does with Chris on the spanners... Back on the car and Chris approximates a very basic setup and winds the dampers to full soft. The idea now is to go out and assess the springs. Surely removing 40Nm rear and 20Nm at the front would be noticeable? It was, but only at one end: the front. Well, OK, not quite. The rear was definitely better, but there was still a distinct crash and bounce on less than perfect surfaces. The front, meanwhile, was almost floating over Chris's challenging test route. It was something of a disappointment as I anticipated another delay in proceedings as we waited for even softer rear springs. Oh, me of little faith.
“Let me think about this,” said Chris. So I did. It transpired that Chris had been slightly at odds with Ohlins’ chassis bods in relation to the rear spring rates and the percentage front to rear in terms of stiffness, and in the end settled with Ohlins’ recommendation. Ohlins’ concern had been that there wouldn't be enough damper travel and anything softer would become 'coil bound.' I just wanted a car that would handle... I wouldn't have to wait very long.
The solution was sort of staring us in the face, in that we now had two sets of springs to mix and match. Happy that the front was spot on and that both the 120Nm and 80Nm rear springs were too stiff, that left the original 60Nm front springs. Given that Chris had proposed a 40Nm/70nm F/R split, he reckoned that it would be worth trying out the 60Nm springs on the rear. So off came the rear damper units again and in went the springs at fully half the rate of the originals. In a further effort to improve refinement Chris and right-hand man, Pete, made up some thin rubber spacers to sit between the spring cup and the top mount, where previously it had been effectively solid mounted. Springs and damper units back together, the rear end was reassembled. On the basis that there were no other spring options available there and then, Chris decided to go for a full geometry/ride height/corner weight setup as per our 'factory settings' and to fit the stock C2 anti roll bars. He also set the dampers at 28 clicks back from full stiff at 32. This
...reckoned it would be worth trying the 60Nm springs on the rear
was either going to work or it wasn't.
The improvement/difference was immediate, as you would expect from a further reduction of 20Nm from the spring rate. Reversing out of CG'S workshop and onto the road and there is a particularly vicious expansion joint, which previously had sent a low-speed shockwave through the body. Now there was just a muted thump. I was beginning to get excited! Chris's test route no longer phased the rear, not even the cobbled town centre loop, which was particularly knobbly as you would expect. The rear wheels were now working with the surface and not just being deflected.
But how would it work on the more demanding 'driving' sections of the route, and would the dampers have the range to control the softer springs? “It floats!” exclaimed Chris. And indeed it does, but in a good way. This was/is more like it. Whereas before the suspension just didn't want to work with the road, it now handles whatever is thrown at it. The compliance and body control is just where I want it and has hit what I would call a UK road sweet spot as opposed to something that would suit the smoother Tarmac of the continent. Irritating frequency vibrations/rattles are now muted and I'm no longer bracing myself for the rear end 'crash' that always comes. Hardly surprising given that the rear spring rates have been halved!
I'm pretty sure that, with the help of Ohlins and Center Gravity, I've now got my 996 to where I want it to be: a fast cross country machine that will soak up the worst that our challenging roads can throw at it, roads that are unique to the UK and so require a specific setup that cannot be catered for off the shelf. It might not be slammed, it might not look the part on its 17in wheels, but it works and that surely is the point.
Back on Center Gravity’s chassis rig for the final push
Bennett finally happy with the handling of his 996. Been a long but worthwhile journey
Left: New springs in the foreground, while Center Gravity’s, Chris Franklin gets the micrometer on the new roll bar, to make sure it is a stock C2 item. Above: Reassembling rear damper unit
Spring rates and damper settings are just half the story. Of equal importance are ride heights, camber settings and corner weights
Far left: Mo30 roll bars replaced with standard M029 C2 bars. Left: Further rear end refinement created by separating spring cup from top-mount with a rubber spacer