PORSCHE PROJECTS

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

911 Porsche World - - Contents -

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

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