My first visit consisted of a Health Check - the objective is to benchmark the car’s handling against the original factory set-up, which inevitably changes after all the years of works, and wear/tear to components like the bushes and ball joints. It includes a full mechanical inspection, a road test where Chris drives the car under a variety of conditions, and of course the use of their state of the art geometry kit. Once all the tests are complete you discuss what needs replacing and what geometry adjustments are required to suit your driving style. Even though my car was already running Bilsteins with H&R springs, and was riding lower than standard ride height, I learnt that my car was far from where it should be - a bit erratic, a bit ‘darty’, prone to oversteer, due to geometry, and with some unnecessary ‘play’ in the suspension, due to worn components. So, it wasn't bad, but there was definitely room for some improvements. I booked in for the full treatment!
For more information of the Health Check check Renn Eleven’s vlog; ‘The best Porsche suspension maestros in the UK?’
Here's the list of works for my return visit and since part of the experience is being able to watch and learn whilst the work is being carried out, I jumped at the chance of sticking around for the day...
1) (Approx 1hr) Remove front wishbones, de-bush front forward bushes and replace with Super Pro’s (which have a lifetime guarantee by the way!) to eliminate ‘play’ in the front of the car.
2) (Approx 1hr) Replace rear right control arm with a refurbished Hartech one - in essence, they are OEM arms that have been re-bushed and re-ball jointed and are 'like new'. In Chris’ experience they are the same quality as a 'new' OEM arm, but at a fraction of the price.
3) (Approx 1hr) Remove and strengthen 2x steering dampers (on the ZF steering rack - which Chris describes as a “Jewel” of engineering). Over time, these rubber isolated parts will deteriorate again, so this is an upgrade to 'RS-fy' the steering, by welding the existing rod ends, removing any play from the steering system.
Before / After:
4) (Approx 3-5hr) Full geometry. Chris was open to discuss requirements and explained to me the pros and cons of lowering my car further - I've always wanted to lose the 'air' between the top of the tyre and bottom of the arch. The brief was to achieve that aesthetic, one which closely related to RS, whilst maintaining a geometry that is optimised for road use. Obviously, the lower you go the more it negatively affects the camber - which is great for racing drivers, but not optimal for my road use, so I had to make a slight compromise on the rear camber. Below is my final geometry, with factory specs for comparison. I'm running RS-1mm on the front and RS-10mm on the rear, with a rear camber of -2deg, compared to a factory standard maximum camber on the rear of -1.25deg. Judging by the car’s performance on the test drive the rear grip seems perfect and Chris says won’t adversely affect stability on roads. Admittedly the ride is a tad bumpier than before, primarily due to the loss of front ride height and the limiting travel to the internal bump stops - this in effect increases the front spring rate. And there's noteably a little increase in the rear tyre stiffness as the extra negative camber places extra load on the inner side wall and shoulder as well as increasing the lateral camber thrust. So over bumps I can expect a little more thud and wiggle, and perhaps some accelerated wear on the inner edges of those rear tyres - but, all in all, I love the lowered look on 993s and it’s also reassuring to know that if I get the chance to push the car to its limits, whether that's an advanced driving course or track day, it will be more than capable ;-)
Worth noting, that we decided to avoid anything unnecessarily costly - for example, some people like to get into replacing the 'wheel carriers' (with RS front uprights + Tie Rods) to eliminate bump steer, but for my requirements Chris advised against this. And it wasn't necessary to replace the other rear control arm to match the new one. Since only the ball joint had failed, Chris replaces the new bush in the Hartech arm with the old bush to eliminate bias on the other side of the car.
It was a long day in the end. I arrived at 8.30am and left about 10pm. But what a thoroughly enjoyable and educational experience. I loved seeing the improvements being made to my car and learning about the science of geometry in the meantime. The test drive after all the work had been done was awesome - it felt like a different car - smooth, tight, direct, predictable, planted and for sure stickier on hard cornering. And it looked great too. Thanks to Chris and his 10,000 hours experience. A true expert. I highly recommend Centre Gravity. Just be prepared to make tea for him - white, one sugar ;-)
Sadly, the drive home was dark, wet and windy, so I didn't get the chance to take any decent photos or have a proper drive - can't wait for the next time I'm out...
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