Chris Wallbank

Leeds, UK @chris_wallbank @chrisjwallbank

As mentioned last month, I booked into suspension specialists Center Gravity in a bid to get a bit more compliance back into my 997 Cabriolet for some longer road trips I have planned in Europe later this year. I know some of you may remember I only just fitted a brand-new Bilstein B6 suspension with Eibach springs to my car last summer; this setup has been amazing on fast, smoother winding B roads and my original intention was to reduce roll in corners and the slight vague feeling I sometimes had on faster corners with the standard setup. The Bilstein B6 and Eibach springs setup did exactly that, but as the B6 is a ‘sport’ gas compressed damper the ride was inevitably going to get a little firmer than stock and, being a Cabriolet, has produced a bit more flex in the cabin. It’s not too harsh in my opinion for fast road use, but with me now having purchased the BMW E92 as a dedicated track/fast road car I’ve decided I want to make the 997 Cab into a more forgiving weekend grand tourer that will be more comfortable in urban environments and longer trips. I’m clearly showing signs of getting older!

On arriving at Center Gravity Chris and Pete had a good chat with me to talk through what I wanted to achieve before Pete took it out for a calibration drive on his usual route, pointing out a few things straight away – a lot of understeer on sharp cornering, a fair amount of bump steer and wandering steering. He put this down to a few possibilities, incorrect geometry for my needs and five-plus year old Pirelli tyres. But he also did suggest that I may want to switch back to my factory Bilstein B4 suspension given my change of intended use for the car as more of a road trip tourer, which let’s face it… is what a Porsche 911 Cabriolet is made for.

Back in the workshop Pete took all necessary measurements including ride height before taking an alignment reading, and he instantly noticed that the front toe was out considerably, causing the excessive understeer in sharper corners, and the camber on the front was more than that of recommended factory specification too, which causes unnecessary wear on the inside edge of my tyres and less contact on the road, which in turn can also affect ride quality in day-to-day use.

After quick appraisal of the original suspension we came to the conclusion

I would probably be best going back to stock dampers but still utilise the Eibach springs; I did question using the Eibach springs with the standard dampers in terms of stiffness, but Pete assured me that after testing lots of stock PASM cars back to back with the Eibach springs, they actually have a softer initial spring rate than the OEM PASM springs. My original springs were also showing signs of corrosion.

So after fitting the original dampers and Eibach springs it was onto setting up the geometry, but this time to better suit my mode of use, rather than ‘fast road’ or ‘factory’ settings.

Using the Eibach springs meant that the car sat a little too low at the front for Pete’s liking, so to maintain the correct rake angle we fitted an extra rubber spring isolator above the spring to put the car back to stock GT3 height. This also meant that we were able to achieve the correct front camber values Pete wanted for my driving style, and as an added bonus it placed the wheel aesthetically better in the wheel arch to match the rear.

Once off the alignment ramp it was onto the damper health check plates, which basically put the dampers through their paces to check tolerances. All four dampers exceeded the required 0.30 damper theta value, ensuring that my old OEM dampers were still in great health. Then it was time to test the results, which was a definite improvement in compliance through harsher urban city roads, and much less understeer.

But I was also made well aware that new tyres would now be the next step, as the tyres are worn in a wedge shape, due to the previous excessive negative camber and toe out. This causes some strange handling traits now that the geometry has presented the tyre flatter onto the road.

Pete told me Pirellis are also renowned for having much harder side walls in comparison to tyres such as the Michelin PS2S and PS4S. So I’m thinking new Michelins is next on the list… it’s going to be an expensive year!