Monday 18th July 2011

PH Fleet Update: Mazda Eunos Roadster

Plans for new springs and dampers have finally borne fruit, but not before Dan's driving comes under scrutiny to see if he's worthy...

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I've been wittering on about having the suspension done on my Eunos from the moment I bought it and now, six months in, it looks like something might finally be happening.

I'd initially talked to Bilstein, but the choices seemed limited to a basic B6 Sport monotube set-up with a specific tune for Mk1/NA MX-5s or, at the other extreme, a bells-and-whistles B16 kit with clicker adjustment and tweakable ride height. As this is a kit for Mk2/NB cars this would have required a change in top mounts to fit, but as this also increases suspension travel this wouldn't have been such a bad thing.

IsTrent worthy of trick suspension work?

But then Phil at Performance 5 got in touch with bold boasts about his SportDrive kit. So started a chain of events that eventually had me meeting up with suspension engineer Dave Turner, Phil's in-house expert, for an assessment of both car and driver's abilities. No pressure, then...

Trained as an engineer, Dave worked on suspension for military vehicles, including main battle tanks. He and his colleagues must have been onto something too, the Americans apparently stunned in the first Gulf War at the speed British military vehicles could carry over the rough desert terrain. After a spell as a police accident investigator he's since worked as a senior instructor for Cadence Driver Development, an advanced driving school with the emphasis on giving drivers the skills to enjoy performance cars safely.

Dave from Performance 5 looks unsure...

The thinking behind Performance 5's Sport Drive kit is rather more sophisticated than most, Phil and Dave keen to preserve the essential character of the MX-5 rather than follow the route taken by many and simply make it lower and stiffer. And it's all designed in-house, bar a few off-the-shelf seals and washers, it's all built to his specification from scratch.

High- and low-speed damping in both compression and rebound are all configurable but the adjuster knob on the top of the unit controls only the rebound curve for fine tuning. Spring rates are raised considerably, the fronts alone going from 170lb/in to 350lb/in with the aim of reducing roll and maintaining a consistent tyre contact patch without sacrificing ride comfort. According to the P5 blurb, the natural understeery tendency is reduced to a more neutral balance that encourages throttle adjustability. Sounds good to me...

...And makes complete sense when you've had a drive with Dave and tasted a little of what Cadence Driver Development preaches. It's classic 'making progress' stuff, Dave encouraging much earlier and harder braking for corners than I'd instinctively make but much, much earlier on the power and barely moving the wheel, steering the car as much by accelerator as wheel. And, no, this doesn't involve any 'dab of oppo' showboating, just very subtle adjustments in attitude based on reading the road properly and knowing how and where to carry speed.

Dave seemed satisfied I hadn't bought a complete shed and, in a roundabout way, seemed to suggest I wasn't an entirely lost cause as a driver too. Which was nice of him. Am I worthy of the SportDrive kit though? Well, the Eunos is now with Phil at Performance 5 and, I'm hoping, next time I see it will have the dampers in place. Phil's also going to bolt some of his own chassis rail braces onto the underside to help stiffen it up a bit, one of my concerns being that a significantly stiffer chassis would only result in more body wobble.

"It's best to go as soft as possible with the springs and pair that with good damping," says Dave, pointing out that a stiff set-up - as I'd feared - would simply end up using the body as an (undamped) spring. The proof will be in the driving but Dave assured me the SportDrive kit actually reduces the shake, rattle and roll you get on any bumpy road. Compliant it may be, but Dave clearly takes pride in the fact the SportDrive kit means even on standard 14-inch wheels and, in his words, crummy tyres the car can carry 1g lateral loadings.

Speaking of which, I recently put the standard wheels and crummy tyres back on to test a theory and, much as I love the 15-inch OZs, I have to confess it does feel a little more natural on the 14s. The Tigar tyres are comedic though, wet grip levels alarmingly/entertainingly (depending on whether you're in the mood) low and offering plenty of opportunity for exploring Dave's throttle adjustability theory. At 20mph.

I'll try the OZs when I've got the new dampers on before I make a final decision, but I'm rapidly coming round to the opinion that lightweight wheels are one of the most noticeable mods you can make to a car and the standard ones might well be best for preserving the Mazda's balance.

Further discussions with Dave and Phil did suggest the half cage/door bars idea I've been playing with might not be a bad route for stiffening the car further and it was suggested a smaller steering wheel for increased response might be an idea. I love the skinny-rimmed Momo, though, and won't change it unless I find something equivalent.

As I write, the car is with Phil with a deadline looming in the shape of a return to the Welsh roads and Anglesey circuit I so enjoyed back in the spring. If that isn't an opportunity for the P5 kit to show its mettle nothing will be; my date there with the MX-5 GT race car, promising an intense hit of Mazda-based delights over coming weeks.

[Tankslider]

Great stuff. Phil's stuff is brilliant.