Our Maldive Blu Z4 crunched onto the gravel of our car park in July 2003, which was perfect timing as last year's scorching summer was well and truly into its sunny stride. The prospect of roof-down motoring and a booming straight-six engine seemed the perfect way to wean myself off the invincible Audi RS6 that I'd previously been running.

In typical BMW press car tradition, our model was loaded with plenty of optional extras, which added nearly ΂£5000 to its price tag, including sports seats (although calling them 'sports' is overdoing it a little as they offer little in the way of side support), parking sensors (a debatable option as the Z4's pert rear is only two feet behind the driver), a ten- speaker hi-fi system (΂£675, but fantastic sound), and finally, the widescreen sat-nav costing ΂£1935.

Happily, the standard kit includes the electric roof that stows away in just ten seconds. It's simplicity itself to use; press a button on the centre console and let the electric motors do their work. I'd be nit-picking if I complained that you have to be stationary to operate it. Another button on the dash gives you a choice of three temperature settings for the heated, electric seats. On the move you notice other little luxuries that help make life that bit easier, such as the radio that adjusts the volume up and down depending on background noise, or the headlights that come on automatically when darkness falls, the cruise control that lets you stretch your right leg a bit on motorways, or the automatic wipers that start-up when the inevitable summer shower appears from nowhere. For goodness sake, I thought this was meant to be a sports car - it's amazing how much luxury car-buyers expect these days.

The Z4's best feature, though, has to be that fabulous 3-litre engine. God, it's good, and stirring it along with the terrific manual gearbox (which possesses the most beautiful mechanical feel), hearing that muscular, lusty straight-six howling its way to the 6500rpm red line in a beautifully cultured way, is very close to perfection. The Z4's performance balance seems perfect too, always feeling quick enough to entertain but never excessively quick to scare you.

I hardly ever used the 'sports' button beside the gearlever. This quickens-up throttle response and steering feel, but I found the throttle action became a bit too aggressive, while the steering never felt any different, despite the alleged drop in assistance mentioned in the handbook. Regularly stretching the Z4 to the red line didn't seem to dent fuel economy either, with 30mpg easily achievable on long runs.

But is the Z4 really a sports car? Now that's where the controversy lies. Our Z4 featured BMW's sports suspension as standard, and I really wish it hadn't: the ride's simply dreadful. It dominated every journey and became incredibly irritating over time. There seemed to be no handling benefits on offer to offset the constant pummelling that drivers and passengers received when on the move. It had none of the precision you get with a Boxster, for example, nor the control you'd expect from such a firm set-up. In fact, Honda's recently revised S2000 felt like a limo in comparison.

The other problem was that unless the tarmac was super-smooth, the Z4 seemed to wander from bump-to-bump, sending confusing messages to the driver as to what was really going on. It felt like an advanced form of tramlining and became christened the 'Thrill of Writhing' in the office. At first I thought it had to be the fault of the standard run-flat tyres, so after the Z4's disappointing performance at last year's eCOTY (063), we swapped the Bridgestones (having covered 11,000 miles, they were around 60 per cent worn) for a set of Vredestein Ultracs. The initial ride coarseness certainly improved on the Ultracs, while wet grip was transformed. But even so, the Z4 never felt really relaxed unless the road was glassy smooth.

The real culprit was finally revealed on the Mercedes SLK launch last month. Mercedes brought in a Z4 for evaluation during the SLK's development and had noticed the same strange chassis behaviour that we'd experienced. After putting the car on a chassis rig, the explanation seemed to be a noticeable change in rear toe angle when the Z4's rear suspension moved up and down, meaning it would start to 'steer' from the rear on undulations. Now, increased toe-in on compression is great on track as it tucks the car into the apex, killing understeer in the process, but pretty useless on our lumpy roads as the change in toe angle can cause the constant wandering we'd experienced as the rear wheels steered their own independent course to the fronts.

The Z4's saving grace is just how easy it is to live with. Here is a roadster that can be used every day, even by old gits like me, with none of the discomforts you have to endure with cars such as the VX220 or Elise. But it also has proper performance: 0-62mph in 5.9sec and a 155mph limited maximum.

At 14,398 miles an oil service was carried out, costing ΂£131.79. And that was the only time the Z4 visited the BMW dealer, although we did call out a mobile technician to investigate a strange noise and vibration coming from the bulkhead where the throttle pedal is attached. Although the cause was never found, the problem disappeared over time. The Z4 wouldn't have needed another service until around the 30,000-mile mark, although the original brakes were getting a bit grumbly when pushed and might not have made it that far.

So, after ten months and 23,000 miles, I'm left with the conclusion that BMW was a little confused as to what it wanted the Z4 to be. It's a real shame it handicapped the 3-litre version by fitting the sports suspension as standard. Perhaps having two versions would make more sense; one a stripped-out Z4 with sports suspension and the other a fully-loaded SE version, without the compromised suspension. This way, buyers would have the choice of a Z4 to use as a comfortable everyday car or as a stripped-out weekend special.

Having said all of that, the Z4 has been great fun to drive as an everyday car; that world-class engine/gearbox combination and ultra-quick folding roof are fantastic companions on any journey and balance-out some of the chassis' failings.

However, it probably helps that the majority of my long drive home every night is on super-smooth tarmac which, strangely, was newly-laid just in time for the arrival of the Z4. BMW has always gone to extraordinary lengths to ensure good copy for its cars, but this is getting ridiculous.