Across three generations, the Mazda MX-5 has been almost entirely a joy to write about. I have been captivated by Mazda's execution of its long-ago idea for a small, simple sports car and loved nearly every example of it I have driven.But it's a delicate concept, and one which Mazda itself has demonstrated on several occasions can easily be spoiled. The car tested here proves the point.The last MX-5 I drove was an SE Roadster. I could never have one of those because its fabric roof requires bracing bars, one of which remains in solid and painful contact with the top of my head in normal motoring. What would happen to me if I were in a Roadster that turned upside-down is not something I want to spend much time considering.So, no, I couldn't have an MX-5 Roadster. I would need a Roadster Coupé, whose more substantial roof doesn't need bracing and therefore does not cause the problem mentioned above.That niggle aside, I loved the SE because it made me feel the way I did the day I passed my driving test and was allowed to take to the road on my own for the first time. The Sport Tech is different. I had this car for a week, and it did not make me feel anything like that.It's a substantially different car in many ways. For a start, it has a 158bhp two-litre engine rather than a 124bhp 1.6. Personally I don't think straightline performance is important in an MX-5, but some people might think differently, so fair enough.It also has a six forward gears where the SE has only five, and for another £600 those gears can be part of an automatic transmission. The idea of an automatic MX-5 has never sat well with me, but it might be worth considering nowadays since Mazda currently has a lot of difficulty devising a smooth-shifting manual, and changing gear in its little sports car is a crunchier and much less delightful experience than it once was.Other, unobjectionable upgrades from the SE to the Sport Tech include front foglights, heated leather seats, cruise control, a BOSE audio system with seven speakers, Bluetooth connectivity, an auto-dimming interior mirror, brushed aluminium style bars and alloy pedals.Nothing to complain about there. Unfortunately, the Sport Tech also has 205/45 tyres on 17" wheels (the SE has 205/50s on 16s), revised suspension and a limited slip differential, the last of these being included to reduce the extent to which the rear wheels can turn at different speeds and therefore improve traction in a car which I never though of as having a traction problem in the first place.I think the diff (as we motorsport types call it) may be Mazda's greatest mistake with this car. Even if it's not entirely to blame, the combination of all the things mentioned in the previous paragraph certainly has a devastating effect on the MX-5, and makes the Sport Tech a disappointment where the SE was a delight.The basic problem is that, once you've got the car settled in to a corner, almost regardless of how quickly or slowly you're going, any application of the throttle immediately makes the nose want to push wide. The only options are to fight against this with the steering or backing off the throttle again, though you have to be careful with the second method because it can lead to snap oversteer which then requires further correction.Well, that's no good. If I wanted a car that handled like a badly-driven 1980s hot hatch I'd buy a 1980s hot hatch and drive it badly. It's not the kind of behaviour I want from an MX-5.I almost despaired of finding a way round this, but I eventually did, and am now in a position to say that you can reduce the effect by getting on the throttle before you've started to turn the wheel and accepting that the car will smudge inelegantly round the corner. Again, though, I don't see why I should have to employ such a wretched driving technique to overcome a basic error in the set-up.This whole business turned me off the Sport Tech completely. During this test I found that I enjoyed having the car parked outside my house far more than I enjoyed driving it, and that can't be right. To me, the SE is the "proper" MX-5, the Sport Tech a sadly inferior product that happens to look very similar. Engine 1999cc, 4 cylinders Power 158bhp Transmission 6-speed manual Fuel/CO2 36.2mpg / 181g/km Acceleration 0-62mph: 7.9 seconds Top speed 136mph Price £22,995 Details correct at publication date