Most, though not all, of the manufacturers who build small family cars include a small diesel engine in the range in an attempt to achieve impressive official fuel economy and CO2 figures. With the new 3, Mazda hasn't done that.The only diesel you can have in a 3 is a 2.2-litre unit producing up to 148bhp. It's not inconsiderably splendid. A bit grumbly, perhaps, but very flexible, and strong enough to give the car a 0-62mph time of bang on eight seconds.This is not at the expense of the issues mentioned in the first paragraph. Despite its rapidity, the 3 diesel has a CO2 rating of just 104g/km, which means you're required to pay the Chancellor less money each year than you would spend if you took him out to dinner. And according to the EU test, you should be able to travel 72.4 miles for each gallon of fuel.In light of that, you may be disappointed to hear that the car itself told me I averaged just 48mpg on one tankful during this test. There are, however, two reasons for not taking this too seriously. First, the trip computer seems to under-read - according to my own measurements I'd beaten 50mpg.Second, I'd driven along nearly the whole of the M6 while battling against sidewinds of such ferocity that two articulated lorries fell over. I hope the drivers were okay, but the economy of the Mazda must have suffered badly. In better conditions, something like 60mpg might be possible.There was rain as well as wind on that trip, and this called attention to a flaw in the design. The test car was a Fastback, Mazda's oddly-chosen name for the saloon body style, and unlike the hatches in the range the Fastbacks don't have rear wipers. In the wet, it's almost impossible to see behind you, though this is difficult in any case because of the stupid window design.The 3 was quite comfortable on a long journey, and it behaves magnificently on very smooth tarmac. When the roads are more challenging the dominant factor is the weight of the engine, which is not carried well. Both the ride and the handling are disappointingly compromised as a result.This may not seem to chime in with my launch report, in which I said that the diesel 3s were vastly better to drive than petrol ones. I was wondering about that myself, but by a rather lovely coincidence a petrol model happened to be delivered to the office just as I was starting to write this review. I popped out in it, and sure enough it's not nearly as good, even though it doesn't have the engine weight problem that the diesel has. All versions could be improved, but the petrol ones need fixing first.The test car had black leather upholstery which is standard with the Sport Nav trim level if the car has the 163bhp two-litre petrol engine but a £1000 option otherwise. It's nice, but worth avoiding if you plan to carry large passengers in the rear as it compromises the amount of space back there.Luggage space doesn't seem to be affected. The Fastback has a useful 419 litres of this, which is pretty good for the class, though access through the shallow boot opening isn't nearly as good as it is in the hatch.Whether you agree with this final point is a matter of your personal preference, but I do like the way Mazda has incorporated the facilities for communication, navigation, audio and what not into the central touchscreen. It's all very easy to use, as is not always the case with these things, and the graphics are lovely.All I'd ask is for the satnav to accept postcode inputs. In order to find my way to a venue on an unnamed road I had to use a map, which would have been fine in a car that didn't have a navigation system but seemed peculiar in one that did. Engine 2191cc, 4 cylinders Power 148bhp Transmission 6-speed manual Fuel/CO2 72.4mpg / 104g/km Acceleration 0-62mph: 8.0 seconds Top speed 132mph Price £22,145 Details correct at publication date