The original idea was that this article was going to be a supplement to our earlier short test on the sportiest diesel Mondeo. It had to be revised when, after 99 miles, one of the alloy wheels which does such a good job of improving the car's looks broke in half. That sorry incident isn't really within the remit of a road test, but you can read it here.Fortunately, the mileage I was able to put in was enough to confirm the previous opinion of the car. Its best feature is without doubt the excellent 2.2-litre TDCi engine, which gives the Mondeo superb mid-range performance.It also means that the car can sustain exceptionally high gearing - 2000rpm in sixth is enough to put you well over the national speed limit - and although you have to drop to fifth or lower if you plan on accelerating anywhere, that long-legged top gear makes for exceptionally relaxed cruising (with one exception which we'll deal with shortly).What this car lacks is the genuinely sporty behaviour of the petrol-fuelled ST220. The diesel version is certainly quick in a straight line, but it's not nearly as much fun as the ST220 to drive.Specifically, this model does not carry its weight particularly well. Even on a smooth, flat road, it's not as wieldy as I'd hoped it might be. If the tarmac has any significant humps and bumps in it, the TDCi can't deal with them at the same time as maintaining good handling. Soaking up the undulations takes up all its attention, and you have to wait for them to be processed before asking the car to do anything else.This comes as something of a surprise, considering how well Ford's ST team has done with this and other platforms in the past. The 220 looks like a sports saloon, and it really is. The TDCi looks similar, but it's a different animal entirely. And the compromise in ride quality - a constant jiggling as the low-profile tyres fail to soak up uneven road surfaces - means that although the engine is relaxed on a long and gentle cruise, the suspension isn't, and therefore the occupants aren't either.I wouldn't mind about the ride so much if the TDCi handled more sweetly, and I would be more likely to accept the handling if the ride were better. As it is, the TDCi seems to be neither one thing nor the other. The looks and the straightline performance are splendid, but I was expecting more. And don't talk to me about the alloys.