IF you look at any of the one-off cars built to impress the crowds at motor shows there's a constant design theme - huge alloy wheels.

Car designers love the way they add a sporting poise to whatever metalwork they're supporting, never mind their potential for spoiling the ride in the real world and making an owner wince at the cost of replacement tyres.

But Renault's design chief, Dutchman Laurens van den Acker was not to be thwarted when he decreed that the new Scenic and slightly stretched Grand Scenic had to have big - really big - alloy wheels across the range.

You will pay a small fortune on the likes of an Audi for an alloy wheel upgrade, but the Scenic siblings have 20-ins rims, and that's that.

There's no doubting the cars look better for their racy wheelsets, helping van den Acker and his team produce a couple of handsome machines that make you think 'stylish' before 'practical', which counts as a win in today's style obsessive world.

But they are practical - with lots of room inside for people (and a third row of seats in the Grand Scenic) and come with engines and safety systems that ought to make them fine family workhorses.

Back to those wheels, though. Renault has fought the potential downside of such generous sizing, firstly by making replacement tyres available from three makers at £107 a pop. That's not a figure likely to frighten anyone running a modern car and wanting first grade rubber on the road.

Then, the tyres are taller and narrower than those typically found on such large alloy wheels, helping roll more easily along the road and disturb the airflow less too.

Because they wheels turn more slowly than if fitted to smaller wheels, the tread reaches the road less frequently, so ought to last longer.

It all sounds convincing enough to move on to other aspects of the newcomers without a nagging doubt about running costs.

Doing so, you'll discover a range of cars that start at £21,445 for a Scenic with 115 horsepower petrol engine and top out with the £32,445 Grand Scenic and its 160 horsepower diesel and automatic transmission.

Stretching the car by 228mm (around nine inches) to produce the seven-seat Grand Scenic adds about £1,800 to the price of an equivalent five-seat non-grand Scenic and provides space in row three for a couple growing children or smallish adults.

The demand for compact MPVs like the new non-identical twins is declining slowly as the onslaught of SUVs continues on its seemingly unstoppable way, but we still buy a lot of them.

Renault claims, with some authority, to have invented the compact MPV with the 1996 introduction of the Scenic; since when more than six million of them have been sold before this new, fourth generation car arrived.

There is no lack of choice (that big wheel size apart) with this latest car. Two petrol and three diesels are available now - the 110 horsepower diesel is likely top seller - and a mild hybrid version with a powerful battery helping out arrives in the spring of 2017 with a tax beating 92g/km of CO2.

Choose the right car from today's price list (that'll be the dCi 100) and you can have 100g/km and 72.4mpg in the official, if optimistic, tests.

The Scenic and Grand Scenic are each available in 18 versions, with active emergency braking, lane departure warning, traffic sign recognition and auto dipping headlights standard across the range.

The seats in rows two and three can be individually folded with buttons in the boot - or on the dash display in some versions, and a sliding storage box between the front seats adds to the versatility of the car's interior.

Out on the road in the 110 diesel the new Scenic impressed with its ride comfort (those big wheels firmly in the background) and the clear dash display, with high definition screens, would have looked space age improbable to the owner of an original Scenic in 1996.

A five star Euro NCAP safety rating and four year or 100,000 mile warranty are figures that help the new Renaults stack up well against the opposition, but it's the looks - even with cars designed to be family favourites - that will win admirers this time.