Today's car designers come up with some truly boundary-pushing vehicles: eye-popping body styling and fantastic new technologies abound. But one aspect of the modern motor that rarely gets challenged is the number of wheels it should have: Four is the consensus. Four wheels help a car stay balanced (unlike three wheels), while any more than this is generally unnecessary - unless we're talking about articulated lorries.
Nevertheless, there have been a few notable vehicles that feature either three or six (plus) wheels. Here are 10 of our favourite...
This three-wheel concept car appeared way back in 2006 and lies somewhere between a motorcycle and a car. Liability worries meant this car never went into production. Imagine this in yellow with Trotter's Independent Traders stencilled on the side…
If you thought Ford's F-150 Raptor could do with a couple of extra wheels, have a word with Texas-based tuning specialist Hennessey Performance. Their VelociRaptor 6x6 boasts 20-inch wheels, off-road tyres and a plethora of exterior design features. Hennessey call it a prototype, yet they will still give you one in exchange for £250,000.
By John Chapman (Pyrope) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2676504
This six-wheel F1 motor may look like it was designed by the Wacky Racers animation department, but it actually existed. Featuring four tiny front wheels and two large rear ones, it was one of the most unique cars ever entered into Formula One. It bagged a single victory in 30 races before being abandoned in 1978.
We're not sure how useful this Defender would be on the average hilly British farm, but perhaps the designers weren't targeting the UK agricultural sector when they dreamt it up. Created by Kahn Design, the chassis was stretched by 400mm to fit on the extra wheels they also swapped out the original engine for a 500bhp 6.2-litre V8 from General Motors.
By Kevauto - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=67147339
The Slingshot is categorised as a motorcycle and is fitted with a GM Ecotec 2.4L four-cylinder engine. This nippy three-wheeler does not come with air-bags - and, since it features no roof, climate control can be tricky.
This ostentatious mode of transport was very probably influenced by the Tyrrell P34 (see above). It first appeared at the 1977 Earls Court Motorfair and featured an 8.2-litre Cadillac V8. Each door had its own telephone, while there was a TV on the dashboard. The price tag at the time was £39,950 - considerably more than a contemporaneous Italian supercar.
By Balansboy - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=39423111
The Elio P5 looks like a futuristic Robin Reliant, but is far more fuel efficient than Del Boy's famous yellow runabout - delivering 84mpg. The P5's design is similar to the preceding P4, but features three air-bags, power windows, AC and a 0.9-litre engine. It can go from 0-60 in 10 seconds.
Looking like the slightly-less-wacky offspring of the Panther 6, the Covini C6W featured four small front wheels and two large rear ones. The mid-mounted Audi V8 could propel the machine to 185mph, apparently. It is not known how many were built.
Photo by Byrek on Wikimedia Commons / CC BY 3.0
This 100 horsepower three-wheeler is powered by a 750cc Honda V4 engine. The Polish designed and built machine can reach a top speed of 118mph, say the manufacturers.
By Milhouse35 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=27574625
If the Mercedes G-Wagen is not sufficiently OTT for you, take a look at the G 63 6x6. One of the world’s largest road-legal pick-ups ever built, it's nearly six metres long and weighs three tonnes. Originally designed for the Austrian army, civilians can buy one too - but we're not entirely sure what they’d use it for…