This will not be a scientific test. The plan, if you could call it a plan, will go something like this: brim these two hybrids at the start of the day, so full that you can see the fuel in their filler necks, because that seems like a road-testery thing to do. Then drive them in London side-by-side and check their trip computers to see which is more economical in town. Then take them up the M1 to Millbrook test track near Milton Keynes to check which is more economical on a motorway cruise. Note the results and scratch chins and say ‘hmmm'.
Then, at the track, hand them over to the Stig and ask him to jump them. Yes, to get them a long way into the air. Yes, airborne, wheels in the sky, flying. You can't calculate a Top Gear Combined Cycle without a maximum-attack Stig thrashing, and you certainly can't test hybrids without understanding how they soar - not in Top Gear's books, anyway. Five laps of Millbrook's two-mile high-speed bowl at full throttle, to see which is faster and more efficient at maximum speed, will finish the day.
Then we'll fill them to the filler necks again in an extremely road-testery way and see which car has been more economical. After further chin-scratching and the making of sounds like ‘fnrrrrr' and ‘errherr', one car will be declared the winner, assuming it has survived Stig's big air car kicker. As I said, this will not be a scientific test.
Before we set off, let's look at what we have here. A new Toyota Prius, and a new Honda Insight. Regular readers will know that we quite like them both, but we've never put them together. They are both hybrids, and unless you've been living under a rock for 10 years, you should know that means they are powered by both a petrol engine and an electric motor, and that they store power for the electric motor in a big bank of batteries, which is charged by the petrol engine, by regenerated energy from the brakes and energy created on the overrun.
Technically, they are quite different under the skin, and we should be sure we understand those differences before we get them airborne. The Toyota's system, called Hybrid Synergy Drive, has an 80bhp electric motor, which it uses as its main motivating force. It can move off with this engine from the lights - if you're gentle - and will run comfortably at town speeds using it and it alone... that is, with the 1.8-litre, 98bhp petrol engine completely separate and switched off. The petrol engine cuts in when needed and does so incredibly smoothly and almost inaudibly. Quite brilliant. So, this is, in character if not its makeup, an electric car with petrol assistance.
The Honda's system, called IMA (Integrated Motor Assist), uses a much smaller electric motor of only 13bhp to - as the name suggests - assist the petrol engine. It uses that engine, a 1.3-litre, 89bhp unit, all the time when the car is moving - that is, it always turns. But it doesn't always use fuel. In the right conditions, on a gentle throttle at speeds of up to 30mph, the electric motor alone will power the car, while the petrol engine shuts off some of its bits in a clever fashion and drinks not a drop of gas, even though the crankshaft is still turning. However, the very fact that it's turning means that the system is less efficient than the Toyota's. The upside being that it is that much simpler and, crucially, cheaper to make. It is also lighter: the Insight weighs 1237kg, the Prius a full 143kg more. That will be critical when the cars leave the ground completely, later.
First, note that the Prius, in its two previous generations, has sold over a million units worldwide, the vast bulk of them in the US in the last six years. Honda - which introduced a two-door Insight hybrid to Europe in 1999, let's not forget - wants a piece of that action, and this new Insight is the result. Honda is pitching it as the first ‘affordable' hybrid. Oh yeah?
The cheapest Insight, the SE seen in this test, is £15,990 - a full £2,400 less than the base T3 Prius, which is similarly equipped. The Prius you see here is a top-of-the-range T Spirit, priced at an eye-watering £21,230. Whether the Insight's £16k is ‘affordable' depends on your frame of reference. Just don't look too closely at the price of highly efficient small diesels like the £13,920 Renault Clio Dynamique 1.5dCi if you want to pretend the Honda's ‘affordable'. Such a car, or the equivalent Ford Fiesta, is also well equipped, will do 61.4mpg on the combined cycle and emit only 123g/km CO2, compared with the Insight's 105g/km and the Prius' quite outstanding 89g/km. Small diesels take some beating.
Still, we should applaud these Japanese companies for producing effective, efficient hybrids and making them recyclable and environmentally sound. In fact, we should bow to them in deep respect before we honourably make their cars fly like birds. Off we go then, into the heart of the Congestion Charge zone in London, for which they are both exempt. In normal driving, the Prius spiked up to ‘infinity' mpg far more often than the Honda - that is, trundled along using its electric motor alone. Which would explain why, given virtually identical mileage, acceleration, deceleration and driving style, it averaged 58.4mpg over 25 miles of city driving while the Honda only averaged 38.9mpg on its computer. The manufacturers claim 72.4mpg and 61.4mpg respectively for their official city cycles. Hmmm. Round one firmly to the Toyota, then.
They are very different cars from the driver's seat. The Prius is like nothing you've ever driven, unless you happen to have driven an electric golf buggy. God knows I've driven a few of those on golf courses all over the world, and driven them to the very edge of lunacy. Yes, they're good fun, and you get a very direct relationship between the throttle pedal and the way the buggy accelerates, but it's not like a normal internal combustion-engined car. The Prius isn't, either. Not really. It moves away silently and there is no sense of ‘engine'. It feels heavy, the instruments are in the centre of the dash, and it has an ovoid steering wheel. You are not encouraged in any way to drive it zippily, and that's the whole point. You should drive it to be efficient and to save fuel.
The Honda is more familiar. The petrol engine - a quite thrashy, harsh and non-Honda-ish little sewing machine... please give us a sweet little VTEC next time, Honda... ah, you will in your funky new CRX hybrid sports car, good - where was I? Yes, the thrashy-sounding petrol engine starts on the key, is much more audible, and starts and stops with many more little thumps and knocks and lurches than the Toyota's. It feels cheaper, so it's a good job it is. And it's quite hard to make it work in electric-only mode.
But you can enjoy the drive, something you can't really do in the Prius. After our motorway run at 75mph - nearly a dead heat, at 51mpg for the Insight, and 49.9mpg for the Prius, and very little acceleration available from either above that speed - we confirmed the Honda's fun factor advantage at the test track, by introducing the cars to the Stig.
He actually walked past both at first, looking for the car he was driving. Then he walked back again and jumped into the Prius and did lap after lap after lap - eight or nine. Our scientific test went right out the window at this stage, because we waited for Stig to finish and swap cars, then ran out of time. God knows why he did so many laps in the Prius - he only did three in the Honda. Maybe he felt more obliged to extract a time out of a car that's so blatantly unsporting.
ut thrash it he did, and boy did he get it a long way into the air. I did my best to jump both cars, too, and found that the Honda was infinitely better at landing than the Toyota, maintaining a much more natural flight path and plopping to the earth without fuss. The Toyota seemed to want to go nose-high in the air and landed with a lurch. The big message here is that if you enjoy your driving, and your mode around town is ‘zippy', the Honda is the car of choice. All the Prius has going for it is grip.
The high-speed banking yielded an indicated 113mph max for the Insight, at a low average of 16.7mpg, and the Prius a top speed of 121mph, while its average wouldn't dip below 18.2mpg, even with the throttle pedal jammed so far into the carpet it started to become slightly on fire.
To the end, then - to the fuel station to finish our silly day. Remember the Prius did more Stig laps, so our scientific umming and ahhing took that into account. Despite that Stig disadvantage, the Toyota averaged 37.2mpg, using 3.58 gallons of fuel to cover 134 hard miles. The Insight was less thrifty, using 3.28 gallons to cover 120 miles - an average of 36.5mpg.
So the Prius wins - and its victory in town was absolutely decisive. It's more expensive, yes, but it's worth the higher price if your driving is done in the city, and you don't particularly care how the car responds in the air. If you like to jump your hybrid high and far and there's a little bit of Stig in the way you enjoy your cars, then the Honda is the one. It feels like a normal, almost nippy little thing, not an electric buggy, but it also feels a lot tinnier and cheaper and much smaller, which it is. You get what you pay for.
And, in this case, Stig's opinion is irrelevant. He strode away in the direction of Lidlington, not impressed, because he knew the Prius was a better hybrid and therefore a better car.
The Stig?s flying hybrids - BBC Top Gear