The numbers from the Spanish Grand Prix say it all - qualifying gap between Sebastian Vettel and Lewis Hamilton, one second per lap; race gap: rarely more than a cigarette paper. In fact, as Hamilton said: "If I could have got past I think I would have pulled away."

It was perhaps the most extreme example this year of the anomalous difference between the Red Bull and McLaren, according to whether it is a single lap on a Saturday or a series of them on race day.

Barcelona was probably McLaren's most competitive race this year, in that their China win came more through strategy than a basic pace advantage whereas the Spanish Grand Prix boiled down to a straight fight that called on all of Vettel's considerable skills to fend off what was essentially a faster car.

"We have to look at where our pace has gone," said Vettel. But perhaps it's not so much missing Red Bull pace as enhanced McLaren speed - and the basic fact remains that the Red Bull has got a reduced advantage in the race.

Why should this be so? There are several potential explanations.

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"I believe it's these tyres," says Red Bull team boss Christian Horner. "You can get a lap out of them but they are very fragile and need to be looked after in the race."

Horner is implying that the RB7's pace advantage is potentially there all the time but can be accessed only sparingly in order to keep the tyres alive long enough for competitive stint durations.

It is an interesting theory. The Pirellis are indeed fragile and the way a tyre degrades, according to how much downforce is acting upon it, is quite a delicate calculation.

A tyre has only so much energy contained within it and, other things being equal, the more downforce you apply through it, the faster you use up that energy.

The harder the tyre is being squashed into the ground, the more you take out of it and that downforce squares with speed.

Other things are not always equal though and there is a balance to be struck, because if the tyre slides too much - because there is not enough downforce acting upon it - it overheats its surface and degrades that way.

So it can be that a tyre wears quicker through having more downforce acting upon it - or less. The trick is in having it at just the point of equilibrium.

The suggestion is that the RB7 has too much high-speed downforce for the fragile Pirelli to be able to deal with for very long and therefore has to be nursed more than on the McLaren.

During the tyre war of the early 2000s - and even to an extent with the tough control tyre Bridgestones of the last few years - it used to be that the more you could load up the car with downforce, the faster your stint time would be.

That is not necessarily the case any longer - although it still allows you to be devastatingly fast in qualifying.

The RB7 has clearly got a lot more high-speed downforce than the McLaren, as Hamilton emphasised.

"They were massively, massively quick in the high-speed Turn Three, Turn Nine and through the last corner," Hamilton said. "His downforce was incredibly clear for me to see."

That tallies with pretty much every speed reading taken at various points on the circuits this year.

"But we were quicker through other corners, so it was almost balanced," Hamilton added.

It could be that the McLaren's tyres were not overstressed through the slow-to-medium-speed corners because they had not just taken such a high-downforce battering through the fast corners.

"I think if we were still on Bridgestones," said one rival team engineer, "the Red Bull would be winning races by half a lap or more. They're just limited by the Pirelli."

That's not the whole story, but it's probably most of it.

"When you compare the rear wings of the Red Bull and McLaren," says Williams technical director Sam Michael, "one has a small chord and large flap, the other a large chord and small flap. The Red Bull wing will gain much more drag reduction and therefore lap time from operating the DRS wing."

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The significant point here is that DRS can be used freely throughout the lap in qualifying but only at one specified place in the race. The McLaren would therefore be expected to be more competitive in race than qualifying.

There is also speculation that Red Bull's engine supplier Renault is finding more time from hot-blown diffuser mapping than other engine manufacturers, having been the ones who pioneered it.

This technique - which allows the fuel-air mixture to ignite in the exhaust when the driver is off-throttle, thereby increasing the velocity of the flow to the diffuser and increasing downforce - is widely used in qualifying, but only sparingly in the race because of the increase in fuel consumption.

If Renault has indeed got a lead here, then the Red Bull would be expected to show better in qualifying than race.

But in this case you would also expect to see a similar performance pattern with the Renault car and that pattern is simply not evident.

Furthermore, both Mercedes and Ferrari are adamant they are finding a lot of qualifying lap time from the technology and there is no reason to suppose they are lagging behind Renault Sport in this respect.

Finally, there's the matter of the Kers energy recovery and power-boost system to consider.

Red Bull's Kers is famously unreliable and can be used only sparingly in the race. But team insiders reckon than even when it is working it is not worth as much lap time as the 0.5secs per lap of the Mercedes or Ferrari systems.

Backing up that theory, Vettel was able to qualify around one second faster than McLaren even without Kers in Spain.

So if differences in the effectiveness of the hybrid technology are responsible for some of the differing levels of competitiveness of the two cars race to qualifying, it cannot account for all of even most of it.

So take your pick: the Red Bull has too much downforce for the Pirellis to be able to use; it derives more drag reduction from its DRS; it has better hot-blown diffuser mapping and loses Kers performance. Or some sort of combination therein.

Mark Hughes has been an F1 journalist for 10 years and is an award-winning author of several books