Everyone thinks very highly of Spa - it is one of the world's great circuits, and a huge test for both the drivers and the engineers.
Spa-Francorchamps with its challenging 180mph curves and undulating Eau Rouge.
The greatest part of that test used to be the daunting 180mph-plus left-right-left swerves, dip and rise through Eau Rouge.
In the past, taking those corners flat-out was every racing driver's challenge - and the same went for the engineers, trying to set the car up to enable it to do so.
These days, Eau Rouge is not as difficult as it used to be. It's what they call "easy flat" for everyone on a qualifying lap. Although the high speeds involved and the extreme gradients mean it is still very challenging.
The track layout there has not changed, but the safety facilities and the capabilities of the cars have.
The extra run-off area means that, mentally, the drivers do not feel as constricted, and the cars now have greater downforce through there which is also more stable than it used to be.
In the past, the diffusers would stall in the compression at the bottom of the hill, robbing the car of downforce. Then, as the car went light over the crest in the final part of the corner - which is known as Raidillon - they would lose some again.
Now, with the advances in aerodynamic development, the cars hang on to their downforce much better in both those critical areas.
COMPROMISE IS THE KEY
Spa is split into three distinct sections as a circuit, and it is difficult to decide on the best set-up compromise.
The first part of the track from the start-finish line, through Eau Rouge and up the long straight to the chicane at Les Combes, and the final part - the long flat-out section through Blanchimont and back to the pit straight - both require reasonably low downforce, to ensure speed on the straight is not compromised too much.
By contrast, the middle sector, through all the demanding medium and high-speed corners from Les Combes to Stavelot, requires reasonably high downforce.
The key is finding the right compromise - and deciding whether to lean more one way or the other.
Belgium Grand Prix facts
Circuit de Spa-Francorchamps, Belgium
7.004 km (4.3 miles)
First Grand Prix:
308.052 km (191 miles)
Most wins (drivers):
Michael Schumacher (6)
Most wins (constructors):
These days, because of the way races have developed with Pirelli tyres, you need to overtake. Even if you qualify on pole, you're very unlikely to be able to stay at the front all the time. So a team are likely to veer towards the low-downforce approach.
The middle sector is now the most demanding part of the track. The corners are all pretty fast and the car needs a very good balance to ensure it does not damage the tyres.
The double-left known as Pouhon is particularly tricky - it's 150mph or so, and you're in it for a long, long time. If the car is not set up just right, it can destroy the tyres very quickly indeed.
And the rest of of the corners through that part of the track, while not as fast as Pouhon, are all long and put a lot of strain on the tyres.
So if you have a car that is quick in a straight line but sliding around too much in that sector, you will eat up the tyres.
All this makes Spa one of the most demanding tracks to get the car set up right for the compromise between one-off lap time and making the tyres stay alive on Sunday.
They have in the last few years always tended to set their car up for optimum lap time, rather than worrying too much about straight-line speed, and tried to control the races from the front after Vettel qualified on pole.
World championship standings
It has worked very well, but it is a risk, especially when more cars are competitive.
In the past, particularly in 2011, they had a big speed advantage and were able to quickly build the advantage they needed in races.
That has not always been the case this year. They have not got as far away before the first stops and they can drop into awkward traffic - and a good example was in Hungary last time out, when Vettel's chances of victory evaporated when he got stuck behind Jenson Button's McLaren.
That will make for difficult decisions at Red Bull this weekend, given the qualifying performance of the Mercedes, which has been on pole for six of the last seven races.
WATCH OUT FOR MERCEDES
I think there is still more to come from Mercedes in terms of absolute pace.
From worrying about the tyres, they can concentrate more now on making the car faster. So I think they will be moving forward and competing for wins at most of the races from now on.
Red Bull have done a very good job this season, but from the numbers I work out they are not making the dramatic steps forward in performance they used to.
They have a good car and they are doing a very competent job each weekend and have been benefiting from other teams tripping up, whether it be Mercedes with the tyres, Ferrari slipping back or Lotus not quite being there on absolute pace.
Ferrari needed to spend the break having a real think about the way they are approaching their racing.
They have gone backwards and they need to work out why. I think they are guilty of being too cautious and not making decisions with the car,
as I discussed after the last race.
If you don't make decisions, you don't make mistakes, but you don't give yourself the chance to make the right choice and move forwards either.
Sometimes you just have to stand up and make a decision and suffer the consequences if it goes wrong. But the Ferrari guys are clever enough not to be going wrong.
I suspect the Pirelli engineers will be heading to Spa with a few concerns in their minds about the tyres.
Those are the two tracks that make most demands on the tyres - and Eau Rouge is particularly tough.
In the compression at the bottom of the hill, on top of the aero load, which is already very high because the car is going so fast, there is about 1G of extra load acting vertically on the car - that is the car compresses by its own weight again.
That's another 640-800kg of force into the tyres depending on the fuel load, which puts a lot of extra strain on the shoulder of the tyre - where the sidewall meets the tread.
So Pirelli will be recommending quite high minimum tyre pressures to ensure that stress on the tyres is kept under control.
Gary Anderson is the former technical director of the Jordan, Stewart and Jaguar teams. He was talking to BBC Sport's Andrew Benson
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.