Yo creo que dependerá del circuito. Unos serán de día, otros de noche. No se :-\...
Macau, China
Famous for its inner-city bike races, Macau is a track split into two. The city centre has open roads and lots of room to get your speed up. Some of the elevated sections might cause your vehicle to catch some air, but nothing you can't handle. Take one of the mountain roads though, and you'll see a whole different Macau. Twisting, fast, narrow, and (in places) tunnelled. Remember, what goes up(hill) must come down(hill)!
Prone to tropical storms, Macau's track surface can become a nightmare when wet. Adjust your throttle appropriately when the rain starts falling!
Las Vegas, USA
Set around one of the famous lengths of tarmac in the world, The Strip, most of the tracks in this Nevada city all follow a simple formula: massive long straights with an intense hairpin at the end of them. Make sure you apply the brakes early to get your speed down and follow the rumble strips, and you should be able to swing around just fine. Remember that bikes generally corner slower than cars around hairpins, so be extra vigilant when riding two wheels instead of four.
Las Vegas is most spectacular at night, and so it's only fitting that this is how it appears in PGR4. Don't get too distracted by the neon though, and remember that weather is now a feature. Yes, it does very occasionally snow in Vegas in real life... although you will probably see it a bit more frequently in PGR4!
London, England
Start your race on the banks of the River Thames, and speed past the Houses of Parliament. London is a historic city, so remember that its streets weren't designed with cutting-edge sports cars and superbikes in mind. Runoff is virtually non-existent in the city centre because of the close proximity of the buildings to the road. Stay away from the barriers to keep your speed up, and be careful when riding your bike through the slaloms.
Watch out for the infamous London fog and rain... it can wreck havoc in the tight inner-city areas of the track. Learn the routes before you go flat out.
St Petersburg, Russia
This Russian city consists largely of open roads with lots of runoff to play with. Expect high speed driving, but you'll need to experiment with your racing lines to find the fastest route through the open areas. The terrain is mostly flat, but watch out for the humpback bridges! Use them to grab some extra Air Kudos during a race.
There are some tighter roads around the central canals area; don't let the shorter corners take you by surprise. Overhead tram wires add to the sense of speed, but don't let them deceive you; you'll need to contrast your driving between the super-long slaloms and the turn-on-a-penny square corners.
Tokyo, Japan
Japan's largest metropolis returns to the PGR series, with wide roads and plenty of space to jostle for position. There are various corner types, ranging from super-long sweeping bends to insanely tight hairpins. Taking motorcycles for a spin in Tokyo will be a humbling experience the first time around, especially when trying to tackle the descending circle turn at the Shinjuku bus terminal! Remember, bikes make up their ground on the straights. When cornering, brake more than you normally would in a car and make sure your racing line is good.
New York City, USA
The two giant bridges make a comeback, this time with new vehicles and weather conditions. It is possible to push the fastest cars and bikes to their limit in New York, but watch out for the absurdly tight corners at either end of the Brooklyn Bridge. You'll need to get your speed right down; otherwise you'll become a little too acquainted with the Armco!
Shanghai, China
Shanghai at night is an amazing sight, with neon signage to rival Las Vegas. However, don't be distracted by the beautiful skyscrapers or dramatic lighting; you'll need to stay alert when racing here. Almost all of the roads are several lanes wide, meaning that it becomes less a task of avoiding the barriers than it does getting the perfect racing line. Most circuits are suited to fast cars, meaning that Shanghai is sure to become a "Class A whore's" favourite.
If you're going for a fast lap in Shanghai you'll need to let the rumble strips guide you in and out of the multiple chicanes. That doesn't mean it's not fun though; Shanghai is a perfect playground for Kudos grabbers to practice their trade. A wet race in this city is hardly ever without incident. Pay attention and don't let the speed creep up on you.
Quebec, Canada
Racing Quebec is like riding a twisting rollercoaster ride through narrow streets and hills. Most corners are long and slender, suited to either car or bike, and can be taken at high speed. However, there are a few awkward bends which you'll need to learn by heart in order to take at pace. A nice highlight is the gated city walls, which some circuits snake right through.
As you might expect in what has been described as PGR4's answer to Edinburgh, there is very little runoff and thus no margin for error. Watch those barriers!
Nurburgring, Germany
The "Green Hell" makes a comeback in PGR4, this time bigger and badder than before. This time around you'll have to contend with fog, rain, and snowdrifts. It's tough enough to complete a lap in good weather... wait until you see it under a foot of snow!
The Snow 'Ring has actually been modelled on a completely different mesh to the Clear 'Ring, this letting us do cool things like swap out the trees for ones sporting a new "leafless look", pile up snow on the grassy areas, and cover certain rumble strips in snowfall. If you're looking for the ultimate Gotham challenge, you just found it.
Michelin Test Track
As the icing on the location cake, we have also added a fictional Test Track to PGR4. This performs a similar function to the test track from Gotham 2, in that it's a great place to take your cars out and push them to the limit. However, unlike the test track from Gotham 2, this one serves a purpose in the Single Player career mode too. Several invitation challenges take place on the Michelin Test Track, sometimes on the Nascar-style oval, sometimes on the windy service roads, and occasionally on the dirty great skid pan located in the centre.
Despite the track being fictional, it has been inspired by a particular famous racing circuit in the States which I won't mention. But why sponsored by Michelin I hear you ask? Well, not only does this add some real racing authenticity to the game, we also get to include a couple of 40 foot high giant Michelin men in there. So everybody's a winner really.