Moto GP is the top tier of motorcycle racing, but there are three classes of GrandPrix (GP).
Moto GP is the top class, then there is 250cc and 125cc, these are regarded as feeder classes, and there used to be a couple more engine capacities but these have gone - the 50cc class and the 350cc class.
They all used to have 2 stroke engines, and the top class back then was 500cc, but the manufacturers, especially Honda, wanted to run 4 strokes, but this needed an engine capacity hike, so now all the bikes in the premier class have 1000cc 4 stroke engines.
There are other formats of bike racing(most are based on production machines modifed to the racing bodies regulations - whatever regulations happen to apply to that particular format), but GP is the prototype class, its the motorcycle equivalent in regulations as F1, there are few restrictions on what you can do, although there is a lower weight limit on the machine of around 156kilos, and a fuel capacity limit.
Technology has moved on so much that the bikes are getting too powerful for the circuits, some are turning out around 250bhp, which on a bike with such a low weight is pretty dramatic, as you will have seen.
There are proposals to reduce the engine capacity to 800cc, I’m not sure if this will be in one step down or in several steps, probably in one go as it would be very expensive to keep developing engines by stepping down in bits.
You won’t find mirrors on these or any other track machines, they spoil aerodynamics, they are something that would certainly be smashed off in very short order, you’ll have seen just how close these bikes get to each other, and anyway, they are not needed, the bikes are plenty noisy enough for the leader to know how close someone is and which side they are approaching.
Its also no advantage, if it were, then they would be fitted, the lead rider is only concerned with taking the best lines and making sure that others have to find the long way around, its up to the followers to make it past.
Spinning means that the back wheel, instead of making one revolution per circumferance of ground plane, loses grip and spins several times more than the ground it covers.
Uusally this is not desirable as it wears the tyres out, once they lose the depth of rubber their temperature falls and with it grip falls.
However, spinning the wheels up is desirable to a certain extent, the reason is that if you can keep your back wheel spinning faster than the travel distance when going into a corner, you can keep the engine turning over at its best rate to give you maximum torque, and when you straighten out, you don’t have to wait until your engine revs climb, you just release the front brake completely and you fly out. This technique was pretty much essential in the days when the top class was 500cc two strokes since their engines tended to have a fairly narrow power band, the engines needed to be kept turning at a high rate to make sure they were making their power most optimally.
Nowadays with 4 strokes spinning the back wheel is not quite as crucial the skill it was(but is still very useful), but in the lower classes, especially the 250cc 2strokes, its still essential, and very difficult to learn, to such an extent that riders either spin up their wheels or are out of the running altogether, and if they spin and don’t learn the skill they end up in hospital.
This spinning of wheels, even sometimes when the front wheel is also sliding under massive braking, is what makes it so hard for riders in other motorcycle racing to transfer to GP style as other formats are not running quite to the same absolute limits. Oddly enough US flat dirt track racing develops this skill to the extent that there have been quite a lot of very notable US riders in the past.
The flat dirt track racing is just about as far away as it is possible to get, from the corporate world of MotoGP, in terms of budgets, image, and speed, but its very relevant in terms of skill.
Tyres are pretty crucial to the whole thing, but another important point is the amount of fuel carried, which is held relatively high up on the machine(in a tank under the riders ass), and having longer races would mean carrying more fuel, or having fuel stops, along with tyre stops, and it would all be very difficult to control safely. Carrying large amounts fo fuel would change the handling of a machine considerably during a race as the total weight fell .If a badly fitted wheel falls off a racing car - its not good, but how much worse would it be on a motorcycle doing up to 220mph ?I’ve seen this happen even in F1 following pit stops.
Endurance is another issue, these riders are extremely fit, every corner the braking forces are like having to do a handstand with a couple of rucksacks full, the blood rushes from one place to another, causing the forearms to swell with some unfortunate riders - look up Marco Melandris problems. I doubt that riders could actually stand significantly longer events because of these physical demands.
Hauling the bike from side to side in chicanes and quick left-rights-lefts(or vice versa) is essential, the idea is to flick the bike from one side to the other before the suspension has time to unload and then have to recompress to deal with the cornering forces. It’s takes pretty much the entire body to do this quickly enough.
I’m portuguese actually. Good guess though, the following of motorcycling GPs in Spain is huge.
Roadracing is in a category of its own, pretty much outlawed in continental Europe (I don’t know of any exceptions). The Isle of Man TT is spectacular racing but it’s difficult to make a comparison to anything else.