Clément Barbeau Vermet said:
I don't get why you need a tank transporter for the PzH 2000, it is only 10 km/h slower than Archer. We could also make it faster and lighter by making it 2-man crew, taking off the commander sight and fire-control and re-engine it with a more powerful but just as big euro pwr pack.
The thing is as big as a tank, and has tracks like a tank. Tracked vehicles require that you have to place them on a tank transporter or something similar to reduce the wear and tear on the tracks. The huge weight of the tank (or a self-propelled gun the of the same weight) combined with the relative weakness of the track assembly makes the maximum road speed of such a vehicle in reality a burst speed, which can be kept up for only a short time before there is a mechanical breakdown. Although the maximum off-road speed is lower, it cannot be kept up continuously for a day, given the variety and unpredictability of off-road terrain (with the possible exception of plains and sandy deserts). Prolonged use of tracked vehicles without being placed on a transporter places enormous strain on the drive transmission and the mechanics of the tracks, which must be overhauled or replaced regularly.
When moving in a country or region with no rail infrastructure and few good roads, or a place with roads riddled by mines or frequent ambushes, the average speed of advance of a tank unit or tracked self-propelled artillery unit in a day is comparable to that of a man on a horse or bicycle. Frequent halts must be planned for preventive maintenance and verifications in order to avoid breakdowns during combat. This is in addition to the tactical halts needed so that the infantry or the air units can scout ahead for the presence of enemy antitank groups.
Wheeled vehicles have the advantage of being able to self-deploy; there is no need to drag them around as there is less maintenance involved with wheeled vehicles, and there is less chance of a breakdown. In the rare case that a wheel bursts, replacing the wheel is very quick and easy (jack up the wheel, take a wrench and unbolt the tyre, take the tyre off the axle, swap with a new tyre, bolt it back on the axle, lower the vehicle, and off you go), while a thrown track takes hours fix.
Edit: In fact, I have a book "Into The Storm: A Study In Command" by Tom Clancy and retired US Army General Fred Franks, Jr., regarding the 1991 Gulf War. The book mentions the logistical difficulties in getting the tanks to the front lines in the 1991 Gulf War, to the point where the British 1st Armoured Division, when they found themselves short of tank transporters had to drive across the desert to their positions which was murder on the tanks. I suggest you read the book, as it is a good read.
http://www.chapters.indigo.ca/item.asp?Item=978042519677&Catalog=Books&Ntt=Into+The+Storm%3A+A+Study+In+Command&N=35&Lang=en&Section=books&zxac=1