I also did some researching, so we can (hopefully) finally get the specs right.
It's quite hard to find technical data about them these days as most articles (e.g. sources linked in wiki) seem to have disappeared in the meantime. Fortunately, there is webarchives.org.
T68 should be (according to
this sheeet)
seats: 86 + 122 standing capacity
empty weight: 49t
acceleration: 1.3 m/s² acceleration -> 64 kN (asumed acceleration is given for empty weight)
braking: 1.3 m/s² -> 64 kN, emergency braking up to 2.6 m/s² ->127 kN using mechanical brakes in addition
power:420 kW
monthly costs: 31.66
It would be nice to have a T68A available from 1999
power: 480 kW
The follwing are guesses from "The three–phase ac motors were lighter, more reliable, require less maintenance and were more cost effective."
empty weight: 48t
kilometer cost: 0.46 = 0.95*0.1*480
monthly costs: 30 = 0.95*31.66
Btw. I gues this thread rather belongs to Pak128.Britain-ex subforums
Oh well, didn't read your above edit yet:
What I have a problem is how the weight is balanced to get approximately right axle_load?
There is no easy way to calculate this. It greatly depends on the exact position of wheels and exact per-car weight and even if we knew that, we had to place further guesses like weight being evenly distributed over a car, which is often not true.
In fact, train manufacturers may aim at getting as much weight as possible on accelerated axles, as that will help to get more force on rails without slipping.
I'd like to quote the mentioned T68 paper for this: "Under full–load conditions almost 70% of the weight was on the powered bogies, which assisted the hill–climbing ability of the trams."
For T68, that means an axle load of 63.56t*0,7/4=11t (assumed 49t + 208*70kg=63.56t loaded weight)
Which makes me wonder how the current 5t were calculated or assumed?
Even asuming currently used unloaded weight of 45t and assuming the weight was evenly distributed results in 45t/6=7,5t
However, I guess for simutrans purposes it should be fine to assume an even distribution of weight over the train.
In reality, tracks maximum axle load of 17t does not mean none of the axles of the train is ever allowed to exceed 17t. In fact, there may even be exceptions to the "maximum" axle load that do not imply any reduction in speed.
E.g. SNCF, the national railway company of france restriced their high-speed tracks to a maximum axle load of 17t but allows power heads to exceed that maximum by up to 2t
It is assumed that this value was intentionally chosen to allow TGV trains, whose power heads have an axle load of 18t but not allow ICE 1 and ICE 2 trains whose power heads have an axle load of 20t (ICE1) or 19.5t (ICE2)