You really shouldn't add up the m/s² values based on amount of driven axles like that. 2.6 m/s² is way too fast for a train and will knock everyone off their feet. Even 1.3m/s² is among the higher values a train can achieve IRL.

The m/s² value is a bit arbitrary anyways. The only reason it's in the game is because it's easier to understand for most. The defining factor is the max kN a train can provide (and that the couplings can handle!)

So, no need to go above 1 - 1.3m/s for any train, and only the kN really matters.

I use 1 - 1.3 m/s² for multiple units that serve S-train type lines. For locomotives I even limit this to 0.85m/s² for realistic acceleration. Sure a locomotive alone can accelerate much faster than that, but they don't do that in passenger service.

Actually you got your KISS numbers wrong in your mods. e.g. DB KISS has the same power as the sbb one: 4MW permanent / 6MW max. power. but the diffrent gear ratio decreses tractive effort to 320kn and max. acc. to 0.85 m/s^. prices are quite low, they do cost a bit more(new) (i know, more realistic prices people don't use the mod...)

Trouble is, most trains have a much higher max. kN than they can actually bring onto the rails. put putting the max kN down to the actual value (on the rail, not wheel) would confuse people, as it's listed diffrently basically everywhere.

you can go to stadlers website, they published the numbers for diffrent projects. comparing them yields the numbers for the theoratical other variants.

KISS (BLS) has 400 kN (216t) which gives almost 2 m/s^2 with only half the axis driven. but in reality it can only do 1.3 m/s^2 in this configuration.KISS ODEG with only 1 / 4 of the axles driven has 200kN but can only do 0.63 m/s^2.

And yes, it acctually makes little sense to make a KISS all axles driven and able to speed up at 2.6 m/s^2. but since my mod allows for all possible configurations of the KISS platform... i leave it up to the player to decide how insane he wants to go.

The game also allows for insane passenger numbers and a lot of other things.



there is nuance, as heads / middle cars do not weight the same... so comparing something with a diffrent number of middle cars will not be accurate.

locos are acutally much more limited in inital acceleration if they have a lot of cars hanging on.
so a RE 460 with 5 wagons attached will perform not as well as DB KISS (ca. 300kN both).
F= k* N with N simply being the weight on the driven axles. (k = 2 seems to be possible at low speeds)

N for RE 460 = 84 kN , DB = KISS 130 kN (not accounting for weight of the pax in the heads)
so eff. max. tractive eff: about 168kN for the RE 460 , 260 kN for the DB KISS

If you go by max tractive kN and weight alone, the should do a little over 1 m/s^2 for both.

Attach 11 wagons to the same RE460 and it still only brings 168kN to the rails max.
There is a reason that all new passenger trains no longer use classical locos.

max. acc. is basically limited by the weight on the driven axles (and kN). until P / V takes over and becomes the limiting factor.

so if you can only use 10% / 25% / 50 % or 100% of the weight of the train to create friction forces between the driven axles and the rail makes a huge diffrence.

Changed to max. tractive effort values to what can actually been brought to the rail (using k = 2, used stadler KISS SBB/BLS data to calculate it).
That should yield reasonable results.

You can put the m/s² at 5 if you want to, IRL it will be limited by the tractive effort.
The only thing you can realistically do (and which is what I do) is give that acceleration value a lower value than what the tractive effort allows to simulate drivers not going pedal to the metal, which they don't IRL either.

Something to keep in mind is that the way NIMBY handles max TE is a bit weird if not specified...
If a train mod (eg. the default trains) does not specify max TE, then the max TE for every car is based on its weight and max accel, even it does not have power. I don't believe this is realistic. Additionally this is based on empty weight, so the train will not hit max accel when carrying load. If your max accel is based on service considerations, then you should simply set the max TE to a very large number so that it is ignored (I wonder why this isn't the default behavior).

Your observations are a bit off.

-A car without power does not provide any tractive effort. (in game and IRL)
-When you don't provide tractive effort in your mod the game indeed misbehaves. It changes the tractive effort (turn it into a changing value) to maintain the acceleration you specified. This is of course nonsense IRL.

Providing the acceleration on it's own as a 'setting' factor in a mod is a bit whacky. Acceleration is a product of weight, power output and tractive effort.
You can however use the acceleration value to limit the acceleration to get more realistic accelerations on for example TGV/ICE/HST trainsets, which are slowly accelerating at slow speeds but faster than regional trains at high speeds.

Practically speaking I do not find acceleration even when set at defaults (1 m/s/s and up to 1.3 m/s/s in some mods) to be an issue at all. I put in real life schedules on some lines around Japan, and if anything I need to slow these trains down. Just looked up shinkansen a current N700 model, and it lists acceleration at just 0.72 m/s/s, surprising low as I know you can actually feel nice acceleration as it takes off from a station.

If the game uses the lowest value across multiple wheels, I think this actually makes sense, because at any higher values the powered axles with lower acceleration would be forced to rotate faster than their motor can make them rotate, which will then pass this faster rotation to the motor and potentially damage it. Unpowered axles are not connected to a motor, so they can rotate at any speed. Alternatively you could disconnect a powered axle from its motor (i.e. not apply power to it) but then it just becomes unpowered and does not contribute to acceleration.

IRL it's really the s-bahn trains that excel at acceleration. even subway's often stay below 1 m/s^2, as the rather focus on frequency and cheaper prices.
both high speed and high acceleration do make trains a lot more expensive.
if you put max. trac. eff. to min[max trac. eff. according to manufactuerer, max weight on driven axels*2] you get something resonable. if there are pax sitting in over the driven axles you can add max pax*80 / 1000.
you also notice that both sbb / bls use over 1 m/s'2 acceleration capability (for s-bahn, not for intercity-trains). they do not actually use it on regular basis, but it does allow trains to catch up to scheudule, even if they stop very frequently.
if you want to compare to real life: unless it's a metro / underground, a stop of only 30 sek will in general be insufficent. most cars would only allow for boarding / unboarding of 4 pax / s or only 120 pax in 30 sek (N700 probably about 2 / sek/ car). so in japan / switzerland with lot's of travellers (and punctual trains) you have considerable longer stop times.
if the train allows for unlimited boarding you always run ahead of scheudule.