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"Power to weight ratio" in relation to "terrain resistance"


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CeeDee_2 #1 Posted 17 July 2017 - 03:07 PM

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I understand power to weight ratio (horse power per ton, whatever you call it). It is weight of the vehicle divided by horse power. More is better :)

 

I understand the terrain resistance for high, medium and soft ground. The higher this number is, the more engine power is "absorbed" by the ground you are driving across. Lower is better.

 

Compare two imaginary tanks X and Y. X has high power to weight and high terrain resistance. Tank Y has lower power to weight, but also lower terrain resistance. Assuming flat ground, it seems to me that there comes a point where tank Y actually performs better than tank X.

 

I guess this is a long way of asking if anyone knows exactly how (mathematically) the terrain resistance modifies the power to weight ratio. It can't be as simple as:

 

effective hp/t = hp/t ÷ terrain resistance

 

... because that would cause something like the FV4202 (12.26 hp/t) to have excellent effective hp/t on hard ground since the terrain resistance on hard ground for it is 0.38.

 

Anyone have an idea?

 

Regards, C.


 



cro001 #2 Posted 17 July 2017 - 03:13 PM

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I think developers stated that reducing the terrains resistance by 20% roughly increases P/W ratio by 20%. I don't know if that's true.

RamRaid90 #3 Posted 17 July 2017 - 03:22 PM

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There are too many in game variables that we as players are not aware of.

 

But i think IIRC you can divide the horsepower by the terrain resistance to get the tanks effective HP on a certain ground type.

 

Then divide by total weight in tons to find the effective HP/t.

 

For example.

 

BC25T has 720 HP and a standard 28 hp/t.

 

Resistance on hard ground is 0.86. So 720/0.86 = 837 effective HP 837/25.2t = 33.2 hp/t effective.

Medium Ground = 29.7 hp/t

Soft Ground = 18.6 hp/t


Edited by RamRaid90, 17 July 2017 - 03:22 PM.


Tr0gledyte #4 Posted 17 July 2017 - 04:19 PM

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Good question, now I'm interested as well. The fact that terrain resistances can be lower than 1 complicates this a little since anything below 1 would increase a vehicle's hp/t if you can divide its hp/t by its terrain resistance, which imho doesn't make sense. A tank has a certain engine power and weight and it's a bit weird that this ratio can increase due to terrain.

 

Would've been easier if 1 was the base minimum and they could increase the terrain resistances or play around with the engine power to balance it out. Is there a source stating you can simply divide the hp/t by its terrain resistance to get the effective hp/t? 


Edited by Tr0gledyte, 17 July 2017 - 04:20 PM.


tmp #5 Posted 17 July 2017 - 05:18 PM

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Does anyone know if terrain resistance is, you know, actually terrain resistance and not just a divider for power-to-weight?


 

If it's actually terrain resistance, then tanks with high power-to-weight and poor terrain resistance would, for example, climb better than tanks with the opposite.  Accelerate better too, I think.



Gvozdika #6 Posted 17 July 2017 - 05:26 PM

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It's one of those hidden parameters like dispersion on movement/rotation/turret which WG have never really made any attempt to publicise. They've never explained the precise mechanics of it (unlike camouflage which is fairly simple and now shown in the garage) and until they do it's always going to be a grey area. 

 

Quite why is anyone's guess.

 



HidesHisFace #7 Posted 17 July 2017 - 05:35 PM

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I don't think it is as simple as "effective horsepower" somebody posted above. 

The prime example is T25 Pilot 1. It has completely crap hp/t ratio but amazing resistances. 

 

According to the posted formula it should have very decent 21hp effective on medium terrain and nearly 30 on hard terrain. I can guarantee this isn't the case - the tank still feels sluggish at times, even though general mobility is FINE. But there are moments when horse-power shows. It is especially visible when climbing the hill or when turning at high speed.

So... The terrain resistance is definitely NOT just a simple hp/t divider.



BP_OMowe #8 Posted 17 July 2017 - 11:28 PM

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Perhaps it is a weight multiplier?

Also consider that the known formula (effective turn ratio) does not include hp/t at all.



tmp #9 Posted 18 July 2017 - 12:02 AM

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If that formula is the one I think it is, it _does_ include both horsepower and weight, and you can trivially rewrite it to use hp/t instead if you want.

BP_OMowe #10 Posted 18 July 2017 - 01:23 AM

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View Posttmp, on 18 July 2017 - 12:02 AM, said:

If that formula is the one I think it is, it _does_ include both horsepower and weight, and you can trivially rewrite it to use hp/t instead if you want.

 

Be my guest, for from what little I know about mathematics, only the ratios between base and current power and weights are used, and not a ratio between power and weight.:
http://wiki.wargamin..._Traverse_Speed

Tr = Tn x (Ec / Es) x (Rh / Rx) x (Ws / Wc) x Pc
Tr = Real traverse speed (deg/s)
Tn = Nominal traverse of a tank, including bonus from clutch breaking, drivers' skill and consumables (deg/s).
Ec = Current engine horsepower (HP) including any bonuses from equipment and consumables.
Es = Stock engine horsepower (HP).
Rh = Tank's terrain resistance on hard terrain, including bonuses from Ventilation, Brothers in Arms, Off Road Driving and consumables.
Rx = Tank's terrain resistance for terrain one is calculating traverse for, including all the bonuses.
Ws = Weight of stock tank without equipment (kg).
Wc = Current weight with used modules and extra equipment (kg).
Pc = Neutral (centre) turn capable, or pivot (locking one tread) steered, 1 for pivot tanks, 0,95 for neutral turn tanks.


tmp #11 Posted 18 July 2017 - 01:34 AM

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Tr = Tn x (Ec / Es) x (Rh / Rx) x (Ws / Wc) x Pc = Tn x Pc x (Rh / Rx) x (Ec / Wc) / (Es / Ws)

Edited by tmp, 18 July 2017 - 01:35 AM.


Swoopie #12 Posted 18 July 2017 - 01:38 AM

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http://forum.worldof...ed-calculation/

 

Btw troolen later found out that these dont apply to swedish TD's, they seem to have a new hidden factor we dont know of.



tmp #13 Posted 18 July 2017 - 02:27 AM

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Quick SCIENCE! showed that a Himmelsdorf climb that takes about 50s with FV4202 (12.26 hp/t, 0.38 hard, 0.48 medium, 0.96 soft) took about 30s with Pz T25 (22.67, 1.21, 1.43, 2.85) which is consistent with terrain resistance being actual terrain resistance.


 

Also, on flat hard ground FV achieves nearly 50km/h after a long, slow acceleration.  T25 hits something like 30-40km/h rapidly, and then struggles, which also points at terrain resistance being actual resistance.


 

EDIT


 

Since the OP asked this, it seems that effective hp/t = hp/t - constant * terrain_resistance * tank_velocity.


 

EDIT 2


 

After a quick purchase of AMX 40 - for SCIENCE! - and some _very_ quick testing, it seems like the constant is in the 0.30 ballpark.


 

EDIT 3


 

I goofed with compensating for 50% crew.  SuperPershing with 100% crew gave 0.26 and since it's a result that is approaching the real one, the proper constant is probably 0.25.
 


Edited by tmp, 18 July 2017 - 09:17 AM.


CeeDee_2 #14 Posted 18 July 2017 - 02:17 PM

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Very interesting. I threw these numbers into Excel for the FV4202 and Centurion 1, for speeds from 0 km/h to 50 km/h in 5 km/h increments and then graphed the result.

 

It shows clearly that at low speeds the higher power to weight ratio of the two (in this case the Centurion 1) has the advantage. However, as speeds increase the better terrain resistance (FV4202) starts to gain ground, and at around 30 km/h the effective power to weight ratio of the FV4202 becomes higher than the Centurion 1. On hard ground at 50 km/h the hp/t for the FV4202 is 7.51, for the Centurion 1 it is 4.7 (12.26 - (0.25 x 0.38 x 50) = 7.51).

 

If you do that for soft ground then the power to weight ratio of the Centurion 1 goes negative just above 35 km/h (effect hp/t = 0.775 at 35 km/h). Which shows that on soft ground it can't go faster than that regardless how long it has. The FV4202 doesn't go negative until just above 50 km/h (hp/t = 0.26 at 50 km/h).

 

It would be interesting to know what the purpose of the constant (0.25) is. Perhaps a way of tinkering with this without changing the terrain resistance numbers of all tanks in the game? Or maybe it varies from one type of tank to the next?

 

Thanks for the help on this!

 

Regards, C.



gpalsson #15 Posted 18 July 2017 - 02:23 PM

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I don't see why WG won't just write the real stats on tanks in the garage. 


Edited by gpalsson, 18 July 2017 - 02:27 PM.


tmp #16 Posted 18 July 2017 - 06:57 PM

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I suspect that in primordial WoT all tanks and terrains had same resistance, and they just added multpliers for different types, defaulting to 1.


 

Anyway, with 0.25 constant you'd predict that something like T34 premium tank on medium terrain had a top speed of about 30 km/h rather than the stated cap of 35, which is pretty much exactly what happens so it seems that at least heavy and medium tanks use the same constant.



qpranger #17 Posted 18 July 2017 - 07:22 PM

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View Postgpalsson, on 18 July 2017 - 03:23 PM, said:

I don't see why WG won't just write the real stats on tanks in the garage. 

 

Like an honest business would?

Dr_Oolen #18 Posted 18 July 2017 - 07:25 PM

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Interesting, i remember back in the days when we were figuring out the real traverse speeds richardnixon also said hed be looking into real hp/t, but nothing was really finished as far as i know. Nice to see people still care and do testing now.

 

I always felt/thought real hp/t would also be based on nominal hp/t and terrain resistance with dependency on one other variable, which i thought would either be slope of terrain the tank is on (where, say, 20 hp/t and 1 resist would be better than 10 hp/t and 0.5 resist, while on flat ground both would be +- the same) or something to do with inertia (as in on the same terrain a 20 hp/t with 1 resist would start accelerating faster than 10 hp/t with 0.5 resist, but at higher speeds the difference would diminish as the tank gets inertia).

 

But i have my suspicion that since the last physics update terrain resistances dont matter and there is a new hidden parameter that takes over (but which was set for all the tanks at that point in the game to behave as terrain resistances did in the previous physics for those tanks, to keep same performance, thus on those tanks its indestinguishable from terrain resistances).

 

If anyone wants to bother measuring stuff id suggest looking into grille (t10), ikv 90b, udes and possibly strv103s and then compare those with mediums/heavies/lights with similar hp/t and terrain resistances. Unless i completely lost any feeling for the game id expect you to find out that at the least grille and 90b accelerate slower than they should given their hpt and terrain resistances. The siege mode tds apart from the t10 all have fucked up traverse speeds, so its possible the actual hp/t on them is also "wrong".


Edited by Dr_Oolen, 18 July 2017 - 07:26 PM.


tmp #19 Posted 18 July 2017 - 07:57 PM

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One thing to take into account is traverse.  Grille has medium tank's power and resistance values, but it has a TD's traverse.  So it's probably going to feel pretty sluggish if you actually have to steer it while moving.  Need to test to actually tell for sure, of course, but this is a possibility.


 

It seems like siege mode TDs have one set of values for siege mode and other for drive mode.  But the game - OF COURSE - only shows you one set.


 



Tinbawx #20 Posted 18 July 2017 - 07:58 PM

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View Postgpalsson, on 18 July 2017 - 02:23 PM, said:

I don't see why WG won't just write the real stats on tanks in the garage. 

 

How does WG like to put it again?

 

It might be to "confusing" for players. :trollface:






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