Power-to-weight ratio calculations?

[Smallhorses]

Maybe this is me, but bear with me....

As I understand it, a Power to weight ratio is, given by the weight of the car in kilos, divided by the horsepower, right? Seems to work for some of the cars in GT3, e.g. Nissan 300ZX TwinTurbo 2by2 has weight of 1580kg and 276HP.

1580/276 = 5.724 which is what the game says.

However, the Toyota Supra RZ which has a weight of 1510kg and 276HP gives a power to weight ratio figure of 4.631. Where has this number come from?

According to my trusty Casio calculator (which has seen me through GCSEs, A-Levels, a BSc and an MSc and is therefore unlikely to be lying )

1510/276 = 5.471

Clearly that's an enormous discrepancy!!!

Can anyone explain this? Am I just being stupid? Its not unheard of!

I love making things hard for myself by trying to complete races with the largest Power to weight ratio that I can, but I've been doing PD cup in the aforementioned 300ZX and thought I'd compare it to the other cars in the race.
According to the game stats, it looks impressive until you do the real maths.

____________________________Game Value_________Calculated Value

300ZX 2by2__1580kg 276HP________5.724____________5.724
Supra RZ_____1510kg 276HP_______4.631_____________5.471
Lancer EVO VI GSR__1360kg 276HP___4.358____________4.928
Impreza 22B-Sti___1270kg 276HP____4.379____________4.601
GT-R Vspec II (R32)_1500kg 276HP___4.885____________5.434
GT-R Vspec (R33)___1540kg 276HP___4.904____________5.579

Its bloody good fun so far, won 5 out of 6 races mostly by 4 - 10s (except SS5 II which I trounced them at by 49s, but the AI has never been any good at SS5 II in any car!!!) Seattle II was a 🤬 though, finished 2nd....

Any ideas what happened to PD's calculators then?
Ridicule this idiot if I'm wrong!!! (as if you need and invite to ridicule me anyway!)

 

[ceiling_fan]

this is a pretty observation. I have no idea.

💡
Maybe Famine knows!

 

[Eagle]

haha... I love how when we don't understand something, we call for Famine. Where would we be without his scientist ass?

I could understand if all the calculations were wrong, but the fact that your car is correct and the others are skewed doesn't make sense at all.

 

[spike10h]

You know the actual HP of a car sometimes changes after you buy it. For example the R34 is advertised as 276HP correct? But after you buy it, the HP changes to something like 310HP. Bottom line, the ratios may actually be correct.

 

[3rdgenracerX]

You know the actual HP of a car sometimes changes after you buy it. For example the R34 is advertised as 276HP correct? But after you buy it, the HP changes to something like 310HP. Bottom line, the ratios may actually be correct.

The horsepower increase only occours after you change the oil of a car. If you buy a car with 276 hp and dont do anything to it and go to your garage its hp will still be 276, it will only increase after you put some miles on it or if you change the oil. if its one you bought from a car dealer the HP will increase after you put a few hundered miles on it. If its a prize car it will come with max HP, all you have to do is change the oil to obtain its maximum hp "this excludes modding the car since that will obvisouly increase hp"

 

[Smallhorses]

And then again maybe not.....

Take for example the Toyota Supra RZ. In the Car Dealer it appears with 276HP and 1510kg and power/weight ratio of 4.631. (Should be 5.471 according to calculation!)

Buy the car. No oil change, or mods.

Now it appears in Garage with 316HP, still 1510kg and power/weight ratio of 4.778 (which is correct! Even my trusty Casio says so!) D'oh.



What the feck is going on?

 

[Famine]

Spike10h is right - few of the 276hp cars, when bought, appear in your garage with 276hp. The showroom section has the power ratings as "manufacturer advertised" (hence the 276hp/280PS, to fit in with the Japanese manufacturer's "gentleman's agreement" nobody observes). And the prize car equivalents come already broken-in.

Taking the sample list:
300ZX 2by2, 1580kg, 276HP. Stock purchased garage power: 267hp -
Supra RZ, 1510kg, 276HP. Stock purchased garage power: 316hp (prize car 326hp)
Lancer EVO VI GSR, 1360kg, 276HP. Stock purchased garage power: 302hp (prize car 312hp)
Impreza 22B-STi, 1270kg, 276HP. Stock purchased garage power: 281hp
GT-R Vspec II (R32), 1500kg, 276HP. Stock purchased garage power: 297hp
GT-R Vspec (R33), 1540kg, 276HP. Stock purchased garage power: 305hp

The power-to-weight ratio given in the showroom screen is the standard weight of the car divided by the true, broken-in power of the car. The Supra RZ prize car (remember, prize cars come already broken-in), at 326hp, gives a value of... 4.631. The Lancer EvoVI GSR prize car, at 312hp, gives a value of... 4.358 (be aware that just dividing 1360kg by 312hp gives 4.359 - the power figure displayed is rounded up, so it's likely that the EvoVI's true power is 312.1hp)


As it is, GT3's "Power-to-weight ratio" is incorrect, as that implies an amount of power per unit weight, the higher the better. PWR is measured in horsepower per tonne (or hp per ton, for Imperial types, or PS per tonne for metric types). GT3 uses "Weight-to-power ratio" - an amount of weight per unit power, the lower the better (measured in kg per hp).

 

[phattboy]

haha... I love how when we don't understand something, we call for Famine. Where would we be without his scientist ass?

Well stated Eagle!!!

I think we should start a thread called an "Interview with Famine" Then he wouldn't have to roam all around the forum looking for the last voice he heard calling him with a question. He could just pop in to his interview room, rip off a few answers to the folks and be on his merry way. Anyone wanting to know anything about the game would then only have to search three things... Der Alta's compendium, the prize car/car list stuff on this site and "Interview with Famine". If you couldn't find it there, you wouldn't need to know

Thanks for all you do man!!! We are all better because of your effort!!

[/being nice mode]

phattboy

 

[Smallhorses]

Thanks for clearing that up Famine.
So it seems comparing power to weight figures in the game is a good way of figuring out how hard the race is going to be. (provided the cars you're competing against are in the respective dealers) Even if their calculations are backwards!

Another question then, (and apologies if this question appears elsewhere, but it now seems relevant here) at what point is a car deemed "Broken in"?

At what point does it become "past it"? i.e. even with an oil change the HP never returns to maximum as the car has too many miles on.

e.g. I have a Mini Cooper on my 2nd memory card (100% complete with some miles on at least 1 of every car in the game) which has over 1100 miles on it.
When it was new it had a max HP of 179 (the highest you can get the Mini up to)
Now, even with brand new oil it only gets back to 174HP.

 

[truenodrifter]

yeah depending on what lancer you buy you could get it in your garage with 306 or so horsepower without even touching any oil change. famine i fear your knowledge.... lol

 

[Famine]

Another question then, (and apologies if this question appears elsewhere, but it now seems relevant here) at what point is a car deemed "Broken in"?

At what point does it become "past it"? i.e. even with an oil change the HP never returns to maximum as the car has too many miles on.

There's a thread from "BadBatsuMaru" in this forum called "Everything You Ever Wanted to Know About hp, Break-In and Oil Changes". That's the definitive guide to this kind of question.

And cheers guys

 

[Eagle]

If we were actually clever and kind, we'd have a "Famine" button at the top of the forums beside search in his profile, which would be a link to a search setup to find all posts made since he last logged on with the word 'Famine' in them, to help him find where his help has been called for.

 

[ExBrock]

Famine the All Knowing saves the day once again.
My text color is still better though.

 

[Tedehur]

If we were actually clever and kind, we'd have a "Famine" button at the top of the forums beside search in his profile, which would be a link to a search setup to find all posts made since he last logged on with the word 'Famine' in them, to help him find where his help has been called for.

You mean, something like the Bat-signal that would pop up on his screen when help is required !

 

[Smallhorses]

You mean, something like the Bat-signal that would pop up on his screen when help is required !

Ner Ner, Ner Ner, Ner Ner, Ner Ner.
Ner Ner, Ner Ner, Ner Ner, Ner Ner. FAMINE!

Holy Limited-Slip Differentials Robin!

 

[Smallhorses]

Alright. Now I'm thoroughly and utterly confused.

According to the BadBatSuMaru thread the Famine lead me on to, there is a
-5% penalty for dirty oil (from dealer, and then every 189 miles)
-3% penalty for not broken in and (broken in is considered after 189 miles)
-2% penalty for old engine. (at 378 miles for a prize car, or 567 miles for a purchased car)

So, I'll refer back to the 300ZX Twinturbo 2by2 I've been using in PD Cup. (write up to follow in a separate forum )

According to the figures above, as a purchased car, it shows in the dealer with 276HP, but should be penalised -8% when bought for having dirty oil and not being broken in. this would give a total of 254.334HP in garage. Not so. 276HP is what it shows in garage too. Now then, changing oil should give back 5%, right?
In this case 5% of 276HP should give total of 289.8HP. Also not true, changing oil on this car from brand new gives 281HP. This corresponds to the value you get if the car is not broken in (276 * 0.97 = 267.72HP) with the oil changed (267.72 * 1.05 = 281.106HP) even though the car immediately shows 276HP in the garage brand new.
Hmmmm

After 189 miles (about 4 races in PD cup) the HP had dropped back to 276HP.
According to figures above, 281.106 * 1.03 * 0.95 = 275.06HP

The HP remains at 276HP for the remainder of the races, until after completing all 10, and clocking 522 miles, the HP displayed in the garage is now 274HP.

So then, after giving this poor beat-up car a bath and a drink of fresh oil it should have how many horses under the bonnet? (or hood if you prefer?) 274 * 1.05 = 287.8HP

Which it did. (D'oh, guess I've now answered my own question haven't I? !!!)

Now then, if I'm to drive this car another 45 miles, are you telling me that with fresh oil it'll still suddenly drop 6 or so HP to 282, and never be recoverable?

I suppose I should have studied harder at Maths instead of becoming a Chemist!

Bollocks to it, it was still a very fun car to race!

 

[Smallhorses]

Another thought... What are these cowboy car dealer doing selling cars with Zero mileage and dirty oil anyway?!!!! They need a damned good kickin' for that sort of behavior!

 

[DRIFT4EVA]

Ner Ner, Ner Ner, Ner Ner, Ner Ner.
Ner Ner, Ner Ner, Ner Ner, Ner Ner. FAMINE!

Holy Limited-Slip Differentials Robin!

Good one

 

[Famine]

So, I'll refer back to the 300ZX Twinturbo 2by2 I've been using in PD Cup. (write up to follow in a separate forum )

According to the figures above, as a purchased car, it shows in the dealer with 276HP, but should be penalised -8% when bought for having dirty oil and not being broken in.

Nup. The figure in the dealership is an advertised figure which has no bearing on actual power figures (well - they're close). You can only work off your garage power. All dealer cars come with not-dirty oil too (see the next bit), so the garage power should only be 3% lower than the peak, due to the not broken-in engine.

276HP is what it shows in garage too. Now then, changing oil should give back 5%, right?

It should have only a small effect, if any. The oil in the car is unused - but the coding in mk's programme indicates that it's not necessarily the same as fresh oil from the oil change.

Now then, if I'm to drive this car another 45 miles, are you telling me that with fresh oil it'll still suddenly drop 6 or so HP to 282, and never be recoverable?

Yep. 3% up on the new, dealer car with a worn-out engine and fresh oil.

Also remember that the power ratings given are correct to three significant figures and no decimal places. 276hp could be 275.500 to 276.499 really.

 

[Eagle]

Are they handled as integers or floating points? I'm just thinking truncation errors is all.

 

[Famine]

Pass. BadBatsuMaru or flat-out would be best positioned to answer this.

 

[Tedehur]

Pass. BadBatsuMaru or flat-out would be best positioned to answer this.

I'll try a guess, though I'm not certain I'm best positioned for that.
No power value is stored in the gamesave, it seems to be simply calculated from other values like oil dirtyness, extra parts, etc. It is then hard to guess whether they are integers or not.
Anyway, it seems to me (just a feeling, no clue about it yet, just easy calculations) that the rounding is done in the most stupid way : by simply removing all decimals. So that 276hp would be in fact between 276.00 and 276.99.

One last thing : on a mathematical point of view I don't quite agree with the way Smallhorses did the calculations.
If removing 3% is done by multiplying by 0.97 (which makes sense), then adding back the 3% shouldn't be done by multiplying by 1.03 but dividing by 0.97.
A simple example to explain why :
You start with 276hp, remove 3% (*0.97) and add 5% (*1.05) to get 281hp.
Then you do the opposite operations add 3% (*1.03) and remove 5% (*0.95) and come to 275 instead of 276.
If you had done *0.97 then /0.95 you would have had 281hp, but the opposite operations /0.97 and *0.95 would have given exactly 276hp.
(Same if you had chosen to always use 1.03 and 1.05, the error is due to mixing 1.0x and 0.9x).
Sorry for this, it's far from being interesting, I must acknowledge. And before somebody asks, I'm no mathematician, I'm a chemist too.

 

[Famine]

Sorry for this, it's far from being interesting, I must acknowledge. And before somebody asks, I'm no mathematician, I'm a chemist too.

You're right. I had the same problem the other day when trying to remove VAT (Value Added Tax - 17.5%) from a product's listed price. Quick forehead slap when I realised the error there..

 

[Tedehur]

You're right. I had the same problem the other day when trying to remove VAT (Value Added Tax - 17.5%) from a product's listed price. Quick forehead slap when I realised the error there..

Very common mistake indeed. My job is to train people on a shop management software, so adding or removing VAT is a daily calculation.
BTW, I would have written realized instead of realised. Would it then be the US form ?

 

[Famine]

Yep - most English words end -ise where US English words end -ize.

I had to check your location then. If you're actually French, you SO embarrass half of the English kids I encounter at other forums. Their written (or typed) English skills are laughable - and it's their own language!

 

[Eagle]

You mean, something like the Bat-signal that would pop up on his screen when help is required !

Starvin Marvin would be more appropriate for 'Famine'.

 

[Tedehur]

Yep - most English words end -ise where US English words end -ize.
I had to check your location then. If you're actually French, you SO embarrass half of the English kids I encounter at other forums. Their written (or typed) English skills are laughable - and it's their own language!

I am French indeed, but when I do something I like to do it properly. Speaking/writing english included. (I still have a copy of the Oxford Dictionary next to my bed, just to browse from time to time).