Modern Vespa

In the UK, most figures for cars are given at the crank. A 700hp Lamborghini has an engine that produces 700hp and we ignore that different transmissions have different losses.

My Vespa is quoted by Piaggio as having 11hp / 8kw.

Is this figure at the crank or at the wheel?

I also see that in the UK when we tune bikes / cars, the dyno will calculate the true hp at the wheel(s), but then the operator lets go of the throttle and as the dyno naturally slows down, it approximates the drivetrain losses and gives a slightly less accurate "hp at the crank" figure. We will then always tend to refer to that slightly less accurate "at the crank figure", but I think stateside, you tend to prefer figures at the wheel(s)?

Are your vehicles then advertised with wheel hp or crank hp when new?

See "Engine power test standards": https://en.wikipedia.org/wiki/Horsepower

My BV 300 has 16,3kW as max power.
That is what is in the users manual, but it is not specified how it has been measured.
Normally, and at least in Europe, the measurement is according to the DIN standard. DIN stands for Deutsche Industrie Norm.

It is the max power at the crankshaft with all auxilieries active on the engine as how it is in the vehicle. So with alternator, with water pump aso.
But before the transmission.

Crank

My US GTS300 HPE is rated by Piaggio at 23.8 hp, and I assume that's read off the crank, and not actual rwhp.

If I'm wrong, someone can correct me.

Robot struck the HPE on a dyno. Iirc it was 19.5. so Piaggio specifies crank.

In some cases, the HP rating is theory, not actual.

Give me an example!

Every American muscle car engine ever built. All HP reports built on theory, but it helped sell magazines.

Okay, so I see you don't have an example.

I would not try to prove a theory is true. I almost always refuse to attempt to teach those that will not hear. this is my opinion, would any smart person attempt to prove it not so?

Theoretical, crank, etc:

If i remember in the next day or so I'll post an interesting graph about this and the ECU in the HPE ... (I think I'm riding all day tomorrow so won't get a chance).

^^ very relevant

You are correct. There is a saying "horsepower sells cars, but torque wins races". There is no true measurement for HP, its a theoretical number based on torque.

To increase HP, you have to also increase TQ. A car with 300 TQ and 150 HP will accelerate much faster than a car with 300 HP and 150 TQ. Example Honda S2000 240 HP and 153 TQ. It was a fun car to drive as long as you keep the RPMs above 7000 because such low TQ and peak TQ was at 7500 RPMs.

I know there have been examples of people reporting lower figures.

In Japan, they are wary of producing mega high hp vehicles, and the Nissan GTR R35 was quoted by Nissan as having a lower figure than it actually had.

The stock McLaren 720s also would run on the dyno at a higher hp figure than quoted, this was assumed to be because it was stepping into the territory of their much more expensive cars and so they wanted to market it as a cheaper lower powered car.

If it was the other way round, and a manufacturer was quoting a higher hp number, I assume they could then be sued for false advertising.

When it comes to hp numbers for the GTS300's, the old saying 'Ignorance is bliss' kind of applies.

It's published hp rating is one thing, and not particularly impressive, but 'it's seat of the pants' performance rating is excellent.

Ok here we go ...

GTS 300 HPE

In the ECU there is a map that is apparently the Torque. Here is the 3D graph of it (Throttle in degrees vs RPM).

I've also run the Throttle wide open part through a Torque to HP calculation and graphed it in Excel.

Obvious comment: the peak Torque is less than quoted but peaks at the right RPM and when converted to HP we get the almost the quoted peak HP at the right RPM ...

To continue the above comment and the whole point of relevance of theoretical vs measured:

How did Piaggio come up with the torque number in that map? did they connect the crank to a meter and record it at a range of throttle v rpm? And how did they come up with the slightly higher number in the manual? One of these two has to be theoretical else why would piaggio be disagreeing with themselves?

^^^^Exactly this. Hp is easy enough to figure out mathematical. But the hp figure is not a big selling point when it comes to Vespas. On some motorcycles, sure, that might entice a potential buyer, But on a Vespa it is as JB mentioned - the seat of the pants performance is what counts.

Have you seen the torque figure from the Vespa Elettrica? It apparently has 200nm / 147.5ft lbs... in reality, I'd enter quick hills at 28mph / 45km/h and would gradually under full throttle drop down to 16mph / 25km/h by the top.

In England we'd say "it couldn't pull the skin off a rice pudding" - so no idea how they came up with that torque figure either!

iirc the figures for ev bikes are typically the max that can be held for short times due to the battery heating up rapidly when at full throttle. So maybe their 200 is correct but not for long. (Not even discussing the traction control sorta thing and speed limit etc)

Edit:
here's a line from a review of the BMW CE04 "electric motor, which is rated for 20 horsepower as nominal output, but can jump to over twice that - 42 horsepower - for short bursts"