BHP .v. HP

[SpikeOne]

The engineer in me started to think about how these two measures relate to each other, and I came to the conclusion that they don't really, because losses to the back wheel aren't connected to the BHP figure and are more to do with the individual gear train design on the bike.
Looking at manufacturers published figures, I decided that they, mostly, quote BHP because it's a more impressive figure, (and who wouldn't), but am interested in finding out what my own bike does. Where would one start looking? Is there a website anywhere where true horse power figures are recorded?

[R1K SU]

I read somewhere that the loss from engine to back wheel is almost 15 bhp on the 650 burg and similar to other scoots.

[MrGrumpy]

I read somewhere that the loss from engine to back wheel is almost 15 bhp on the 650 burg and similar to other scoots.

See my post on the Scooter-Station Maxi comparison - there are some dyno results which illustrate how much of the claimed power at the crank gets to the wheel. The tests show that the Aprilia manages to lose around 1/3 rd of its power in the transmission, the BMW 24%, TMax probably around 20% and Integra 17%

[anonstarter]

See my post on the Scooter-Station Maxi comparison - there are some dyno results which illustrate how much of the claimed power at the crank gets to the wheel. The tests show that the Aprilia manages to lose around 1/3 rd of its power in the transmission, the BMW 24%, TMax probably around 20% and Integra 17%

QUICKLINK: http://www.maxi-muppets.co.uk/forum/vie ... =5&t=11402

[TmaX9]

There is no such measurement as just HP, except for 'shire' horses.
All measurements of mechanical power units are rationalised into either
BHP (brake), measured raw at the crankshaft - no losses except friction within the engine itself taken into account and the often used figure by manufacturers
IHP (indicated), a theoretical mathematically calculated maximum used by engine designers - probably never achieved outside of high end motor sports like F1.
SHP (shaft) measured at the drive shaft or axle so including basic transmission losses - never seen this one quoted anywhere
EHP (effective) measured typically on a rolling road and therefore all frictional losses and wheel bearings are taken into account - often dismally low compared to BHP especially on FWD and 4WD vehicles.

[Data]

I've dyno'ed several bikes and cars in my time as a tech. The results are often very interesting. It also varies a lot depending on weather, temps and humidity etc. Even using the same dyno you can test a machine in the morning and in the afternoon test the same machine again on the same dyno that hasn't been used since your morning session and you'll get a different reading. Sometimes this can be a big difference too, but usually not unless the temps and humidity etc has changed a lot. Dyno's give a rear wheel reading of hp or ps, and can determine how much torque the engine produces and where it is located in the rev range. It can estimate the actual hp or ps at the cranshaft too. Overall, dynos are quite acurate. My Vstrom 1000cc had a claimied output of 97ps at 7600rpm at the crank. When dyno'ed it measured 99ps at 7550rpm (estimated) on a very carefully setup dyno. The actual rear wheel figure was 92ps at 7550rpm. Pretty good. This was the average of three runs too during which the figures differed little. The PS figure sounds more impressive than HP. My B400 is 33hp but 34ps. Those are at the crank figures. But be careful, there are several different HP measurements to include metric, SAE, and DIN. There are some others too but not used in 'Urop'.

[SpikeOne]

Sorry Tmax9, but that's not true.
There is indeed a unit called "horsepower", (in fact it's really the only unit in this context), as the rate of doing work, and defined as 746W, (although that's very much retrospective, as the horsepower was defined first).

The others are modifers designed to more clearly explain how the unit is applied to the vehicle.
As I understand it, brake horse power is the measurement taken at the crank, and is called such because a brake is placed on the drive in order to measure the power at that stage, horsepower is more generally used to define that that comes out at the road wheel, (I guess this is what you refer to as EHP, which isn't somehting I'd heard before, although I accept that it is correct). The rest are probably only used internally by technically people in the design stages and are irrelevant to the average user.

[gn2]

Horsepower is a meaningless non-standard unit.
It's time we started using the proper unit, watts.
(named after a Scot)

[Earl]

Horsepower is a meaningless non-standard unit.
It's time we started using the proper unit.
(named after a Scot)

How the hell is a 'Hamish' going to tell me the power of my Mana????? PMSFL!

[gn2]

Same way anyone does, he'll just make it up.
As it happens I know that a Mana makes about 76 Hamish Powers.