93.2 BHP measured at the crank or at the wheel?

[dogwafter]

Okay so riders who have passed the new A2 can restrict a bike down to 46.6 BHP as long as the bike originally didn't make more than 93.2 BHP. Naturally us young riders want bikes that are bang on 93.2 BHP or damn close. There are a few bikes out there that will hit 93 BHP on the dot or are a bugs dick away. But when you read the specs you find they put out 100+ at the crank.

So my question is, is the 93.2 BHP figure measured at the crank or at the back wheel?

[J.M.]

Go by the specs.

If you end up in court for riding a bike with more bhp than your licence allows, what is the court going to believe? Big company stating the bhp of the vehicle or you saying "but it's 93bhp really!"?
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2004 R1 & 2018 XSR900

[DrDonnyBrago]

You may as well get something only putting out the max allowable power and let it rev clean, it'll run nicer than a restricted bike.

However, I think both are at the crank.

[N cee thirty]

it's a laughable law to say the EU member states can choose how they implement them.

Very lazy on the DSA's part.
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'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[Rogerborg]

[Quoting myself from posts passim]

See:

The Motor Vehicles (Driving Licences) Regulations 1999 S3 Interpretation

and

The Motor Vehicles (Driving Licences) (Amendment) Regulations 2012

The wording is "maximum net power output of the engine" which is open to debate. Does "engine" include gearbox, i.e. is it at the crank or output shaft? Dunno, ask The Man.

You could file it as a Freedom of Information request. I'd suggest DSA, DVLA, DfT, VOSA and the CPS for starters, although I expect you'll get the same answer from all of them: "We do not hold that information, and nothing in the Freedom of Information act requires us to create it."

Go for it though, it's a laugh.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[RhynoCZ]

The manufacturers mostly measure the power output at the crank with no gearbox, external coolant and oil pump and the engine does not have to charge the battery. So in the end the bike has, naturally, less power on its rear wheel.

I do not know if the UK law system allows you to use a expert evidence at court. If so, you might would have won, but I wouldn't do that. As stated, the specs are what the administrative Offices want to see.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Rogerborg]

I wonder if any manufacturers are going to suddenly "discover" that their 600s "really" make bang on the 70kW "net power output" limit.

Probably not, biking does seem to be one of the last refuges of silly Top Trumps numbers.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Teflon-Mike]

Power is not something you can measure. Its a rate. It's a derivative not an real 'thing'.
It has to be calculated, after measuring real actual physical commodities that are related to it.

Power = Rate of Change of Energy

So the real things you need to measure is energy... which itself is a bit tricky to measure directly, and time.

Muck about with a bit of maths though and you get a more useful equation;

Power = (Force x Distance) / time

Do a bot more maths on that to apply it to rotary motion and you get

Power = Torque x Revs

You can measure the Torque delivered by a shaft by reacting it with a brake... much like a wheel-brake, a disc or drum gripping the shaft with friction, and you can a torque to that brake with a long lever and some weights, like torque reaction bracket on a rear wheel brake.

Count the 1Kg weights you hang on the beam, and times by 9.81, you get Newtons force, times by the length of the beam, you get Nm of torque.... then all you have to do is count how many times the shaft goes round in a minute and you have the revs, AND you can CALCULATE the power.

Specifically Shaft Brake Force POWER, or Brake Horse Power.

It is CALCULATED not measured.

OK... that's the BRAKE power

Now, you can attach your "Brake" or more correctly "Brake-Force-Dynometer" via a flex link direct to the end of the engine's crank-shaft.

If you are an engine maker, this is pretty reasonable; your customers want to know the power they should get, and that's where they get it, and the engine probably comes with some sort of flange on the end of the crank, to take its power to whatever its going to drive.

And in the Development lab, tuning the engine, finding the optimum cam-shaft profile, the best inlet manifold arrangement etc etc etc, you'll be running your test engines on a test-bed against a B-F-D to measure improvements and efficiencies anyway.

OK... engine ow goes into a vehicle..... for the sake of a car, and specifically an American Muscle Car, lets say a General Motor's 1967 Camaro Z28.

This is a car that sells on power; so GM want as impressive a power figure to put in the brochure as possible..... Unfortunately the 350 cubic inch V8 that chucked out about 200bhp on the test bed... only manages to put about 160bhp of that out at the wheels, if tested on a Rolling Road Dynometer....

A lot of the power is 'lost' churning transmission fluid in the heavy automatic transmission; driving the power steering pump, the air-conditioning pump, the big alternator to supply the electrics and work the power windows and roof, etc etc etc.

This figure doesn't look anywhere near so impressive.

So they go back to the Engine room, and ask.... "Was the Alternator fitted when the engine was tested? What about the water-Pump" Discover that yes they were.... and so tell the lab-rats to take them off the engine, cool the thing with water from a hose on the tap, and to power the ignition from a battery and battery charger not an alternator, and to take any other unnessential 'Ancilliaries' off the engine.......

And they get a crank-shaft 'Brake' power figure of maybe 215bhp... which looks even better in the brochure.

Now Ford, are vexed because thier 302Cubic inch V8 is at a dissadvantage to the GM 350, to begin with, and they thought that they were doing pretty good to get 200bhp from it... but they had already used up all those tricks cooling from the tapo and igniting via lab-supply etc to get it...... So the lab rats scratch thier heads, and remember that when they were looking at combustion efficiency tests, they wanted to measure the effective force at the piston tops.... so they measured power at the crank, then after doing a Dyno Run, turned the ignition off, opened the throttle fully, then used an electric motor to drive the engine to the same speed; measured the power needed to drive the engine..... make the crank move, pushrods go up and down, valves open and stuff... then took that off the power they got, to find out the 'Piston-Power' for different combustion chamber profiles.... BUT thinking a little, those are 'efficiency losses' so if they added that power to the crank power..... they could get an even BIGGER number, maybe 225bhp, that would ace GM's....

Now... apply that same principle to measurements taken on a rolling road, its called 'Back-Motoring' and you can pretty much fudge the numbers to get an engine to apparently deliver as much or as little power as you like!

And you have even MORE scope to fudge the numbers if you start messing with the semi-variables of things like atmospheric pressure, air quality, humidity and the like.....

And you get some VERY powerful maths, in which the overall limits of accuracy, compounded from experimental measurement tolerences, then each stage of derived calculation and correction, give HUGE margins either side of any CALCULATED number, that may or may not be very close to the actual power the engine can supply....

THEN for a 'production' engine..... you have to allow the variability of manufacturing tolerences, to account for the likely difference between power numbers obtained from actual test engines, and averaged between them, to what any untested engine off the line might actually make.

Which is WHY we have things called 'Standards' and we have standardised test procedures.

SAE, Society of American Engineers... acronym you are probably more familiar with in associuation to grades of engine oil, to answer the debate between the car makers in the 1960's, playing the Brake-Game to get more impressive BHP figures for muscle cars, wrote standardised BHP test procedures for them, so that thier 'quoted' power numbers were more comprable.

The DIN standards agency in Germany did a similar set of standards for Euro Makers; BSI in the UK yet another. And there are many many more.

In Recent years, however, the drive of European Legislation, to bring down enngine emmissions, has seen MOST quote thier power figures on the Standardised Test Procedures in EEC Legislation for Motor-Vehicle Construction & Use regulations.....

SO... you can measure the power of almost ANY motorbike, pretty much anywhere you like really....

You can measure it at the back wheel on an Inertial Rolling Road Dynometer, or you can hoik the engine out the frame and measure it off the gear-box sprocket on a test bed brake, or you could make up a coupling to replace the primary drive pinion and take your power to a brake straight off the end of the crank.

You can play the Brake-Force Fudge game to your hearts content; taking the thing to the top of a mountain to get 'thin' rarified air, or to the bottom of a sub-sea-level lake to get denser air; you can add or remove as much 'parasitic load' as you like, employ as much back-motoring compensation as is possible, and then play around with the numbers within the tolerences of experimental and calculation error, to your hearts content.

BOTTOM LINE

Law will ask to 'what' recognised standard the engine was tested... and they take one with legal standing to be 'most' representative.

Ie one referenced by law.... which is in the C&U regs, and the one that the manufacturers use to get thier 'Quoted' power figures.

Use anything else..... get anything else.... and it makes no odds.

BIKE makes whatever power the manufacturer CLAIMS in the brochure specification, when sold as new and complient TO that specification.

NO-ONE will be interested in your argument that you bought a Honda Hornet that the brochure says makes 101BHP, but that the actual one you bought, on a rolling road only delivered 92bhp, ther-fore YOU think you ought to be able to restrict it.... court would tell you that your Dyno or calculations must be wrong, or that you are merely unlucky getting a bottom limit example from the factory....

What counts is the MANUFACTURERS DECLARED SPECIFICATION

If that is over the limit; TOUGH you cant restrict it.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[RhynoCZ]

And Mike strikes again
____________________
'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Sload]

[Rogerborg]

tl;dr version - you have to use the manufacturer's bullshit number rather than a dyno shop's bullshit number.

Otherwise you could take a ZX-14R, bung a throttle stop on it, dynomaths it at 70kW, then fiddle with the stop, dynomaths it at 35kW and ride on an A2, innit.
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Copycat73]

[dogwafter]

Cheers guys

Does anyone know the manufacturer stated power output of a gixxer 600 SRAD 96-00 ?

I cannot find it anywhere on google, visordown says 92 but I just want to be sure...

[Sload]

[Rogerborg]