Why Don't Motorcycles List Horsepower Rating?

[gemeniguy]

From what I've been able to gather from the same question asked on other internet sites, it's not done because it's misleading in representing specific operating conditions. But this doesn't make sense to me because engine displacement is listed and I have to believe that horsepower is generally directly proportional to engine size. In addition, horsepower is specified for cars and trucks. In the case of a truck, you could be driving at top speed unloaded at times and at slow speed with a fully loaded truck at other times. I don't see how from a technical standpoint horsepower ratings are not misleading for trucks (or are they?) and are misleading for motorcycles. Any answer to this?

[72degrees]

So long as figures quoted are measured in the same way at the same place (crank, gearbox output or best of all rear wheel) they aren't misleading. The operating environment in terms of altitude and temperature can make a difference if the differ greatly from the test conditions if that's what you mean. Standardised testing should give reasonable comparisons though.

If you consider a road race 125 cc two stroke single and a 1200 cc four stroke twin cruiser it's pretty obvious that horsepower is not directly proportional to displacement. It may be related, up to a point, for similar engine types.

What matters is real rear wheel dyno results and in that case torque (particularly the curve) is just as interesting as power. The only bike I had that I was certain of the power of was my tuned Gilera Nordwest which I had dyno tested (on a known reliable dyno) at 55 BHP with a nice fat, flat topped torque curve, while I watched.

Perhap motorcycle manufacturers are just more coy than car makers for fear of adverse comparisons?

If looking for a new bike I google for quoted figures, average the results from manufactures specs., if any, reviews and best of all actual dyno tests and take with a large pinch of salt. In particular I'm looking at the rpm that max torque is delivered at not just max power.

[William1]

Simple answer is that to measure output, too many variables. Air density of test day. Tires used, tire pressure. Fuel quality, dyno accuracy, operator skill, smoothing and on and on and on. TYest methods for motorcycles are not SAE certified like they are for trucks and cars.

HP numbers have barely any real world value. To similar machines will have similar power (IE both MX race bikes or both trail plonkers) It is how that power is delivered and the skill of the rider that makes the difference.

A Suzuki DRZ 400E makes 39 Hp. A Suzuki DR650 also makes 39 Hp. Many reasons why. The DRZ is a much more capable off road bike and stinks on the road. The DR is the opposite.

[72degrees]

Horses for courses.

HP has one real world value in the UK, at least for road legal machines. You are restricted to a certain power output machine when learning and a higher output until you have passed a test and had a licence for two years (ignoring direct access for over 21s). After that there is no limit (unlike the 100 'hp' limit in France). I suspect the manufacturers have to certify to an ISO or British Standard that a machine complies (as it leaves the factory) to be "learner legal". They are actually stated in Kilowatts and so any maker that wants to sell such a bike in the UK has to state the horsepower.

Even so, the paltry 33-46 bhp allowed for the two years can be delivered in a different way. A 'full' power-valve 125 two stroke is a very different riding experience to a learner power limited 650.

All the more reason to go 'off road', or off public highway, where all bets are off until subjected to a seat of the pants test

[gemeniguy]

Thanks for the inputs. It looks like lack of SAE certification (for whatever reason) is the underlying reason.

[grayracer513]

Let me say this with all the well deserved cynicism due the subject: all advertised horsepower figures are lies, distortions, or just plain wrong, and yes, even the few that have some basis in fact are nonetheless misleading. As a single example, I offer the 1999 Z28, capable of sub 13 second quarter mile times and 160mph while tipping the scales at over 3700 pounds. All those who seriously believe that car had only 275hp, please raise your hands. I have some things for sale you might like.

And, of course, part of the blame goes to the Feds efforts to make the ratings more accurate. Total failure, naturally, but the real problem is that the gov't prescribed methodologies have been changed more than once to add to the overall confusion.

Horsepower ratings for motorcycles mean very little in terms of how they actually perform, in any event.

[temporarykiwi]

also the type of dyno used makes the figures acheived  variable, a mate of mine who is a respected tuner in nz told me that only a brake dyno will give an true torque figure, inertia dyno's only calculate torque from the hp figures

[ballisticexchris]

Here is an example of a real dyno chart of my 650R.

It's not the only HP but the air/fuel ratio that makes the engine run to optimum performance. Please note the near perfect stoichiometric AF ratio achieved. It took a lot of time on the dyno to get it that good.

 

 

IMO, It's just not worth the trouble on a dirt bike. It's where the power curve is that really counts. If you want max HP you simply uncork the motor, get maximum air flow and jet rich. Of course, then the bike becomes all but unridable on the trail.

[temporarykiwi]

THATS GOT TO BE ONE NICE MTR YOU'VE GOT THERE, WHAT SORT OF MODS YOU RUNNIN?

[highmarker]

width of powerband has always been as important as hp riding offroad

[adam728]

Here is an example of a real dyno chart of my 650R.

It's not the only HP but the air/fuel ratio that makes the engine run to optimum performance. Please note the near perfect stoichiometric AF ratio achieved. It took a lot of time on the dyno to get it that good.

IMO, It's just not worth the trouble on a dirt bike. It's where the power curve is that really counts. If you want max HP you simply uncork the motor, get maximum air flow and jet rich. Of course, then the bike becomes all but unridable on the trail.

Nice dyno run for sure. But I see it running a solid 13:1 A/F, not stoich (for gasoline anyway).

[grayracer513]

13:1 is roughly an ideal AFR for power, but you're right, it's not stoichiometric.

[ballisticexchris]

13:1 is roughly an ideal AFR for power, but you're right, it's not stoichiometric.

 

I said almost perfect. Perfect stoichiometric AFR is 15:1……

[ballisticexchris]

THATS GOT TO BE ONE NICE MTR YOU'VE GOT THERE, WHAT SORT OF MODS YOU RUNNIN?

 

Nothing more than uncorking it, exhaust and Power Commander. I just sold it a few weeks ago. 

[temporarykiwi]

a power commander? on an xr650r?, you saying you got 20hp from jetting and an exhaust?

[ballisticexchris]

a power commander? on an xr650r?, you saying you got 20hp from jetting and an exhaust?

Not 20hp, more like 7hp or so. A bone stock 650R puts out just under 60hp at the rear wheel.

[adam728]

a power commander? on an xr650r?, you saying you got 20hp from jetting and an exhaust?

I'm thinking ninja 650r, not xr. Look at the rpm level it reaches as another clue.

[ballisticexchris]

I'm thinking ninja 650r, not xr. Look at the rpm level it reaches as another clue.

Yep!