True Rear Wheel Horsepower

1 Mar 2015 | Author: | Comments Off on True Rear Wheel Horsepower
Bimota SB8R Sport Bike

True Horsepower – Effective HP scale – The I ndustry wide achievable HP standard

Today, about 75% of the entire world’s hp values are a mess of dynojet hp and dynojet dyno clones’ rough approximations of dynojet horsepower. some brake dyno mfgr’s dynojet channel that’s +/- 10% of a dj number. some dynos that out exaggerate the dj numbers and imply that they know what the transmission hp and crank hp is, and even other dynos with the most expensive brochure that read whatever the user wants them to read, True, Real, SF and DJ. or make up your own inflation factor (sigh. )

All because some guy thought that a 1985 over bored 1400cc prerelease version V Max made 145 crank hp according to the marketing dept. and he couldn’t have his new inertia dyno read 90 hp on a stock dealership V-Max. Well, he was correct at 90-95 effective hp, but he made it read 120 to sell more of his dynos. And that’s where the chassis dyno hp mess started. Read more about inflated hp numbers


Corrected True HP is the:

Actual power under Steady State (preferred)

or Sweep with CORRECT inertial mass value at 20 f/ps

delivered to the drive roller of a chassis dyno

to which is ONLY added the dyne coast down parasitics and then

corrected to existing atmospheric test conditions.

Factory Pro has confidentially refused to exaggerate measured and corrected horsepower figures to sell more dynos.

Since Factory Pro hasn’t rescaled horsepower for the last 20 year and our software reads the same files the same from the very first EC997 dyne system.

Some Dynamometer companies add to measured rear wheel power readings a factor that is based on ESTIMATED rear wheel power losses (under what power conditions? 125cc? 1200cc? under coasting conditions? with a 3.00×17 bias ply tire? a 190×17 radial tire?

New heavy radial tire vs. worn old, light, stock bias ply tire? Who knows?)

In short, there is NO meaningful average tire to get a correct rear tire power transmission loss measurement for all bikes – so obviously, unless they actually measure the power lost in the rear tire, under driven load conditions, NO dyno company should BE ADDING incorrect power figures into the measured power. It’s simply wrong.

The fact that they add varying amounts of power to the actual, true amount of power delivered and measured to the surface of the drive roller creates a situation that makes it an onerous task to compare power figures from different brands of dynamometer systems.

On simple inertial dynamometers, some (most, actually, all that I know of in the MC market) companies use an average for the inertial mass value of the engine, transmission, rear wheel, sprocket and chain on every bike – as if a YZ125 has the same rear wheel or internal rotating mass as a 1340cc Harley Davidson. Needless to say, if the software thinks that the YZ125 had a HD rear wheel on it, it would look like the 125 makes more HP at the rear wheel than it does at the crankshaft. It’s simply wrong.

And – that’s why you hear of 125cc Karts that make 43 hp at the rear wheels.

Bimota SB8R Sport Bike

It’s expensive to measure frictional losses in the engine and drivetrain, requiring the dyno to be able to drive the vehicle with engine off. Add the cost of a 50+hp electric motor, controlled power supply, etc. It’s just not likely that $20,000 dyno will be equipped with that equipment.

It is also common for dynamometer companies to add to the power readings by adding transmission and primary gear/chain losses back into the measured power readings. Some companies make a concerted effort try to measure frictional losses and, optionally, add the power to the measured readings. Other companies – some that would surprise you – say that it’s not important and give a blanket, single factor for frictional losses in every engine.

That includes some $25,000-$35,000 dynes.

Some simply say that there is a meaningful average for every motorcycle,(2 stroke, 4 stroke, 1 cylinder/1 transmission, 4 cylinder/1 transmission) and apply it to every bike and that it is not a significant difference.

Blanket estimates of average losses and corrections are, quite simply, incorrect. At the upper levels of the industry, (we are talking about $150,000 – $500,000 AC or DC 4 quadrant dynamometers) it is not tolerated – shouldn’t be – and needn’t be.

There is a dyno company that actually has different versions of software that displays their own identical data files as different amounts of power depending on whether you use the DOS version or the Windows version of their software!!

True Rear Wheel Horsepower ™ is Factory Pro’s standard of measuring the power that is actually delivered to the rear wheel. It is honest, true, fair and duplicable. It is the ONLY standard that can be duplicated by the entire industry – regardless of the dyno manufacturer.

Following is a reference table so that, if you are used to rather inflated HP figures, you can see what your vehicle would generally make on the True HP Scale.

True HP as compared to DJHP

It’s not possible to give an absolute conversion factor, as it appears that dj dynos don’t all read the same (my experience, other’s, too – and Mag Articles and 2002 Roadracing World gsxr1000 and R1 comparison articles), but, you can take True HP from EC997’s and produce an average djhp of of an average dj dyno – empirically derived, over 20 years of comparison of the two hp scales.

Bimota SB8R Sport Bike

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