Are you often confused when conversations come up about motorcycle horsepower? Or when you hear someone say, “Yeah, it’s fast! It’s got 160 brake horsepower!” Or you might hear a rider make this comment, “It’s got 140 horsepower on the back wheel!” And as odd as it seems, “brake” horsepower has nothing to do with braking!
Here’s the scoop on motorcycle horsepower basics.
Often those speaking the mighty “HP” talk, HP being the abbreviation for horsepower are not often clear themselves. Is it the engine measurement? Or the actual output to the wheel? Good questions considering how the gearbox, final drive and all those assisting parts in your motorcycle cause loss of “horsepower” through the process. The actual motorcycle horsepower delivered to the driving wheel is less in measure than the raw output of the engine and so forth.
Horsepower was invented and discovered by James Watt, the same person whose been immortalized by the definition of Watt as a unit of power, i.e.. the light bulb. The Scottish engineer created this metric measure originally aiming to prove and substantiate the power of the steam engine he invented.
The Various Measurements of Horsepower (HP)
bhp: Brake horsepower, net, bottom line crankshaft horsepower -the power delivered directly to and measured at the engine’s crankshaft, it's minus (net) frictional losses in the transmission — gears, bearings, oil drag, wind, and so forth.
ehp or thp: Effective horsepower is the power converted to useful work. In the case of a motorcycle, it’s the power that’s been turned into forward motion on a chassis dynamo-meter. In its cleanest form, it’s also called “True HP” – wheel power.
nhp: nominal horsepower from the size of the engine and the piston speed and is only accurate at a pressure of 7 psi.
ihp: Indicated horsepower or gross horsepower (academic capability of the engine) minus frictional losses within the engine (bearings drag, rod and crankshaft windage losses, oil film drag, etc.
SAE: an American standard rating measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices.
As motorcycle riders, we are most interested in the first two points mentioned above: bhp and ehp “effective horsepower” in simple terms specified as wheel horsepower.
In order to measure motorcycle horsepower, you need to hook your motorcycle engine up to a dynamo-meter that places a load on the engine and measures the amount of power that the engine can produce against the load. A service easily found at the track or at dealerships.
In addition, just so you know thp is generally about 10-20% lower than the engine’s power “bhp” ratings because of the loss experienced through the drive train, and especially the tires.
Horsepower (and apparently, lots of it) is one of the status things associated with motorcycle performance and ‘cool factor’. The theory is, the more you’ve got, the better rider you’re supposed to be. It’s a total myth! Many riders have way too much hp- far more than their skills ability. There are many motorcycle riders and competitors with an average (sport bike) of 100 thp who’ll be able to lap a 140thp rider most easily. It’s really all about the weight to power ratio and more about torque actually. It’s very exciting to own a lightweight motorcycle packed with a lot of hp’s. But it’s another thing to have the skills and ability to use it. In fact, it can be rather dangerous if your skills are not up to the “horses” HP, so to speak!
So now you know the facts and won’t feel left out of the loop when amidst one of the most common discussions of motorcycles and horsepower.
More Dense Motorcycle Horsepower Stuff
Bhp defined: Horsepower is a measure of work (energy) done over time and yes it was calculated using the work of a horse.
1hp/one horsepower is 33,000 lb.-ft/minute.
Motorcycle Horsepower Calculated
Use this popular analogy… if you lifted 33,000 pounds, one foot over a period of one minute, you would be working at the rate of one horsepower—and have spent one horsepower-minute of energy.
1 (mechanical) horsepower unit is equal to 746 watts
So if you took this 1-horsepower horse and put it on a treadmill, it could run a generator producing a continuous 746 watts.
One mechanical horsepower equals 745.699 watts or .746 kW (kilowatts) of electrical horsepower–and if you really want to talk HP you could refer to the 0.0268 horsepower light bulb in your lamp as opposed to the using the mundane 20-watt measurement.
Frequently we’ll hear riders talk about how much horsepower their motorcycle makes. These claims are sometimes unbelievable. We’ll also hear some riders state that they prefer more torque over horsepower. Harley-Davidson performance means different things to different riders. To some, it’s just about getting a little extra power and better sound from their Harley. Others want to produce 100HP or more.
Most Harley riders will feel the greatest benefits with torque gains in the low to mid rpm range. When you talk about Harley-Davidson performance, do you mean torque, horsepower or both?
• Torque is pulling power. It’s this power that gets you moving and pushes you back in the saddle.
• Horsepower is the higher-end spinning power that keeps you moving and generates top-end speed.
For most Harley-Davidson riders, it makes little sense to try to increase engine performance in the 4,000 to 6,000 rpm range, when most of your riding occurs between 2,000 to 4,000 rpm, especially when doing may negatively affect your torque output.
You can get good low to mid-range performance out of your Harley-Davidson engine without a ton of modifications. If you’re looking for better performance, the first question you need to ask is; “Torque or Horsepower?”
Here are some numbers that your stock Harley are putting up…
Harley-Davidson Twin Cam (1450cc / 88” 45 degree single plug v-twin with F.I.) – 62hp & 77 ft lbs of torque
Harley-Davidson Twin Cam (1584cc / 96” 45 degree single plug v-twin with F.I.) – 66hp & 82 ft lbs of torque
Harley-Davidson Twin Cam (1688cc / 103” 45 degree single plug v-twin with F.I.) – 83hp & 95 ft lbs of torque
Harley-Davidson Twin Cam (1800cc / 110” 45 degree single plug v-twin with F.I.) – 95hp & 110 ft lbs of torque
103 and 110″ Twin-Cooled bikes Touring 103″ 76.40HP 90.20TQ 110″ 84.80HP 98.94TQ