HP Sauce??

[Marknz]

Okay, this is a real clown question to be asking in this environment but someone else will be wanting to know the answer and is too scared to ask. Me, I can take the piss out of myself any time I like.

So HP. It's so & so measured at the rear wheel and so and so at the crank.... what's the bloody difference?

If anyone can come up with a clear Joey Bloggs answer for me I'll consider sending them a beer voucher for their next pint.

[Two Smoker]

Okay, this is a real clown question to be asking in this environment but someone else will be wanting to know the answer and is too scared to ask. Me, I can take the piss out of myself any time I like.

So HP. It's so & so measured at the rear wheel and so and so at the crank.... what's the bloody difference?

If anyone can come up with a clear Joey Bloggs answer for me I'll consider sending them a beer voucher for their next pint.

Some of the HP is lost through the transmission of power going through the clutch, gearbox, chain etc, therefore the HP at the rear wheel will be less than that at the crank....

[merv]

Typical loss would be something like 5 - 10% between crank and rear wheel. So your VTR is probably about 110 at the crank, 100 at the rear wheel if still stock.

[Zed]

Okay, this is a real clown question to be asking in this environment but someone else will be wanting to know the answer and is too scared to ask. Me, I can take the piss out of myself any time I like.

So HP. It's so & so measured at the rear wheel and so and so at the crank.... what's the bloody difference?

If anyone can come up with a clear Joey Bloggs answer for me I'll consider sending them a beer voucher for their next pint.

Horsepower is related to torque, and torque is turning force. Place a lever on the engine's crankshaft and measure the twisting force produced, and you have torque. Note that time is not a factor - torque can be constant over time. Horsepower, on the other hand, is the rate at which the torque is produced.

Horsepower is a measurement of the engine's ability to do work. One horsepower can lift 33,000 pounds up one foot in one minute. Horsepower is measured over time. The more horsepower a vehicle has, the more mass it can move in the same amount of time, or it can move a fairly constant mass (the weight of the car) in less time. In simple terms, to get a vehicle accelerating quicker, we need to produce torque faster.

There are many different ways of measuring the power of an engine. Brake horsepower is a common term and refers to the power measured at the crankshaft using a "prony" brake. A prony brake was a simple lever that was connected to the crankshaft with a brake. As the brake was applied, the lever would deflect and power was indicated. Nowadays, computers and strain gauges are used to measure the power.

Rear wheel horsepower is just what it implies - horsepower applied by the rear wheels. A chassis dynamometer is used to measure the power transferred by the drive wheels onto the dynamometer's rollers. Brake horsepower is much lower than the horsepower specs provided by the manufacturers, because of all the power used by the transmission, final drive, and accessories.

Gross horsepower is the power measured at the crankshaft without any engine accessories. This includes removing the air cleaner and ductwork, exhaust system, water pump drive, and any other devices driven by the engine. Prior to 1973, horsepower specifications were listed by the manufacturers as gross horsepower. After 1972, manufacturers provided net horsepower specifications.

Net horsepower is also measured at the crankshaft before it goes into the transmission, but this time the engine is operated as it is installed in the vehicle, complete with accessories and ductwork.

Excerpt from Horsepower and Torque Explained
by Jim Kerr

[Yamahamaman]

You can buy it at you local Supermarket. Comes in a square bottle and it is an import from Brittain.

[pete376403]

While at the supermarket getting your HP, don't forget to stop by the stationery (pens and paper) dept and pick up some power bands. They come in various sizes, wide and narrow, and from small to large. Most common materials are rubber and elastic.

[tlronny]

Typical loss would be something like 5 - 10% between crank and rear wheel. So your VTR is probably about 110 at the crank, 100 at the rear wheel if still stock.

The later VTR's are'nt as grunty so its more like 95 hp really

[Lou Girardin]

Very good Zed, except brake horse power can be gross or net, it's usually measured with the SAE system. Very few modern engine makers quote gross horspower now, they're too worried about litigation as Mazda found out when they had to buy back thousands of MX5's and RX8's in the US.
Lou

[curious george]

OI! Zed cheated! He should not get the beer voucher! Jim Kerr should!

[James Deuce]

Just as a point of interest, there are 3 measurements of power you are likely to come across: HP - used in the UK and the US, kW used by Japan and most metric systems, and ps (pferdenstarken) which is German for "horsepower".

Units of Power:

kW x 1.360 = PS
kW x 1.341 = HP

PS x 0.7355 = kW
PS x .9863 = HP

While I'm on a roll and my brain is still functioning here's torque units you'll see quoted and conversions:

Units of Torque:

N-m x 0.1020 = kg-m
N-m x 0.7376 = ft-lb
N-m x 8.851 = in-lb

Zed, great explanation. Thanks for posting that.

Jim2

[White trash]

Heres my interpretation of torque.

Triumph Rocket III. 2300cc in line tripple. As much torque as almost any TWO other bikes. over 140ft/lb or 200nm @ 2500rpm. 90% of this torque is availabe at just 1800rpm.

It will pul 1.2g of acceleration TWO up. A modern sportsbike can physically only pull around 1g any time!

It is speed restricted to 160mph! And Wellington Motorcycles have a demo coming in June/July! Give me the keys!

Price? A mere $31000 which makes a V-Rod (my other favourite cruiser) look very silly.

[speedpro]

It always makes me laugh when I see huge torque figures quoted at low rpm, typically for something like a Hardly Driveable. As mentioned power is basically torque multiplied by rpm. Because these quoted vehicles typically have low rpm limits they are therefore restricted to low power,even though they have high torque. It doesn't matter how much torque the engine makes, what matters is how much torque is available at the rear wheel. If your HD torque monster makes say 100ft/lb (or the metric equivalent) at 1500rpm and your jap scooter makes 50ft/lb at 4500rpm, then the Jap scooter makes more power and will accelerate faster if both bikes are both doing the revs as noted at the same speed. This is because the rear wheels will be doing the same speed give or take a bit and therefore we will have to consider gear reductions and therefore the torque multiplication. If the wheels were doing 500rpm (keeping it simple) the HD would have a gear reduction of 3:1 and the Jap scooter would have a gear reduction of 9:1. Torque multiplication in this simplified case would result in available rear wheel torque of 300ft/lb for the HD and 450ft/lb for the Jap scooter. Remember both wheels are doing the same speed so as power equals torque multiplied by rpm the Jap scooter makes more power at the point where it matters. Either way you look at it, torque or horsepower, the Jap scooter in this example will toast the "torque monster" in a roll-on competition, even though it makes only half the torque. :confused2

[White trash]

Point taken. But, the Rocket III also makes 140hp.

A V-Rod makes 115hp and my wifes boarder shut his R6 down at 240kph because he couldnt get passed the V-rod on Sunday.

In testing, the big Triumphs have wasted every bike tested against to 60mph.
GSX-R1000 makes more power and is almost half the weight. Still gets nailed.

Hmmmmm, seems the theoretical explanation and practical tests don't match.

Any theories why?

[speedpro]

ZX6R versus HD "late model lump" would suggest theory is sound.

Doesn't an R6 make about 100+hp? That would sort of make it even with the V-rod depending on gears and who's thrashing harder.

As for the big Triumph and the GSXR I have a similar issue with CB125Ts versus my RG/MB100 bucket. Mine weighs less and makes more power but I don't have a hope in hell of beating a well ridden 125T to the first corner at Mt Wgtn. Huge wheelies in amongst the pack can ruin your afternoon. It's all about getting it to the ground in that case and keeping the front wheel in front.

[merv]

V-rods are the first Harleys to do around 9,000rpm in stock trim so they can rev relatively speaking. However they are still a long bike and they will have no chance of staying with an R6 in sharp corners when equal HP doesn't matter.