Total Motorcycle Community Forums

(I've pulled this across from another thread in the new bikers forum, thought it warranted its own thread!)

jmillheiser wrote:The 125s that Kal and Henriettah have are probably a bit quicker than an EL125 as they are 2 strokes which have power figures more in line with a 4 stroke 250

Thats very interesting to know.
How do you define the BHP of a bike?
In the UK, we are restricted to the BHP we can ride until we pass certain tests. How likely is it you would be caught riding something out of your league - would you have to raise the suspicsions of your local bobby, by ragging a small bike with 'L's around more than it should be capable of?
(I'm presuming a BHP test is not standard with MOT's.)

In other words, what if my 125cc bike has a larger BHP than 14.6? And how would I ever know this..?

Hen.

You wont know the power for sure without putting it on a Dynamometer and that isn't something anyone is likely to carry in their tool kit.

jmillheiser wrote:The 125s that Kal and Henriettah have are probably a bit quicker than an EL125 as they are 2 strokes which have power figures more in line with a 4 stroke 250

Different power characteristics but not the same power. Most 250 twins will be putting out around 30 horsepower be it 2 or 4/stroke. Singles will usually be a bit less.

2/strokes tend to be lighter than 4/strokes and this might give a performance edge in the smaller cc range but 2/strokes tend to use more fuel.

Brake Horsepower and all the other horsepower measurements are going to be fairly similar at the low end of the hp scale. Just different ways of measuring it.

1 horsepower= 550 foot-pounds/second. Your bike should be able to lift 7975lbs one foot in a second. So you know what to tell the cops when they want to check that you aren't breaking the power limit .

Manufacturers will publish horsepower numbers. More than likely, there is some kind of accepted list for different bikes in each model year that are within each category. They probably just use published hp ratings. The authorities might require from manufacturers a specific test procedure (SAE, etc.) as a condition for certification for sale in the country.

I'm sure the MOT doesn't test bikes. If you're caught on the wrong bike, there'll be a penalty.

Far too much info about the many definitions of Horsepower are available at the Wikipedia.

BHP is the horsepower measured at the BREAK (hence the b before HP). Basically, where the crank comes outa the engine to connect to clutch/trans. WHP (be it front or rear, in the case of bikes, rear) is the measured HP that the wheel puts to the ground. The WHP is less then the BHP do to the inefficiancy of the trans/other parts. 2 strokers are deffinatly more powerful than the 4 stroker kin. For example, a 4 stroke Kawa KX250F makes 43 BHP. The Kawa KX250 (2 stroker) makes 56 BHP. That's a 13 BHP increase! And another thing about a 2 stroekr, their power is generally "all there" at a twist of the throttle, where as a 4 stroker needs to actually rev up to make it's power. Now, a 250 road bike isn't going to make 43 BHP, more like the 30ish that was stated, it's just that it's easier to compare this way. It'd be pointless to compare a 2 stroke to a typical road bike sense the 2 stroker is generally in a "race" version of a bike (well, dirt bikes). For example, a kawa KLX 300R makes 33 BHP, less than the KX250F. Perfect example of a high-strung race prepped motor. Even a Kawa KLE 500 street bike makes less BHP than the KX250 (48 BHP). Now, the KX125 (2 stroker) makes 39.7 BHP (Almost as much as the KX 250F! From HALF the displacement). A big part is comparing two like bikes. Can't do the entry level 125 learner bike against a race prepped 125 2 stroker monster. Be the learner a 2 stroker or 4. But yes, a 125 2 stroker is just as or even more powerful than the equivalent 250 four stroker. Just as a 250 2 stroker can be more powerful than those big thumper enduros (KLR650, "only" 33 BHP).

I hope that isn't too much all at once to let soak in. It woulda sounded a little less confusing if spoken/could ask questions while explaining. But hey, i love explaining thisngs like this, so please, ask away .

PS - Is this your bike?: http://www.bikez.com/bike/index.php?bike=18428 if it is, you're a little over 14.6 BHP (Another example of 2 stroke vs 4 stroke, that 125 road prepped bike is as powerfull as my 200CC 4 stroke dirt bike.)

Another PS - http://science.howstuffworks.com/two-stroke.htm HowStuffWorks article on how 2 strokes work
http://science.howstuffworks.com/engine.htm HowStuffWorks article on car engines (4 strokes, same basic principal as a moto engine.)

Brake Horsepower

http://en.wikipedia.org/wiki/Horsepower

GeoffXR200R wrote:Is this your bike

Nice post!

That is the same bike except mine is a 1985 markII. I doubt there is much if any difference in the performance - all I could find different in the specs were:
markI: max.power (DIN)... 21.1PS (15.5kw)@9,500rpm
max.torque (DIN)... 1.6kg-m (16.0Nm)@9,250rpm

markII: max.power (DIN)... 12.2PS (9.0kw)@7,500rpm
max.torque (DIN)... 1.2kg-m (11.9Nm)@7,000rpm

to be honest, I don't know if those values are equal, at equal rpm's Maths never was my strong point!

Henriettaah wrote:

GeoffXR200R wrote:Is this your bike

Nice post!

That is the same bike except mine is a 1985 markII. I doubt there is much if any difference in the performance - all I could find different in the specs were:
markI: max.power (DIN)... 21.1PS (15.5kw)@9,500rpm
max.torque (DIN)... 1.6kg-m (16.0Nm)@9,250rpm

markII: max.power (DIN)... 12.2PS (9.0kw)@7,500rpm
max.torque (DIN)... 1.2kg-m (11.9Nm)@7,000rpm

to be honest, I don't know if those values are equal, at equal rpm's Maths never was my strong point!

Well, if that 12.2 PS is the actuall bhp of your bike, then you're golden. PS is interchanged with HP when using the DIN standard. I duno what they go by on your side of the pond, but over here we go by the SAE standards. But either way, it'd be legal for you... I see a motor swap possibility here...