Nobody's revealing horsepower these days. The first time I really noticed was in December when I was at the KYMCO booth asking how their 250 Venox cruiser can go freeway speeds. What horsepower does it have? I asked the rep at the booth, who quickly replied, "We don't reveal the horsepower because it doesn't matter, you have to measure different aspects…blah blah blah" and I went away thinking that they didn't want to tell anybody because it was so low. But now I've been reviewing all these really high-powered bikes and they don't talk about horsepower either. I asked a few people why horsepower is considered a wanky measure, and it my dad (as usual), gave the best answer. I look forward to your wisdom on this topic, too.
They both have meaning if measured the same way. If you put a Harley
and a Yahama in 6th at 30 mph and lay down on both, the Harley will
probably leave the Yahama for a while because the torque hp of a Harley
is probably greater than the Yahama. However when they both get wound
out and up the Yahama will probably leave the Harley. So for a horsepower
to have true meaning it must be stated like "687 foot pounds of torque
at 3200 rpms at full throttle," or something like that.
tractor or semi to have a lot of torque. You want a racer to have a lot
of brake horsepower at high rpms. You can use gears to help match them up. An
example of the numbers being phony goes like this: A 100 watt light bulb
generally puts out more light than a 60 watt bulb, but it doesn't need
to, because the wattage is just an indication of the power it uses. It has
nothing to do with the light it produces. But we have been hoodwinked
in to thinking blindly that it does. So horsepower in general means
this bike is more powerful than that one. But who cares if the
horsepower tests are only real above 150 mph?
2 + 2 does not = 4 if you are adding 2 cups of water to 2 cups of popcorn.
I also found a nice little writeup about torque and horsepower in fairly plain English by Bruce Augenstein as related to automobile engines, which translates well to motorcycles, I am assuming, where the author states this, some of which I can relate to:
thing that a driver feels, and horsepower is just sort of an esoteric
measurement in that context. 300 foot pounds of torque will accelerate you
just as hard at 2000 rpm as it would if you were making that torque at
4000 rpm in the same gear, yet, per the formula, the horsepower would be
*double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful
from a driver's perspective, and the two numbers only get friendly at 5252
rpm, where horsepower and torque always come out the same.
From there, my eyes start glazing over, and I find myself still wondering how a consumer is supposed to compare power between one bike and another without having to have a math degree. Because despite understanding torque and horsepower — which this article thankfully provides in an easy-to-digest manner — the manufacturers don't give us the numbers. And considering all this, I can hardly blame them.
Still, when I compare specs on the two bikes below, nothing in the numbers tells me that the Vulcan is going to give me an overall smooth and powerful cruiser ride, and the Boulevard is going to rip me off the back of the bike if I turn the throttle on a little too hard, right?
Published specs:
Engine 4-stroke, liquid-cooled, SOHC, four valve per cylinder, 50° V-twin
Displacement 1,552 cc
Bore and Stroke 102.0mm x 95.0mm
Compression Ratio 9.0:1
Belt Drive
Transmission 6-speed with overdrive
Found with some research:
Torque peak of 108 ft-lbs at 2750 rpm
HP peak of 89 at 5000 revs
Published specs:
Engine 4-stroke, 2-cylinder, liquid-cooled, OHC, 54° V-twin
Displacement 1,462 cc
Bore and Stroke 96.0mm x 101.0mm
Compression Ratio 9.5:1
Shaft Drive
Transmission 5-speed, constant mesh
Torque (can't find)
HP (can't find)
If you can tell me – it would be much appreciated.
You are right! For years I have ridden scooters and motorcycles of all types. What good is horsepower if it is only made at higher rpms than I ride? I want to feel “power” which is different than horsepower. “Power” allows me to accelerate out of a bad situation. “Power” makes me smile. “Horsepower” is a number on a peice of paper and does not readily translate into my visceral pleasure when I grab a handful of throttle.
Vaughan
Part of the problem is that there are several ways to measure H.P., so they need to agree on a standard. The Dynometer test @ rear wheel is best, but the result is less than measuring engine output in a lab. So instead of trying to outdo each other on test results, they just decided not to publish them at all. Still, the consumer wants it, and at least it gives you a ballpark idea.
I had the same experience as you did when I queried a Ridley rep. Theirs is the V-twin with automatic transmission. I later found out that their 750cc motor is a highly modified Kohler industrial engine which is only rated @ 27hp. I would guess that Ridley’s version puts out about 40hp, less than a Harley, which their bike resembles. It works well with the CVT transmission, which can’t handle too much power. Still, the Ridley is one of the best motorcycles for women riders, because of the low seat height and no shifting. It looks cool too, like a custom bike.
Righto Steve – I wonder why the manufacturers can’t decide on a standard. Maybe I’ll ask the AMA. Regarding Ridleys, http://www.ridleymotorcycles.com/, there was some discussion last year about them being great women’s bikes, and I got a whole lot of guys writing in saying heck, they’re tired of shifting, they want the bike because their hands get sore.
Anyway, I guess you can’t judge a bike by the numbers. I think you just have to ride it to see if the hp + torque equation feels right to you.
By the way, WRN has a nice article on the Ridley:
http://womenridersnow.com/PublicFiles/Departmentviewer.asp?ArticleID=451
we like to talk horsepower, but we tend to buy torque because that is what you feel particularly when you are just getting moving from a stop.
I disagree with the assessments that torque is meaningful but HP is not – the opposite is the case.
Firstly, ‘torque’ as a measurement is no more informative than HP, because it is, in just the same way, a peak figure, and only one measurement throughout hte powerband – e.g. if your bike makes 100ftp of torque at 5k rpm, that still tells you nothing about what the bike does at 2krpm or 10krpm.
HP is a peak figure as well, and the reason I expect people object to it is because it usually occurs higher up in the powerband than peak torque. To that extent, I agree entirely: I have an SV650, a v-twin sportsbike, which makes around half the (peak) HP of the new-model Japanese 600s. But, that is comparing near-redline on my bike to near-redline on theirs – on the track or dragstrip that matters, but not on the street.
To understand how fast a bike is, you need to be able to see the power-curve – i.e., not just peak HP, but HP in the useable ranges. My bike has a very broad powerband, which has decent power everywhere from 4krpm to 10krpm. A 600 might make very little power until 10krpm, not make much more from there, but then have a sharp spike between 15k rpm and 18k rpm. So, if you’re cruising on each bike (say 5krpm on mine, 6krpm on a 600), mine might have more power at that rpm, which is what is really important – power at the rpm that you are actually using.
As far as torque goes? It is impossible to compare torque figures without artificially recomparing rpm. HP is simply torque x rpm (with a correction multiplier). This is because of gearing: my bike probably has a similar (peak) torque figure to a 600 of its day. But because mine makes it at 8k rpm, and the 600 makes it at 12k rpm, it means if I am using peak torque in 4th gear, the 600 can be using peak torque in 2nd (at the same speed) – and we all know what happens when we shift down, right?
Now putting all this together to understand torque and HP curves:
a torque curve will tell you ‘how’ a bike will feel if you’re openning the throttle and letting it spin out, but not how fast it will go – it will tell you that the bike will pull hardest at peak torque, and relatively how hard it will pull at other rpm. (e.g. with my bike a big flat torque curve will tell you that if you’re in 4th and you wind on the throttle you will get the same response in a wide range of rpm, but on a 600 you will get little response until 8krpm, and no real kick until much higher). Note that this tells you the distribution of force, compared to other rpm, not how much that force is.
To work out how fast you will actually go, how much the bike will pull, kick, or take off – whatever subjective word you want to attach to accelerating, because when it comes down to it its all the same – YOU NEED TO LOOK AT THE HORSEPOWER CURVE. If you know what speed (rpm) the engine is spinning at, HP at that rpm (not peak HP) will tell you how much acceleration you will get. So if you know you cruise at 4krpm and have fun at 5-7krp, looking at the HP figures here will allow you to compare different power figures. (This won’t necessarily allow you to compare bikes exactly, because RPM usage will change, but it can make a very accurate way of comparing engine modifications etc.)
If you want to compare bikes, overlaying power curves will tell you exactly how they will accelerate in comparison (as long as you can match the gears up to speeds on the road…)
I feel like I should be going in to more detail, but then I don’t know if I would be any less confusing… overall, though, I don’t think many of the previous responses you have gotten – referring to what you have quoted – have done justice to the different functions of torque/HP measurement. And in particular, I disagree with the importance people place on torque figures, and am frankly bemused why they get quoted at all. I think people like hearing and comparing them – in the same way they like hearing and comparing peak HP figures which occur too high up in the power band to actually be of any use. (The difference is that peak HP could make a difference, if you did get to that rpm – peak torque never will.)
Two (technical) results/provisos:
1. if you are accelerating through a power curve (i.e. winding through the revs), how quickly you get through it depends upon the total HP figures over the whole of the curve… so if you really want to get technical, the speed of the bike in that situation (e.g. a 1-gear drag race), depends upon the size of the area underneath the curve. But understanding that is getting pretty damn mathematical. (technically: you’re interested in the derivative, not the antederivative, which is what the torque curve is)
2. peak torque can be used to make a very, very approximate comparison if you use it to make an assumption about the shape of the power curve: if peak-hp occurs at peak torque, you know the curve is very pointy. If peak hp is at, say 10rpm, and peak torque is at 5krpm, you know the power curve is going to be very flat, and the bike will pull at a wide range of rpm. (Mind you, it would make it much easier just to know the HP at peak torque, not the torque figure.)
Regards comparing the above two bikes which you have listed specs for? Well there isn’t much info to go off: the only grounds for comparison are the bore x stroke and compression ratios. I can tell you that (often, not always) shorter stroke engines are typically designed to rev higher, and so will have more power=HP for the same engine size (or, for the same torque), but might also be designed to have less power at lower revs. (As far as I know there is no reason they wouldn’t have more, but often they wouldn’t be designed that way.)
For most engines, other things being equal, a higher compression ratio will mean higher power (for all rpm) – it is more efficient.
If you really want to compare the bikes, get power curves for them, work out what speed they redline in first gear, and overlay the graphs – they will tell you exactly how the bikes compare on the road. (You will probably find the Vulcan makes more power at lower rpm/speed, but the M90 making more power at higher rpm/speed. But you don’t know until you try it.)
I know I’ve gone far enough, but for the sake of completeness, Steve Fray is quite right: these comparisons only make sense if you measure power in the same way… manufacturers tend to have a thing of measuring power in the most irrelevant ways to get higher figures.
Good luck in your forays into a very complex topic. I’ve been scratching my head over these questions for about five years (and have completed a mathematics degree in the meantime), so I don’t want to imply it’s easy.