I was surprised I couldn't find any previous topics on horsepower compaired to torque here. Well, maybe not too surprised considering our bikes aren't torque monsters by any means, but I wanted to see if some more experienced people could share some information about the two with me.

I understand the difference between the engines HP output and what actually hits the ground, and I also understand that HP is nothing more than the answer to an equation involving torque(HP=(RPM*Torque)/5252), so really the HP completely depends on the torque and what RPM you're at, but if that's all that's between, why do people make such a big deal between the two? Such as how V-twins are known for torque, and inline-4s are known for HP. Shouldn't it all be the same? Is the only difference the fact that because HP is multiplied by the RPM, high revving bikes like to talk about the high HP, while V-twins just stick to the torque numbers, because the lower power curve keeps the HP from hitting as high of numbers, since the lower RPM's that the power is reached at doesn't give off as impressive of a HP number?

I generally look over the stuff because someday when I get another bike I'm looking to spend a lot of time riding in lower RPMs, and would get more usable power with a larger bike. I'd like a 900-1000c, but only because I intend to ride it around town, and won't be trying to drag my knee around corners and won't be going 170mph on the highway, so I'm not too worried about the extra power killing me. The only reason I really look at the numbers, is because I'll probably end up with an older bike, and I'm curious how much power a 15 year old 1000cc really put out compaired to a newer 600, if it's really worth getting the bigger bike, and then when you throw the v-twins in there, it really screws with things too.

Everyone always spends more time talking about HP, but I feel as though strictly looking at the torque numbers will give you a much better idea of how the bike will feel, but if that's the case, why is everyone so conscerned with HP? just because the majority of race bikes are I4s and the uneven curve lets them boast bigger numbers? I mean as far as numbers go, my dads sportster 883 is supposed to make 40 something HP, and so is the GS, but if the GS revs to 12k rpm(can't remember the real number), and the sportster only revs to 6k(don't have a clue what it revs to), then the sportster actually makes twice the amount of power, just with the same amount of HP because you're only multiplying it by half the RPM of the GS???!?!! I would otherwise be led to think it's sad that my dad's 883 only makes the same HP as the GS500

haha, I hope that makes sense and that someone can clear it all up for me.

Also, with the difference between the crank HP and the rear wheel HP, which is supposedly lost through the drivetrain, is it assumed that as time goes by, and more efficient drivetrains are made, those two numbers are just going to keep getting closer and closer? ...well, as close as a thick 35psi tire will allow as far as efficiency goes?

Just ride the bike.   

Quote from: tt_four on July 27, 2009, 09:02:03 AM
Such as how V-twins are known for torque

What does being a "V" twin have to do with torque ? why not parallel twin ?.

Popular misconceptions cause people to make critical errors and lets manufacturers lead you like sheep to their drinking post.

There are more things in your post ... but twins V or otherwise spin to a lower rpm cap for a given displacement. V twins have more rotating parts and more bulk in general than parallel twins. Like 2 whole cyl heads, 2 sets of cam shafts, 2 cam chains etc etc compared to parallel and yes compensated by primary balance when its a 90.

But, aside from that, a twin with a 600 displacement has much larger and heavier pistons than a 4, so they make it run a lower redline. That means everything is built around that limitation. You dont cam it for a 15000 redline you cam it for a 10K redline, valves, heads, carbs/FI etc etc etc is all designed with that 10K in mind.

The harley bikers used to claim in the old days The bike had push rods so it makes a lot of torque ... wtf ... since when ... the push rods kill the thign's rpm, 5500 -7K max, so you work with that number and optimise it for its limits.

Cool.
Buddha.

There is a whole lot to discuss with this question, I will try to keep it as short as possible to answer your question.

first off, I think you understand this allready, but if an engine makes more torque then hp it will not rev over 5252, or not much at least.  If an engine has more power then tq it will rev over 5252.

HP is the more important number for racing, or acceleration, even though torque is what is providing the acceleration.  here is why...

if you have 2 engines, in any configuration, engine 1 makes 100 hp with 40 lb feet of torque, and engine 2 makes 40lb feet or torque, but only 35 hp.

you start them both off in first and they will accelerate at the same rate(assuming they weight the same and have similar gearing) engine 2 has to shift into second when it reaches its 5000rpm limit, engine one can keep going in first till it reaches its 13,000rpm limit. when you shift into another gear, you are decreasing your tq to the rear wheel.  for example (I am just making these numbers up but they are close to actual)  1st gear is 3:1 not including the final gear ratio, but we will leave that out for now.  if your bike has 40lb ft of torque in first you will actually have 120 lb ft of torque at the wheel(again this is theoretical, not including final drive here) .  engine two has to shift into 2nd gear way earlier 2nd gear is 2.5:1 so instead of 120 tq it will only have 100.

I hope that makes sense, I am not really good at organizing my thoughts sometimes especially on technical things  like this.

a little about engine design.

a large reason the v twin type engines have large torque numbers and less power too, is the stroke.  longer stroke engines have more torque, and they do not like to rev as high because the piston would be moving so much faster.  with diesel engines, they could physically rev 5000rpms, but the piston would be moving faster then the gasses pushing the piston down.  diesel burns slower then gas.  also as mentioned above, the piston is bigger and that is more mass to be changing direction and accelerating all the time.  diesels have over a 4 inch stroke most of the time.

Quote from: Roadstergal on July 27, 2009, 09:17:46 AM
Just ride the bike.   

+1

Who cares

Quote from: The Buddha on July 27, 2009, 09:20:19 AM

What does being a "V" twin have to do with torque ? why not parallel twin ?.

Popular misconceptions cause people to make critical errors and lets manufacturers lead you like sheep to their drinking post.

That's kinda my question, is there really a difference between any engine as far as the real power goes, or is it all just the way the numbers are configured that make things look different? I just said "V twin" because they seem to be a little more common in a lot of the bigger bikes that are compaired. Smaller CC bikes have inline 4s, inline twins, v twins, single cylinders, 2 strokes, for the most part though, once you hit 600cc and larger, it's usually either an inline 4 or a V twin, and that's when you seem to see guys going back and forth about HP this and torque that. I also think that's where my head was going, because all the bikes I'm looking at for the future are either Vtwins or I4s.

As far as what I do understand to be most common, is that I4s rev high, and that's where the peak power is, and that twins are usually known for better lower/midrange power. Now no matter where that torque comes from, the only difference is what RPM it's at, there's no difference in how much force it actually puts out. It seems like torque is the only number that actually means anything, and HP is just a way to fudge the numbers to make high revving sportbikes sound more powerful than anything else. I mean 50 ft/lbs of torque at 5k rpm feels exactly like 50 ft/lbs at 10k rpm, but magically the HP goes from 47.5hp up to 95hp, which sounds great, but it's all the same thing, right??

Technically, if you had the physical ability to make an engine spin this fast, you could take an engine with only 2 ft/lb of torque, and make that engine rev up to 105k rpm, you'd have 100hp, which sounds great! but really you've still only got an engine that puts out 2 ft/lbs or torque, so it's just a numbers game, right?

Quote from: rockyrunner99 on July 27, 2009, 09:52:58 AM
first off, I think you understand this allready, but if an engine makes more torque then hp it will not rev over 5252, or not much at least.  If an engine has more power then tq it will rev over 5252.

Why ? Cant the 1st engine that has more torque than HP just have a very peaky torque curve so the torque drops off faster than rpm climbs.

Now cant the second engine very much have no capacity to rev due to weights of the rotating masses - ok unlikely on that one but the first scenario is very possible, in fact there are several engines I know that will easily be close and can be modded to exactly fit that criteria ...

Cool.
Buddha.

Really - ride the bikes.

I could talk all day about the differences between, for instance, my FZ6 and my SV650, but 10 minutes of riding them back-to-back will make it clearer than 10 pages of Internet discussion.

(And then you get to personal preference.  With money less of an isse, I'd have an FZ1 as my primary streetbike; with money less of an issue, m'boy would have a gi-fooking-normous twin standard as his primary streetbike.  And then there's the purpose - an ideal track bike will be more aggressive with riding position and suspension stiffness than an ideal streetbike.  And then there's maintenance intervals...)

Quote from: tt_four on July 27, 2009, 10:05:30 AM

Quote from: The Buddha on July 27, 2009, 09:20:19 AM

What does being a "V" twin have to do with torque ? why not parallel twin ?.

Popular misconceptions cause people to make critical errors and lets manufacturers lead you like sheep to their drinking post.

That's kinda my question, is there really a difference between any engine as far as the real power goes, or is it all just the way the numbers are configured that make things look different? I just said "V twin" because they seem to be a little more common in a lot of the bigger bikes that are compaired. Smaller CC bikes have inline 4s, inline twins, v twins, single cylinders, 2 strokes, for the most part though, once you hit 600cc and larger, it's usually either an inline 4 or a V twin, and that's when you seem to see guys going back and forth about HP this and torque that. I also think that's where my head was going, because all the bikes I'm looking at for the future are either Vtwins or I4s.

A twin and a 4 are very different. In theory if they are both targeted at the same market segment and of the same displacement ... the twin will need to have larger pistons, or sweep through a longer stroke or in reality, both, because rigidity decreases with the square of the diameter, a piston that is twice the diameter will be 1/4th as stiff, and when you want to compensate for the loss in stiffness, the dome thickness will have to be more, and luckily that depends on the cube of the thickness if I recall. A piston that is 2X the dia will ahve to be near about 6-7 times as heavy - and mind you it is only that top dome part and I am assuming they dont change the curvature or skirt or anythign else to offste their lack of strength.

So twin pistons are slightly larger and they run longer strokes. The net result is a lower rpm, but its built to fill compress and burn with that limitation in the fore front of their design. As a result V twins make more torque, have less hp and are typically mated to wider ratio transmissions that will let you hit the speeds you would hit on their competetors. However you rev it to a lower rpm each time between shifts and you revto a lower rpm overall. if you run 100 at 10000 the 4 will run 100 at 150000. The 4 will be fitted with a closer ratio transmission and you will need to row through it a lot to get the bike moving.

You rev and shift a 4 and you rev a lot less and shift a lot less (AKA drop it in 3rd gear and run all day) with a similar displacement twin.

V twin vs Parallel twin - the parallel does have a counterbalancer but the V has an extra cylinder casting with its own cam chain, a separate head, 2 cam shafts instead of 1, a siamese'd carb rack or 2 separate ones (like a intruder 800 series) and a a whole set of hoses and crap for water cooling if it has it. Its in all considerations a more complicated and heavier design. So it really is a testament (I think its a testicle but I digress) to how sheitteity the ER-6 kawi is, that it makes less power and handles worse and weighs more than an SV650. Better idea, much much worse execution.

Cool.
Buddha.

Quote from: Roadstergal on July 27, 2009, 10:11:07 AM
Really - ride the bikes.

I could talk all day about the differences between, for instance, my FZ6 and my SV650, but 10 minutes of riding them back-to-back will make it clearer than 10 pages of Internet discussion.

That's easy to say when you have a GS, an SV, and an FZ6 in your garage for side by side comparison. I don't think I'll get the same benefit riding the GS back to back with my wife's moped. I would just like to understand what people are talking about. It's more the mental stimulation at this point than it is me being conscerned about how much HP one bike has compaired to the torque of another.

power=tau*omega=tau*2*pi*f

silly imperialists and your magic numbers. 5252? where does that number logically come from?

anyways, the torque curve is probably most important. a bike for city riding should have a resonably flat torque curve over its RPM range. this will compensate for those times when youre not always in the right gear, or something needs to be done in a hurry.

remember that the power formula is a continuous formula, so dont just multiply redline by peak torque and think that youve got a good number.at zero rpm your bike makes zero horse power, and if it had a flat torque curve it makes twice as much power at 9000 rpm than it does at 4500 rpm... think dyno charts.

also remember that the kinetic energy of the bike is proportional to velocity squared, meaning that the slope of the energy curve (derivative, here comes highschool calculus again) is proportional to the velocity, meaning that you need power to increase with velocity to maintain constant acceleration. this is why if you have a flat torque curve the bike appears to pull linearly until you shift gears.


also, ride every bike you get your arse onto... whore yourself onto everything with tires. it will make you a better rider, and give you a huge baisis for comparison. ride all your friends bikes, then your friends friends bikes.

dont make me start plotting things in matlab.

Quote from: Dr.Sparkie on July 27, 2009, 10:49:29 AMride all your friends bikes, then your friends friends bikes.

+1

They don't have to be sitting in your garage for you to ride 'em.  Also, used bikes at dealerships - they tend to be better about letting people test-ride those than new bikes.  Just don't drop any of 'em...

I think 5252 is the rpm where the torque curve and the HP curve always cross. haha, but yes, in general our numbers for measurement are rediculous.

and I would love to ride all my friends bikes, but none of my friends have bikes, it's just me and my GS, well my dad has a harley, but that's too big of a jump to really be able to compare the 2. Dealerships like you to atleast show interest in buying a bike from them. I'd definitely love to attend a bike demo at some point in the near future, but I don't know when any are happening.

I really refrain from riding other people's bikes. I work on them yes, I test them with them in order tp pinpoint the issue, then I fix it, and then ride it after they do to make certain its fixed.
I dunno, its a habit I have, some people really set their bike up differently than I do and I dont learn/un learn that quick.
But of course I own the various versions I am talking about ... in fact I own 652 CC single and twin from suzuki which are intended to be cruisers just ~3 years apart ... so I can quite easily tell.
Cool.
Buddha.

Yeah, my range at this point, has been a yamaha xt550, my first bike which I believe was an inline twin, to an ex250, also an inline twin, then I had my speed 4 which was an inline 4, and then we got Heather's GS. I've ridden a kawi 636 around a parking lot, and I rode a 900rr on a bigger parking lot, but that's it. Ooh, and the joke of a motorcycle that are bmw's as a loaner when they were fixing my triumph. I'd say that was also an inline twin, of not a single cylinder 650. So I've had a good range of engines, just not a big variance of engine styles.

My sister just bought a late 90s zx6r, which I'm ready to test ride, but she lives in DC so I have to wait until she's in Pittsburgh again.

Anyway, I understand the power curve, and I understand what it would feel like to have more low end power or more top end, but I guess I'll just have to wait it out and see what I can find. Even if they can be scummy, I don't feel like wasting a salesmans time, and leading him on just so I can test ride a couple bikes I'm not going to buy from him. I'm just gonna grab whatever is a good deal on craigslist over winter or spring, I'm not too conscerned with whether it's a twin or an I4, I just like to know what people are talking about when I read motorcycle reviews or comparisons. I know reading/talking about bikes isn't as important as riding them, but I still enjoy both.

Even different V-twins are different.  My 650 is revvy, while 'boy's 1000 is super-grunty and not as rev-happy.  And it's not the size; other high-displacement twins are revvier.

IMO, if you're looking into another bike, your best bet is to figure out the bikes that best fit your needs and wants.  Then you do have reason to show interest and get a test ride.

when I get another bike I'm looking to spend a lot of time riding in lower RPMs, and would get more usable power with a larger bike.

In general, the bigger bikes will give you more down low, because they simply have more all over.  Bandit 1200s are notorious for having good low-end for an I-4; the other semi-modern bike with a lot of low-end is the SV1K, as above.


I'd like a 900-1000c, but only because I intend to ride it around town, and won't be trying to drag my knee around corners and won't be going 170mph on the highway, so I'm not too worried about the extra power killing me.

I don't quite follow the logic, but OK, you want a liter bike.


The only reason I really look at the numbers, is because I'll probably end up with an older bike, and I'm curious how much power a 15 year old 1000cc really put out compaired to a newer 600, if it's really worth getting the bigger bike, and then when you throw the v-twins in there, it really screws with things too.

That's where character comes into it, and that's where I think the talk is obscuring the issue.  If you know yourself, and know you don't want to rev the bike, don't get a rev-happy bike like a race-replica 600.  And power is not the only difference between an older bike and a newer one.  Brakes, suspension, tuning to purpose - there are other things that new bike design has brought into the equation.  And, of course, service intervals - Yamaha has really been pushing longer valve check intervals with its streetbikes, and bless them for that.

Why will you 'probably' end up with an older bike?  Price point?

I'd consider the SV1000.  It's an underrated bike, too much confused with its smaller sibling when its componentry is better, which makes the price point lower than it should be - and its engine has character that sounds along the lines of what you're interested in.  You can get Helibars or LSL risers to make the S more comfy.

Honestly, for a 'round town bike, I care more about light weight and manuverability, but if grunt is what you want, that's a good one to consider.


BTW, the myth about V-twins having more 'torque' - the dynos I've seen show comparable torque between the GSX-R 600 and the SV650.  The GSX-R just makes it at higher revs.  "Torque" is a figure; "low-end grunt" is an engine characteristic.

Quote from: tt_four on July 27, 2009, 10:05:30 AM
I mean 50 ft/lbs of torque at 5k rpm feels exactly like 50 ft/lbs at 10k rpm, but magically the HP goes from 47.5hp up to 95hp, which sounds great, but it's all the same thing, right??

It is the same amount of torque, but it's delivered in a much different way.

Saying a cruiser has 30 HP isn't all that impressive.  But if you say it's got 80 ft-lbs of torque at 2k RPMs, it gives you a much better idea of what the bike will act like.  Good, strong low-end acceleration, less need to down shift, etc.

The same with a sport bike, it may not have as much torque, but it's got 100 HP at 13k RPMs.  That tells you that it's not too quick at low RPMs and likes to be rung out to get the full power from it.

Ideally, the manufacturer would show the torque curve or at least give the HP and torque with the associated RPMs.  But for the sake of marketing, they usually just stick with the more impressive number.  And that's usually what the owners go with as well.

SV1000 yes +1 on R'gal's suggestion ... but whatever you do ... do not never never ever get LSL bars.
The bars I scored from R'gal are extrorginary - yes extra-orgy-nary. But ... no lsl ... and definetly no drilling into that damn top triple. The R'gal bars are an unknown machined unknown metal (cant quite make out Ti or aluminum) ... but they are adjustable for everything and super cool looking. Think alloy connecting rod look.    to R'gal.

You will need for true blue naked hooliganism on a sv1K, a set of buddha top triples which let you fit the guages into the triple, a set of nice dual headlights and yes I know on chicks we want bigger, but on a bike smaller may be better ... or is that butter ... wait ... that is what you do to big headlights on chicks and that is why they get bigger ... mmmmmm butter mmmmmm ...

OK so where was I ... yea billet upper triple to fit guage in it made by buddha (soon to be and target $125-150 max), then carriers and some weird ass bracket for the lights.

The heli bars etc need some nifty cable and wire mods. I am yet to make it all work too well ... so I have to let you know.

But the headlight and uage mods are comming up fast and I wont make risers and dirt bike holes in it, but I'll discreetly put a small circle where you can punch it. And its solid 6061 not cast crap like the stock, so you can unch it there wihtout weakening it.

Cool.
Buddha.

Quote from: Dr.Sparkie on July 27, 2009, 10:49:29 AM
anyways, the torque curve is probably most important. a bike for city riding should have a resonably flat torque curve over its RPM range.

Wow, this just reminded me of an instance in which a friend of mine, who has a car with a huge turbo on it, test rode my bike. When he stepped off, the first words out of his mouth- "This thing lags worse than my car." He was referring to the fact that my left cylinder kicks up at about 6k rpm, but lies dormant below that. I just thought it was funny you should mention a flat torque curve . . . . mine is probably about like this
                                                                                                                                   -(9k)-------------------(10k) ------------(11k)
                                                                                                                                 /
                                                                                                                          (8k)/
                                                                                                                         -------
                                                                                                                 _(7k)/
                                                                                                       _(6k)/
                                                                                                      /
                                                                                                     /
                                                                                                    /
                                                                                                   /
                                                                                                  /
                                                                                                 /
                                                                       (4k)______(5k)_ /
                                           ______(3k)______/
             _(1k)_________(2k)/

I guess there are two things I need to emphasize a little more

1.  The configuration of an engine has very little to do with weather it will have more torque or power.  other engine designs, such as stroke length, displacement, compression, cams lift, timing and duration, piston size, rod ratio, on and on.  Like I mentioned before most diesels are in line 6 engines that barely rev to 3000 rpms, they commonly have 1200lb ft of torque and 300hp,  that does not mean it is because it am inline 6.   The Toyota supra also has an inline 6 yet a moderately modified version will have 600hp and 500 lb ft of torque, with peak tq being around 4000 rpm and peak power around 6500.  The high amount of torque from the deisel comes from the long stroke, around 5 inches, a compression ratio of around 15:1 before the 30lbs of boost is added.

2.  The point made above, about a high torque cruise being in the right gear for quick acceleration, that is the point of low end torque.  Unfortunately, there is no way to make low and torque and high end power in the same engine.  but look at it this way, if you are on a cruiser, cruising along at 50 in top gear with a ratio of .6:1 with an engine that puts out 40lb feet of torque.  You will really only be getting 24lb ft of tq (again not counting the final drive ratio)  now if you on a gs 500 cruising along at 50 in top gear, and you want to accelerate, so you drop down to second where you would be around 9000rpms I think.  You would have 25lb feet of torque from the engine going through a gear of 2.5:1 (don't quote me and I am somewhat guessing) that would give you 62lb ft of tq for accelerating.  And it has NOTHING to do with the other engine being a v twin and ours a parallel twin, I garantee you the v twins stroke is much longer then the gs 500!  I would bet anything.