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Power Question

Discussion in 'Bike Reviews, Questions and Suggestions' started by boxman, Sep 19, 2010.

  1. Hey Folks,

    I think I am missing something here.

    I currently have a GS500F, according to Suzuki, It has 47 hp @ 9200 rpm (34.3 kW)

    I am looking to upgrade to a Moto Guzzi Breva 750, which is listed as having 35.5kW at 6,800 rpm which is roughly 47 hp.

    As I am looking for more power, logic would suggest that the Breva is the way to go, but on paper I am better off with the GS.

    Can somebody please explain?

  2. better off? probably. But who cares about better off? it's a guzzi.
  3. 34.3KW vs 35kw

    Why bother changing at all?

    If the Suzuki is lighter, then your power / weight ratio will obviously be better.
    Apart from that, I doubt you'd even notice any difference.
  4. Since the Guzzi develops the same amount of power as the Zook, it isn't actually going to be any faster.

    But because it has more *torque*, it's going to *feel* more powerful and *feel* faster, and is going to be more flexible (i.e. you're more likely to get some go even if you're not in the optimal gear).

    Guzzi: ~ 60 Nm @ 3200 rpm
    Zook: ~ 40 Nm @ 7500 rpm
  5. and the guzzi will break down, so you won't have any power at all.
    Guzzi ~ 0 Kw @ 6,500 rpm / 0 Nm @ 3,200 rpm

    won't really matter though, so long as it made it to the cafe to get your moccachino latte... it's main function is to park out the front, so that you can sit beside it in full racing leathers and sip your latte.
    In fact, you could even leave it parked there for the next 6 months, while you wait for parts to arrive from Italia.
    this will cement you bond with the Ducatti owners who also parked their bike there... however, if you really want to fit it with the exotic Italian bike crowd, you are going to need an awful lot of botox injections with that head.
  6. Monkeyman- say it ain't so- i'm sure the Guzzi's are a bit better these days.

    Captain_Slow- thanks for that, so as a general rule, should I look at Nm before Hp (not the sauce) ?
  7. You have to look at both of them as a combination. Generally high torque will drive you quickly out of a corner whereas high horsepower will give you high top speed.

    Guzzi is a bike that you don't buy for the horsepower/torque figures. It is more than that. You won't get it till you ride it. You might not be "better off" in terms of outright numbers on paper but it will feel better on the road.
  8. Ride one and see how it feels. More low down grunt may suit you or it may not. Grunty bikes tend to be easier to ride briskly on real world roads, even if they lose out to the rev-monsters on the track.

    Personally, given two bikes that make equal power, I would tend to go for the lower revving lump for general use. I like the feel of such engines and they tend to be better at hauling pillions and things around.

    Again though, I would emphasise, get a test ride.
  9. Mate I did the "upgrade" from the the GS and currently have the Breva 750.

    Once you test ride it you will feel the difference. If you are after some sort of sportsbike though or if performance is high on your list - you can rule out the Breva.

    The Breva is just a great allrounder being as good if not better than the GS in town and far superior for touring. The shaft drive is a massive plus, why all bikes don't have shaft drive is beyond me.

    I've used my Breva literally every single day for over 12 months (it is my daily commute and weekend toy) without any mechanical issues, although I do ensure that I maintain it well.

    Admittedly some parts will be a bit more expensive for the Breva than the suzuki, but if you decide to go ahead I can give you some pointers and websites that can cut those costs dramatically.

    If you like it go for it.
  10. Heres an example. I have two bike, a Honda XR600 (big 600cc single cylinder) and a Suzuki GSX-1100EF (big 1100cc 4cyl). Both are brilliant to ride through the twisties, and even though the XR only has 1/3rd the power of the GSX it has brilliant torque delivery. You migh not be able to go very fast on it (currently geared for 140km/h max) but you can really pull out of corners well. The GSX will let you go over 200kmh and is very flexible for a 4cyl bike, but just doesn't have as much low-low-down as the 600 due to its engine setup, gearing, and 110kg of extra weight.

    Cheers - boingk

    EDIT: And yes, if you're looking for extra power then please testride some bikes. It will give you an idea of what you're looking for. You may find the Breva irritating, but love a Honda CBR600. Or vice versa. Ask mates/family with bikes if they'd be willing to help you out with some hassle-free testrides.
  11. Power is what drives you out of corners. Power adds kinetic energy to the motorcycle, and that is what accelerates you. Power measures the rate at which kinetic energy is added.

    Power = torque x rpm

    There is no "torque is better out of corners, while power determines top speed", it's all power. Torque x rpm is power. A motor can have a lower crankshaft torque than some other motor, but can still accelerate you stronger out of a corner if it can rev high enough.
  12. you could also try a triumph street triple, kawasaki z750 etc
  13. Technically true Flux but torque is what you feel everyday and a broader torque distribution makes the power more accessible under "normal" riding conditions.
  14. A half hour of googling and I'm an expert in physics now. Ahem.

    kilowatts are a measure of how much power can be produced or used by something over a certain amount of time. When they rate the kilowatts of something, they are usually talking about kilowatt hours. For example, a 1000 watt heater uses 1 kilowatt every hour.

    I believe that when you measure the watts of an engine, that also is what it is capable of producing over an hour. So an engine rated at 50kw can produce 50,000 watts over one hour. This is enough energy to power 50 of those 1000 watt heaters for that hour. Or 833 60 watt light bulbs for one hour.

    You'll notice that we're only talking about *energy* here. Kilowatts (and horsepower) are not a description of how much *force* a system uses or creates; it is just a rating of how much energy is used or produced by a system.

    If you remember back to your highschool phsyics class, they would talk about how many "newtons" of force is applied to objects. 1 newton is equal to the force needed to accellerate a 1kg mass at a rate of 1 meter per second per second.

    If newtons are used to measure the force applied to an object, what about angular force? Thats what torque is. Torque is a measure of the angular or rotational force applied by a system. Torque is measured in Newton metres, and is a measure of the angular force.

    So what the hell does this mean to us? I think it means that KW is a lousy way to measure the performance of a vehicle, and torque is much more useful. KW can tell you what the potential power output of a particular engine is, but torque tells you exactly how much of that power can be applied to the wheels.

    I kept hoping someone who actually knows physics would step up but it hasn't happened yet. Sorry if you do know physics and the above is wildly inaccurate - would appreciate being corrected. But this is how I understand it after the aforementioned 30 minutes of googling. :)
  15. A few points chrome.

    A Watt is one Joule of energy applied over 1 second. If a motor is running at 50kW, it is producing 50,000 Joules of energy per second. Over 1 hour, it's producing 50,000 x 3600 Joules. A kWh, being a measurement of energy in Joules too, and which is equivalent to 1000 x 3600 Joules, is just a handy way to talk about big numbers of Joules without so many zeroes.

    So, when something is measured in kilowatts, that's the amount of energy per second (known as work). It's not measured over an hour.

    Torque is rotational force, very correct. What most everyone forgets though when talking about engine torque values is that there's a primary gear ratio, the gear box, and the final drive ratio, that all affect the torque that is applied at the rear wheel. It is for this reason that quoting engine torque values are almost useless. It's the torque at the rear wheel that is your driving force, but there's a lot of torque conversion going on between the engine crankshaft torque and the rear wheel.

    An engine that makes 10ft-lbs of torque that is geared down by a factor of 10 will produce the same torque at the rear wheel as a 100ft-lbs engine connected directly to the rear wheel. You wouldn't be able to tell the difference. I've said it before, you can gear down a mouse on a running wheel far enough that it can outpull a diesel locomotive.

    Now, since power = torque x rpm, said 10ft-lbs motor will need to spin 10x as fast as the 100ft-lbs motor to make the same amount of power, but so long as it can, once again the motors will act the same in terms of driving force and power output.

    Torque at the motor means little. Torque at the rear wheel means lots. When you see engine torque ratings, it tells you nothing about the torque at the rear wheel.
  16. All quite true FLUX, but the characteristics of the internal combustion engine will mean that a smaller engine spinning at a million RPM will deliver that torque in a very very narrow rev range right near the redline. Thus requiring 500 gears and someone willing to tapdance on the gear lever to take advantage of it. Fine for a race track, not so endearing on the street.
  17. I guess this is why Dyno results are important, as that tells you exactly how much torque is produced at the rear wheel, and how much energy you need to expend to get it.

    Of course not every bike has a dyno chart available for it, so really the only solution is to test ride them. Looking at "Max power" and "Max torque" numbers on manufacturer's websites really tells you very little about how the bike performs.

    Damn. Does that mean I'm going to have to test ride like 20 bikes in a week's time? Sucks to be me. How will I ever manage to survive. :(
  18. The dyno chart will tell you quite a bit about the way the power will be delivered. What you want to look at is the area under the line. The larger the area the better. The earlier and steeper the line rises the better the real world power delivery. The peak number is not the be all and end all. Other than for the dyno queens.
  19. If talking about Internal Combustion Engines, it all depends on what we're comparing here. If comparing a 250cc engine to a 1800cc 4-stroke twin, then yes, what you say is true. If we're comparing motorcycle engines of about 600cc and above, people don't really need to tap-dance even though the torque values vary immensely.

    For example, compare something like a Honda CBR600RR with an 1800cc Harley (all stock for both bikes). The Harley has over 2x the torque, but the CBR will out-accelerate it pretty much everywhere because its geared lower, and spins higher more easily than the Harley benefits from its higher torque.
  20. Which, if I'm not mistaken, is pretty much exactly what the OP was asking yes? More or less.