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Explanation for a newbie?

Discussion in 'Technical and Troubleshooting Torque' started by kate, May 2, 2016.

  1. I have been told that it is not just engine capacity that influences the overall "power" of a bike, but that power to weight ratio plays more of a role (ergo, LAMS list). So, how does engine capacity, power, weight and torque impact speed, acceleration and braking or any other aspects of overall performance? How would the performance of a light bike with a small engine compare to a heavy bike with a large engine?

    How does one go about deciding what combination is better for them? Does it just come down to personal preference as to what individual riders prefer, or are certain power to weight combinations better for certain types of activities? I can see the obvious benefit of high power, low weight and high torque in a racing setting. But what role does power and weight play in day to day riding?

    - Question from a newbie who does not own a bike!
  2. Takes energy to do work,make things move.Less weight,is a very good thing.Less Unsprung weight is even better.
    That's talking pure performance,there is more to a bike that pure performance,Did I just say that.That's obviously wrong.Just like in the old TV add,its about the feel,the physical experience.Even the sound and that's getting a bit poetic.
    We are getting close to the if you have to ask comment made to people who don't know. Hope I have cleared all that up for you,my work is done.
  3. I think as a newbie, who does not own a bike yet, you are asking the wrong questions. I would first try and determine what sort of a bike I want to ride and then look into the performance issues.
  4. For a first bike, light is good,so is lowish power.Low seat high and cheap is also good, sit on a few at a shop and see how they feel,feet to ground and ease of reach to the bars. After you master basic riding then more tech stuff enters the mix and by then you should have picked up what interests you performance wise. Some bikes are very narrow focus and some are more jack of all trades. The narrow focus ones tend to be more exciting
    • Agree Agree x 1
  5. katekate, liken it to cars, take a Mazda 3, small, light weight, small engine, good fuel economy, nimble to drive around town might not be as comfortable on a long trip,struggle at freeway speeds and gets blown around by the wind, compare that to a statesman, large heavy car, large engine, not so good for city driving but comfortable and relaxed on the open road. LAMS bike take the power of the engine and compare it to the weight, someone might chime in with the equation. First thing to do is consider your statue - can you touch the ground easily, get on and off easily, and the riding position you are after, sitting upright like a cruiser, trail, adventure bike or tucked up like a sports bike, also consider the weight, if you are smaller you don't want anything too heavy or a high centre of gravity for a first bike. Look around and sit on as many lams bilkes as you can to get a feel of what you like
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  6. Hi Kate,

    Power (horsepower or kilowatts (kW) determines how much work a motor can do. If you want to go very fast or carry big loads you need lots of power but the amount of power available today in top end sport bikes is way more than anybody can use on the roads.

    Torque is a measure of twisting force, that determines how hard the motor can spin a the output shaft and how quickly the engine can accelerate and how much resistance to turning it can overcome. A tractor has a lot of torque as it not only has to be able to drag itself through soft ground but it has to be able to drag ploughs and things through that ground too. To some extent power and torque go together, but they are also affected by the number of cylinders in the engine and the shape of the cylinders how long and how wide the cylinder is (stroke and bore in technical terms).
    Motors are designed for different types of uses so yes, there are typically different configurations for different uses.

    The other things that come into it are the steering geometry (rake and trail), distance between wheels (wheelbase), stability at speed, rider comfort and so on.

    Dirt bikes: Generally light, smaller capacity engines are used and for serious trail riding 450cc is a big motor. These bikes need quick handling, good torque and outright power is not that big a deal.
    Small single cylinder engines with narrow bores, long strokes and comparatively low revving are usually used. The steering head angle (rake) is usually pretty steep and the distance the front wheel contact patch sits behind the steering access (trail) is short so they steer quickly and are nimble. This gives you a bike with the torque to pop the front wheel in the air to cross obstacles like fallen logs and the power to plough through sand and mud while being light enough to muscle around on rough ground and tight corners. The riding position is set up to allow you to stand up on the pegs which gives you better control of the bike on rough ground but means that you tend to be sitting up more and get more blown around at speed. The downside is that they don't tend to have good high speed stability, weather protection, they tend to vibrate a fair bit and they're usually low geared and have lower top speeds. The brakes tend to be on the soft side too as it's very easy to lock up the brakes in the dirt and that does mean being a bit more proactive on the road.

    Sport bike: These are designed to go fast, be stable at speed, corner well and brake hard. There is a wide variety of sizes and configurations, from little 125cc bikes to1000cc superbikes. The LAMS approved ones tend to be the smaller capacity ones or have restrictors built in to moderate the power output, but you would usually see them as twins or triples in the LAMS range as these give a good compromise between power and torque at road legal speeds. Steering geometry tends to be short trail and steep rake again as fast steering is important. They are fun, and nippy, but the riding position is targeted for fast riding so it tends to be forward leaning, foot pegs further back, so you can get right down on the tank and get out of the wind blast behind the fairing and screen. The smaller capacity sport bikes are still a lot of fun. The downside is that they aren't very comfortable (built for speed and comfort adds weight), tend to have short fuel range, their fast steering tends to make them feel a little twitchy at speed, you're doing a lot of little steering corrections.

    Dual Sport: These tend to be larger capacity singles or twins, in the 600+cc size that still have some ground clearance and dirt road ability but are capable of more comfortable high speed travel on the motorways. For Australian roads they're a good compromise, especially once you get away from the coastal strip.

    Touring bikes: You can tour on anything you can strap a bag to, but dedicated touring bikes tend to be big, powerful enough to carry two and luggage for a long trip and with big fairings and wind screens and the ability to have hard luggage fitted. The suspension tends to be on the plush side soaking up the bumps very well but getting a bit vague at high speed compared to a sport bike. They tend to be heavy, with somewhat gentler rake and trail so they don't turn as fast but are very stable at speed in a straight line. Very comfortable, relaxed, long distance mile munchers, but not what you would call nimble and you're lane splitting, ducking diving and weaving nimbleness in traffic is but a distant memory. Most of these aren't really LAMS bikes.

    Sport touring bikes: Pretty self explanatory really. A compromise between track weapon and full dress tourer. My VFR800 will give a 1000 cc fireblade a run for it's money in the standing quarter mile, and won't be far behind in the twisties, but has longer fuel range and far better comfort for longer trips. They big sport bike will pull away fast on the track though where the overall speeds are higher.

    Adventure touring: These are a fairly recent innovation. They are essentially monster trail bikes. They have big capacity high performance motors, which are really too big, heavy and powerful to control in rough dirt for the average rider, but have electronic control systems and technology that actually makes them work amazingly well. But they're very high seat heights, very heavy to pick up if they fall over (something that happens to dirt bikes fairly commonly) and they tend to eat back tyres with frighteningly expensive regularity.

    Cruisers: Classic American style bikes, that are well suited to the long straight open roads that are found both in the US of A and the Australian continent. Almost universally V-twins with large capacity motors and heaps of torque. They have typically fairly gentle rake and long trail that makes them pretty close to steer themselves on the open road. They tend to have an upright riding position with the foot pegs in front of the rider, some have foot boards that you can move your feet around on. They look and sound fabulous with a variety of options to customize them to individual taste. The downside is that the riding position while looking very comfortable often doesn't feel comfortable on a long ride. It's really hard to stand on the foot pegs to get control of the bike on loose surfaces or help soak up the bumps on rough road. They certainly don't steer quickly in the tight turns and can be a handful if you're trying to make it though traffic on the daily commute. Some people also complain about cruisers having poor lean angles and ground clearance and they generally are restricted in this respect compared to sports bikes, but what they have is generally more than sufficient for public roads at legal speeds you just don't have as much reserve lean angle up your sleave if you misjudge the corner.

    What you choose is going to depend on what your needs are, your physical size and what fits you and to a greater or lesser extent, which bike tugs your heart strings and whispers sweet nothings to you. Bikes aren't just about logic and reason after all, there is a usually a bit of passion involved too.
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  7. Engine Capacity = Physical size of the engine (cylinders)
    Generally the bigger the engine the more torque it will have. A 1000cc bike has an engine 4x the size of a 250cc bike.
    Torque is best described from a non technical point of view as the shear pulling power of the engine.

    An engine that has very high torque can often generate lots of power at very low rpm as simply put 'HP = RPM * Torque'
    Imagine a big 1400cc Harley accelerating away from the lights going from 700rpm and shifting at 3000rpm.
    A sports bike with less torque. ie a CBR250RR will have to accelerate to 14000rpm to match it

    Different engines can be tuned differently, this is why we use Power:Weight as opposed to a flat no bigger then 400cc rule.
    A brand new 500cc watercooled, fuel injected engine will generate much more power then a similarly sized Aircooled engine with carbs.
    This also comes back to engine design, smaller engines tend to rev much higher then larger aircooled engines
    This is why harleys are just as slow as ninja 300's despite being 1600cc monsters. :p

    100%, ride a bike you feel comfortable on and enjoy.
    Larger more high powered bikes tend to be harder to ride and less forgiving hence why they are normally restricted.
    As a beginner look around the 250cc mark, this is normally the best balance of weight/performance/cost
    • Agree Agree x 2
  8. kate, I think you are over thinking this thing. Learn to ride one first, then begin to think about it. - hows that for a smug response? Actually, you are doing more of others should do.

    I can see how where someone just wants to get it right the first time, they want to ensure they get something that is going to be right for them.

    The power/weight ratio - simple really, the more power there is per weight, the faster the bike will accelerate. Top speed is more dependent on just the power and the physical size of the bike. Lighter bikes tend to stop more easily.

    Power vs torque? Torque can be likened to how quickly an engine can change the amount of power it delivers. Some bikes, notably those with two stroke engines are very powerful, but only make their power at a specific and narrow range of revs, often referred to as the "power band." In this zone, the bike will accelerate quickly, but to get the best out of the engine means keeping the revs in this zone, by changing gears a lot as one's speed changes and they are not exactly a relaxing ride, but can be a lot of fun if you are up to it. Such bikes often have very little useable power at low revs, there is a place in the rev range where the bike behaves as one would expect and a place where it turns into Mr. Hyde. They've fallen from favour a bit. Most bikes that people buy for road use are 4 strokes.

    4 strokes make their power across a larger range of revs. At low revs, they will accelerate, but they won't take off like a scared rabbit when they hit some "sweet spot" in the range of RPM possible. There is still a point at which the power available surges quite noticeably.

    Different engine designs can often produce different engine behaviour for the same size engine. More cylinders can usually mean more power, fewer cylinders with larger pistons generally translates into more torque. This is because the force developed inside a larger cylinder can be greater than a smaller one. A 600 cc single will chug up from very low revs - near idle to its max, and have useful power very early compared to a 4 cylinder 600 which might need to be turning at more than 3000 rpm to start accelerating quickly and have what you would call throttle response or useable power, by the time the single is running out of puff, the 4 cylinder bike will be seriously on song and ready to go harder.

    Beginners find torquier engines easier to ride. They are less inclined to stall, respond briskly to throttle input at very low revs and one does not have to pay quite so much attention to which gear one is in around town. Similarly powered, less torquey engines stall easily on starting out and if you get a gear or two wrong, you've got no power at all.

    As N C has pointed out above, there are other considerations. How you fit the bike (physical size) type of posture you prefer. - learners often benefit from a bike which permits an upright posture, and which is not too large. The power characteristics are probably less important than these, BUT are a consideration.
  9. Way too many numbers and words for a newbie. Minimum for comfortable street riding is about 30hp. Then ask which bike which bike based on other needs; your size, strength, reason for riding and likes/dislikes?
  10. Given you're up in NT, I'd want to look at something that has some dirt road ability. But as others have said, go and pester the staff at bike shops and sit on everything. See what may or may not work for you. Then get license and ride the ones you liked, see what clicks.
  11. Thanks for the thorough overview. This definitely helped a lot!