Thumper Club Forum
Club House => Chatter => Topic started by: Propellor on May 11, 2015, 08:48:30 AM
-
Read an article recently, about aero drag and motorbikes. Saying how unaerodynamic a motorbike was compared to a car. That a good indicator of the drag is how much power is consumed to propel the vehicle to a certain speed, given that aero drag is by far the most deciding factor at high speed.
I go along the power consumption thing, but I have difficulty with what represents drag.
Reason I say this is because it seems that a modern car will need double the horsepower to achieve the same speed as a bike. Looking around the 130 mph mark.
So if consumed horsepower is the indicator of drag, a bike Seems to have less of it.
Clearly there's more to overall drag than just a slippery shape.
Ok, when it comes to saving the planet, or at least the oil reserves, how efficiently the respective vehicle musters up its necessary horsepower is a different thing again.
-
I think you would have to compare a motorcycle and car of the same weight for the comparison of the effect of drag to be meaningful between the two. ;)
-
I think you would have to compare a motorcycle and car of the same weight for the comparison of the effect of drag to be meaningful between the two. ;)
I'm not sure weight has that much to do with it. Ok, more weight will probably add slightly to rolling resistance due to increased friction in the bearings and maybe tyre contact. More weight generally adds to the bulk of an object, which may affect drag, depending where and how the bulk is placed. But, by the same token you could quite conceivably take a motorcycle and add weight to it but also make it have less drag. Quite easily, in my eyes.
Weight affects the rate of acceleration in a big way, yes. But once the vehicle stabilises out at a given speed it isn't accelerating any more, but the drag still counts.
Acceleration rate sometimes limits top speed because you simply run out of road!
-
Weight affects the rate of acceleration in a big way, yes. But once the vehicle stabilises out at a given speed it isn't accelerating any more, but the drag still counts.
Yeahbut, if a 747 is cruising at 500mph and three of its four engines cut out, it won't be able to maintain that speed in level flight.
It always takes more power (hp) to accelerate to a given speed and maintain that speed for a heavy vehicle than a light one, all other variables being equal.
-
Weight affects the rate of acceleration in a big way, yes. But once the vehicle stabilises out at a given speed it isn't accelerating any more, but the drag still counts.
Yeahbut, if a 747 is cruising at 500mph and three of its four engines cut out, it won't be able to maintain that speed in level flight.
It always takes more power (hp) to accelerate to a given speed and maintain that speed for a heavy vehicle than a light one, all other variables being equal.
First sentence doesn't change a thing I said. Second sentence doesn't take into account time and wrongly (IMO and with respect) places emphasis on weight when considering top speed.
Let me put an example forward of what I said earlier.
Take a bike. Say... A gpz500. Take all the bodywork off and all steel structure supporting it. Run the bike on as long a road as it takes to reach top speed.
Put the bodywork and supporting structure back on, thus ADDING WEIGHT. Run again under exact same conditions but still allowing as long as it takes to reach top speed.
Which version will reach the higher speed?
-
Which version will reach the higher speed?
If you added the exact same amount of weight back in by filling the frame tubes with lead, then it would be slower. If you add the weight back in by adding the bodywork back on, it may be faster, depending on whether the design of the bodywork reduces drag from the air by enough of a margin to offset the additional weight.
At least this is my understanding, but it's a long, long time since I did physics at school......
-
Which version will reach the higher speed?
If you added the exact same amount of weight back in by filling the frame tubes with lead, then it would be slower. If you add the weight back in by adding the bodywork back on, it may be faster, depending on whether the design of the bodywork reduces drag from the air by enough of a margin to offset the additional weight.
At least this is my understanding, but it's a long, long time since I did physics at school......
Filling the frame tubes is a brilliant thought experiment. It doesn't change anything with regard to the shape. But I disagree with your conclusion. It would lower the top speed very slightly due to very slightly increasing rolling resistance (not to be confused with inertia!) IMO. But only for that reason. It doesn't change the drag at all so I would expect it to reach near enough the same speed. I would expect adding back the fairings etc to make a noticeable change upwards in top speed because the drag is lowered even though the weight is increased.
Regarding rates of acceleration, that's a different thing.
There's a very simple graph in kevin Cameron's sportbike handbook which has available horsepower plotted against mph with the curve being the combination of rolling and aero resistance. The bike will keep accelerating until the power available is no longer able to overcome those two combined factors. We're not taking time into account here, only ultimate top speed. Nowhere on his graph does it mention weight.
-
There's a very simple graph in kevin Cameron's sportbike handbook which has available horsepower plotted against mph with the curve being the combination of rolling and aero resistance. The bike will keep accelerating until the power available is no longer able to overcome those two combined factors. We're not taking time into account here, only ultimate top speed. Nowhere on his graph does it mention weight.
It probably doesn't take weight into account as it's effect, given the similarity in construction of modern sports bikes and the available power, is insignificant. However, ride a CG125 at top speed an then repeat the experiment with somebody slightly smaller (to reduce the effect of drag as much as possible) but equally heavy sat snugly behind you and I'll guarantee you wont reach the same speed.
If weight had no effect then surely the makers of Moto GP bikes wouldn't spend millions on trick carbon and magnesium components trying to reduce it?
-
Crazy frog and meself have fired a few posts between us, but can I just add, ladies n gentlemen, this is not an argument! At least not from this end and I don't detect any of such from crazy frog. :)
-
Indeed not, just an interesting discussion, and I suspect we are both right in parts.
We just need someone to come along who has more knowledge of physics (not difficult in my case!) to set the record straight!
-
A) It probably doesn't take weight into account as it's effect, given the similarity in construction of modern sports bikes and the available power, is insignificant.
B) However, ride a CG125 at top speed an then repeat the experiment with somebody slightly smaller (to reduce the effect of drag as much as possible) but equally heavy sat snugly behind you and I'll guarantee you wont reach the same speed.
C) If weight had no effect then surely the makers of Moto GP bikes wouldn't spend millions on trick carbon and magnesium components trying to reduce it?
A) possibly. That's certainly true. There's little to choose between em at any time. But, reading the chapter in context, I think it is just demonstrating what limits top speed. Available horsepower versus the combined effects of rolling and aero drag. The book considers just the principles which lead to performance. These principles just happen to lead to the sportsbikes we now see.
B) however the pillion affects rolling or aero drag will determine the top speed. The weight, in proportion to the power of the cg125 will lower the acceleration rate considerably. But if you have a road long enough and conditions don't change, then the theory, as I interpret it, says it should reach a very similar top speed. Chances are, in the real world, you'll just run out of road or the conditions will change enough to render the experiment unscientific.
C) has no effect on what? It affects acceleration no question. It affects dynamics. It affects lots of things which determine the chances of winning a race. Also, racetracks have straights of a very finite length. Very short, relatively speaking. So a heavier bike will need a longer straight to reach the same speed. That won't win it the race though.
-
Indeed not, just an interesting discussion, and I suspect we are both right in parts.
We just need someone to come along who has more knowledge of physics (not difficult in my case!) to set the record straight!
Good man.
Yes! Or someone who goes to the salt flats. Their objective, I predict, would be to lower rolling resistance, lower aero resistance and increase power. If adding weight tipped the balance of that equation in the right direction they would add it.
-
Read an article recently, about aero drag and motorbikes. Saying how unaerodynamic a motorbike was compared to a car.
Aerodynamic, as I understand it is a concept, rather than something qualitative. So saying something is aerodynamic just means that its been designed in a way that it lessens the disruption to the airflow over it and therefore reduces drag.
Motorbikes have shed loads of bits sticking out which can disrupt flow, amongst these are indicators, handlebars, footrests, mudguards, riders etc etc. As such the air flow is more likely to be disrupted and as such could be considered less aerodynamic. (Yes there are are exceptions, but we are talking generalities here).
A car, even if it is more aerodynamic (in design), will present a much larger surface area to the airflow and as such drag increased, hence the need for more power.
Weight has nothing to do with top speed, apart from as propeller mentioned, increasing drag on the tyres.
-
Having visited The Denny ship model experiment tank at Dumbarton at the weekend (The Scottish Maritime Museum) can I throw a large 'spanner' and suggest that the formulae to calculate ship resistance and powering might be similar to the 'slippery' ponderings you are having?
William Froude's laws maybe applicable. I quote "Froude considered that the total resistance (Rt) of a model or ship could be subdivided into two parts with little interaction, and each part being subject to different scaling laws i.e. resistance due to skin friction (Rf) and resistance due to wave making known as residual resistance (Rr), such that Rt = Rf + Rr. (J Craig Osborne, 25th, January, 2007)".
There are then Froude's empirical formula for frictional resistance Rf = f A V 1.825 and further proportional relationships, with speed being the square roots of two vessels lengths and the resistance of the two vessels being the cubes of similar dimensions. These are all summarised from the pamphlet purchased at the museum.
Can you treat air the same as a liquid? Because, I perceive them to be similar in their movement when an object passes through them. The mathmatics appear simple, but I do not know if they are applicable?
Maybe reference to something in this 'Google' search will do the job; "wind tunnel simulator".
All of it way beyond my CSE Maths of 45+ years ago! ;)
Good luck with your deliberations and hypothesis.
My regards, Bill
-
Nice one bill.
Is that the same froude as in the water dynamometers I wonder?
I think you are right to associate the two mediums, but only to a point. Gas is compressible for one thing.
The thing with acceleration and reaching a theoretical top speed is that as you near the top speed figure the rate of acceleration tends to slow down. So when you're dealing with high weight and little power the last little bit of acceleration takes (seemingly) forever, so in the real world it seems that you never actually make it. The theory says, given the right amount of time and perfectly stable ambient conditions, you will make it.
One thing I do know is that crazy frog is a gentleman and I respect his opinion.
Cheers
Andrew.
-
Read an article recently, about aero drag and motorbikes. Saying how unaerodynamic a motorbike was compared to a car.
Aerodynamic, as I understand it is a concept, rather than something qualitative. So saying something is aerodynamic just means that its been designed in a way that it lessens the disruption to the airflow over it and therefore reduces drag.
Motorbikes have shed loads of bits sticking out which can disrupt flow, amongst these are indicators, handlebars, footrests, mudguards, riders etc etc. As such the air flow is more likely to be disrupted and as such could be considered less aerodynamic. (Yes there are are exceptions, but we are talking generalities here).
A car, even if it is more aerodynamic (in design), will present a much larger surface area to the airflow and as such drag increased, hence the need for more power.
Weight has nothing to do with top speed, apart from as propeller mentioned, increasing drag on the tyres.
This is getting towards my OP point. A bike has a generally un aerodynamic shape, but in its favour it is narrow and has less in contact with the ground. The losses it accrues by the air tumbling etc it seems to more than compensated for by having a narrow front and less in contact with the ground. The performance figures of a few examples seem to bear this out.
A cg125 was mentioned earlier. Its 11HP goes an awful long way compared to a car. Imagine 11HP in even a smallish car.
Turn things around. Take the power of an Audi Q7 and put it in a bike. The bike mashes it in the top speed stakes, no matter how much time the q7 is allowed to accelerate.
-
Aye Andrew,
One and the same!
Link for edification: Froude_Hoffman (http://www.froudehofmann.com/index.php/history)
Am I not correct in thinking that if you add weight (Mass) and frontal area to an object then the two act in tandem to absorb kinetic energy and increase friction with the air? They are separate and individually calculable yet produce a combined effect on the objects ability to travel from A to B in a specific time. Once accelerated the mass has no effect and has a value of zero, whilst the friction with the air continues to rise. The reverse is true with deceleration, the kinetic energy stored in the mass continues to propel the object, whilst the friction with the air is reduced. Well, in my 1 + 1 =2 world it does, although I acknowledge the abilty to distinguish and separate the influence of the 2 forces and their respective effects requires more grey porridge neurons than I can muster!
Off to "sheet alley" to rest my neurons! ;)
Arrivederci!
Bill
-
Look at the difference in power to speed on static dynometer tests. You will go as fast as the engine will rev on the rolling road but take it out on the open road with weight and no aerodynamics and see the difference in top speed. Power falls off at the top end of the rev range so it would be impossible to achieve the top speed of the engine at max revs in the same gear as tested on the rolling road. Applying resistance on the rolling road will give you a brake horse power reading. All tests will be done at maximum throttle opening and revs. As a rule of thumb 40 BHP would get you over the ton.
This may not be to relevant to what your post is about but thought I would throw it in anyway.
-
Look at the difference in power to speed on static dynometer tests. You will go as fast as the engine will rev on the rolling road but take it out on the open road with weight and no aerodynamics and see the difference in top speed. Power falls off at the top end of the rev range so it would be impossible to achieve the top speed of the engine at max revs in the same gear as tested on the rolling road. Applying resistance on the rolling road will give you a brake horse power reading. All tests will be done at maximum throttle opening and revs. As a rule of thumb 40 BHP would get you over the ton.
This may not be to relevant to what your post is about but thought I would throw it in anyway.
Good point. I think it's relevant. It proves a point. That maximum power revs will coincide with top speed. But the tricky bit is that you have to pre know what the theoretical top speed is, so that you can fit the exact gearing to coincide the two parameters. Oh eck. That is virtually impossible to know to the enth degree. On the road wind and gradients muddle up the science anyway.
-
Wow, this is starting to make my brain itch.
Great discussion though, conducted in a civilized manner and a credit to the forum.
I agree that once an object is accelerated to a given speed, it's mass is irrelevant. It only becomes relevant when trying to increase or decrease the speed again. However, in the real world rather than in the vacuum of deep space, a vehicle is effectively constantly having to accelerate to maintain a constant speed (due to frictional losses from air resistance and in it's wheel bearings etc etc. slowing it down),otherwise you could switch the engine off once you have reached 70 on the motorway, and continue at that speed indefinitely! Does it not therefore follows that mass (weight) is relevant in both reaching and maintaining a given speed, and the amount of power required to reach and maintain that speed must vary with the mass of the object.
I now remember why I hated Physics at school! I can report though that regardless of the laws of physics, I have just de-baffled and re-jetted my SLR 650 and it now sounds fantastic and goes like stink.... ;D
-
Wow, this is starting to make my brain itch.
Great discussion though, conducted in a civilized manner and a credit to the forum.
I agree that once an object is accelerated to a given speed, it's mass is irrelevant. It only becomes relevant when trying to increase or decrease the speed again. However, in the real world rather than in the vacuum of deep space, a vehicle is effectively constantly having to accelerate to maintain a constant speed (due to frictional losses from air resistance and in it's wheel bearings etc etc. slowing it down),otherwise you could switch the engine off once you have reached 70 on the motorway, and continue at that speed indefinitely! Does it not therefore follows that mass (weight) is relevant in both reaching and maintaining a given speed, and the amount of power required to reach and maintain that speed must vary with the mass of the object.
I now remember why I hated Physics at school! I can report though that regardless of the laws of physics, I have just de-baffled and re-jetted my SLR 650 and it now sounds fantastic and goes like stink.... ;D
Very good point. My understanding of the physics is that if there's no change in the inertial status quo then you're not accelerating or decelerating, imagine being in the,back of a huge truck playing ping pong. The truck is fully enclosed, travelling at perfectly constant speed on a perfectly flat road etc. You can play ping pong just the same as being stationary. That's because you are stationary, in an inertial sense. Relative to the thing you are stood in. The vehicle still needs constant but steady power to maintain the status quo against the effects of rolling and aero drag.
Dunno if that is lucid or not! On.my mobile so not easy.
-
Enough of this mumbo, jumbo. Just get out there n ride it like ya stole it I say. LOL.
-
The very reason I gave up Aeronautics and took manufacturing. The physics is mind bending!
I always like the thermodynamic approach:
Energy is never made or destroyed, only changes form.
Any process has multiple results and an efficiency ratio of less than 100 %
The bike converts chemical energy into movement, heat, noise, a bit of radiation etc. So does the car. The bikes proportions are less efficient. To add one Joule of potential to the bike you start with more petrol and the air you passed through gets slightly hotter as a percentage. Make the bike more aerodynamic ( it's a number without a unit, only used in the efficiency) and you get cooler air and a faster bike for the same petrol. Add weight and you end up with either more potential energy or less speed cos Energy is mass times velocity squared according to both Einstein and Steve Davies.
Andy
-
..........Add weight and you end up with either more potential energy or less speed cos Energy is mass times velocity squared according to both Einstein and Steve Davies.
Andy
I happen to pretty much agree with what you said prior to the bit I've quoted above. In fact the weight and potential energy thing I agree too, it's just that I think it may not be applied quite in context. I have no problem with threads drifting at all, I think it's good, but just to put my perception of the physics as follows.
Yes, more mass for a given speed equals more potential energy, but this potential energy was built up during the acceleration period and once a stable speed is reached it remains potential until such time as we start to brake, and then the energy is converted. This phenomenon I don't see changing the point previously under discussion. Namely that for a bike or car to achieve a certain max speed the factors are available power versus the combined effects of aero and rolling drag. With more weight you end up with less speed only if you allow the same time. Allow more time and eventually the same speed will be reached. Unless the extra weight has an adverse effect on either aero or rolling drag. As I've suggested, it may help!
Regarding einstein's equation, do you mean e=mc^2? If you do, C is the speed of light, is it not? A constant.
-
............Add weight and you end up with either more potential energy or less speed cos Energy is mass times velocity squared according to both Einstein and Steve Davies.
Andy
How about another approach as a response to the above. My maths only goes so far, so I'm sticking my neck out!
To know velocity we need acceleration and time. To know acceleration we need mass and a force.
The torque produced at the rear wheel produces tractive effort. A linear force ultimately. You'll need to know the mass then to get acceleration. Given a certain time you'll end up with a certain velocity. The higher the mass, the longer the time taken to reach the same velocity.
But that casually ignores the real world factors, as pointed out by crazy frog. That being that there are opposing forces all the while acting to tend towards preventing the production of required velocity. Namely: rolling resistance and aero drag. Both forms of friction, but still considered as opposing forces. I think!
Phew.
Don't know if that made any sense or even if it is right! ;D
-
Impulse: E=M V ^2
Total energy in the system is mass times its velocity squared. Snooker balls, playing marbles or Newtons cradle.
( The white ball of course runs slightly cooler, but that gets out of Newtons nice neat world into Einstein and Hawking and the mind bending stuff)
Andy
-
AAAAAhhhhhh! The bells! ::)
Regards, Bill
-
A railway engine cruises for much of its journey out of gear and that is a heavy mass of built up kinetic energy pushing the whole thing along without power. Doesn't have a lot of resistance between rail and wheel.
-
A railway engine cruises for much of its journey out of gear and that is a heavy mass of built up kinetic energy pushing the whole thing along without power. Doesn't have a lot of resistance between rail and wheel.
What you guys are on about here is surely inertia? I'm still not convinced that this applies to the scenario of a car or bike maxing out top speed. The inertia affects the rate of acceleration and deceleration. Which will affect top speed if sufficient time isn't allowed. But in that case the top speed will be false, because the vehicle would have still been accelerating as it was forced to come off the power.
The really heavy train runs on for ages, but then it would have taken a very long time to reach the speed in the first place. Either that or a LOT of power. (Traction would dictate the amount)
Crazy frog suggested that to keep maintaining top speed against the two forms of friction, we are constantly accelerating. If he's right then what you are saying would apply. But I'm not sure he is right. Think of putting an accelerometer on there. Once top speed is reached, will it show a reading? I would suggest it would show zero. You would be in equilibrium between the force pushing you forward and the net force of aero and rolling drag pushing back against you. As soon as another force is added eg more wind or a gradient, then acceleration or deceleration begins again.
-
Impulse: E=M V ^2
Total energy in the system is mass times its velocity squared. Snooker balls, playing marbles or Newtons cradle.
( The white ball of course runs slightly cooler, but that gets out of Newtons nice neat world into Einstein and Hawking and the mind bending stuff)
Andy
I can see how a heavier vehicle travelling as fast as a lighter one would posses more energy. It would cause more destruction if impacted a brick wall. Or even how a lighter vehicle travelling at a much greater speed would cause the same damage as the heavy one travelling slower. So the equation tells us something in energy terms about a moving body. How do we apply that to the context of the op?
-
Surely top speed will depend on horsepower,drag/friction and area? Two objects with identical power,drag,weight etc but different in frontal area ought to have different top speeds???
-
The overall drag is a combination of the frontal area and the drag coefficient (cd). The main problem with a faired motorbike and rider is that, its not a smooth shape along the sides, and the air at the rear is very turbulent which gives a poor drag coefficient. An unfaired bike is very poor.
Incidently the Powerbronze fairing on my XBR gave around an 8MPH increase in top speed with the right gearing.
-
Thanks for input chaps.
It seems, from using stats online as proof, that a bike, in spite of its poor drag co efficient, still trumps the car in the overall stakes, because what it looses in poor drag coefficient it seems to more than make up for by having a very slim frontal area. That fact should be heralded. (Assuming you agree!).
The influence of weight is very much under discussion.
The stats I looked at were based on power consumed to achieve max speed, I looked at vehicles who's top speed was around 130mph. Now, if we drop to the national speed limit, logically the motorbike's case should strengthen further, because at that speed the emphasis swings a lot more towards rolling losses and less towards aero losses. Does it not? Theoretically, the motorbike should really trounce a car? Is that the case?
-
Streamlining a vehicle does not have much effect below 70 MPH
-
Streamlining a vehicle does not have much effect below 70 MPH
Unless it's a bicycle. This one hit 83mph. Reduced frontal area and very thin very hard tyres to decrease rolling resistance.
(http://www.ihpva.org/graphics/land.jpg)
-
Streamlining a vehicle does not have much effect below 70 MPH
Unless it's a bicycle. This one hit 83mph. Reduced frontal area and very thin very hard tyres to decrease rolling resistance.
Chuff me! That's incredible.
Don't suppose you know if they recorded power input? Or even gearing etc?
-
http://www.popsci.com/diy/article/2005-10/worlds-fastest-bike (http://www.popsci.com/diy/article/2005-10/worlds-fastest-bike)
Gearing is going to be pretty huge - probably well over 100" - difficult to power directly so the system uses an intermidiate drive gear between the chainwheel and the final drive sprocket powering the rear wheel. Guy Martin used a similar system on a ( more or less) conventional bike when he set the bicycle speed record.
(http://cycleexifcom.c.presscdn.com/wp-content/uploads/2013/12/rourke-cycles-speed-1.jpg)
There is a formula here for working out power needed to propel a hard shelled recumbent - I'm not even going to try to work it out as it makes my head hurt but you need over 250watt to hit around 50mph.
http://www.recumbents.com/wisil/demma/downhill_physics.htm (http://www.recumbents.com/wisil/demma/downhill_physics.htm)
You'll probably also need legs like these!
(http://images.smh.com.au/2012/08/06/3530766/320_forste.jpg)
-
.........
There is a formula here for working out power needed to propel a hard shelled recumbent - I'm not even going to try to work it out as it makes my head hurt but you need over 250watt to hit around 50mph.
.......
Thanks Steve. Not looked yet, but at 250 watts it's making my theories on weight look a bit shaky. Gulp.
Ps. If you could crop the second photo I'd be obliged. ;D
-
Trawling for some back up evidence.
Not digested this yet as I'm busy filing lumps of aluminium, but quick read seems to back my case?
http://lofi.forum.physorg.com/Weight-And-Top-Speed_14909.html
-
What I want to know is how did you manage to get hold of the photo of my legs, that was supposed to have been destroyed along with my first marriage certificate. :) :P
-
What I want to know is how did you manage to get hold of the photo of my legs, that was supposed to have been destroyed along with my first marriage certificate. :) :P
Yes, your technique of kickstarting a high comp xbr with both legs really is something to behold.
-
Fantastic thread guys. Really interesting stuff, which is why I love this forum. Only wish I had the knowledge to make further comment. Now if I could only get my brother in law on here. He's been an aerdynamacist for F1 for over twenty years in Arrows/Jaguar/Red Bull :-\
-
Fantastic thread guys. Really interesting stuff, which is why I love this forum. Only wish I had the knowledge to make further comment. Now if I could only get my brother in law on here. He's been an aerdynamacist for F1 for over twenty years in Arrows/Jaguar/Red Bull :-\
That would be something.
-
I will give it a try. You never know till you ask ;)
-
Looks like this discussion has run its course, for the moment anyway.
Can I just add that in spite of me pushing the case for weight not being a factor at theoretical top speed (assuming that to be true), I believe that in the real world we will only ever be accelerating or decelerating.
Imagine you kept the bike on full throttle from the moment you left the drive. The load on the bike from wind and gradients would constantly alter. Going around a corner would add a different force vector as well as changing the gearing slightly. So the times that we would be in true equilibrium or steady state would be very short indeed.
So in that case weight constantly comes into the equation! ;D
-
Maximum speed is exactly that, the vehicle cannot go any faster, there is NO change in speed so no acceleration (which is the rate of change of speed) and as such weight has no effect.
If the vehicle starts to slow down ie decelerate then weight will have an effect. BUT, on a flat road, at the point where the speed is neither increasing or decreasing it has no effect.
-
Maximum speed is exactly that, the vehicle cannot go any faster, there is NO change in speed so no acceleration (which is the rate of change of speed) and as such weight has no effect.
If the vehicle starts to slow down ie decelerate then weight will have an effect. BUT, on a flat road, at the point where the speed is neither increasing or decreasing it has no effect.
I agree. But what I'm suggesting is that in real life weight (inertia) always plays a part because there will never be a time (perhaps not even a moment) when the true steady state situation applies. The speed will constantly change.
In a situation where the gradient goes downhill or the wind force changes to our advantage ( no matter how slight) the equation will work to our advantage and speed will rise. Next moment the opposite might happen. Basically I'm suggesting that conditions constantly change.
-
somewhere along here I lost the will to live......
-
RIP. SteveL. Another member lost. Oh dear
-
Yeah and I've been reading these threads as well. If someone invites that 'expert' along you can count me out as well. Some people do talk a load of crap. The basic principles of weight, friction (in it's different guises) and power will always effect speed. School kids can understand that. Stop trying to confuse the situation. I will not even open this thread in the future. If you find this interesting, you've got a problem.......and before you question me I used to work as a Production Tooling Engineer (BAe Military Aircraft) and teach Science at Secondary school.
Get a life, go ride your bike and accept that if you cannot go fast, get a bigger engine!
PS I'm with SteveL on this.
SteveD
-
yeah, it lost me some time ago ???
(http://images.lighterside.com/images/products/en_us/altview_large/p110754ab1.jpg)
Whatever happened to those traditional TC debate topics,
The flatulent effect of Jerusalem Artichokes?
Gas or petrol?
Lucy Verasamy ( Weathergirl)
Those I can keep up with!
-
Oh my goodness I dare anyone ?? A teacher, cos let's face it they are the font of ALL knowledge
-
Yeah and I've been reading these threads as well. If someone invites that 'expert' along you can count me out as well. Some people do talk a load of crap. The basic principles of weight, friction (in it's different guises) and power will always effect speed. School kids can understand that. Stop trying to confuse the situation. I will not even open this thread in the future. If you find this interesting, you've got a problem.......and before you question me I used to work as a Production Tooling Engineer (BAe Military Aircraft) and teach Science at Secondary school.
Get a life, go ride your bike and accept that if you cannot go fast, get a bigger engine!
PS I'm with SteveL on this.
SteveD
Ok no problems. Good lucks guys.
-
Thankfully (I'd like to think) it's a relatively free forum. Opinions are part and parcel. Diverse opinions should, in theory, make life on here more interesting and stimulating.
It is nice if things are kept civil, but strong feelings should be listened to. Heckling, in an attempt to get people to stop posting things they don't like, for whatever reason, is a very weak and pathetic tactic in my eyes.
-
In the words of our very well established parliament . HERE HERE. Well said. Could,nt av put it better myself
-
Thankfully (I'd like to think) it's a relatively free forum. Opinions are part and parcel. Diverse opinions should, in theory, make life on here more interesting and stimulating.
I may be mistaken..... but I think that's what's been going on in this thread.... and like most threads...they run their course... with good, bad & indifferent comments...
so now we're all fed up with this one.... we'll start another on :De ... and life goes on.... well for us in the uk..... not for the poor sods on rotting hulks stuck in the Mediterranean sea .....
-
........now we're all fed up with this one.... we'll start another on :De ... and life goes on.... well for us in the uk..... not for the poor sods on rotting hulks stuck in the Mediterranean sea .....
Off you go then. I would imagine that the same people who have come under attack would be the least likely to try to stand in your way.
-
.......
The basic principles of weight, friction (in it's different guises) and power will always effect speed. School kids can understand that.
........accept that if you cannot go fast, get a bigger engine!
SteveD
According to the basic principles mentioned, there are alternatives to "a bigger engine". You forgot to mention that.
Who exactly are you adressing your comments towards? Surely you can't mean the whole thread is a load of crap?
Why not explain things your way?
-
Well, you'll be glad to know, I didn't invite my brother-in-law onto this thread. But that's mainly cause he's an arrogant t@@@ ;)
-
http://www.wallaceracing.com/Calculate%20HP%20For%20Speed.php
They want an input for weight.
-
http://www.wallaceracing.com/Calculate%20HP%20For%20Speed.php
They want an input for weight.
Putting vastly different weight figures into their calculator doesn't affect required hp much at all, so I think they are estimating the difference in rolling resistance. In that case I'm sticking to my guns! ;)
Interesting to put some figures in though and watch how the power required changes alarmingly as the speed goes up. It also shows how little power is needed to reach the legal limit, with a, low drag coefficient and a small frontal area.
-
Now we are getting into the realms of perpetual motion.
-
Now we are getting into the realms of perpetual motion.
How so?
I don't get what you mean.
-
One day I will sit down and read all five pages of this thread, one day :-\
-
yes its on my bucket list too, :-\
-
I watched a couple of guys in superkarts lap the Pukekohe Racecourse several seconds faster than anyone had before. The previous tryers were in F5000 cars, F1 cars, GP bikes, you name it. Superkarts are long karts with very slippery bodywork in which the driver is more or less lying down with only his eyes visible. The engine is a water-cooled 250 2-stroke producing maybe 100 hp. The whole thing weighs pretty much nothing and has hardly any frontal area.
That probably contributes nothing to the discussion but the karts sounded wonderful.
-
I watched a couple of guys in superkarts lap the Pukekohe Racecourse several seconds faster than anyone had before. The previous tryers were in F5000 cars, F1 cars, GP bikes, you name it. Superkarts are long karts with very slippery bodywork in which the driver is more or less lying down with only his eyes visible. The engine is a water-cooled 250 2-stroke producing maybe 100 hp. The whole thing weighs pretty much nothing and has hardly any frontal area.
That probably contributes nothing to the discussion but the karts sounded wonderful.
I once saw a super kart of the day back in the late seventies race Ron Haslam around Silverstone. The kart would have had an air cooled yam twin I guess. It was just Ron on a bike against the kart, prior to the main race meeting. I think the kart won from memory.
-
I'm not sure I see zeno's stadium paradox as a paradox. I think I can accept it at face value. It seems ok to me to be able to cover unequal distances at the same time. You can choose which object you want to declare as your frame of reference surely? And have more than one going on at the same time. It happens all the time doesn't it?
The one thing wrong with it, in my eyes, is that it deals with straight line parallels. I'm not sure they exist. Anywhere.
Dunno. I'm probably wrong. ;D
-
It's hard to believe, looking at the footage, that the ISS is travelling at 17,000 mph. Or that the value of gravity is 90% of what it is on earth's surface.
A drag related thought: when a space rocket headed for the ISS takes off, once it has enough thrust to overcome gravity, is it in its interest to accelerate as slowly or as quickly as possible?
-
I think you would have to compare a motorcycle and car of the same weight for the comparison of the effect of drag to be meaningful between the two. ;)
Read a posting on bike EXIF with a lovely engineered BMW Landspeeder custom. There's a comment by the guy regarding the effect of weight on top speed. Sorry, but I couldn't help thinking of the discussion on this thread. ;)
http://www.bikeexif.com/bmw-landspeeder