June 19, 200718 yr In my case I'd have to wear such a huge helium-filled balloon that increased wind resistance at any speed would invalidate any results . Stuart.
June 20, 200718 yr While I agree that a comparison of different bikes would be a great help to potential buyers I do have to agree with Flecc in that there are too many uncontrollable variables to make meaningful testing by users viable. As Flecc has pointed out it would be very difficult to ensure the testing ground is perfectly flat, but in addition to that the biggest uncontrollable factors influencing results would be rolling resistance and air resistance, the former being influenced by road surface type and condition and the later by rider position and clothing. At a constant speed on a level road almost all of the power delivered to the drive wheel is expended overcoming the above and therefore any variation will heavily influence the results. In addition there is the effect of ambient air temperature on battery performance and, very significantly, the age of the battery to consider. Even if it were possible to test and compare bikes under closely controlled conditions I'm not sure how relevant the results would be to the very variable conditions that exist in the real world. The tests may may reveal those bikes that are either very good or very bad, but I fear would be meaningless for the vast majority.
June 20, 200718 yr Author yes I agree that judging the range would be difficult - however I disagree with your interpretation of 'power'. During an imaginary range test we can assume the motor will be running for an extended period of time at constant revs and the power that would be employed over the whole test would not be 'peak power' however high or low that may be. It would be the constant power that the motor is capable of - which for all purposes should be the nominal rated power of 200W. That quoted number must mean something after all; now whether it is quoted truly by manufacturers is another matter. flecc I did not read the tests you are refering to - but I think if there is any pedalling involved it would be highly subjective and therefore worthless. About 'judging the flat road' - I did propose a solution - do it in both directions and this would cancel the effect of any inperceptible incline and to a certain extent wind, don't you think ? On the question of road surface unless it is a totally smooth brand new road I don't think you would get too much difference, on my previous bike I did get a more or less consistent 13mph computer reading of top speed on most city roads. The point is - on other bikes this speed would be higher or lower and this would be a very important consideration when buying a bike - especially when no such data is available at the moment. FYI I live in Cambridge fenland where most roads are flat as is most of this country I find
June 20, 200718 yr science teachers searching for "fair testing" ideas could start here!! how about I get to ride all your bikes at the New Milton rally:) while you all have a nice cup of tea. I will take the winning bike home as a prize... teaching year 10 kids the 'way to do science' is supposed to get more real life contexts. This kind of discussion is exactly what we should be doing with them but it is difficult
June 20, 200718 yr Hi chazpope What Ian says is true: the nominal motor rating e.g. 200W/250W is the power the motor uses when running at maximum efficiency which occurs at the maximum loaded rpm of the motor i.e. top speed on a bike. Any extra load (work) put on the motor e.g. friction from knobbly/profiled tyres, air resistance from loose clothing, upright ride position, large frontal cross-sectional area etc. will increase the power output required of the motor and reduce efficiency too, so the exact power being used by the motor is unclear. There are meters (watts-up, drainbrain) that gauge the power output, current, voltage etc. if you want to go to such lengths. As flecc said earlier this thread... What we really need is for the manufacturers/suppliers to give us three things the correct net power output in watts' date=' the point at which peak torque occurs in mph, and the precise weight of each bike as supplied. Then a very accurate comparison chart would be easy to produce.[/quote'] ...if bike suppliers gave these very basic specifics, the overall bike performance would be very easy to calculate fairly accurately - probably much moreso than tests would reveal given the huge number of variables that need to be controlled for any results to be accurate or useful, and thats once you've decided what to test and not accounting for possible errors in measurements etc.: it really is a minefield! I'm really of the view now that dealers and manufacturers simply must give this information: if not, how can anyone judge a bike's capabilities? Relying on impressions or reviews simply isn't good enough. I have to consider lack of information as either an indication of weakness of product for purpose or lack of expertise/professionalism, and view it exactly as I would lack of product support & development when problems are identified. For now, its probably best to have a good idea of a bike's performance if possible e.g. from asking/reading here, then try it out, preferably on terrain similar to your proposed use. Stuart. Edited June 20, 200718 yr by coops
June 20, 200718 yr teaching year 10 kids the 'way to do science' is supposed to get more real life contexts. This kind of discussion is exactly what we should be doing with them but it is difficult Just to add to my last post, the upside of the dificculty of getting useful results from "tests" is that, so long as the bikes behave the way they "should", it is really quite easy to estimate their performance from those few specifics. It is far simpler to start with bike & motor performance specs & then guestimate, with good enough accuracy, how a given rider will affect performance, than to try do it the other way round i.e. estimate a bike & motor performance from tests which by nature will have many (unnecessary) variables reducing accuracy, making measuring much more difficult & harder work than it need be. Much better to isolate the unneeded variables e.g. road surface, gradient, tyre type, rider weight, frontal area, clothing, wind speed, temperature, battery age & charge state, bike condition, bearing friction, sticky brakes etc. etc. for clear, accurate results & then extrapolate to the other variables as needed. Which is why we need those specifics. ADDED: a motor torque graph plus bike weight is enough. Stuart. Edited June 20, 200718 yr by coops
June 20, 200718 yr flecc I did not read the tests you are referring to - but I think if there is any pedalling involved it would be highly subjective and therefore worthless. Some bikes (all, if the EU bureaucrats had their way), including the new Ezee Forza are pedelec only, ie they must be pedalled, so comparative testing would be difficult. FYI I live in Cambridge fenland where most roads are flat as is most of this country I find I agree the fens are mostly flat, plenty would disagree about that applying to most to the country though. What Ian says is true: the nominal motor rating e.g. 200W/250W is the power the motor uses when running at maximum efficiency Flecc said it actually Stuart, but it is certainly true so I don't mind The problem is that by definition the motor is there to assist the rider, these bikes are not motorcycles and are meant to be pedaled(One of the fastest bikes available can hardly start without the rider pedaling), therefore testing without pedaling will not show the performance of the machine in the context which it is designed to be used and the results could be misleading. likewise, as you say, pedaling does introduce another imeasurable variable making the results meaningless. If all bikes were designed to be the same then there may be some value in comparative testing but that is not the case, bikes are as different as the people who ride them and the terrains over which they are ridden.
June 20, 200718 yr And of course, some have to be pedalled with some effort put in for them to work at all, the Giant Twist series for example, based on Japanese law requiring rider and motor power are at 50/50. For those bikes the test would be meaningless.
June 20, 200718 yr Author What Ian says is true: the nominal motor rating e.g. 200W/250W is the power the motor uses when running at maximum efficiency which occurs at the maximum loaded rpm of the motor i.e. top speed on a bike. Any extra load (work) put on the motor e.g. friction from knobbly/profiled tyres, air resistance from loose clothing, upright ride position, large frontal cross-sectional area etc. will increase the power output required of the motor and reduce efficiency too, so the exact power being used by the motor is unclear. Yes Coops but this is the whole point - when the bike is constantly running at its max speed - then it is using its full power - and this is what its nominal power is - because through gearing, wheel size etc the bike is designed to do just that. When you turn the throttle from stop - the bike accelerates until the increasing load consisting of friction, gears wind etc becomes equal to the power that the motor can supply in a continuous (not momentary, peak etc) mode - then you have a ballance of power whereby the power supplied at the motor rotor is equal to the torque * rpm required to push the bike ahead at that particular speed. so my point is - when the bike is running at its full/throttle/speed - then it is using it full and nominal power, give or take a few design faults. This assumes of course that the speed limit cut off point is not reached. in other words if two 200W bikes of different make attain and maintain their respective top speed you will have a case where both motors are supplying the same 200W of power. The more efficient bike will be going at a higher speed but the power used will be the same. so therefore - the bike that can attain a higher speed on the flat will also have a longer range - because (given the 2 batteries have the same capacity) the range-running time for both bikes will be the same, proportional to an identical capacity/power ratio. hope that clears this academic point Re whether or not we need these tests - it is the same as with a car - it has a nominal bhp rating but also a 0-60 and top speed rating that tells you about its mech and aero efficiency and overall performance - and those fugures do matter when choosing a car.
June 20, 200718 yr Tests In my humble opinion all tests under throttle only and otherwise are very important. These could easily be achieved if all bike retailers, agents and manufacturers were to get together and trial their bikes under strict supervision. We could all meet at a central point with a flat low friction surface - say Silverstone, and run all the bikes through their paces. Maybe we could ask a local university to run the trials for us. We could also get one rider to ride the bikes flat out over half a mile to get some results for pedelec mode. Wisper would be delighted to take place in such trials but I dare say we would have butterflies all day! I would imagine however that it would be tough to get every one to enter their bikes as there has to be a winner, and a looser at the end of the trial! I would imagine that some myths would be exposed. There would of course be an expense but I would think that any one representing a particular bike would be happy to stump up £100 or so for the day. I believe that tests like this should be carried out annually and maybe Pedelec would like to host them and give a stamp of approval to all bikes tested. We for one would love to have fair comparisons done. If we weren't the best it would spur us on to improve for the next trials, I imagine everyone involved in the industry would feel the same. If anyone was particularly nervous then perhaps the first year's results could be kept private? Wouldn't that be a great way to ensure that we are all doing our utmost to ensure our bikes are as good as they can be? If anyone else is interested please drop me a line and I will get it organised. I imagine you have all heard that the Chinese government have just introduced a 4% export tax on electric bikes. This will be in place from the 1st July so expect price increases. Best regards David Edited June 20, 200718 yr by Wisper Bikes
June 20, 200718 yr so my point is - when the bike is running at its full/throttle/speed - then it is using it full and nominal power, give or take a few design faults. This assumes of course that the speed limit cut off point is not reached. in other words if two 200W bikes of different make attain and maintain their respective top speed you will have a case where both motors are supplying the same 200W of power. The more efficient bike will be going at a higher speed but the power used will be the same. almost all bikes will easily reach the UK limit without reaching maximum motor power simply because it requires somewhat less than 200W to overcome friction, drag and rolling resistance at 15.5 mph. The limiting factor is usually the maximum rpm the motor can attain at the applied voltage. In cases where the motor can achieve higher rpm an electronic limiter is fitted. If one bike can attain a higher speed than another on the flat then that is not an indicator of better efficiency, just a difference in design or materials. An example would be if a motor had weaker permanent magnets then it's maximum rpm at a given voltage would be faster than the the same motor with stronger magnets, but it would be less efficient under most conditions. The 200/250W rated power of e-bike motors has absolutely no meaning other than to satisfy the legislation and is derived at simply from the fact that an average of 200W is all that a motor needs to supply to propel a 15.5 mph limited bike on a typical journey. Most motors are capable of supplying 2 to 4 times the nominal 200W and will do so continuously in sustained hill climbing, but as stated above will only be delivering something like 170W at the legal limit on the flat.
June 20, 200718 yr in other words if two 200W bikes of different make attain and maintain their respective top speed you will have a case where both motors are supplying the same 200W of power. The more efficient bike will be going at a higher speed but the power used will be the same. hope that clears this academic point Clearing an academic point? You have to be joking. A motor's nominal power of 200 watts is NOT it's peak power, and peak power is NOT a momentary peak. For example, if the nominal 200 watt Powacycle Salibury and nominal 200 watt eZee Sprint accelerate to their respective top speeds, they aren't using 200 watts. The peak power of the Salisbury is 272 watts and the Sprint 500 watts, but both delivered at lower speeds. I've pointed this out to you before and observed that the 200 watt legal figure is purely notional, not a scientific measure of motor power. You've chosen to ignore that which is fine is you wish to believe in a fantasy, but it's wrong to potentially mislead others in this way just to promote this performance measurement idea. If your performance measurement idea has merit, it should stand on it's own, and not be supported by pseudo science. P.S. I've just seen that Ian has got in before me with the same correction. I do hope you take note of it this time. . Edited June 20, 200718 yr by flecc
June 20, 200718 yr I imagine you have all heard that the Chinese government have just introduced a 4% export tax on electric bikes. This will be in place from the 1st July so expect price increases. Best regards David And there was us thinking, expect margin decreases. .
June 20, 200718 yr In terms of determining the range and hill-climbing ability of ebikes, the best approach I can see is to look at the relevant contributions of each part (rider, bike & motor) separately & then to add them up. Given that the basic "bike" part is sound, a motor torque graph, plus bike & rider weight, plus tyre type, and bike gearing are enough information to quite easily get a very good idea of the performance. It's interesting what you say chazpope, because I was asking a closely-related question recently, regarding hub motor design, torque & speed and your point illustrates how hub motor design can, it appears, affect the usefulness of the torque it produces, and so highlights the trade-off between low-speed torque for efficient hillclimbing or high-speed torque for maintaining a speed on the flat. I agree with you that, all other things being equal, the bike which maintains a higher speed on the flat for the same power output will have a better range, and is more efficient - on the flat. But... as Ian said it will be less efficient under most conditions: the gain in range on the flat will be quite small, and the loss in hill-climbing ability and range in mixed terrain with moderate to steep hills on the same bike will be much greater, due to it having torque for maintaining speed, not climbing hills, making it a poor choice in general for use on other than gentle slopes & flats. That's just one way that hub motor design can affect the overall capability, efficiency and range of ebikes: there are others: The steepest slope manageable depends largely on the motor's peak power output, the speed(mph) at which that occurs, weight of bike & rider & gearing/pedal contribution. The range in hilly terrain depends largely on how much and how fast the motor's efficiency drops as the speed drops from its point of maximum efficiency and revs (also minimum power) on the flat to its point of minimum useful efficiency (and maximum power) at the peak torque point. The lower the efficiency at or near peak power, the more energy is used to do the same amount of work: usage goes up, so less distance can be travelled for the same amount of energy. A bigger battery may take you further, but will not improve your efficiency & will be unnecessary extra weight if a better, more suitable & efficient motor could give the same range as the heavier battery. A bike efficient for hills should also handle headwinds ok. Range on the flat with no wind, for the same battery capacity varies less than in hills and is easier to calculate, any good motor running close to maximum efficiency at normal cruising speed. Stops & starts may impact efficiency/consumption, & thus range, on some bikes more than others, but those could be picked up on quite easily, and in most cases the style of riding (throttle use etc.) can be modified or learnt to get best range from them. That covers some of the motor aspects. Put all the pieces together & add the rider & bike contribution elements & you get a good picture of the overall performance for each bike. Until you get a puncture or crash . Stuart.
June 21, 200718 yr Tests Surely amongst all you Pedelec Wizards there must be some consensus of opinion on what would constitute a good unbiased test! We are all agreed that we need one. As I said in my previous post I am sure all committed Pedelec manufacturers would be delighted to test their vehicles on an even playing field (even if it had a 3% incline ) and pay for the privilege. How many components should the test have? If we could initially agree on that we would have a starting point. All tests should have a rider weighing 75kg with weights making up the exact 75kg They could be. (Suggestions taken from previous posts) Throttle only 1. A timed 0 to 100m 2. A flying 100m 3. An incline to be decided over a given distance. 4. A range test at 15.5mph on a circuit. Regarding the pedelec mode, it would be simple to rig up a rolling road with resistance control and apply an 240v A/C electric motor to the crank with torque control, this could be regulated quite easily. And put a weight on the rear rack to stop tyre slippage. Run all the tests three times and take a mean average. All the Pedelec tests would be based on 0 to 100m. What do you think? Too simple? Beast regards David
June 21, 200718 yr No tests are needed in my opinion David. All we need are first. the power curve for the motor with consumption and net power plotted against watts on the vertical axis and mph on the horizontal, and second, the bike's weight as sold complete with battery. That gives us the maximum speed and the hill climb/towing capability. From that, ranking charts can be produced in moments which could include the variable of rider weight, without which any test results are useless. For example, on bike X, I at eleven stones weight can climb a sample steep hill in bottom gear contributing 100 watts, very easy. A sixteen stone rider on bike X would need to expend 350 watts to do the same, which could well be impossible for very many riders. Thus a good climbing bike for me could be a completely useless one for some, illustrating why provision for rider variations is essential. Ridden tests would be less accurate for comparison due to variables like air conditions, temperature which can affect batteries adversely, road surfaces and unmeasurable small incline variations, tyre pressures, rider bulk and clothing etc. Furthermore, a test on one incline won't easily indicate to a prospect a bike's ability on very different inclines. I could easily set up a cheating status with any bike and circumstance to put it in a better position on any surface test. The figures I'm asking for cannot be fiddled without subsequent risk of exposure, they are so easily checked. Technical details on power and weight is what the highly experienced motor industry has supplied for many years, and I think we should learn from their considerable experience and knowledge. As with them, we can leave the road testing to the independent magazines. . Edited June 21, 200718 yr by flecc
June 21, 200718 yr In my view the only valid test would be a scientific measure of the efficiency of the electric drive train over the entire operating range. The only way that could be done would be to put the bike on a dynamometer in a lab, something the better manufacturers can do but is beyond the scope of the average user. All bikes are designed differently, some for speed, some for range, some to be inexpensive, some to comply with legal requirements in various countries, some bikes are designed for use by experienced cyclists who don't want a lot of help, others are designed to emulate mopeds. They will all perform differently, but to publish a simple comparison of performances would be very misleading, the tests done by experienced independent reviewers who can interpret the results are far more meaningful.
June 21, 200718 yr Hi David, That's an interesting proposal you made for an ebike "trials" event and I'm sure many here would welcome the chance to try out many different bikes in well-designed "trial" conditions (hopefully we'll come up with some crackers, don't you worry ) if it can be organised. I don't think there would necessarily be a single winner or loser in such a trial; while some bikes may be better "all-round" performers, others may excel for a particular use and such trials should help to show that. Flecc and Ian got there first, but I think we're speaking on the same lines: While I am in favour of trials to test the feel of a bike & its performance, the most important ingredients of a good bike are good design & quality components and build: in my view, any tests or trials, public or private, should be to verify that the design works and the build is durable, and if they are both ok, then good performance should follow :-). Styling & feel are subjective, but with performance everyone speaks the same language . It would be advisable for anyone to re-read this entire thread before posting test proposals: as said before, the performance of an ebike, including energy efficiency & range in any terrain, maximum/most efficient speed for climbing any given gradient, top speed, steepest gradient attainable for any given fider, can all be fairly easily and accurately calculated from the design, and so tests would simply be a confirmation of how well the design works & the quality of the parts used, and that has practical benefits: a range test not strictly necessary, for instance, because if the power consumption for different gradients is measured a good estimate of range can be easily calculated for terrains of different levels of hilliness for riders of different age & ability, taking into account the assistance the bike's own gearing gives too. So again I say, since real-world measurements are rather too messy to give reliable, accurate results which can be used to determine likely performance for a given individual, your test proposals are not too simple, but rather are unnecessarily complicated. It would be far better for manufacturers to give full information relevant to performance, and to have confirmed their designs are working & evaluated these figures beforehand in a controlled way, so that any tests/trials are just that, not measurements (and then they'll be a more relaxed and enjoyable experience too :-)). I'm sure the side-by-side results of any trials should then be a reflection of the performance figures; they should certainly not be the prime source of them, since that puts the onus to prove performance on the individual, not the manufacturer, and with all due respect that will not do . I am encouraged that you show keeness to ensure that you are doing your utmost to ensure your bikes are as good as they can be, you are clearly enthusiastic about them and I wish you success . With best wishes, Stuart.
June 21, 200718 yr Author almost all bikes will easily reach the UK limit without reaching maximum motor power simply because it requires somewhat less than 200W to overcome friction, drag and rolling resistance at 15.5 mph. Ian do you mean all this in conditions without pedalling ? My experience with 4 Cambridges and 2 Salisburys is somwhat different from what you describe. The Cambridge gets up to about 12-13 mph, haven't got a figure for Salisbury, but it is slower by at least 10%. If you then start pedalling the motor is happy to help you up to about 15 miles and afer that you are on your own. During this transitional period I can see that the motor current drops (battery voltage goes up) - because now the total torque is split between the chain cog and the motor and the motor draws and delivers less power. So why do you think that is ? Both look like commuter bikes - designed to cruise on the flat - no point to put the peak power at the low revs point. Because the top throttle speed I am getting is less than the legal limit I assume at that point (where the motor is running out of steam) it delivers its maximum continuous power, also I would think the bike would be designed (geared) to do that ? Even if this is not the 'peak' power - it is the 'kind of power' that I think most cyclists are interested in. I am also considering that on the flat the power required is greatly and non linearly affected by the speed. As an example - according to some math models that claim to be reasonably true - to get from 12.5 mph to 15.5 mph you would need 50% more power, that is an awful lot. So my interpretation of this is that the max throttle-only speed is defined by the motor power rather than its top rpm spec ? In my earlier post I suggested only 2 tests. I am not at all sure to what extent if you can derive the range from these, I am simply trying to have a discussion about it, far from trying to promote it with pseudo science as some test-sceptics would suggest. However I think that the 0-100 and flying 100m tests would (to a potential buyer) be very indicative of the bikes overall performance. The 0-100 test would put the bike through its torque curve, peak power will be reached at some point during accelleration. The second test - whether or not related to 'power' - would be also in my opinion a very important buying point - after all you don't want to be overtaken by people with 'normal' bikes on your way back from work. Right now if I have to choose between Cambridge and Salisbury (both rated 200W) on the blind - what have got to go on ? Having these figures will make my decision much easier. Also I 'promote' these tests because I believe they could be at this stage easily done by bike owners rather that manufacturers and hopefully manufacturers will get the message and start quoting some meaningfull figures. Looking at bike models you find that 5 kg +/- in cyclist weight adds or takes only 2-3 Watts, so no big issue with varying weight there. Speed on the other hand - especially above 12 or so mph has a much greater effect on power. Publishing torque curves would of course be nice but what good would it be to the general buyer - also consider the fact that the controller has a play in it as well doing voltage or pulse modulation. I am not sure how the motors are driven but 'constant voltage' theory may not always exactly apply. At this stage I think it would help the discussion if we had some figures from interested participants.
June 21, 200718 yr Figures. In a typical case of an eZee Quando, the motor power rises as speed increases to a maximum of about 470 watts net at 8.6 mph. From then the power gradually declines, down to about the 170 watts at 15.5 mph that Ian mentioned in a post earlier. The 470 watts point is also the maximum torque point at which it's climb limit exists. The point of maximum efficiency is just short of the 15.5 mph, that not referring in any way to maximum power but to the lowest use of current relative to power. In other words, green efficiency, not the Top Gear variety. The above is broadly true for all our bikes that are geared to attain roughly the legal limit. I'm sorry that you just don't seem to want to accept that relationship of speed and power, but I can only post the facts. A to B magazine agree with you in their test on the Windsor, the step through version of the Salisbury, in that they said 13 mph was about it, though it would run on to 15 in favourable conditions. The basic problem is that it's one of the lowest powered bikes around at about 270 watts maximum, so is geared accordingly. As said before, the only difference that Carl of Powacycle observed on the Cambridge was a gearing difference. Since any of these motors have an optimum gearing, I assume the poorer performing one is that one that differs from that optimum. .
June 21, 200718 yr Flecc has illustrated above the fact that maximum power does not (and the laws of physics say it cannot) occur at maximum rpm in the case of a permanent magnet motor such as used on bikes. I do see your point wishing to see comparative testing but due to fact that most machines are designed to pedalled testing them without pedalling is meaningless and will give very misleading results. For example I own two bikes, both have the same meaningless nominal power rating. Bike number 1 can be ridden like a moped easily reaching 16mph on the flat. Most of the time the pedals serve merely as footrests, only needing to be used on the very steepest hills. This bike would perform very well in your proposed tests and has received excellent reviews although has no outstanding achievements to it's credit Bike number 2 is reluctant to pull off without assistance, accelerating slowly to 10 mph above which it performs well until a hill is reached. This bike would perform badly in your tests and yet an identical example has won the tour de Presteigne on both occasions, has successfully completed the Royal British Legions annual London to Paris ride and has numerous other accolades to its credit. The reason being that it is designed to pedalled, and when ridden as intended will wipe the floor with most of the opposition, but it will not perform without being pedalled which shows how pointless such testing would be without an experienced and unbiased reviewer to qualify the results. A further factor which no amount of theoretical testing will reveal is how "ridable" the bike is, in the case of my bikes number 2 is the most ridable and fun by a very large margin.
June 21, 200718 yr Ian do you mean all this in conditions without pedalling ? Yes, he does! (correct me otherwise Ian) on the flat at least :-). Almost all bikes that can reach the legal limit of 15mph, more or less, should consume less than 200W gross at that speed for the reasons given, unless they are rather inefficient. Your bikes are most likely either lower geared or lower powered or both. So why do you think that is ? Both look like commuter bikes - designed to cruise on the flat - no point to put the peak power at the low revs point. Yes there is, unless you never need to go uphill! (but you are lucky in that respect!) Peak power/torque for a hub motor is usually around mid revs anyway, and any gradient requires power roughly proportional to the speed you climb at, so any bike will climb better the lower the speed its peak torque occurs at. Even if this is not the 'peak' power - it is the 'kind of power' that I think most cyclists are interested in. Only if you never need to go uphill! (ask flecc, he'll tell you about hills!) - I see a pattern developing here if you've ever had to cycle uphill, you'll know it takes much more power than on the flat. Most hill-capable bikes have peak power of ~5-600W. I am also considering that on the flat the power required is greatly and non linearly affected by the speed. As an example - according to some math models that claim to be reasonably true - to get from 12.5 mph to 15.5 mph you would need 50% more power' date=' that is an awful lot. So my interpretation of this is that the max throttle-only speed is defined by the motor power rather than its top rpm spec ?[/quote'] Yes, thats pretty much it: the 50% increase sounds a bit high, but from 15mph to 20mph power consumption on the Torq doubles . The max throttle-only speed, as you pretty much explained yesterday, occurs when the forward driving force of the motor (through the tyres) is equal to the retarding forces opposing forward motion, mostly air & road friction. The motor's driving force depends on numerous factors including power output (voltage x current), gearing and efficiency, not totally unlike a cyclist except an electric one with a fixed riding style . Essentially the motor's design dictates what speeds it runs at with what torque & efficiency. You're right that we have no definite criteria by which do judge one bike from another, because we are not given the performance information to do so; we aren't even given enough information to calculate performance ourselves! But I could tell you that those bikes are low powered and which would have more power, from information on those and many other bikes in this forum, and none of it based on a useless 200W rating. It would be better if suppliers and manufacturers gave us real performance figures rather than leave us largely to guesstimate like we have to. The absolute minimum information we need has been specified earlier in this thread, several times.If I had just that much information for any given bike I could tell you, quite accurately, how fast it can go on any gradient, how far it can go in any terrain, for any battery type & capacity, for any rider of any age and ability and for any tyre! Is that enough?! Looking at bike models you find that 5 kg +/- in cyclist weight adds or takes only 2-3 Watts' date=' so no big issue with varying weight there. Speed on the other hand - especially above 12 or so mph has a much greater effect on power.[/quote'] I don't understand what you mean, chazpope, do you mean on the flat? On hills weight increase adds proportionally to the power needed, so if you're twice the weight, twice the power needed. Publishing torque curves would of course be nice but what good would it be to the general buyer - also consider the fact that the controller has a play in it as well doing voltage or pulse modulation. I am not sure how the motors are driven but 'constant voltage' theory may not always exactly apply. Yes, I accept that, which is why I've tried now to lay it out as a "worst-case" scenario: preferably we should be given both performance figures and raw data, but the raw data is more useful since we can derive the results from them, whereas we all know where "up to 30 miles range" gets us voltage variations and the like can be accounted for quite easily, unlike the large number of unaccountable variations from trying to measure performance from the bike itself. Stuart. Edited June 21, 200718 yr by coops
Join the conversation
You are posting as a guest. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.