How to calculate the power loss of a poorly inflated bicycle tire?
Once again, I felt like I was barely making any progress and had to re-inflate my tube.
How many watts does an under-inflated tire actually produce? It depends on many factors, but how can you practically measure and calculate it for yourself?
Thanks to pedelecs/bike monitors/apps, you now have more data available than with a bio-bike. A colleague and I think we've found a mathematical solution for this. But I'd like to ask again if you might have a suggested solution. One is often blinded by one's own path.
Background : You could simply compare the wattage of the entire route. However, I discovered that too many parameters vary (wind, traffic lights, etc. suddenly come into play). You could also try keeping the speed constant and simply adjusting and reading the power accordingly. However, that's more difficult than I thought, especially since you also have to pay attention to traffic. It's therefore easier to simply pedal at what you normally pedal, which for me is an average of 200 watts, and then read the speed. This results in the following…
…parameters :
- same section of route in a wind-protected zone without e-support
- System weight (pedelec+rider+luggage) approx. 150 kg (does not play a role in our calculation)
- Top speed of "poorly inflated" tires 18 km/h (approx. 4.3 bar)
- Top speed of "well-filled" tires 25 km/h (approx. 5 bar)
- Pedal power (Ptritt) each time approx. 200 watts
So, I lost speed due to the poorly inflated tire (4.3 vs. 5.0 bar, by the way), even though I put in the same amount of power. So, how many watts am I losing due to the poorly inflated tire?
(2 votes)
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That’s the same when you get the performance up and the speed goes off.
You even get an additional factor in yourself: At a different speed, you have another air resistance, and that’s even a square relationship! At 18 km/h you only have half air resistance as at 25 km/h…
Right. This has the advantage that the air resistance remains the same.
I don’t understand the problem. It should be clear that one makes such a comparison on any field path, where one does not encounter a sauce, there are no lights and the like.
There are hundreds of thousands in Germany.
First of all, I find it amazing that you get only so low speeds for 200 W. So I know I’m sure I can’t kick 200 W all day, but I know I have a whole day with one Averagespeed of 26-28 km/h can be…
Secondly, I think it’s amazing that you were faster with the plated tire than with the badly pumped up.
And thirdly, the life experience from 20 years of cycling simply contradicts the idea that a 14 % reduced air pressure sometimes “freezes” 28% of the speed.
Much less than you think.
There is a beautiful side bikerollingresistance.com. They measure the rolling resistances of individual tire models at different air pressures. The method does not correspond 1:1 to the real conditions (the fewest cyclists drive around 1 m large metal rollers), but one gets an idea of the magnitudes.
The Trekkin handles between 4.1 bar and 5.2 bar Tire pressure about 3 to 4 W Difference. So all 2 % of your allegedly delivered trespass.
No, you won’t get 28% slower because of 2% less power you can use against the air resistance.
___
I think it is more likely that your 200 W will not vote. Firstly, this is too much power for too little speed, and secondly you will have achieved different performance in both attempts. And that the lower air pressure was only a small side effect of this difference.
Even if you have a very accurate watt meter, you won’t be able to perform a constant performance. Especially since the expensive watt meters have only an accuracy of 1-2%… which is about the order of magnitude in which your increased rolling resistance moves at a slightly lower air pressure.
But you can keep a weight constant and if you roll the same distance again and again, you also have a constant gradient. This results in a constant slope output force.
So I’d be looking for a gangway that I can just roll down. Without traffic and without curves, so you don’t have to brake. Not too much gradient – much faster than 10-15 km/h you shouldn’t be because otherwise the air resistance will ruin the test. And instead, of course, as long as possible; the difference between 120 and 125 seconds of rolling time is easier to capture than the difference between 12 and 12.5 seconds of rolling time.
And then, in order to reduce the influence of individual wind blows or the like, I would carry out every roll test several times. So 5x with high and 5x with low air pressure.
Well possible. Bosch certainly also means the value so that the value does not always jump up and down.
Good idea. Although not directly on the route is much closer than a possible field path. Just a way up the hill…
Good points, but unfortunately we have only 1 to 3 km and then always equal to 20% gradients (with traffic). Therefore, the desire for a solution on the working path. But I can well understand your points. Find your experimental setup very interesting, though not yet feasible for me at the moment. But what currently can’t be done. For now, however, a credible calculation has to be made. Thanks for the input!
Let’s see if I can answer it in a slide or have to split it in time…
No, there are no traffic lights and co.
I haven’t thought about it yet. Thanks for the hint!
On the way to the field, the conditions are not only completely different from on the commuter road to work, even the conditions cannot be kept constant there, since 1 cm deviation from the first track could already be x stones/slamm/… more or less. I would also be exposed to openly changing winds, which I am less/not in windproof road. Apart from that, I wouldn’t have the time or would be on the move with followers, which makes the result even more complex.
Nobody says I’m driving a bike all day. I have to work too. Also I don’t know how hard you are, what kind of bike you drive and you don’t even drive the same 500 m route I used for this. I think comparisons are really hard. If, however, the comparative section of the route is always identical for the calculation.
Was a copy error, see pressure: 4.3 = slow, 5 bar = faster.
I’ve never been cycling, and maybe there’s the problem. Then you might have been driving a race bike and I’ve always been MTB and City Cruiser. We would have completely different tires, weights etc. But because I’ve always felt so much different and finally could read it on a tacho, I really wanted to figure it out.
This shall be calculated. 🤗
I’ve already pushed this side. My tire isn’t here. Unfortunately, they always use only 42.5 kg as weight. However, I have not found any site where the weight had been changed. This influence is missing completely there.
Maybe the rest of your air resistance will come. In addition, I drive 50-622 Schwalbe Big Ben tires and no trekkin grips. Could also be a factor. Of course, there are still measurement errors – so I can of course not guarantee constant wind silence. Here I have to make a comparison more often to exclude more measurements. But before I make the effort, a good way of calculating would be worth knowing and this could be closer to reality than artificial laboratory measurements.
It’s possible. I guess the 200 watts should fit. I don’t have a sports bike. In order to turn the crank with my belt, I only need 0.6 to 0.7 kg and my hub gear will also swallow something.
The air resistance I have mentioned, which is only half as large as 25 km/h at 18 km/h, means that you have only half as much energy left to overcome it and therefore cannot become faster. Which means that the part of your performance you invest in is missing half the power. This part is either performed less from the outset or is obtained when other resistances are overcome which were still smaller beforehand.
Speak: If you step 20 W against the air resistance and 10 W fall away against the higher rolling resistance due to a lower air pressure, you only have 10 W against the air resistance and accordingly achieve a lower speed.
The point is that at 25 km/h you have not only 20 W against the wind. And not exactly 90% of your 200 W for the rolling resistance.
But that the tires 10 W more “eat”, that is a realistic order of magnitude. Again, you misunderstood me:
I didn’t want you to look after your concrete tire. Or after a certain pressure. It’s because you’re looking at what size it is. So whether you talk about “zig” watts or just a few watts.
One time, in order to make basic considerations of plausibility and one time, to make fundamental considerations about the experimental conditions.
As said, that you have only 20 W air resistance at 25 km/h and 180 W other resistances is unrealistic. This would be necessary, however, for 10 W more rolling resistance to slow down to 18 km/h.
And, as far as the experimental conditions are concerned, you try to determine a difference that is a few percent. It should be clear that you don’t come with a “pi mal thumb, will fit” test setup to a meaningful result.
Weight only plays a role if you want to compare certain air pressures. In the end, as I said, it is about the rolling behavior of the tire. Whether you are looking at a lower weight at lower air pressure or a higher weight at high air pressure, it is completely wiped – as long as the tire equally strong walks, you come to the same rolling resistance from the tire.
And again the hint: I’m talking about you Number the multiresistance to be expected.
A calculation can never be better than the values you calculate. Therefore, if you expect readings that have a large error interval from the outset, you will necessarily get a high error interval even in your calculation result.
And this cumulates: If you have ±5 % in the wind, when the tyre pressure (if your manometer has been calibrated last time?) ±5 %, when the power measurement is also ±5 %*… then you have to expect your calculation result to differ by 15 % from reality.
(*EDIT: After a search, I come to the impression that the Bosch Kiox performance measurement probably has up to 10% deviation, especially upwards)
For this reason, one should build up a calculation as much as possible on secured data (e.g. a recognized computational model for the walking behavior of bicycle tires) and if empirical values are computed, then it should be seen that they have the highest possible quality.
It has its reason that scientific investigations usually take months. That’s not because it’s so slow! In order to obtain the required empirical data, it is necessary to establish a test with as little uncalculated influencing factors as possible.
I made it and I came to the conclusion that my feeling on the street says something else – which of course can deceive. And that I do not find any comparisons on the Internet, as they are too idealized and possibly too low. But it is still a good idea to assume that I might only find small differences.
I’ll give you the right. But I can’t even know how to build the test without a computer. I don’t know what parameters I should take/constant. But we will help your and the input of the others.
With skillful computing path and experimental setup, a lot can be eliminated. For example, I always use the same pump, apart from the fact that I don’t care about commuters. The air resistance is actually something I underestimated. I really need to repeat the measurements in time. But my pedelec will help me too. If I hadn’t been driving up the mountain before, it shouldn’t be a problem with Pedelec.
What makes you think you have a specific link? But even if I don’t see it as a problem. As long as the value is always exceeded by, for example, 10%, the error is eliminated again in comparison.
I definitely need to improve the experimental setup. But I haven’t seen a reason when I don’t have a plausible calculation model yet. Not until I get this, I’ll do more work.
I didn’t say anything else. On the contrary, I am aware of this. Therefore, my original desire to be able to do this on the way to work or back. Because I’m quite sure it could cost me a lot of attempts. You don’t just do that. That’s why I ruled out that field. And because it can cost a lot of effort/measurements, I would like to have a reliable calculation formula with the data that can be collected to me. Only then I know if it’s worth it. And even if the rolling resistance turns out to be a zero number, then I will be able to learn more from the others personal large or small influencing factors.
According to this link (at Optimum and on a Holland/Citybike) there are 80 Watt difference. grafik3.gif (530×494) (klara-agil.de) So I would have to count this 80 watts off the “good” tire or on the “bad” tire. But that would be very big. So I have to start from a measurement error on my part. I have hardly made repeat measurements (only 2 times with low pressure and once with better pressure on the same section). Then we come back to the test setup where you already had some good tips.
Thus it is in theory and via test stands (with unfortunately too little loading and other tires). It’s just my curiosity to find out again and to really measure it out in the field outside and maybe it comes out that the pedals or something else are more of the cause of the power eating or maybe there is no power eating at all and everything just feels or depends on the day form and was just accidentally connected to the tire. After all, I’m just looking at the tire when it’s hard and not when it’s easy – who knows.
I’ll give you the right. But I already said that in this table I lack various load cases. Maybe the spreads would be much bigger if there was more weight (as with me). Also comes factor real road vs laboratory. But yes, this may help to find out the “righter” calculation and experimental setup. In fact, these tables only suggest a little below 10 watts.
That’s what your abdominal feeling says, which I don’t want to question, because it’s so harmonious for your marginal conditions. Maybe I can only reach 18 km/h with 180 watts and with 200 watts already at 25 km/h. For this, I need a formula to better understand the relationships/dependencies, which is the goal of my question, among other things.
If that’s just such a small difference, I’ll give you the right. My feeling has so far only said that this statement cannot vote. Now it is important to find out why I always had that feeling.
Yes, but that also means that with my high weight, I may move in the printing range of the table from 1.5 to 2.5 or so and I cannot see these values because I am not a pro user. But also that I can’t know exactly. Perhaps I also move in the range from 0.5 to 1.5 bar(?) and I assume that the walk work is not linear to the pressure(?).
Power is power times speed. If you have both stepped with the same force and reached 18/25 of speed, 7/25 of speed and 7/25 of power have lost.
Hmmm… But at 18 km/h, the air resistance should be only roughly half that at 25 km/h. So I would now have meant that half of the power is otherwise “freed” and is no longer available for overcoming the air resistance.
Or where is my mistake?
Right, I underestimated the influence of the air resistance and its rise in this speed range.
Good objection. I had left wind out now. Thought at Windstille it is constant at both… on the Internet stands 18 km/h approx. 80 Watt and 25 km/h approx. 160 Watt. Got a City/Holland bike. But then I would actually have an energy winner with the praller tire, which is not possible. 🤔
Ah, clear: only half of the power requirement is missing, which is available for overcoming the air resistance. Thus, almost the 25 km/h total 14/25 of the power went against the air resistance and the remaining 11/25 went on to overcome the (speed-independent) rolling resistance.
An interesting approach. But then why not just put into proportion? If I consume 200 watts at 18 km/h, I consume 25 km/h 278 watts. That I only consume 200 watts with the better tire means that the plated tire consumes 78 watts more so that I do not reach the 25 km/h or the better tire swallows 78 watts less.
25/18 = x/200 => x= 25/18*200 = 278.
At the end, however, we went the way over the kinetic energy W= (m*V2)/2. Then we came to about 96 watts.
I’ve been talking to a couple of people, talking about the different formulas.
My approach with the ratio equation would be linear and that is probably not the speed system. So really would only be a rough point of reference.
Your approach only takes into account the pulse set/pulse law but no power consumption/use.
In the end, everything is more likely to be a formula with kinetic energy. What do you say?
Do you know this page here? There is even a table with roll friction coefficients for different wheels and pressures.
https://www.leifiphysik.de/mechanik/friction-und-fortmotion/ausblick/friction-kraefte-beim-fahrradfahr
More experimentally, I would find it to start and roll out with the same kinetic energy. Then you can see how far you still come with different tire pressure and how long you roll until the kinetic energy became zero. The influence of the air resistance is thus also comparable.
Your approach was to enter with constant power and see what the final speed is. This actually entails more experimental uncertainties.
There is a treatise for this purpose, from page 99 it is described in section 5.2.3 Experiment No. 3 (determination of performance by rolling out):
https://www.physik.uni-wuerzburg.de/fileadmin/11010700/_imported/fileadmin/11010700/Didaktik/Zulassungsarbeit/HA_1622196_Bielmeier_Carsten.pdf
Does it sound good just how do I express this as a formula to be able to calculate the performance, e.g., from that rollout path? I also don’t know how to measure the way exactly. 🤔
Ah super, thank you for the link! It’s pretty vivid and you can count a little around :).
No, the power loss cannot be generally reduced to air pressure. It only applies to the tire and only then to the appropriate air pressure. For example, in my fatbike with 0.7 bar (!) I have less rolling resistance than in a “normal” tire with 2 bar. I always drove my bike with over 7 bar, each bar less made it harder to kick.
A Big Apple also has much better rolling properties than many other tires…
Of course, I always go out of the same tire. So e.g.
Fatbike 0.7 versus 0.4 bar
Racer 7 versus 4 bar
etc. Overall, however, I found that the wind has a much greater influence (in the end it also says the literature). Of course, you can measure it worse.
I found this by driving a few days further with less air. If I’ve stepped hard, of course, I’ve always looked at the tire at the moment and then pumped up again. If you don’t do that, you realize that it doesn’t have much influence at all, but that was the wind direction/winding speed that lets you believe.
In practice, this can only be determined theoretically: zalto has shown the formula for this. However, there are a variety of backgrounds during a cycling trip. It’s asphalt. Let’s see the headstone paver, Mal Schotter. Sand. In sand, for example, an excessively well filled tire is counterproductive. You just slip and you don’t have a gripp. So always the right tire pressure for the right terrain. Leave emergency pressure and then pump it up again. … Because then a well-filled tire can not only hinder the progression, it is also associated with falling risk.
I’ll give you the right. But I’m on the road in 95% because it’s the way to work. Therefore, this bill is very interesting for me and certainly also for many other commuters. For someone who only likes hobby, e.g. Downhill does not drive at all.
I’m on a bike tour now. Every day between 80.120km and there is what I wrote…
Okay, but that doesn’t answer my question now. Or what is your assessment of a daily asphalt driver?
So I actually do regular rolling tests with my 4 different bikes, different tires and different pressures. Just surrender when I make a small tour in the evening for fun over kilometer long, straight roads with very light gradient on the way back.
My Credo: Less is more! I had once read a contribution by a professional who found that the optimal pressure is usually too high. It’s confirmed to me. The race wheel runs e.g. super good with a pressure of only 5.5 and 6.0 bar. The professional who calculates the right pressure for individual drivers for each stage of the TdF meant that he rarely comes over 7 bar.
So I can’t follow you. 4.3 bar is not necessarily too little. I also have thick tires with 4 bar already too much. For most everyday cyclists without a good pump with manometers are 4.3 bar ‘big hard’. Just like Redpanther, the enormous difference of your measured speeds does not shine to me.
However, I have no experience with such high system weights. I don’t want to rule out that there is a limit for your special tires, under which they just don’t work properly anymore.
It is not to exclude that my measurement results have been influenced, for example, by wind.
I have to do a lot more measurements. But before I do, I would like to know if I can calculate something meaningful with the values at the end. And if the rolling resistance is not measurable, then it may be the difference whether jacket on or too and much more important how much is the difference with you personally and not with a fictitious laboratory measurement. I would like to fascinate by myself if you could measure more in the field/practice with the help of today’s pedelec technique. This could then lead even more to topics such as power loss chain vs belts with hub connection where there is (at least in my knowledge) just a single comparison diagram in the entire global web.
Yeah, the wind is the first problem. Windproof means protected against side wind. And if this is so, it can be that you drive in a straight wind tunnel;). You can really feel the wind only from about 20 km/h. 10 km/h from the front or from the back could explain your readings.
Yes. I had just kept the wind as constant, because it wasn’t open in the field, but as you said, it could even have been worse because of the channel effect. The question has already been rewarded here alone to become aware of its influence.
Imho is completely wumpe if 3 or 4 bar..
I’ve actually taken a tour without traffic lights and other stops to drive them at Windstille on different days. For measurement purposes, I had a small battery and always the maximum power, so a cut of about 23 came out.
Then I have a series of measurements, starting at a bar, and the trips are repeated three times. Always empty until battery. It had come out: (format 42-622, the non-plateable of Schwalbe) from 1 to 1.5 bar brings 30% increase in range, further increase to 2 bar again 10%, 2.5, on the other hand, only unessentially what, and everything about it is in the range of measurement tolerances. On the contrary, from 3.5-4 bar and more, the ranges tend to be lower again, but beyond 2.5 the comfort decreases significantly.
Thank you for your experience. What is the maximum pressure/bar on your tire? Do you use shock absorbers or none?
Recommended area is so between 3 and 6 bar, but I mean I only have suspension for the fork, but nix dolles.. But honestly, all over 5 is like solid rubber tires and makes no fun at all in the streets we have here, and consumption tends to increase. Not much, but measurable.
2-2.5 IMHO is the best compromise between range and convenience, 1.5 go also, but then consumption increases. This is for me the sign that something has to be in the air again.
For me counts the rim and an Fsst plate is when I could put on the same very fast at Huckeln.
Well, it depends on what you call “plated”. In some cases, a slight bulging of the tire is already a complete catastrophe, and for others the tire is only plated when one (wife) drives more or less on the rim.
Well, it might also come to weight and tires (have 50-622). At 3 bar, I actually have a plate. At 5 bar he’s just so perfectly filled with me. With my girlfriend, there’s only 3 bar.