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Author Topic: How fast can a postman pedal?  (Read 3387 times)

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Offline moblet

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How fast can a postman pedal?
« on: January 26, 2011, 05:12:04 AM »
Moderator note: split from Towards a balancing spreadsheet for vehicles.

Concerning horses and other biological vehicles:
The current horse drawn carriage settings are a bit unrealistic, with a single horse producing 10kW
10kW is about right for peak horsepower. What we call one horsepower is what a horse can sustain all day. But I guess that only helps to complicate figuring out what value to use.
Quote from: AEO
In real life a mail bike would be no more than 120kg with the rider and mail. A horse in real life would produce about 750W, and an average human on a bike would produce less than half of that, about 250W.
The average healthy human couldn't sustain 250W for very long, although someone with an elite athlete's genes certainly could. Chart here, about halfway down the page under The Human Engine. Whatever power and mass assumptions are used, I would nominate 15km/h as the speed outcome for an unimpeded postal bike on flat terrain, falling to 10km/h or below when going uphill. For reference, 15km/h is the pace of those Chinese rivers of bicycles (have ridden in them and measured it). One should not assume that even if one gets off and pushes a loaded bicycle up a steep hill, that they will travel at a minimum of "walking pace" (i.e. 6km/h). I don't know what is the assumed gradient of a sloped tile in Simutrans, but having ridden loaded touring bikes over a few hills I should be able to convert a gradient into an expected speed. I've roughly calculated what my power output would have been while climbing long passes on cycling trips, and what I could sustain for hours a day, for the equivalent of a working week, was somewhere in the order of 100W.
« Last Edit: January 28, 2011, 12:40:42 AM by jamespetts »

Offline ӔO

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Re: Towards a balancing spreadsheet for vehicles
« Reply #1 on: January 26, 2011, 05:51:14 AM »
a fit person should be able to do about 20km/h average speed on a bicycle for around 2hrs. what I would do, is set it for 45km/h maximum, but only give it enough power to go 18 to 20km/h. Which should make it an interesting choice compared to horses on hilly terrain. Historically, bikes allowed 3 times the distance of travel by a single person, so 3x as fast as foot should be a good number.

The power output of a human will vary over time, but I don't have a clue as to how long a work day it is for a bike postal worker.


the graphical slope in simutrans is around 22.25deg or 41% gradient, but I think the actual physics uses a lower number, because 41% gradient would be steeper than the steepest road in the world.

Offline sdog

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Re: Towards a balancing spreadsheet for vehicles
« Reply #2 on: January 26, 2011, 06:38:10 AM »
Quote
Chinese rivers of bicycles (have ridden in them and measured it)
i envy you! i was never allowed, wife said i'd be to stupid and western to do so :-(


postal bikes are rugged old beaters, single speed, 20km/h is fine. you don't want to go much faster downhill either since breaks are usually crap. Especially as we're talking about a pre 1919 bike. (stable is not available afterward - can't be bought) Oh and don't forget it's not sport but work, so go for low powers.

it's 1t, power is too high. so what, seems to work quite well for the job at the moment. thought about reducing it's load to one bag of mail?
« Last Edit: January 26, 2011, 06:47:34 AM by sdog »

Offline moblet

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Re: Towards a balancing spreadsheet for vehicles
« Reply #3 on: January 26, 2011, 06:55:58 AM »
As sdog just said, I don't think we can apply amateur sports performance parameters, where people train and choose to participate and can take as much rest as they wish between efforts, and which are often seasonal, to employees, who have to make their efforts day in, day out, regardless of the season and whether they feel 100%. If a postal worker sorts their own mail then an eight hour day would be maybe three hours' sorting and five hours' delivering, if it is sorted for them then their entire day is spent delivering. Also, we are talking about postal bicycles, not sport bicycles. 45km/h on a descent is nothing on a road racing bike but unsafe on a loaded postal bike, which is designed for efficient mail handling, not high-speed stability. 40km/h feels like walking pace in a car but feels quite fast on a bicycle; with unbalanced wheels and/or a lot of weight in that front basket it would be uncontrollable, I would suggest 25km/h as an upper limit. The effort that would produce 20-25km/h on a lightweight racer would barely get you 15km/h on a loaded postal bike. On the 3x assumption 15km/h would be about right, because the pedestrian equivalent is walking with 10-15kg of mail on one's back, not walking unladen.
i was never allowed, wife said i'd be to stupid and western to do so :-(
Did no one tell her that this is the most invisible way for a westerner to travel in China? She should have tried it herself, it is one of the most surreal experiences I've ever had, floating down a river of calm through a busy city.

Offline ӔO

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Re: Towards a balancing spreadsheet for vehicles
« Reply #4 on: January 26, 2011, 07:04:08 AM »
I keep forgetting this a bike from 1919 with brakes that are lacking.
from the design, it would seem that the only thing stopping it from going fast are the brakes.

the front basket design looks like it is brazed to the frame, so that there's no change in steering behaviour when loaded up.

I know for sure, that a modern bike, designed for commuting purposes, can carry around 20kg on the bike itself and another 50kg on a trailer without affecting the control-ability much for speeds above 30km/h. It's just that stopping can become a problem with bad brakes. It's also very easy to hit +40km/h with a slight hill and extra weight.
« Last Edit: January 26, 2011, 07:12:43 AM by AEO »

Offline moblet

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Re: Towards a balancing spreadsheet for vehicles
« Reply #5 on: January 26, 2011, 07:23:35 AM »
from the design, it would seem that the only thing stopping it from going fast are the brakes.
Crashing to the ground usually stops them going fast, too. Remember also that they are being used on suburban streets, not roads closed for cycling races. Like everything else on the road they have to be operated at a speed from which they can safely stop. With poor brakes, or with a high-mounted load over the front wheel, that is not very fast.
Quote from: AEO
the front basket design looks like it is brazed to the frame, so that there's no change in steering behaviour when loaded up.
There is no direct interference with the steering, correct. The problem is the high centre of gravity of the load over the front wheel, which causes three problems:
- If you lean the bike into a corner it will be very prone to the front wheel slipping out and the rider being thrown to the ground. This limits the safe speed in any environment where a change of direction might be required. More than 15-20km/h on a wet or gravel road would demand total concentration.
- The bike will be more prone to somersaulting under hard braking, thus you cannot brake hard, thus it is not safe to reach high speeds.
- The bike would somersault upon striking a rock or pothole at speed (less likely with the more modern postal bikes because the rider's weight is positioned lower).
For stability one would not carry any load in the front basket, but this reduces delivery efficiency. In practice it's more efficient to sacrifice stability, and thus maximum speed, for efficiency at stops.
« Last Edit: January 26, 2011, 07:30:12 AM by moblet »

Offline ӔO

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Re: Towards a balancing spreadsheet for vehicles
« Reply #6 on: January 26, 2011, 07:58:48 AM »
You won't have to worry about the bike doing a somersault with the poor brakes.
It's actually pretty hard to cause it, even if the front is loaded up compared to the rear. I've only managed to nearly do an endo on a touring bike with the front loaded up while going down and hitting a speed bump on a hill and while under heavy braking.

The leading cause for a somersault on a bike is because the bike stops, but the rider wasn't holding onto the bike wel. This causes the rider to crash into the stopped bike, whereby the fulcrum of the front wheel will cause the forward motion to turn into an up and over motion.

On the other hand, some poor road conditions, like gravel on pavement, do cause the front end to wash out under the rider, even while going at a modest speed. Wet cobble stone and brick pavements are also not pleasant to ride on. But on some asphalt or concrete pavement, such speeds, even when loaded up, will not cause a wipe out. It's only when you ride over a painted line or manhole cover does the traction suddenly vanish the rider ends up on the ground, even while going in a straight line.

Not only are the differences in road conditions different from 1929 to modern day, but the  tire and brake technology are also much improved from the past to present. With all these variables, you can end up with a large variety of what is rideable and what is not. If there was an old version and modern version of the postal bike, top speed could be a spot to give them a difference.

I do ride all year around, so I can give a pretty good breakdown of what is possible with a bike. I sure as heck don't want to try going upwards of 25km/h riding a 1929 bike on cobblestone or muddy cobblestones. But give me a bike from at least 1980 and I'd do it.


but anyways, the postal bike is one of those bonus vehicles in the game, where one would only use for the sake of completeness. These bikes get overwhelmed quite fast, because they can't keep up with the capacity demands. And even some of the cars and vans have trouble with this as well.

I think the important part is trying to strike a balance between realism and play-ability of the goods road vehicles, because they're basically unplayable right now.
« Last Edit: January 26, 2011, 08:05:42 AM by AEO »

Offline sdog

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Re: Towards a balancing spreadsheet for vehicles
« Reply #7 on: January 26, 2011, 07:46:17 PM »
Did no one tell her [sdog's wife] that this [cycling in china] is the most invisible way for a westerner to travel in China? She should have tried it herself, it is one of the most surreal experiences I've ever had, floating down a river of calm through a busy city.
She grew up with this stream, and she certainly doesn't stand out there :-). She really doesn't the stream as calm at all. It was not so much out of sorrow i would get hurt, but more the anger i would cause by delaying everyone. But i see some point there, the traffic doesn't follow the rules of law but the rules of a flow. This will likely require the rider to do what other do, this will be quite some difficult thing, as i always lived to avoid doing what anyone else does.


Back to topic, until recently when they got bikes with new disk brakes the postal workers also dismounted when going downhill. There was no way to break the bloody bikes when loaded even with modern breaks. In 1919 the breaks looked like this at best.

But all of this is just a minuscule detail, the postal bikes are at the moment next to uselless as the mail amount produced even by a wee hamlet quickly exceeds the transport capacity of those bikes.

Quote
I sure as heck don't want to try going upwards of 25km/h riding a 1929 bike on cobblestone or muddy cobblestones
Paris-Roubaix!
« Last Edit: January 26, 2011, 07:52:18 PM by sdog »