h a l f b a k e r yOpen other side.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
A bicycle is clamped to a platform/training roller with a force approximating a normal rider. The rollers are tensioned to simulate resistance of a well paved roadway. Alongside this assembly is a framework with a pulley several feet above the ground, and a cable drum centered at same height as the
pedals. The drum's shaft extends to a spindle that will turn the bike pedals.
Wind a cable around the drum, route the end over the upper pulley, and attach a weight - then let it drop. As the weight descends, the drum & spindle turn the crank of the bicycle, engaging the whole drivetrain and rear wheel. Time how long it takes the weight to hit bottom*. After it reaches the ground, also time how long the rear wheel continues to spin against the rollers.
The first timing rates how efficient the bike is overall - a more efficient drive will let the weight descend faster. The second timing simulates coastdown time - isolating the efficency combination of tire, rear wheel, bearings, etc will spin for a longer time. The more efficent combinations will spin for longer.
Test lots of bikes and publish the results.**
In isolation, these numbers would be meaningless. But they could hekp someone chose between two or more differnet bikes that appear similar in other ways.
*: For fixed-gear bikes, the drum/spindle would have to be able to freewheel, as the pedals will continue to move even after the drum has stopped cranking them.
**: For bikes with derailleurs or IGH, publish number for each gear ratio, or at least the high and low ones.
One part -- testing internally geared hubs
https://www.cycling...ing-gearbox-systems
Rohloff can match singlespeed - as long as you stay in 8th gear? [a1, Apr 20 2024]
[link]
|
| |
Any observed differences in efficiency in the test area will be swamped by in-use differences in efficiency arising from how dirty the drivetrain is or how well-inflated the tyres are |
|
| |
[hippo] very true. But just as US EPA issues "fuel economy ratings" for cars - miles per gallon that nobody actually gets in real world use - the ratings give a basis of comparison between different models. A car rated 40MPG on the highway will probably use less fuel than one rated 30MPG. |
|
| |
Same idea applies to comparing new bikes of various models against each other for their drivetrain and coastdown efficiency. |
|
| |
Wind resistance will totally swamp these things. |
|
| |
So don't forget to run the tests indoors, [a1], and well away from the swamp. [+] |
|
| |
// Wind resistance will totally swamp these things // |
|
| |
So I'd be better off with a fully streamined fairing and not worry about smoothly operating driveline, tyre commound/tread/pressure, and all those other details? |
|
| |
There are still people who obsess over chain drive vs belt, deraileurs vs IGH, smoothest wheel bearings, crank, idler pulleys, etc.. And component companies market to them - promotnng gear by how many watts they save or seconds they shave from a 100KM time trial. |
|
| |
This is a great idea[+] but the spelling and grammar irritates me. [-] |
|
| |
I recently tried to catch up with cycling tech by watching web videos, and vids I watched, which tested different tire widths for efficiency, came up croppers. There's a hare's difference in speed increases, unless you do your commuting on mountain trails. |
|
| |
// This is a great idea[+] but the spelling and grammar irritates me. [-] // |
|
| |
Can I have the croissant back if I run it through an AI writing assitant like Grammarly? |
|
| |
// There's a hare's difference in speed increases, unless you do your commuting on mountain trails. // |
|
| |
Tyre width doesn't make as much difference as pressure, tread, and compmound. But your "mountain trails" point is valid in that you should be selecting your tryes based on the kind of riding you do. There's no one tyre design tat's suitable for all of racing, ciry commuting, touring, gravel and other kinds of riding. |
|
| |
Haha, it sounds like you asked ciry to use Grammarly. |
|
| |
Though I generally avoid it, I just asked Bing Copilot to rewrite the idea. Looks good enough ... I guess... |
|
| |
Imagine a bicycle secured to a training platform with rollers, which are adjusted to mimic the resistance of a smooth road. Next to this setup, there’s a structure with a pulley high above the ground and a cable drum at the same height as the bike pedals. The drum is connected to a spindle that can rotate the bike pedals. |
|
| |
Now, wrap a cable around the drum, pass the end over the pulley, and attach a weight. Let the weight drop. As it falls, the drum and spindle rotate the bike’s crank, activating the entire drivetrain and rear wheel. Measure the time it takes for the weight to reach the ground. After it lands, also measure how long the rear wheel keeps spinning against the rollers. |
|
| |
The first measurement gives an idea of the bike’s overall efficiency - a more efficient bike will allow the weight to fall faster. The second measurement, known as the coastdown time, indicates the efficiency of the tyre, rear wheel, bearings, etc. The more efficient these parts are, the longer they will keep spinning. |
|
| |
Perform these tests on many bikes and share the results. On their own, these numbers might not mean much. But they could help someone choose between two or more bikes that seem similar in other ways. |
|
| |
For bikes equipped with derailleurs or Internal Gear Hubs (IGH), the results should include numbers for each gear ratio. If providing data for all gear ratios isn’t feasible, at least the highest and lowest ones should be included. This will give a range of the bike’s performance across different gears. |
|
| |
For fixed-gear bikes, the drum/spindle must be able to freewheel, as the pedals will keep moving even after the drum stops turning them. |
|
| |
These additional details will provide a more comprehensive understanding of each bike’s efficiency and performance. |
|
| |
... except I really don't like the summary line. "Understanding each bike's efficiency and performance" doesn't emphasise the sense of comparison shopping, helping choose between different models, |
|
| |
'Comprehensive Bicycle Comparison Shopping Guide' (no link because it doesn't exist....yet) |
|
| |
Please don't ask me what a comprehensive bicycle is...I beg you. |
|
| |
A man needs a woman like a comprehensive fish needs a bicycle. |
|
| |
My least hated favourite fish would be the comprehensive kind. (see: Htchhiker's Guide to the Galaxy; Babel fish) This is K.A.O.S. Radio, signing off. |
|
| |
This is just a dynamometer for bikes. They already exist, mainly for racing teams. In reality, bikes are already ludicrously efficient outside of obvious things like big, half flat tires. You're really messing around with fractions of one percent. |
|
| |
Yes, dynamometers exist, but what doesn't exist is a standardized rating system bike makers can use to compare against each other. |
|
| |
And having ridden lots of different bikes - and nearly identical bikes with just a few component differences - I believe things like tires, belt vs chain, and derailleur vs IGH all do make noticeable differences. |
|
| |
This is why the dynamometer is the best solution, because it could also account for the placebo effect that I suspect you are demonstrating here. |
|
| |
[Edie] are you in the space time continuum? |
|
| |
Yes. If your papers aren't in order you'll be deported to a neighbouring continuum. |
|
| |