Read: 239 times
|#186579 - Sure|
Responding to: Kai Klaas's previous message
Kai Klaas said:
It's brilliant in its simplicity.
Of course, it is. But the realization is very very expensive!
It's a trade off between precision and cost.
The cheapest solutions aren't too expensive. If living with maybe 10% error after calibration, the Polar chain tension solution has a quite acceptable price.
The solutions with sensors in hub, pedal axis or cranks most definitely have a higher price. Not because they are rocket science but because of the few potential customers.
I guess for someone who needs the power measurement only when going uphill the sigma thingy will be good enough and, it's about ten times cheaper!
But then it's basically enough to use a GPS. No need to buy a bike computer that presents a wild guess.
People who do pay for a power meter aren't interested in potential energy. They are interested in amount of work the body does. Especially as balanced to the work their heart does. Matching output power to heart rate gives a very good indication of training level. Or which rpm (cadence) that the specific person have the highest efficiency - best power output in relation to pulse.
But when not going uphill the power "measurement" of the sigma will be plain bogus.
Which is a reason why it is sold to "hobbyists" because it is cool. But does not bring anything to the table for people trying to optimize their training.
About friction: Riding with too little tyre pressure can totally ruin your day!!
Most definitely. But a race bike would get into lots of other issues quite quickly at too low tyre pressure. The surface area is minimal - less than the size of a thumb print for each tyre. Only a very high air pressure will manage to keep the tyre away from the rim if you hit a stone or hole in the asphalt. So while people on city bikes may run around with really low tyre pressure for comfort, no sane person steps on a race bike without tyres almost hard as stone.
There have also been quite a lot of improvements in the material and goves of the bike tyres to reduce the roll losses while still maintain the require friction when cornering on wet surfaces. By the way - bike tyres can get a quite "interesting" look after a couple of too hard turns in combination with a bit of sand. If they slip just a bit, they get a flat part on left or right side that will then grow larger and more market as each rotation produces extra wear where the tyre is a bit flat.
But the thing is that friction losses from tyres etc are most important at low speeds. The square factor from the wind drag will quickly make it the #1 factor. Next thing is that after the bike have been bought, it's only the riding style (where on the road, where behind another rider and how to sit) that the rider can change to affect the friction losses. So it isn't too important to try to measure the actuall loss between tyre/ground or in the hubs. It's enough that the manufacturers cares about those issues.
|bikey design challenge||Jez Smith||03/09/12 12:14|
|Only 400W?||Per Westermark||03/09/12 12:23|
|Its a bit different on the road||Jez Smith||03/09/12 12:34|
|Brilliant idea in the bath||Jez Smith||03/09/12 13:35|
|Might work||Per Westermark||03/09/12 13:51|
|well...||Jez Smith||03/09/12 14:33|
|So you are yourself saying 400W is a bit low max scale||Per Westermark||03/09/12 14:43|
|O.K then 500 watts||Jez Smith||03/10/12 00:56|
|Battery||Per Westermark||03/10/12 05:11|
|Fun with strain gauges||Oliver Sedlacek||03/12/12 05:57|
|You sure?||Per Westermark||03/09/12 13:48|
|nice ride||Andy Peters||03/09/12 14:31|
|fanks||Jez Smith||03/10/12 00:54|
|Sigma Rox 9.1...||Kai Klaas||03/10/12 09:59|
|Sigma fake||Per Westermark||03/10/12 11:07|
|What do you expect for that price?||Kai Klaas||03/10/12 12:09|
|Head or tail wind? Or riding in a group or alone?||Per Westermark||03/10/12 12:38|
|Way overcomplicating this||Joseph Hebert||03/10/12 14:02|
|Sensors||Steve M. Taylor||03/10/12 14:22|
|how indeed||Andy Peters||03/11/12 12:37|
|Wrong - you are totally missing the drag factor||Per Westermark||03/10/12 14:22|
|Not at all.||Joseph Hebert||03/10/12 16:03|
|Real manufacturers haven't found your idea simple...||Per Westermark||03/10/12 17:09|
|Point made||Joseph Hebert||03/10/12 18:46|
|Some of your points are just wrong||Justin Fontes||03/10/12 19:04|
|Sounds like you expect an infinite acceleration||Per Westermark||03/11/12 06:49|
|Repeat post Ignore||Justin Fontes||03/11/12 11:39|
|I try for a constant power||Justin Fontes||03/11/12 11:52|
|Crank rpm - not back wheel rpm||Per Westermark||03/12/12 00:31|
|I got the two confused||Justin Fontes||03/12/12 10:37|
|Bandwidth + return channel||Per Westermark||03/12/12 12:07|
|Oh dear, so many variable constants||Oliver Sedlacek||03/12/12 06:48|
|rocket science||Maarten Brock||03/11/12 03:58|
|So don't ignore them||Joseph Hebert||03/11/12 07:39|
|Of course, it is...||Kai Klaas||03/11/12 08:18|
|wireless||Joseph Hebert||03/11/12 08:36|
|Costs...||Kai Klaas||03/11/12 12:59|
|cost||Joseph Hebert||03/11/12 13:39|
|Another problem||Joseph Hebert||03/12/12 21:14|
|This was addressed earlier||Justin Fontes||03/12/12 22:02|
|Multiple strain gauges||Per Westermark||03/13/12 00:53|
|Competitive bicycling||Justin Fontes||03/13/12 10:24|
|Pulse||Per Westermark||03/13/12 10:55|
|If I had the power meter||Justin Fontes||03/13/12 11:14|
|Normalizing with heart beats cancels some errors||Per Westermark||03/13/12 12:39|
|Just to get some data to look at||Jez Smith||03/15/12 03:37|
|Jez ?||Steve M. Taylor||04/14/12 04:35|
|Oh Noes!!!!!!||Jez Smith||04/14/12 10:58|
|The plan is||Jez Smith||04/15/12 01:55|
|Brum doesn't HAVE mountains||Steve M. Taylor||04/15/12 14:51|
|Ah yes but no but||Jez Smith||04/15/12 23:23|
|Actualy...||Jez Smith||04/15/12 23:35|
|If I had a power meter...||Oliver Sedlacek||04/16/12 04:20|
|Ive been testing things||Jez Smith||04/16/12 04:41|
|Well, no||Steve M. Taylor||04/16/12 07:41|
|all very well thank you Steve||Jez Smith||04/16/12 08:45|
|Getting nasty||Steve M. Taylor||04/17/12 10:54|
|nasty ?||Jez Smith||04/20/12 12:09|
|More time than money if access to machinery||Per Westermark||03/12/12 00:57|
|Strain gauge elastic fixtures||Oliver Sedlacek||03/12/12 06:55|
|Sure||Per Westermark||03/11/12 09:42|