Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
Per Westermark
03/11/12 09:42
Read: 591 times

#186579 - Sure
Responding to: Kai Klaas's previous message
Kai Klaas said:
Joseph 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.

List of 61 messages in thread
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      

Back to Subject List