The mags I've measured are a waste of time if you want to train at high power (or need moderate
power at low speed). Compared to wind or fluid trainers I've measured, mags just don't generate
that much resistance, and they take some fairly high speed to generate the moderate resistance they
*do* reach.
If you just want to do "grandma" work outs, a mag unit is fine. Or just get rollers
http://www.geocities.com/almost_fast/trainerpower/
[email protected] (Jon Isaacs) wrote in message
news:<
[email protected]>...
> >Not sure about that. If mag resistance works by spinning a disc through a magnetic field then
> >doubling the disc speed will double the induced voltage and pretty much double the induced
> >current. This current flows in a direction that causes a force in opposition to the change
> >inducing it. So doubling the induced current will double the resisistive force.
>
> This topic was addressed extensively in a thread last year. I did some measurements using my
> PowerTap of the drag of my Minora Mag trainer at various speeds.
>
> While it is not power vs speed is not quite linear, it is quite close to linear indicating that
> the drag is nearly constant. Sometime late in the thread, Andrew Coggan pointed out that Chet Kyle
> had some tests and gotten the same results. There was an explanation of the reason for this which
> I have forgotten, some sort of saturation+thermal equilibrium.
>
> Regarding simulation of climbing vs flat:
>
> Climbing, the retarding force is approximately constant, at speed on the flat is is higher order.
>
> The one thing that no trainer can simulate (or at least no trainer I know of) is the inertial
> effects. In my view this is what really makes the feel of pedalling on the road. When you push on
> the pedals on the road, you have an inertial resistance to accelleration which is huge,
> essentially a function of your mass and the bicycles mass. If you push twice as hard, your
> increase your speed twice as fast, which is still not a big differential in velocity.
>
> But on a trainer, there is not mass so a hard push spins everything up in but a second or two.
>
> IN my view, that inertial resistance to acceleration is the first order characteric of pedalling a
> bicycle and simulating the mass of 150 lbs (actually
> 4.66 slugs) or more of a rider and bike is really impossible.
>
> One could use a heavy rear wheel, but it would have to be very heavy because the inertia a wheel
> going the velocity of interest with all the mass at the edge would have to have the same mass as
> the bike/rider combination.
>
> Bottomline: Just get a mag trainer. THey are cheap, they are quiet and they are reliable.
>
> Jon Isaacs
