PT300 Pro Cadence -- Real or Virtual

Is the PT300 Pro's cadence a direct measurement or something virtual? If I change the gear ratio, will its power measurement be affected?

That's a question for Cycleops.

But I haven't seen a magnet. So it's A. measured in the hub B. virtual.
I have read that the cadance measurement in the hub of the powertaps is off when you spin fast or in nice circles. My cadance with the Pro 300PT was never off. It was always related to my speed (40km/hour = 100rpm).

Paul;

Thanks, I do agree with your observations. I bought a new crankset to A) match the 175 mm crank arms on my road bike; B) reduce the gear-inches a bit (52 down to 48) so as to "lighten" the feel a bit. The new chainring is also much quieter.

I did a quick couple tests yesterday and it seems about right. Today I will measure over a longer interval. Beware if you change the crank to use stainless steel crank bolts -- I broke an alloy one.

John

Don't change gear ratio:

With 48t chainring @ approx 60 rpm displayed: 3 minute count 186; average was 58 and count should have been 174.

With 52t chainring @ approx 60 rpm displayed: 3 minute count 178; average cadence was 59 and count should have been 179, which is within experiment error.

John

It's virtual cadence, and your speed should not change while keeping cadence constant and changing resistance.

Not sure about the effect of changing the number of teeth on the chainring. I'll be curious to hear how this works, as CycleOps has clearly said that changing the crank is not recommended, for whatever reason.

__________________

'07 S-Works Tarmac SL, Polar CS600+Power
2008 Cervelo P3C, Zipp 900c+808

'07 Specialized Epic Marathon w/Crossmax SLRs
CycleOps Pro 300PT Indoor Cycle Trainer (my winter ride)

Its definately virtual. CycleOps does not want the cranks changed as a safety reason. If you do, use a track or better yet BMX crank with Cro-Moly chainring bolts.

John