Unusually high PT pro readings

[jeremyb]

Hey guys---i hate asking this question---but i just set up my PT Pro and
i went for a ride with my wireless bike computer (ciclosport 434) still
on the bike and my powertap speed and distance was about twice what my
old/correct computer was reading. If my Ciclosport read 16 mph the PT
was reading like 32. Also my power numbers seemed off---i.e. too high. I
treid switching to km just to see what happened and the numbers were
even higher (which makes sense). I zeroed out the torque readings, i set
the wheel circumference to 2096 (which is what the PT manual says is the
circumference of a 700x23 tire).

But then it gets weirder. I did a hard sprint and the speed readout on
the PT went up and up to like 40-50 mph (obviously wrong) and then they
dropped and equaled the readings from my ciclosport at 26-27 mph and the
power output numbers dropped as well back to a normal amount like 300
watts for 26 mph or so.

What the heck is going on? I read on a forum not to tighten the zip ties
down really tight (which i did) so i just went and took off all the zip
ties and took my bike for a spin the parking lot and the numbers were
still twice as normal.

I've also now taken off the ciclosport computer just in case the computers were doing some sort of cross talk, but that didnt work.

Also, i tried to adjust the position of the pickup sensor, to no avail.
the only thing i havent tried was replacing the batteries.

any help is much appreciated

jeremyb

 

[ianbirlem]

my powertap speed and distance was about twice what my
old/correct computer was reading. If my Ciclosport read 16 mph the PT was reading like 32.

Hey Jeremy,
See the posting above "Powertap recall?"
http://www.cyclingforums.com/t129757.html
Sounds like you have one of the bad hubs. Powertap has experienced some severe reliability problems and quality control issues over the years. So much so that the original manufacturer Tune went out of business (though there were probably other contributing factors). People say they have improved the hub's water sealing, but they clearly are still having problems. See the posting "Powertap still bad in the rain" also.

Ian

 

[velomanct]

i have had my powertap read 5146 watts max, and 280mph in the downloaded screen. it rained on that ride for a bit.

too bad, i wish i really did 5000watts

 

[beerco]

Originally posted by jeremyb
Hey guys---i hate asking this question---but i just set up my PT Pro and
i went for a ride with my wireless bike computer (ciclosport 434) still
on the bike and my powertap speed and distance was about twice what my
old/correct computer was reading. If my Ciclosport read 16 mph the PT
was reading like 32.
jeremyb

Contact Graber - there was a batch which had a bad reed switch/conditioning circuit design. Should be covered under warranty.

 

[mattv2099]

i have had my powertap read 5146 watts max, and 280mph in the downloaded screen. it rained on that ride for a bit.

too bad, i wish i really did 5000watts

I doubt you'd want to do that many watts!

I bet your tire would disintegrate and your chain would explode and maybe your pedal axel would crumple and the grease in your bottom bracket would ignite.

Or something like that.

 

[DeanC]

I doubt you'd want to do that many watts!

I bet your tire would disintegrate and your chain would explode and maybe your pedal axel would crumple and the grease in your bottom bracket would ignite.

Or something like that.

Don't forget how embarassing it would be when the heat from your quads set your shorts on fire...

Happy to help you see the bright side ,
Dean

 

[velomanct]

I doubt you'd want to do that many watts!

I bet your tire would disintegrate and your chain would explode and maybe your pedal axel would crumple and the grease in your bottom bracket would ignite.

Or something like that.

technically i think the bike would hold up, as long as the rpms were above 100. the first thing to go would have to be the chain. (my chain which has 10,000 miles on it still holds up when i do hill accelerations from a stop at ~900 inch lbs torque(which is twice the peak i hit during a flat sprint). don't ask me how it hasn't broken yet, i feel it's time is due soon. i do keep it clean though).

if not the chain, then i would guess the rear cog would fold. or if the wheel was weak, that might go. a friend of mine(big sprinter guy) broke spokes on his kyrsium wheel when sprinting up a 12% grade.

i also heard a story of a local sprinter who broke his pedal axel in sprint. that would be ugly!