PowerTap and cadence data...

bigpikle

I just got my PT Pro+ wheel and am delighted, except I noticed the cadence info is totally inaccurate, as measured by the hub itself. A quick Google search tells me this isnt a surprise, and in fact I had no idea the hub by itself would even measure cadence, so its not a big issue.

BUT, before I rip one of the Garmin GSC10's off one of my other bikes I wondered if there was any point? I am only using a 705 as a head unit and I didnt see any function to disable the hub cadence monitoring function. If I add the Garmin sensor and enable it on the 705 will it record that data in preference to the hub?

thanks

chrisw12

(Like hr) I don't see a lot of point in measuring cadence if I'm using a power meter. That said I have it on one of my screens just for the novelty and to shake my head eveytime someone posts on here that everyone should ride with a certain cadence. If the cadence reading 'broke' I wouldn't be bothered by it and I certainly wouldn't add devices to my bike to measure it.

On the other hand one of the most useful things you can do when you first get a powermeter is to try to find where your 'sweetspot' cadence is and to try to find the relationship between power and cadence for YOURSELF rather than the preachings and generalisations you get on internet forums. For example you might be spinning around at 200 'cause you read it somewhere but actually find using the pm that your optimal cadence is 50.

Oh and why do you say the cadence sensing on a powertap is in-accurate, what examples have you seen? Where have you read that? I don't think it's 100% but surely it's good enough to get ball park readings on a variable where you don't really need accuracy?

bigpikle

I've used cadence on my 705 for the last 15 months and got a very good idea of what my typical cadence is, especially on my regular rides and routes. Today the data from the PT told me I averaged a cadence of 135 and had several periods of >160rpm, and while I favour a higher cadence (100-105) I have never managed to pedal for periods at that kind of cadence I just googled PT cadence and found a few threads on forums where plenty of people said the same thing, so that was enough for me.

I wanted to do exactly as you suggested, and build a picture of cadence and power for me, hence the idea of swapping over one of the Garmin sensors from a summer bike.

a_n_t

Cadence is fine from my PT, its the speed thats way out [not that that really matters either!]

amaferanga

I find cadence from my PowerTap is spot-on unless power is below about 140W. But anything less than about 170W is recovery for me so its not a problem.

fish156

With my PowerTap, average cadence is good. Occassional spikes in cadence data (not surprising as it's trying to determine this from the cyclic variation in power?), so maximum cadence is never valid.

Speed (and hence distance) is always good as well (presumably it's just counting revolutions?). a_n_t, if your PT is still under warranty, I'd suggest getting it checked.

jibberjim

amaferanga wrote:

I find cadence from my PowerTap is spot-on unless power is below about 140W. But anything less than about 170W is recovery for me so its not a problem.

I guess it may well depend on your pedalling dynamics as I often find it a little off.

If you have a 705 it will use a dedicated Cadence sensor over PT data so fit one and it will be accurate.

bigpikle

thanks Jim - thats the answer I was looking for

hopper1

jibberjim wrote:

amaferanga wrote:

I find cadence from my PowerTap is spot-on unless power is below about 140W. But anything less than about 170W is recovery for me so its not a problem.

I guess it may well depend on your pedalling dynamics as I often find it a little off.

If you have a 705 it will use a dedicated Cadence sensor over PT data so fit one and it will be accurate.

I find that for my normal cadence (80-90) the 705/500 reading is accurate. If I go too low (+/-40), or too high +110) then it all goes t!ts!! No big deal...

amaferanga

jibberjim wrote:

amaferanga wrote:

I find cadence from my PowerTap is spot-on unless power is below about 140W. But anything less than about 170W is recovery for me so its not a problem.

I guess it may well depend on your pedalling dynamics as I often find it a little off.

If you have a 705 it will use a dedicated Cadence sensor over PT data so fit one and it will be accurate.

Don't care enough about cadence to have a fugly GSC-10 ruin the look of my bike

I think the same goes for all ANT+ Garmins btw (GSC-10 over the P-T with my 310xt as well).

jibberjim

amaferanga wrote:

Don't care enough about cadence to have a fugly GSC-10 ruin the look of my bike

Fully agree about that

bigpikle

...and I just found that the auto wheel measuring on the latest 705 firmware isnt great either

I just checked todays ride on 2 mapping site and both gave me a 3 mile longer route than the Garmin reported - 25 vs 22? I did a roll-out measurement of the wheel and it showed as being slightly smaller circumference than the 2100mm shown in the 705, but thats not right as that would shorten the ride even more if its tracking revolutions of the wheel!

Now I'm confused...help!

amaferanga

Bigpikle wrote:

...and I just found that the auto wheel measuring on the latest 705 firmware isnt great either

I just checked todays ride on 2 mapping site and both gave me a 3 mile longer route than the Garmin reported - 25 vs 22? I did a roll-out measurement of the wheel and it showed as being slightly smaller circumference than the 2100mm shown in the 705, but thats not right as that would shorten the ride even more if its tracking revolutions of the wheel!

Now I'm confused...help!

Enter the wheel size manually and don't worry about it. Auto wheel size is a pointless function IMO. There are countless stories of it getting confused over on the Garmin forum.