any experiences with either, as a power meter. the polar s720i, or 710 has power too I think. I like all the features of polar, but the powertap seems to be more accurate and less trouble free. what are your thoughts.
thanx
thanx
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Re: powertap or polar [trijunior]
[ In reply to ]
We've had good results with the Powertap unit. It seems more straightforward and easier to deal with than the calibration proceedure on the Polar where you have to weigh your chain.
Tom Demerly
The Tri Shop.com
Tom Demerly
The Tri Shop.com
Re: powertap or polar [trijunior]
[ In reply to ]
I have the Polar 720i and power unit, and have been generally happy with it. It is two pieces: a part that sits on the chainstay, and a part that screws into a rear derailluer sprocket. Plus, you need to hook up the cadence and speed sensors.
My only complaint is the unit is very sensitive to these sensor magnets - if they slip a fraction, no power reading.
My only complaint is the unit is very sensitive to these sensor magnets - if they slip a fraction, no power reading.
Post deleted by Kraig Willett
[ In reply to ]
Re: powertap or polar [Kraig Willett]
[ In reply to ]
Kraig,
Thanks for all the links for info. What a wealth of information. This does qualify as overkill, however. I wish to be the first to recognize that this is not a case of, "if you can't dazzle them with your brilliance, bury them with your bullshit." Keep up the good work!
Ben Cline
Better to aspire to Greatness and fail, than to not challenge one's self at all, and succeed.
Thanks for all the links for info. What a wealth of information. This does qualify as overkill, however. I wish to be the first to recognize that this is not a case of, "if you can't dazzle them with your brilliance, bury them with your bullshit." Keep up the good work!
Ben Cline
Better to aspire to Greatness and fail, than to not challenge one's self at all, and succeed.
Re: powertap or polar [Tom Demerly]
[ In reply to ]
You actually don't _need_ to weigh the chain. If you know what model of chain it is, there's a table on the polar site that has the default values for the weight and length of chain. You enter the length and weight of the chain so that the Polar can calculate the weight per unit length (the "chain density", if you will)....So, even if your chain is shortened, putting in the default values for your model of chain will give you the correct answers.
The only "calibration" that truly needs a measurement is the bike's chainstay length. That doesn't sound like a real tough assignment.
The "calibration" as you call it isn't really any more difficult than "calibrating" a speedometer.
I've had my Polar power unit installed on my bike for approximately 3 months now and I have to say that the installation wasn't difficult (thanks to the many web pages detailing the correct way to do it) and the unit has performed flawlessly since then. I've used it almost every day in training and I've raced road races, crits and TTs with it without a hitch. The breadth of data you get out of the Polar is truly amazing. Not only do you get power, HR, speed, and cadence, but you get temperature and altitude as well. Makes it very easy to review training rides or races after the fact when you can see the power output overlayed on the course profile.
Also, the Polar software is excellent. I actually debated with myself long and hard before buying CyclingPeaks software...that's how good the Polar SW is. I finally decided to spring for the CyclingPeaks because it had a couple of features that I really wanted to use in my training (normalized power, IF, TSS, etc.) and the Polar didn't have these features.
The only place the Polar has any difficulties is when used on a trainer...the power readings can be quite variable. This is most likely due to vibration/resonance issues (the Polar sensor is actually an inductive vibration sensor...much like a bass guitar pickup). BUT...I live in SoCal so the only time I use a trainer is when I'm warming up at a race...and I mostly use HR for that anyway. So...not an issue for me.
The Polar's biggest advantages are the ability to use whatever other equipment you like on the bike. You can use whatever wheels, cranks, bottom brackets, etc. that you wish...it doesn't matter. Additionally, it's one of the lightest (if not THE lightest) options as well....only adds ~1/2 lb.
Finally, if you're willing to "scrounge" a bit, the Polar is by far the cheapest way to get power on your bike. Brand new S710s and S720s can be had on ebay for ~$200 to $225. Brand new power modules can be had for around the same price. Even better, used power modules can be had for much cheaper...especially from people who became frustrated with the few idiosynchrasies (like it's trainer performance)....I was lucky enough to find a pair of used power modules for under $100. My total outlay for my setup (including the CyclingPeaks software) was under $300!
Anyway...that's my 3 month "mini-review" of the Polar system.
http://bikeblather.blogspot.com/
The only "calibration" that truly needs a measurement is the bike's chainstay length. That doesn't sound like a real tough assignment.
The "calibration" as you call it isn't really any more difficult than "calibrating" a speedometer.
I've had my Polar power unit installed on my bike for approximately 3 months now and I have to say that the installation wasn't difficult (thanks to the many web pages detailing the correct way to do it) and the unit has performed flawlessly since then. I've used it almost every day in training and I've raced road races, crits and TTs with it without a hitch. The breadth of data you get out of the Polar is truly amazing. Not only do you get power, HR, speed, and cadence, but you get temperature and altitude as well. Makes it very easy to review training rides or races after the fact when you can see the power output overlayed on the course profile.
Also, the Polar software is excellent. I actually debated with myself long and hard before buying CyclingPeaks software...that's how good the Polar SW is. I finally decided to spring for the CyclingPeaks because it had a couple of features that I really wanted to use in my training (normalized power, IF, TSS, etc.) and the Polar didn't have these features.
The only place the Polar has any difficulties is when used on a trainer...the power readings can be quite variable. This is most likely due to vibration/resonance issues (the Polar sensor is actually an inductive vibration sensor...much like a bass guitar pickup). BUT...I live in SoCal so the only time I use a trainer is when I'm warming up at a race...and I mostly use HR for that anyway. So...not an issue for me.
The Polar's biggest advantages are the ability to use whatever other equipment you like on the bike. You can use whatever wheels, cranks, bottom brackets, etc. that you wish...it doesn't matter. Additionally, it's one of the lightest (if not THE lightest) options as well....only adds ~1/2 lb.
Finally, if you're willing to "scrounge" a bit, the Polar is by far the cheapest way to get power on your bike. Brand new S710s and S720s can be had on ebay for ~$200 to $225. Brand new power modules can be had for around the same price. Even better, used power modules can be had for much cheaper...especially from people who became frustrated with the few idiosynchrasies (like it's trainer performance)....I was lucky enough to find a pair of used power modules for under $100. My total outlay for my setup (including the CyclingPeaks software) was under $300!
Anyway...that's my 3 month "mini-review" of the Polar system.
http://bikeblather.blogspot.com/
Re: powertap or polar [Tom A.]
[ In reply to ]
Tom, I have to agree with your review 100% since i've had it for 4 months and think it works great.
My question to you is how did you mount the sensor to the chainstay? I had to put a lot of risers under it to get it close enough to the chain and although it works it is not a very "sturdy" configuration. I am trying to find a more secure way to mount it to the chainstay.
My question to you is how did you mount the sensor to the chainstay? I had to put a lot of risers under it to get it close enough to the chain and although it works it is not a very "sturdy" configuration. I am trying to find a more secure way to mount it to the chainstay.
Re: powertap or polar [KingK]
[ In reply to ]
When I first installed it, I found some 1/2" thick high density neoprene sheet at the local hardware store. My intention was to mock-up the mount using the neoprene and then eventually create some custom mounts (I have access to a machine shop) once I had the position dialed in. I cut up small blocks from the sheet and put two (total 1 inch thickness) under the front end of the sensor and one under the rear and cinched them down with zip ties. I had to play a bit with the width of the front blocks so that the front of the sensor could be angled horizontally relative to the chainstay and place the sensor more in line with the chainline. This was necessary because of the short chainstays on my bike...along with the fact that the chainstays protrude straight back from the BB shell and then bend outwards towards the dropouts.
Once everything was zip-tied in place, it's been very solid. The neoprened seems to grip the chainstay and doesn't move around at all. It's worked so well, I haven't had any incentive to start working on the custom mounts...I think I'll leave that for a project for next winter.
One last tip....for the cadence magnet, I've found the easiest way to attach it is to use double-sided foam tape and place it along the leading edge of the crankarm near the pedal. Then install a zip tie through the slot and around the crankarm. Tighten the zip tie, BUT NOT COMPLETELY! Just enough to get it out of the way. If you tighten it all the way it will put a shear force on the foam tape (due to the crankarm taper) and it will come off. By not tightening it down all the way, you are then relying on the strength of the tape to hold it in place and the zip tie is just there to "hang on" to the magnet just in case the foam tape fails...just so you don't lose the magnet. The first time I installed the magnet, I used the foam tape and zip tie but I tightened the zip tie all the way...the foam tape failed within a week. I then reinstalled it, but DIDN'T tighten the zip tie all the way...it hasn't budged for 3 months.
http://bikeblather.blogspot.com/
Once everything was zip-tied in place, it's been very solid. The neoprened seems to grip the chainstay and doesn't move around at all. It's worked so well, I haven't had any incentive to start working on the custom mounts...I think I'll leave that for a project for next winter.
One last tip....for the cadence magnet, I've found the easiest way to attach it is to use double-sided foam tape and place it along the leading edge of the crankarm near the pedal. Then install a zip tie through the slot and around the crankarm. Tighten the zip tie, BUT NOT COMPLETELY! Just enough to get it out of the way. If you tighten it all the way it will put a shear force on the foam tape (due to the crankarm taper) and it will come off. By not tightening it down all the way, you are then relying on the strength of the tape to hold it in place and the zip tie is just there to "hang on" to the magnet just in case the foam tape fails...just so you don't lose the magnet. The first time I installed the magnet, I used the foam tape and zip tie but I tightened the zip tie all the way...the foam tape failed within a week. I then reinstalled it, but DIDN'T tighten the zip tie all the way...it hasn't budged for 3 months.
http://bikeblather.blogspot.com/
Re: powertap or polar [trijunior]
[ In reply to ]
Thanks for all the help. The software really seems to be the best part of the polar. Still a little undecided. Tom, have you or anyone else had any problems with holes, for different gears. Is it super finicky to get everything working and to keep it working? Also, I am a low priority dealer for polar, so I can get everything very cheaply. about .5 price. if that helps at all.
Re: powertap or polar [trijunior]
[ In reply to ]
I've had NO problems/anomolies with the power readings on the road (except for the very rare "way wrong" single sample...easily edited out in the software). This jives with various "head to head" tests with Powertaps, SRMs, or both (See Kraig's test for one example). I do a local climb pretty often (~3 miles at 8% ave. grade) and the power numbers I get match up to estimates from www.analyticcycling.com very well (usually within 5 to 10W if I take great care in entering realistic inputs).
Based on the "head to head" results and my own experiences, I totally trust the power readings I get on the road. If you delve into the details of how the sensor works (I did, just to educate myself) you realize that if you enter the required measurements properly, you're going to get a correct power reading.
But...when I first got mine set up, I threw the bike on my windtrainer to see if it was consistent across the gears. In short, it was not. The main problem with doing a "constant speed" power test on a windtrainer is that in certain gear combinations you'll have the condition of high cadence and very low chain tension. When this happens, the inductive signal of the chain pins passing the tension pickup can overwhelm the vibration signal of the oscillating chain and you will typically get high readings from these signals coupling together. What I found was that I had unreasonably high readings in my large cogs.
However, I also found that at normal speeds and cadences on the windtrainer, the power readings were reasonable. Anyway...that's the only drawback of the Polar setup as currently offered...it's "on the trainer" performance. Like I mentioned before, that's not a big deal to me due to my local climate.
One last thing about the Polar power setup is that due to it's sampling/recording algorithm, you won't see as high of peak power outputs as you will with Powertaps or SRMs. The Polar updates it's display every ~1.5 to 2 seconds using an average of integral pedal cycles over that time period, with a greater weight given to the most recent pedal cycles. The display value is then stored every 5 seconds. To me, this isn't that big of a deal since I'm more concerned with my sprint power over slightly longer periods like 20-30 seconds...but, for "bragging rights" this "feature" could be a disappointment ;-)
If you follow the instructions in the web pages referenced in Kraig's post above (especially Robert Chung's page) you shouldn't have much difficulty getting the system to work without much fuss. As far as being finicky to keep working?...I've barely touched mine in 3 months since I installed and I've used it in virtually every day of training since then.
Hope this helps
http://bikeblather.blogspot.com/
Based on the "head to head" results and my own experiences, I totally trust the power readings I get on the road. If you delve into the details of how the sensor works (I did, just to educate myself) you realize that if you enter the required measurements properly, you're going to get a correct power reading.
But...when I first got mine set up, I threw the bike on my windtrainer to see if it was consistent across the gears. In short, it was not. The main problem with doing a "constant speed" power test on a windtrainer is that in certain gear combinations you'll have the condition of high cadence and very low chain tension. When this happens, the inductive signal of the chain pins passing the tension pickup can overwhelm the vibration signal of the oscillating chain and you will typically get high readings from these signals coupling together. What I found was that I had unreasonably high readings in my large cogs.
However, I also found that at normal speeds and cadences on the windtrainer, the power readings were reasonable. Anyway...that's the only drawback of the Polar setup as currently offered...it's "on the trainer" performance. Like I mentioned before, that's not a big deal to me due to my local climate.
One last thing about the Polar power setup is that due to it's sampling/recording algorithm, you won't see as high of peak power outputs as you will with Powertaps or SRMs. The Polar updates it's display every ~1.5 to 2 seconds using an average of integral pedal cycles over that time period, with a greater weight given to the most recent pedal cycles. The display value is then stored every 5 seconds. To me, this isn't that big of a deal since I'm more concerned with my sprint power over slightly longer periods like 20-30 seconds...but, for "bragging rights" this "feature" could be a disappointment ;-)
If you follow the instructions in the web pages referenced in Kraig's post above (especially Robert Chung's page) you shouldn't have much difficulty getting the system to work without much fuss. As far as being finicky to keep working?...I've barely touched mine in 3 months since I installed and I've used it in virtually every day of training since then.
Hope this helps
http://bikeblather.blogspot.com/
Re: powertap or polar [Tom A.]
[ In reply to ]
Cool
Thanks for all the help. S720i, here I come.
Thanks for all the help. S720i, here I come.
Re: powertap or polar [trijunior]
[ In reply to ]
Hey,
Have played with both, the better option is the polar, found the power tap to be a bit tempremental.
710 & 720 both have th power out put possibilitys and can be linked with the inferred, power tap is a lot of wires
Dave
Have played with both, the better option is the polar, found the power tap to be a bit tempremental.
710 & 720 both have th power out put possibilitys and can be linked with the inferred, power tap is a lot of wires
Dave
I have used the Powertap for the last year. If you have two bikes that you want to switch between it is the best option as all you need is a new wiring harness. I did have the heart rate sensor fail on my unit (I think I fried it riding at night with the unit right next to my nightrider light set to flashing mode). The wiring harnesses are fragile and need to be routed carefully (dont pull the zip ties too tight). I think that the Polar unit looks really messy on the chainstays with all the sensors.
With the powertap, when I want to switch from my road bike to TT bike I just transfer the wheel and computer and voila we are right there.
For races I just take the powertap out and put my race wheels in. It has the added bonus of making my bike so much lighter on race day as the powertap unit is pretty heavy.
"train heavy, race light"
With the powertap, when I want to switch from my road bike to TT bike I just transfer the wheel and computer and voila we are right there.
For races I just take the powertap out and put my race wheels in. It has the added bonus of making my bike so much lighter on race day as the powertap unit is pretty heavy.
"train heavy, race light"