44 replies to this topic Post Order

[Chrissie]

Hi, I am thinking of buying a Powertap, but hear that there is a new wireless one coming out soon.

To the current Powertap users out there.. do you think it is worth waiting for the wireless one if you only want to use it for training??

 

Have you found the Powertap useful for training?

 

If you remove the Powertap wheel before races, does the rest of the system add significant weight to the bicycle?

 

[BikeMax]

Chrissie

 

I will try and help;

 

The SL24 wireless may or may not be here this year - the price is ~9999

 

This is a premium of around R1500 on an SL which, unless you are very hung up about no wires on your bike is not worth it IMO.

 

Secondly, I urge you very very strongly to build a wheel that allows you to use the PT for racing and not just training. As a coach, I can tell you categorically that all the best data I get to analyse comes from racing. By building an SL into a lightish rim - you really pay a minimal penalty in weight terms. If you are keen to use a deep section that you may have - then put it on the front.

 

For training (and racing) the PT is the best investment you will ever make in your performance - provided that you take the time to learn how to use it and how to train with power.

 

If you do remove the hub and use another wheel to race then the head unit weighs no more than any bike computer.

 

I hope this helps but please ask if you have any further questions.

 

By the way, did I say - use it to RACE

[Windbreaker]

The wireless one has been coming for years! Saris should probably just set a date somewhere in 2010 and surprise us if they get it right earlier.

 

I consider myself still a novice at this sport but I really believe that without a structured power training program I would be nowhere near the level that I am now. Hey everything is relative so that doesn't mean much except that I am much sharper than I would have been without one.

 

You MUST use it for racing. The data is invaluable for analysis but in my case it also helps me pace myself better. The numbers don't lie. If I am riding well within threshold then I know that I will have something for the break or the last climb etc. Or as in the Redhill ride after 3 minutes I knew that I would not hang in with the break which was going at a pace well above my threshold and I backed off to a level that I knew I could maintain for 15-20 minutes - just to pass some of the guys that cracked later - not to be seen again.

 

There are only two criticisms I have of the PT

a) It doesn't have an altitude sensor

b) The heart rate data is noisy because it is not a coded signal like the Polar

[Michelle]

Bontrager have a prebuilt aero powertap wheel...

Part No.	Rim Dia.	FT/RR/PR	Weight	Type	Color	Speed	Holes	Spokes	Valve	MSRP (USD)
265460	700C	Rear	1080g	Clincher	Black Anodized	9/10	16		Presta	1,499.99
400285	700C	Rear	1014g	Clincher	Nude Carbon	9/10	16	14G		2,499.99

 

It's only 150g more than the standard Race X Lite Aero wheel...

 

I would love one of these for Xmas  (Jason I hope you're reading this )

[Dr. Seuss]

bruce - how is the ERGOMO testing coming on?  i see that cycle tech now advertises them.  no weight in the hub!

[Windbreaker]

 

I'd be very interested to see a comparison between the Ergomo, PT and SRM for both right and left "handed" cyclists. They say that the difference between the power derived from the two legs is minimal but I for one have to focus, especially on the trainer, as my leg leg "cheats".  I definitely can't produce exactly the same power from my left leg during one-legged intervals.

 

The other thing is that the power measurements are derived from a 50% duty cycle (left leg stroke only). That must impact on the accuracy of the data.

[Chrissie]

Is it better to use the powertap on the rear or the front hub?

Will Easton Ascent II wheel (18 spokes in front, 24 spokes rear) be able take the powertap?  I know not all wheels are compatible.

 

It makes sense to also use it for racing!  Thanks for the help

[Windbreaker]

Quote

Is it better to use the powertap on the rear or the front hub?

It can't be used on the front wheel. The principle is that the "force" that you apply on the pedals, through the chain and onto the hub is measured and multiplied by the cadence to give you a power value.

 

The SRM system measures this force on the spider

 

The Ergo measures the force on the bottom bracket but the slight difference is that this force is derived only from the left leg as there is no force on the BB from the right pedal stroke.

[bruce]

Ergomo testing is coming along very well.  The first unit I had was not installed correctly and was underreading by about 50 watts.  In the process of taking it off, the mechanic managed to shear the wires right where they enter the unit - so that one has been sent back to Germany.

 

The second unit has been installed correctly and is correlating well with computrainer and powertap (slight deviation at higher power levels ~350 watts and upwards) and there is a really interesting scientific debate on CyclingForums regarding the impact of this ().  I am working with the engineers in Germany to sort it out.

 

So far, the feature I like the best about it is real-time display of TSS/IF/NP.  This has really helped me stay in the training zones and accurately hit the training stress that Bikemax gives me.  Other nice features are the altimeter and coded straps.

 

I have trained/raced with a PowerTap for over a year - it is a very good device and it's accuracy is unquestionable!!  I took the option of buying a second hand PT Pro built into a Mavic Open Pro rim, and having my Zip 404's built in with a PT SL.

 

In general - my comments would to confirm what Bikemax and windbreaker are saying - every single ride should be down with a power meter if possible.  In term of monitoring training stress, seeing your true outputs etc it needs to be there all the time.

 

[Marius]

How much is the Ergo PM Windbreaker? I'm what ppl call goofy since my left leg is the stronger one but I write with my right hand, anyway, so you saying my reading would thus be out by a few watts?? How many is a few?

[BikeMax]

Quote

Is it better to use the powertap on the rear or the front hub?

Will Easton Ascent II wheel (18 spokes in front, 24 spokes rear) be able take the powertap?  I know not all wheels are compatible.

 

It makes sense to also use it for racing!  Thanks for the help

 

I would think that will work - you can get an SL hub in a 24 spoke count so you would just need a wheelbuilder to put it all together with new spokes.

[Windbreaker]

Quote

Will Easton Ascent II wheel (18 spokes in front, 24 spokes rear) be able take the powertap?  I know not all wheels are compatible.

 

If the rear is a std spoke config rim then probably but they usually recommend the 32 spoke option. E-mail  adrian@bicyclepower.co.za

 

He is really quite helpful with this sort of question. I ended up getting a 32 spoke DT Swiss rims front & back. Not quite as eye-catching as my original rims but hey ... who cares - they are also stronger.

[bruce]

Quote

 

I'd be very interested to see a comparison between the Ergomo, PT and SRM for both right and left "handed" cyclists. They say that the difference between the power derived from the two legs is minimal but I for one have to focus, especially on the trainer, as my leg leg "cheats".  I definitely can't produce exactly the same power from my left leg during one-legged intervals.

 

The other thing is that the power measurements are derived from a 50% duty cycle (left leg stroke only). That must impact on the accuracy of the data.

 

I am left "footed"  but a ride on the computrainer gives me:

 

left 49.85%

right 50.15%

 

At the end of the day, the single most important issue regarding accuracy is that the PM is consistent (or linear).  It is of superficial interest to compare your power numbers to someone else, but it is very important that you compare your numbers to yourself to see your progress.  In this situation the error is constant and can be removed.

 

Obviously errors of greater than 10% are not desireable, but good PM's are all within a 5% range - including the Ergomo.

[Windbreaker]

I agree that it is pointless comparing your numbers to someone else (other than for the fun of it).

 

There have been tests done which show that the absolute power indicated by sensors under test (PT & SRM) were quite similar - within about 5% of each other. I don't doubt that the ergomo will perform similarly.

 

As you point out this is not really the issue - as long as your sensor gives you consistent results and does not suffer from any non-linear effects across spectrum of what ... 50w - 1500w.

 

I've never done a test on a computariner and don't know how the measurements are derived but I definitely have much more difference than you doing the one-legged intervals. I would guess that well-trained athletes have far better figures than untrained cyclists.

 

My point is that because the ergomo derives it's measurements from the left leg only then any differences between the legs are going to impact on the resultant data. Hence my interest in seeing tests from left and right footed cyclists. I'll qualify that now with "untrained left & right footed" because that is where I would expect to see more pronounced differences.

 

It might be the case that a right footed, untrained cyclist would show a greater improvement using the Ergomo than the same cyclist would have shown on the other two systems. And vice versa for a left footed cyclist.

 

All a little academic ...

 

 

 

 

Windbreaker2006-11-01 03:56:17

[Windbreaker]

Quote

How much is the Ergo PM Windbreaker? I'm what ppl call goofy since my left leg is the stronger one but I write with my right hand, anyway, so you saying my reading would thus be out by a few watts?? How many is a few?

 

Marius, I don't know what they cost. I'm saying that in theory people with pronounced differences in their legs would have different results if they were using another system. I don't know that this is the case in practice as they may have some clever way of minimising the effect. The difference between my legs is pronounced - 30w when I try to maintain max for 3-5 minutes. My massage therapist even notices the difference.

 

I personally think measuring data derived from "half of source" is a deficiency but the benefits of being able to use whatever wheels you want may offset this "deficiency" (if it is one). I am very happy with my PT so I also might just be biassed.

[Windbreaker]

Quote

I'm what ppl call goofy ...

 

Some people also call me goofy but I guess that's just cause they know me ....