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Powertap – here’s the rub.

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  • November 29, 2014 at 11:28 am #22800
    Eebijeebi

    This is not a dig at the product as I think it’s very good. This is merely a head’s up to others wanting to get into power.

    I went for Powertap because it was pretty much the cheapest and simplest way into a power meter. So far it’s performance has been exemplary, software update and battery change not an issue.

    The problem now though is that one simply wont do.
    Eying up some carbon wheels for the spring when I hope to be moving along swiftly enough that I wont be ‘all the gear, no idea’. That means buying another one (but I knew that would happen).

    Riding on the trainer flat spots the tyre (is that only me?) which I didn’t I foresee. Last weekend punctured rear though the flat spot. New winter tyres gone on today.
    So to not flat spot the tyre again means swapping tyres every turbo session – or buying another Powertap wheel just for the trainer.

    So, to be in a sensible situation (unless you go with riding the flat spot on the road) you need a minimum of two, or three if you want two sets of road wheels.

    That adds up to circa £1800, although not in one go, but obviously some other systems would have been cheaper in the long run and not restrict wheel options – and that’s the head’s up really. Yes I did read up and research and in the end I wouldn’t have done differently as I was so keen to get into power. Others may not be so rash. I imagined I’d end up needing two – but three may have tipped the balance and convinced me otherwise.

    I always knew I’d need two but I doubt I’m a one off case and most PT users may end up needing three.
    I’m not complaining so please don’t pick holes – just putting what I’ve found into the power meter discussion pot.

    I imagine I’ll move away from PT rather than buy the second and third.

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  • December 1, 2014 at 10:33 am #822099
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    Jimmy Ray Will

    Reference L/R measurement..
    Reference L/R measurement.. from too much time spent on a computrainer I know that at low intensities I am biased to my left side something like 58/42%, then, as the intensity increases, I engage my right leg more and more until at threshold intensity I am 49/51% biased towards my right leg.

    I am not sure how that would look in real terms on a left hand only system, but in theory, my power reading would not be reflective of an increase in effort…

    It would still be accurate to itself I guess…

    Anyway, I digress… as you were.

    December 1, 2014 at 10:18 am #822097
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    KirinChris

    @5th
    Call me a cynic but they
    @5th
    Call me a cynic but they get paid to use stuff – it’s marketing innit. All the teams get paid to ride those bikes, groupsets, saddles etc.

    For all I know Shane Sutton might think Stages is the best thing in cycling since Tullio Campagnolo’s wingnuts got frozen. But I reckon That Team (don’t mention the name – the sound attracts trolls) has plenty of ways to get power data when it matters, whether or not they stick something on their bikes when they appear in public.

    My own, possibly flawed, reasoning is that on a race bike or for race training there is sudden and intense variation. As I understand it the Left Only devices rely more on algorithms for estimates of total power so it may be less accurate for brief periods, even if over the course of 10 minutes or 2 hours it is much the same.

    And I think you and Pierre are both correct. He’s right that a spider-based system is measuring power throughout the stroke so it isn’t one-sided BUT to get a L-R measurement it assumes that power from the down stroke comes exclusively from that side, so it isn’t actually measuring L-R power, it is measuring the total and allocating it.

    I agree that pedal based systems seemed to offer the perfect solution for portability and well as L-R measurement, but I’ve yet to hear that they’ve delivered.

    @Scrufftie I’d be interested to know if you move your Garmin system much, or is it mainly on one bike? Several people I know have them and find the shifting process prohibitive. One guy – very experienced and technically competent – was going on a week’s cycling holiday and left his Garmin pedals at home rather than take them with him, which rather defeats the purpose.

    December 1, 2014 at 9:38 am #822095
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    Pierre

    5th wrote:Don’t forget that

    5th wrote:
    Don’t forget that SRM, oft referred to as the ‘Gold Standard’ of PMs are also single sided.

    No they’re not, or at least not in the sense that you mean. All the stress gauges are on one side of the cranks, but they’re between the crank spider and the chainrings. So they measure the force going into the ring regardless of which crank you’re using to transfer that force (if you’re pushing on the left crank, it turns the axle which turns the spider, just as if you’re pushing on the right crank it turns the spider a little more directly).

    As for flatting the middle of tyres on turbo trainers, it sometimes helps to have higher pressure in tyres on turbos. But, it seems, only with some tyres.

    December 1, 2014 at 9:19 am #822093
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    andyp

    One PT is fine for me. Decent
    One PT is fine for me. Decent tyre on the turbo/rollers and it covers all bases from commuting to training to racing.

    December 1, 2014 at 3:31 am #822091
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    macrophotofly

    No power device is perfect
    No power device is perfect for all situations, unfortunately. I have a PT on my main bike and now a second (winter) bike that I’m contemplating a second PT for. Crank-based was too expensive for me.
    I thought a shoe-based solution would be the ultimate problem solving power device for a person with two bikes (nothing to unbolt!), until a month ago when I popped my shoe covers on for the first time this winter and realised that idea was scuppered…. ~X(

    November 30, 2014 at 11:48 pm #822089
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    5th

    Mtbtomo, there’s a fair
    Mtbtomo, there’s a fair chance that if you’ve got a serious power imbalance between L and R legs then it’ll manifest itself in other ways such as pain from your body compensating for the uneven power delivery. I don’t think you are missing something, I think it’s just the PM companies trying to sell you something that’s ‘better’ when actually it makes little difference. Let’s face it, surely if they’re sticking to their well-publicised theory of marginal gains, Sir DB et al wouldn’t sign up for something that would undo them?

    If you want to get an idea of how to compare PMs have a look at DC Rainmaker’s site; he’s a master of the art of running multiple PMs synced to multiple head units and managing to get meaningful comparisons from them – he definitely has too much time on his hands!

    As I said before, even if you knew you had a power imbalance most people wouldn’t know how to go about correcting it anyway, so unless you can see real issues or have pain that you believe may be caused by this then it matters little, and I’m willing to bet a fair percentage could be sorted out by a decent bike fit to ensure cleats are set properly as I’ve certainly had issues with that on the MTB in years gone by. By way of turning myself into a guinea pig this year I ended up riding nearly 8,000km with a broken saddle (Specialneeds Romin Pro, shell snapped on one side of the cutout) and learnt several things. 1) I’m an idiot and should have swapped it far sooner because 2) the uneven pressure plays merry hell with saddle sores and 3) Fizik Aliantes are far comfier. But I have to say I didn’t notice it leading to any crazy pedal stroke, but I know the rest of my setup is good. Bottom line: if you think you have issues get it checked out before splurging big money on a PM that will potentially tell you nothing when a setup and a basic PM will do.

    November 30, 2014 at 9:41 pm #822087
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    Eebijeebi

    I would imagine that just
    I would imagine that just about everyone has a disparity in leg output. Perhaps it’s different for others, but I certainly have many more things to get better at before trying to equalise leg output – I’d have two even but not very good legs!

    The point about accuracy +/- between sides and that they may not read the same therefore could mislead anyway is a good one.

    Accuracy between more than one device (same or otherwise) would be important, but how you could test? On a trainer at a set gear and cadence I suppose.

    November 30, 2014 at 9:01 pm #822085
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    mtbtomo

    Surely its about consistency?
    Surely its about consistency? Does it matter if one leg is slightly more powerful than the other? Or am I missing something?

    I’ve just bought a Stages mainly cos it was the cheapest system but also because I have Shimano cranks on all my bikes and have a few good sets of wheels I’m happy with. It seems like it will provide a power figure and just making training more specific.

    There are so many other things I’d concern myself with before worrying whether my left leg is more powerful than my right. And a few % inaccuracy overall. Well, its better than having no idea at all like in the days of Eddie Merkx.

    November 30, 2014 at 8:13 pm #822083
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    5th

    I’m glad to see that I’m not
    I’m glad to see that I’m not the only one that thinks that multiple PMs are a useful thing. I’ve been using a Stages since they came into the country on my training / commuting / do everything bike to good effect to record the bulk of my training load, and it also made the swap to a turbo wheel (an old wheel with a cracked rim that prevents road use but is fine with a tough tyre and cheap cassette for the pain cave) so easy and prevents any tyre squaring issues I used to get.

    Unfortunately the crank on my race bike isn’t compatible with Stages so I wasn’t able to get any race data. Luckily I was lent a PT wheel for the majority of this season enabling me to get data on a long training camp and other training rides on the good bike.

    As the PT wheel had an aluminium non-aero rim I never used it to gather race data, preferring to get the aero and weight benefit of my good wheels, but I have to say being limited to only training data made no difference and I enjoyed my best ever season with wins on the road, in TTs and on MTB (no PM on that either), mostly due to the thousands of kms ingraining the knowledge of what it felt like to sustain a certain effort for a certain time. I’d certainly like to know what power I’m putting out in races, but it’s not essential. I’m hopefully going to get a proper TT bike that will be compatible with my Stages so that will change, and I hope it’ll help me understand how to improve again.

    I’m interested in abudhabiChris’ comment about Stages not being suitable for a race bike though – surely Team Death Star’s use of them contradicts that pretty effectively? I’ve seen enough of your work to know the level you’re racing at, but if it’s good enough for them it’s good enough for those a step below surely?

    I’m still unconvinced with the whole L/R power split argument until someone can prove categorically that they can improve on the +/-2% error per PM; i.e. potential error of 4% on a pair of pedals – if it’s showing 4% difference does that mean you’re either perfectly balanced (-4% taking it to zero difference) or 8% difference, and either way what are you going to do about it? Don’t forget that SRM, oft referred to as the ‘Gold Standard’ of PMs are also single sided.

    It strikes me that the ideal situation is either a PM you can shift easily from bike to bike without affecting your use of key components (pedals are the only option here it seems) or multiple PMs to suit your needs / bikes and live with the potential for error. I was personally impressed with the Powertap’s reliability and battery life, but the weight of the lower versions and expense (and some extra weight) of the aero versions rule them out when I already have a pair of race wheels. Having already sunk my funds into the race bike and any spare going into a TT rig I can’t see myself shelling out for another PM yet.

    November 30, 2014 at 9:53 am #822081
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    Scrufftie

    Vector all the way for me.
    Vector all the way for me. Buy the left-hand only version, if you think that’s all you need, and upgrade to the right-hand later.

    On the subject of flatting tyres, this must be a problem with certain turbo trainers. I’m on my trainer for about four hours a week throughout the year using my ‘best’ tyres on mine and have no problems with wear. These are Continental Grand Prix TT tyres or Vittoria tubulars. Maybe, I’m not working hard enough!

    November 29, 2014 at 7:46 pm #822079
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    mtbtomo

    Oh come on, lighten up, it
    Oh come on, lighten up, it wasn’t a serious comment – so perhaps you would have understood the humour if we were face to face.

    November 29, 2014 at 5:55 pm #822077
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    Eebijeebi

    mtbtomo wrote:Is this a “look

    mtbtomo wrote:
    Is this a “look how ‘pro’ I am, I NEED three power meters” thread? 😉 8|

    No it isn’t and it shows that you’re either not reading fully or not understanding.
    Your comment is not constructive and I doubt it is one you would make to me if face to face, so please refrain.

    November 29, 2014 at 5:06 pm #822075
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    mtbtomo

    Is this a “look how ‘pro’ I
    Is this a “look how ‘pro’ I am, I NEED three power meters” thread? 😉 8|

    November 29, 2014 at 4:02 pm #822073
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    Eebijeebi

    Good point re bike to bike vs
    Good point re bike to bike vs 2 (or more) x other systems, and not one that I’d considered. When I used to ride (only re-started this year) it was always ‘fair weather’ as a means of keeping fit out of the rugby season and never in the winter.

    Now I’m already leaning towards the idea of a specific winter bike (unlikely this winter though) having just brought home my baby with mudguards on it due to last week being completely covered in filth – like fitting a roof rack on a Ferrari!

    So yes, a good argument for sticking with multiple PT’s.

    November 29, 2014 at 3:17 pm #822071
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    KirinChris

    Yes that’s a fair comment and
    Yes that’s a fair comment and I also started with one powertap and then got a second one with a set of training wheels.

    I would make two mitigating observations though.

    First, powertap have some good wheel tie-ins and you can pretty much get both for the price of one or at least a very big discount. This isn’t meant to sound snobbish but I am unlikely to spend less than 600-700 quid on any wheels so it doesn’t make that much difference to me.

    Second, where you have a wheel problem with Powertap you can have a bike problem with crank or spider systems. I have a race bike, a spare bike and a TT bike where I want to see power. Two or even three Powertaps are way cheaper than three SRM, Quarq etc.

    I’m about to get Stages for the TT bike but only because I think TT riding makes the left-only solution acceptable – I wouldn’t use it for a race bike.

    The pedal systems were supposed to solve all this but have failed miserably so far in my view.

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