Powertap vs SRM

SteveR_100Milers

Alex_Simmons/RST wrote:

SteveR_100Milers wrote:

Which one?

Race track, TT and road maybe. Train on 4 different bikes (inlc MTB)

I can see initially that powertap can be used on more that one bike, but there has to be some compromise on the rest of the wheel. SRM appears to be limited to one bike only.....

SRM for the track, Powertap for the road, forget the MTB, unless that's the majority of your riding.

Thanks Alex, has confirmed my opinion. MTB is simply an occasional distraction. Now the real decision to make is track or road..... :? I cannot justify two different system, at least I haven't found a sensible way of financing them yet perhaps.

mclarent

SteveR_100Milers wrote:

Thanks Alex, has confirmed my opinion. MTB is simply an occasional distraction. Now the real decision to make is track or road..... :? I cannot justify two different system, at least I haven't found a sensible way of financing them yet perhaps.

Interest Free Credit! It's what made Britain the financial powerhouse we are! Oh, hang on a sec...

Plodingalong

I am no expert but have experienced both a wireless PT built into a DT Swiss rim and a wired SRM pro. Both were bought 2nd hand and the difference in money IIRC was only about £100.
As to which I prefer, I would say the SRMs for a number of reasons:-
1. I can use my good carbon race wheels and disc.
2. Changing the SRM between bikes is as quick as taking the casette off and fitting wheel covers.
3. Overall the SRMs are lighter when paired with my good wheels.

Merv.

liversedge

Alex_Simmons/RST wrote:

So instead of a couple of presses of the buttons on the SRM Powercontrol which takes a few seconds and is simple, you need either a special stick and programming skills, or an iphone for an ap that isn't out yet.

So you buy a power meter, and now you need an iphone as well?

For the same prices as a PC7 I can buy two iphones.

Alex_Simmons/RST

liversedge wrote:

Alex_Simmons/RST wrote:

So instead of a couple of presses of the buttons on the SRM Powercontrol which takes a few seconds and is simple, you need either a special stick and programming skills, or an iphone for an ap that isn't out yet.

So you buy a power meter, and now you need an iphone as well?

For the same prices as a PC7 I can buy two iphones.

How much is the Garmin + iphone? You still need the head unit.

Let's see, here in Australia (A$):
iphone 3: $799; iphone 4: $859 or $999 depending on model *
garmin 500: $295
total: $1094 - $1294 depending on model of iphone

powercontrol 7: $900, but ~ $800 when bundled with SRM system

* Of course you can get an iphone for less if you sign up to a telecoms contract, but what if you already have a phone and don't want to use the provider you are forced to with an iphone?

So now you need an iphone and a phone company contract to calibrate your power meter?

A powercontrol sounds cheap in comparison to me, not to mention far easier to use and definitely more reliable than the garmins. At least it is when I compare the number of lost/corrupt/screwed up data files from garmin users compared to those using native head units.

jonmack

I've already got an iPhone and a Garmin though, and it's not as if the iPhone is a rare device, if I didn't have one I know i'd be able to get hold of one from a friend pretty easily, my 3 closest friends use them, as do a number of my other friends >10, as do 4 of the 5 people I work with. In fact I just checked and last year alone Apple sold nearly 40 million devices...

Alex_Simmons/RST

jonmack wrote:

I've already got an iPhone and a Garmin though, and it's not as if the iPhone is a rare device, if I didn't have one I know i'd be able to get hold of one from a friend pretty easily, my 3 closest friends use them, as do a number of my other friends >10, as do 4 of the 5 people I work with. In fact I just checked and last year alone Apple sold nearly 40 million devices...

I've got plenty of friends that don't have iphones or Garmins.

But honestly, shouldn't this simply be done with a quick click of a button on the head unit?

why should you need other pieces of equipment at all?

mclarent

Personally I'm hoping the Garmin Vector will be released soon and make all these conversations redundant.

Alex_Simmons/RST

mclarent wrote:

Personally I'm hoping the Garmin Vector will be released soon and make all these conversations redundant.

Not really, just adds more issues.

Not available and no pricing, so who knows?

Obviously it could be pretty cool if they live up to their promises. I do however prefer to see real product in the field demonstrate it actually does what it says it does. Given how long it's been since this was promised to be available.

Not everyone will want to use whatever pedal system they are locked into. e.g. for me, changing pedal type would involve hiring an engineer to design and manufacturer a new cleat adapter plate for my prosthetic.

Moving pedal power system across bikes isn't so easy - you also need to move the external transmitters and make sure the calibration/alignment is spot on.

Pedals tend to cop a bit of abuse, certainly more than a hub or crank does. So you have to wonder about longevity.

mclarent

All good points, and probably why it's been so long between announcement and now(!) I bet a real techy could tell us how much more difficult it is to engineer. However, if we assume that they meet the technical requirements, I'm happy to transition to speedplays (which I think they were suggesting?) if it means one power system across bikes - although obv i understand you have your own challenges in that department. I guess the Garmin guys will build the calibration requirements in to their head units as well, although given the issues some people have had with firmware upgrades... Overall, if it does what it promises, and gets released within my lifetime, I'm buying one for sure.

Alex_Simmons/RST

My experience with power meters is that users in first two years of a complete new product are beta testers.

Some like being early adopters more than others.

mclarent

2 years - just about long enough to get sign off from the CFO...

SteveR_100Milers

OK, am now seriosly contemplating going down the rental PT route. Since most of my TT training is on my TT bike on a turbo, or riding it on the road, then it seems that getting one built into a disc or at least a deep section wheel would be the most sensible option, then I can train and race on the same wheel. I don't like the idea of using wheel covers, if only as they seem quite flimsy and possibly about as aerodytnamic as covering the spokes with clingfilm...maybe I'm wrong, just my impression.

Jeff Jones

Steve, it depends on your budget and your current race set up. Disks and deep section powertaps are a lot more expensive than conventional training wheels.

Do you currently race on a disk? If so I'd consider just getting a PT training wheel and dispensing with power data for racing.

I had a PT disk for quite a while before I got a training wheel. I found it was useful in benchmarking my fitness but it didn't help guide my training. It was only when I got the training wheel that I could put it all together. And given the choice now, I'd go training wheel first, disk second.

As for deep section PT wheels, I feel they're a bit of a compromise if TTing is the main racing you're doing. Because you end up with a very nice training wheel but not the fastest racing wheel. If you're road racing, then that's different - a deep section wheel would be quite good.

SteveR_100Milers

Thanks Jeff - so a standard "training" rim with PT hub for using on the turbo. On a second point, I don't have a disc at the moment - I am using cosmic carbones front and rear - given my ambitions (short 22 and sub 56 for 10 and 25) is a disc and maybe something deeper at the front going to be much of a benefit?

joeyhalloran

I would go with a powermeter for your road bike...I haven't tried track racing but by its nature surely it is less prone to conditional changes so if you do a fast pursuit time (for example) it means you put out more power.

lloydy75

I rented Powertap for 12 weeks about this time last year, then bought one at the end of hire a reduced price. Last year I had it set up on road bike and used both on turbo, occasionally using it on my TT bike to get a reading as this is my main focus.

They are great bits of kit and I had my best season so far as I had real numbers to hit and improve in training. I didn't use it to race. This winter I've set it up with my TT bike on the turbo and trained in TT position and I'm finding I'm hitting the same numbers in the lower position.

I agree with Jeff, go for the training wheel as you probably train on the same roads so you can compare the data and then race as hard as you can!

DaveyL

Could someone enlighten me as to how many Watts you save by having a disk wheel vs a bog standard Open Pro (for example) - at a given speed obviously? I have no idea about these things, other than a vague recollection of reading something that said you don't save very much in the rear wheel.

And how much does each Watt then "cost"?

lloydy75

I don't know how much each watt would cost but I think would wouldn't be wrong in assuming most of us would never win enough prize money to pay for the difference in a normal wheel and a disc!

And at a higher level I have seen certain a 'Top' British pro signing on with a team issue disc wheel and racing with different wheel! Why? Because he wanted too, he would have won the event with what Sky issued him with anyway!

I think it's about doing what you can, with what you have, or want to have, to achieve your best time! It's all about personal preference.

jonmack

DaveyL wrote:

Could someone enlighten me as to how many Watts you save by having a disk wheel vs a bog standard Open Pro (for example) - at a given speed obviously? I have no idea about these things, other than a vague recollection of reading something that said you don't save very much in the rear wheel.

And how much does each Watt then "cost"?

http://www.cyclingtipsblog.com/2010/04/ ... equipment/

I think in the above article Wade may have the disc > trispoke savings the wrong way round, so going from trispoke TO disc saves 29s, rather than the other way round.

http://www.hedcycling.com/aerodynamics_technology/

This offers you to compare drag values between HED wheels and other brands, quite cool if you can be bothered to work out the savings that the disc offers vs a standard wheel, but if you use the rough equation that 2g drag difference = 1 second, you're not far off.

SBezza

Steve

The wheel covers are pretty good quality, and are custom fit, so offer the aero advantages of a disc over an open wheel. They will be heavier than a carbon disc for sure, but you could use them for non important races to gather data, and use the deep section for more important races.

As for the deep section rims, I have raced with my Cosmic carbone's front and rear occasionally when I was waiting for a replacement tub for my disc, and they were not really any slower than the disc IMO, still managed to get within 20 secs of my best 10 time, on a course that is not as good.

G-Wiz

Latest rumour on the Vectors is "late 2011" I.e. start writing to Santa and being good. I imagine we'll see some on some Garmin Cervelo team bikes later in the year just before they announce at the autumn bike shows.

My lbs will do finance on a powertap so that's where I'm off to, Alex's comment about pedal longevity has made me stop and think also.

SteveR_100Milers

SBezza wrote:

Steve

The wheel covers are pretty good quality, and are custom fit, so offer the aero advantages of a disc over an open wheel. They will be heavier than a carbon disc for sure, but you could use them for non important races to gather data, and use the deep section for more important races.

As for the deep section rims, I have raced with my Cosmic carbone's front and rear occasionally when I was waiting for a replacement tub for my disc, and they were not really any slower than the disc IMO, still managed to get within 20 secs of my best 10 time, on a course that is not as good.

Thanks Steve for the info on the disc covers - I was going on other opinions of those that had not used, only seen them, and probably hadn't really assessed them properly.

I suspected the difference between a 50mm section rear and a disc is probably negligent when you are my size, with the frontal area of a small van!

a_n_t

SBezza wrote:

The wheel covers are pretty good quality, and are custom fit, so offer the aero advantages of a disc over an open wheel.

Are they from powermeters.com? Cant see anything on their website so how much are we talking for one? Will use my disc 90% of the time but wouldn't mind getting some "race data" on the club 10's. Also. are they easy to remove / put back on?

Alex_Simmons/RST

SBezza wrote:

The wheel covers are pretty good quality, and are custom fit, so offer the aero advantages of a disc over an open wheel.

I have a pair of wheelbuilder.com covers on a Zipp 404 I use for local TT. They are excellent and in some set ups are equal to if not better aero than some disk options. Depends on the rim used.

Alex_Simmons/RST

DaveyL wrote:

Could someone enlighten me as to how many Watts you save by having a disk wheel vs a bog standard Open Pro (for example) - at a given speed obviously? I have no idea about these things, other than a vague recollection of reading something that said you don't save very much in the rear wheel.

And how much does each Watt then "cost"?

The rear provides a lot of time savings.

I performed aerodynamic field testing with a power meter (calibrated Track SRM) using the virtual elevation analysis method to compare my rear 32 spoke velocity aerohead track training wheel versus a Zipp rear disk. All else kept the same. Benign conditions - indoor velodrome.

The disk was 2.5 seconds per km faster. It would be even better at higher wind yaw angles more typically found outdoors (track average wind yaw angle is about about 5-7 degrees).

It is also consistent with some time trial PBs I have set of late (using the wheelcover), which were over 6 years old, set pre-disk days for me. In one case I was 30-sec faster over 7.8km.

hopper1

a_n_t wrote:

SBezza wrote:

The wheel covers are pretty good quality, and are custom fit, so offer the aero advantages of a disc over an open wheel.

Are they from powermeters.com? Cant see anything on their website so how much are we talking for one? Will use my disc 90% of the time but wouldn't mind getting some "race data" on the club 10's. Also. are they easy to remove / put back on?

The wheel covers are from Wheelbuilder.com, in the States.
I have a cover which fits my PT hub x IRD Cadence Aero rim set up. It's a good fit, held together by 8 fasteners.
It will be up for sale soon as I have gone for a disc with Quarq...
About 8 months old, used about 10 times.

SBezza

You can get the wheel covers from a company in the UK as well, they are the aerojacket ones as sold by wheelbuilder.com.

Bike Science in the UK sell them for £89.99 but it takes away the hassle of import duties and the cost of shipping, which I found to be very expense from the USA.

a_n_t

SBezza wrote:

Bike Science in the UK sell them for £89.99

Ouch! For the amount of use they'll get I'll give them a miss. Maybe if I didn't have the disc.

SteveR_100Milers

SBezza wrote:

You can get the wheel covers from a company in the UK as well, they are the aerojacket ones as sold by wheelbuilder.com.

Bike Science in the UK sell them for £89.99 but it takes away the hassle of import duties and the cost of shipping, which I found to be very expense from the USA.

Thats not too bad. Not sure whether to now buy or rent a PT....what is the warranty like on the hubs?