Any thoughts? Pros/cons? Is the SRM worth the price premium? Lots of discussion here on training with power, but which unit?
Thanks.
they both have advantages and disadvantages…
they should be pretty obvious (wheels, etc) the sl pretty much eliminates the weight issue…
either would serve you well and we have clients on both to great success…
g
SRM. If you get the older-style model, you can change crank lengths for less than the cost of most good cranksets, you can use ANY wheel, including a disc, you can train and race on the same set-up (if you want to do that with a powertap, you are either training on race wheel, racing on a training wheel with a cover, or you own two powertaps meaning you didn’t’ save any money), the SRM computer is much nicer than the powertap computer. If you know your crank length and don’t plan on changing, then the new-style DA or soon-to-be-released FSA version is very nice. SRM is THE standard…
You may also want to check out the new Ergomo Pro
<<you are either training on race wheel, racing on a training wheel with a cover, or you own two powertaps meaning you didn’t’ save any money)>>
Not exactly true. If you don’t already have race wheels:
PT Training Wheel $1200
PT Zipp 808 $1600
Total= $2800
SRM (assumes Dura Ace) $3200
Zipp 808 Rear $1000
That’s true. You should probably add $450 to the first case to cover the cost of the equivalent crankset.
$2800 + $450 for D/A-10 crank & BB = 3250
So it is about $1000 cheaper in that particular scenario. But you do have the option with the SRM of buying a Renn disc or using H3’s, which you cannot do with a PowerTap, which would make the cost much closer.
If the new Ergomo is any good, that is the best TCO system. I’d be nervous about friction in the BB with that system as well as proven accuracy until it has been thoroughly reviewed. Mostly BB friction though… But if they can do it right, that system will be great.
I’ve read in several places NOT to buy the SRM amateur, so I’d go with the PT or the SRM professional if you can afford it.
If you go with PT the SL is only 160 grams lighter, which is of little consequence.
I own a Trek 5500 road bike (9spd) and a P3C (10spd) plus a set of 606’s. Put the SRM on the road bike or the P3C? My thoughts were to use the SRM on the road bike, not sure if I want the SRM in races.
It appears the Power Tap would require yet another wheel. I already own 3 wheelsets.The Power tap would require me to upgrade to 10spd on the Trek in order to swap between bikes.
<< That’s true. You should probably add $450 to the first case to cover the cost of the equivalent crankset.
$2800 + $450 for D/A-10 crank & BB = 3250>>
Weeellll…comeon, no one pays $450 for DA Cranks…maybe $400, less if you are upgrading and ebay existing cranks 
Talk to me about BB friction. Let’s assume the Ergomo has the same bearings as my current Ultegra BB. Is there an additional source of friction?
With the Ergomo, you pay $1600 to measure one leg. You can get an SRM pro for $2750 that measures both legs.
Well, in my opinion, if you are racing triathlons, then you should do 90% of your training on the bike you will be racing. I don’t really understand why you would train on a road bike and then race the P3C. It totally violates SAID (specific adaptation to imposed demands). Train how you race, race how you train. You will see HUGE improvements with zero change in training time and intensity if you trained mostly on the bike you raced, and that should be your P3C.
So I really have two pieces of advice. Buy an SRM and put in on your P3C. Then train and race on that bike. Save the Trek for recovery rides and the OCCASSIONAL group or charity ride.
<< With the Ergomo, you pay $1600 to measure one leg. You can get an SRM pro for $2750 that measures both legs.>>
Assuming this is totally true, what difference does it make?
Bitey, what do you mean it only measures on leg?
By that same logic, no one pays full price for an SRM or even a PT. 
The SRM is the hardest to find used, but there was a 172.5 & 175 in the classifieds last week for 2500 ea. PT is cheaper, of course, but perhaps less cheap than it might seem initially, and I think it is less versatile.
BB friction: first off, does it really use the same bearings as your Chorus or Phil Wood BB? Then, is the machining on the axle anywhere near as good? Then, what sort of friction might there be from the sensor mechanism.
One of my big concerns, assuming (and that could be a big assumption) that they used, say, a Phil Wood axle & bearings, is how much friction is added by whatever seals they might need to protect the electronics? How much friction is added by the electronics themselves? I don’t know that there is any. But I’d want someone to test first.
That is the real advantage presented by outboard bearings like on the new FSA and D/A systems. Yes, they are probably a bit stiffer. But that is really irrelevant. Square taper was stiff enough. The real advantage is that the size of the bearings is much larger, meaning less friction. Yes, by being outboard, you may need to replace them much more often than your once-in-a-lifetime Phil Wood BB, but if you keep them clean, there will be less friction. Likely, between the outboard systems and a top quality BB like the Phill Wood or a Campy BB, it is so minimal as to be negligible. But if the Ergomo system is not of similar quality, then you could have real, measurable losses due to the system.
It’s a well known fact. Just stop and think rationally for a second.
If you can measure just one leg and guess what the other leg is doing, why not guess both legs, get a HAC4 or iBike and save hundreds of dollars?
Get the DuraAce SRMs and an extra set of DuraAce BB bearings. Have the bearings installed in each bike and then just switch the cranks from one bike to another as and when.
how is measures (one leg/zero leg/three legs) is really irrelevant–what matters is how accurate/repeatable is the system. Once they’re out, this won’t be hard to tell–just simply riding it and another system (PT or SRM) will give the result.
My guess is that it doesn’t really matter.
Whoever designed that ergomo website should be shot. It doesn’t even tell you how you can buy the damn thing.
If you like riding both your road and tri bike in training then its a no-brainer…get the PT. That is what I do. I actually used to have two powertapped wheels but the wheel cover works so well I just sold the race wheel and pocketed the difference.
I don’t think you need to do a vast majority of your training on your tri bike - those TdF doodes don’t seem to have much problem with it ;). Definitely transition to it a couple months before your race but even then I mix it up a bit.
Powertap is more flexible and cheaper even if you do buy two wheels.
ot
I’m not sure I’d agree that the SRM is really “better”, just different. It’s not without it’s disadvantages. The main one, more me, seems to be that it’s more finicky in terms of the slope moving around and being in need of calibration.
I have both, and I end up using and racing with the TAP on my road bike, and an old SRM pro on the TT bike.
I think that if cost is no object, then there’s a slight advantage to the SRM–but factor in cost, and it’s not even close (I think there are some obvious holes in the cost example given–a PT SL wheel on a deepish rim, with a wheel cover, would suffice as a race/everday wheel, and be as fast or faster than the 808).