I trying to decide which option would be best/most cost effective. Anyone have any experience with using either of these set ups?
Thanks
Best? It’s ambiguous.
I “like” the Powertap better, as it’s more intuitive and doesn’t suffer from zero offset drift anything at all like the SRM. Lots of troubles with all 3 of mine, though (I think I’ve sent them all back for warranty repairs).
The SRM is much more convenient, being in the crank rather than wheel. Much more reliable. Lots more $.
So it all depends on what is important to you.
I agonized over the choice, and finally went with the PT because I could switch it from tri bike to road bike and back so easily. Also half the price.
I switched to a SRM from my powertap and I love my SRM! I wasn’t sure if it would be worth the extra money, but having the ability to run any wheel I want is worth it. Plus you can see all your race data.
If you’re going to spend the money on a power meter you might as well go with the best. You might regret the large purchase at first, but after you start training with it and learn how to analyze the data you’ll be happy you bought it.
If you can’t afford the money for the SRM, a power tap is still a great power meter. I trained with my PT for 1.5 years and it served me well with no problems (even riding in the rain).
If you have the cash I would say spring for the SRM. The ability to be able to change out wheels from training to racing and back is nice. I didnt have the cash for the SRM and went for a powertap pro as I could get it at wholesale. Mine has been good for the last year (knock on wood) and my wife’s SL has worked well despite being ridden in a couple of downpours. Prior to last year I have sent my powertap back a lot for repair.
Kevin
I used a PT for two years and switched to SRM this season. Both systems have their +'s and -'s. They are equally accurate. I’d give the SRM the nod for running problem free (as long as you remember to charge the battery- I preferred the watch batteries of the PT). I had occasional problems with the PT cutting out and dropping signals. The zero offset drift of the SRM is a drag, but unless the weather is changing, it is usually within the accepted range (±10 pts). The PT may be suceptible the same thing for all I know, just that the SRM gives you the ability to see it and dial it in as accurately as possible. If you get a Dura Ace SRM, switching cranks between bikes is a simple process, no more complicated than switching cassettes between wheels. I like the display on the SRM better and the ability to get instant feedback on intervals, you have to download the PT to see interval data.
The main reason I switched was the wheel choices, specifically a disc. The data you get from races is the most valuable, so to get the most out of it you probably want two wheels. At that point, the extra money for the SRM is probably worth it.
Maybe you an give me some info on the SRM.
My current situation is I switch my cranks (powercrnks for training and record for racing). Both use the same bottom bracket though I am concerned that it is getting worn out and may just continue using that bottom bracket for training (with PCs) and switch to the Record ultratorq thing for racing.
Would the SRM be able to work with this?
What exactly is zero offset drift? Lets say you are doing an IM - you set it at 6:30 - its 50 degrees - you come out of the water and 8 a.m. and its 65 degrees - by noon is 95. WHat happens and how do you fix it?
+/- 10 pts? Watts or other units?
Dave
Not trying to hijack this thread but I am facing the same question and one of the options is a used PT Pro w/ wheel cover. Has anyone run this combination for training & racing and could supply some feedback? Did you have to send your wheel back to Saris and if so why? Was the weight penalty significant enough for you to consider not using this option to race? Do you feel this is a good way to start training with power? My other option is wait and save for an Ergomo but I would need to spend extra $$ for a new set of cranks since I run the new Shimano bb.
FWIW - most people that I know are very happy with SRM. The one complaint they all have is price and buyers remorse.
Thanks.
Before you start your ride with the SRM, you are supposed to re-set the zero offset. This is a measurment of the distance between the power measuring part of the crank and the pickup. That # goes into the formula the software uses to calculate the power you are generating. Because temperature change can cause the metal to expand or contract slightly, this number can change. To re-set it is simply a matter of coasting for a few seconds unclipped from the pedals and pressing a button.
I think a wheel cover on a power tap wheel is an excellent choice to get a training and racing setup at a cheaper cost than the SRM. The SRM and PT are the gold standards for accuracy. I don’t know much about the Ergomo, but when I found out that it only measures power from one side of the crank, that ruled it out for me since if you have a discrepancy from right to left, you won’t know your true power.
I “like” the Powertap better, as it’s more intuitive and doesn’t suffer from zero offset drift anything at all like the SRM.
Testing conducted by the AIS has shown that PowerTap is actually somewhat more sensitive to temperature-induced zero offset changes than the SRM. The only reason I can see why some people tend to believe otherwise is the fact that the units of measurement are different with the two systems (i.e., ft-lbs of hub torque w/ the PowerTap; raw signal frequency w/ the SRM), such when converted to power at a typical cadence there is about a 10-fold difference in the magnitude of the smallest zero offset that can be detected (i.e., the way the SRM displays the data is ~10x more sensitive).
Moral of the story? Regardless of which powermeter you use, always, always, ALWAYS check the zero offset before each ride, and whenever you have reason to suspect it may have changed during a ride (e.g., due to a big swing in temperature).
While I am very new to the SRM system, zero offset is really nothing more than a change in the base reference point the meter uses due to the effect of changes in temperature on the strain gauges in the crank. I think in this case, sense thestrain guages essentially measure fractional changes in length, if the temperature changes significantly, so can the length of the strain gauge. The Power Control V allows the rider to compensate for large temperature swings by updating the zero offest at stops during the course of a training ride and not impossible to do during a race, just not as practical. In SRM’s FAQ, the following is listed for changing zero offset while riding:
During your ride, you should check the zero offset whenever you are able to freewheel – make sure you are not applying any pressure on the pedals, but keep the cranks moving in order to keep the PowerMeter activated. Follow the same steps to set the zero offset frequency.
I “like” the Powertap better, as it’s more intuitive and doesn’t suffer from zero offset drift anything at all like the SRM.
Testing conducted by the AIS has shown that PowerTap is actually somewhat more sensitive to temperature-induced zero offset changes than the SRM. The only reason I can see why some people tend to believe otherwise is the fact that the units of measurement are different with the two systems (i.e., ft-lbs of hub torque w/ the PowerTap; raw signal frequency w/ the SRM), such when converted to power at a typical cadence there is about a 10-fold difference in the magnitude of the smallest zero offset that can be detected (i.e., the way the SRM displays the data is ~10x more sensitive).
Moral of the story? Regardless of which powermeter you use, always, always, ALWAYS check the zero offset before each ride, and whenever you have reason to suspect it may have changed during a ride (e.g., due to a big swing in temperature).
Did the AIS test have the auto-zeroing off? I seem to recall that it was, but I honestly can’t remember. Did the PT even have the auto-zeroing function when the AIS did the test? And, which unit did they test? I’m guessing it was the Pro (not the SL).
I have to say that I find no difference on my SL tap whether or not I re-zero when leaving a warm house and going out into the cold. This was not the case with my old Pro, however.
I agonized over the choice, and finally went with the PT because I could switch it from tri bike to road bike and back so easily. Also half the price.
Takes me all of 5 minutes (if that) to switch my SRM cranks from one bike to another. And it leaves me with the ability to use any wheel choice I want. Plus, I do a lot of riding on the trainer. The SRM allows me to use my piece of crap rear wheel on the trainer and not have to worry about putting additional stress on a all-in-one race and training PT wheel.
You’re undoubtedly a better mechanic than I am, but that is VERY interesting information.
Did the AIS test have the auto-zeroing off? I seem to recall that it was, but I honestly can’t remember.
The PowerTap has always had the ability to zero itself, so they must have turned this feature off to conduct their test. You can therefore criticize the external validity of the study, but what it does show is that the PowerTap’s strain gages are no less sensitive to temperature-induced variations in the baseline signal than those in the SRM - they only appear to be (in part) because the PowerTap’s way of displaying this data effectively gives it much less resolution.
It’s really not a matter of being a mechanic, as it really is that simple.
If you’re initially intimidated by it, however, you can bring it into your locla bike shop and have the mechanic show you how to do it and what tools you need.
On an aside, even though I don’t consider myself mechanically inclined, I try to do as much work on my bike as I can. The more I do, the more I learn how to care for my bike, and the more comfortable I feel when riding that I can handle most mishaps. If there’s any concern that I might have done something that makes the bike unsafe, I’ve brought it into the shop and paid to have them inspect my work.
You know, I’ve been riding with a PT for 4 years now and I’ve never once had to zero the torque during a ride except during a 2-week period just before I discovered my hub was damaged and had to be sent back to Saris. I live in Seattle so the weather here is as changeable as any place in the US. In addition, as a test, I haven’t zeroed the torque on one of my PTs for the last year and it has not lost its offset once. As you know, it’s quite easy to tell when a PT requires the torque to be zeroed. I look at my data after every ride so you can’t make a good argument that maybe I’m having abnormal fluctuations in power but just not noticing them (which could be the case with a lot of people).
PTs are solid PMs. You can get 2 easily for the price of one SRM. A PT with a disc cover has proven to be just as effective as any disc in wind tunnel testing.
Having said that, if money is not an issue then SRM is probably the most robust PM unit on the market and offers the most flexibility, imho.
Thanks, Chris
Having said that, if money is not an issue then SRM is probably the most robust PM unit on the market and offers the most flexibility, imho.
Thanks, Chris
My experience with resetting the torque is the same as yours.
And while I know you’re a PT guy so I’m not trying to argue: As far as the ‘flexibility’ argument, that’s the main reason I use PT: I can use any crankset or chainring combination that I want.
People often talk about flexibility of wheel choice, but as someone who uses different length cranks (road/TT bike) and different chainring combinations (single ring on my TT bike for most courses–but not all), this is a big deal. Yeah, I could change chainrings on the SRM, but you really need to do a static calibration each time–and you’ll definitely need to re-calibrate after changing the arms.
As far as the robustness of the devices, I honestly wonder about that one. Of the 10 or so people I know well who use/used an SRM, a significant number (about half) have had considerable issues with them. I think if there were as many SRM’s out there as PT’s, you’d hear a similar number of complaints. The difference is that it’s a lot more cost-effective to have 2 complete PT units, should the need arise to sent a wheel back for service.
Yes, Roady, you make excellent points. Flexibility and robustness is really based on each individual’s definition. I ride in the rain a lot. Although the PT hub has made significant advancements (eg introduction of new o-rings) over the last 2 years to deal with weather issues like rain, the computer cradle is suspectible to water buildup so you have to be prepared with some plastic wrap and a rubber band if you know you’re going to be riding in some steady rain. My experience talking with others in the Seattle area is that SRM has no to little issues in the rain. Although, like you said, I’ve heard of many other complaints related to general problems and how costly it can be when you have to send you SRM back for maintenance.
What is often over-looked is customer service. I’ve said this before but Saris/CycleOps has to be one of the best companies in the cycling industry when it comes to customer support. The only other company that comes to mind who has equal customer support is Wheelbuilder.com but then they’re a very small company is comparison.
Thanks, Chris