# Power meter for Ultegra Di2



## Unkown (Jul 17, 2012)

Considering buying a power meter some time this year, and was wondering what crank based systems would work with Shimano Di2. I have searched around and haven't really been able to find solid information on what is compatible with what. I have looked on the forums using the search but haven't found anything concrete. I am trying not to spend more than $1500 if that is possible, so if anyone has any suggestions, I'd love to here them. If it helps I have a 50/34 and 11/28.


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## misterwaterfallin (Sep 14, 2012)

Crank based? Go SRM. What bottom bracket type do you have? You can also probably go with a Quarq that would be a little cheaper


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## Unkown (Jul 17, 2012)

misterwaterfallin said:


> Crank based? Go SRM. What bottom bracket type do you have? You can also probably go with a Quarq that would be a little cheaper


Thanks for the quick response. With SRM would I be able to get one for around $1500, they all seem extremely expensive to me.


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## misterwaterfallin (Sep 14, 2012)

Unkown said:


> Thanks for the quick response. With SRM would I be able to get one for around $1500, they all seem extremely expensive to me.


You should be able to get something used in your price range. You could get a wired set up for about half of that which will do everything a new one will with the only caveat being you have to run 2 wires from your crank to your handle bars. That's what i use and I love it


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## Unkown (Jul 17, 2012)

Pretty positive I have a BB30, where would you look for those powermeters used?


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## misterwaterfallin (Sep 14, 2012)

Unkown said:


> Pretty positive I have a BB30, where would you look for those powermeters used?


Ebay, craiglist(search country wide or at least the hotspots in CA and CO), slowtwitch, paceline


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## stevesbike (Jun 3, 2002)

I'd check to see what power-based cranks are compatible with di2. I know you said crank based, but for the price range you can get a very nice powertap g3 wheel (which will also add less weight than the crank based systems).


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## Unkown (Jul 17, 2012)

stevesbike said:


> I'd check to see what power-based cranks are compatible with di2. I know you said crank based, but for the price range you can get a very nice powertap g3 wheel (which will also add less weight than the crank based systems).


Would you say that they are about equal in terms of data accuracy? The more research I do the easier and more convenient a hub based power meter seems.

I also checked and i have a BB90 if that would change anything.


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## ericm979 (Jun 26, 2005)

If you get a crank based PM you can run Praxis chainrings if your Shimano rings don't fit on the PM). They shift as well as Shimano rings.

A Powertap G3 hub is 335g. A common rear hub is the Bitex/Bike Hub Store SL211 which weighs about 208g, for a 127g difference. There are a number of significantly lighter hubs. Of course if you compare the G3 to a heavy hub then the weight gain is not so high. But if you cared that much about weight you would not be using heavy hubs...

The Quark Elsa GXP crank is about 120g heavier than the Sram Red GXP crank. The BB30 version is about 150g heavier than the BB30 Red crank. SRMs are about the same to slightly lighter than Quark Elsas depending on the crank they are in.

So which system is lighter depends on what you're replacing.

Powertaps are possibly slightly more accurate than Quarqs because Quarqs report power for a second or so after you stop pedalling. While pedalling they have the same accuracy (assuming each unit is not malfunctioning). The "phantom" power doesn't seem to make a noticeable difference in actual use.

Both Saris and Quarq have excellent service. SRMs maybe not quite so much, and you have to send them in to get the battery replaced! But they are the standard for accuracy. Although the difference between them and PT or Quark is not that great and is only important to wattage weenies.

So the choice boils down to functionality... PT in the wheel, or in the crank.


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## Unkown (Jul 17, 2012)

ericm979 said:


> If you get a crank based PM you can run Praxis chainrings if your Shimano rings don't fit on the PM). They shift as well as Shimano rings.
> 
> A Powertap G3 hub is 335g. A common rear hub is the Bitex/Bike Hub Store SL211 which weighs about 208g, for a 127g difference. There are a number of significantly lighter hubs. Of course if you compare the G3 to a heavy hub then the weight gain is not so high. But if you cared that much about weight you would not be using heavy hubs...
> 
> ...


That added weight for hub PM doesn't really matter to me, price wise I think the G3 is starting to make the most sense for me.


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## stevesbike (Jun 3, 2002)

ericm has good info for you - there are also some threads about Quarq and di2 compatibility (the new red chainring spacing is changed, which I'm not clear on whether it plays will with di2 front derailleur). There used to be some talk about problems with drift on Quarqs, not sure if that is gone with new models. 

I've had 2 powertaps - a wired version and a wireless one. For me they've been bulletproof, and I've known others who have had similar experience. The G3 hub is improved as well (and lighter).


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## Unkown (Jul 17, 2012)

stevesbike said:


> ericm has good info for you - there are also some threads about Quarq and di2 compatibility (the new red chainring spacing is changed, which I'm not clear on whether it plays will with di2 front derailleur). There used to be some talk about problems with drift on Quarqs, not sure if that is gone with new models.
> 
> I've had 2 powertaps - a wired version and a wireless one. For me they've been bulletproof, and I've known others who have had similar experience. The G3 hub is improved as well (and lighter).


How much did you pay for your wireless G3 if you don't mind saying? I am looking around and seeing $1300 which seems reasonable to me.


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## kbiker3111 (Nov 7, 2006)

Unkown said:


> How much did you pay for your wireless G3 if you don't mind saying? I am looking around and seeing $1300 which seems reasonable to me.


I have seen them for $900 or less, but unless you know how to build the wheel you're better off buying it as a wheel.


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## simonaway427 (Jul 12, 2010)

Stages?


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## Unkown (Jul 17, 2012)

kbiker3111 said:


> I have seen them for $900 or less, but unless you know how to build the wheel you're better off buying it as a wheel.


Buying the entire wheelset seems kind of pointless to me because it costs so much more, if I went that route I would rather get a Quarq or SRM. I would need to find a wheel to build the wheel if I got just the hub though.



simonaway427 said:


> Stages?


I took a look at those and they seem like a cool idea, but I am not really sold on them, especially the price. Does anyone know if the G3 can measure how much power each leg is producing individually, because I know Stages can't do that.


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## ericm979 (Jun 26, 2005)

Powertap doesn't measure each leg individually.

Stages always measures the left leg and assumes that the right is putting out the same power. Stages adds only 20g or so to the cranks, but only works on aluminium cranks, not carbon.
Studies show that as at higher power outputs most people's L/R power becomes less unequal.

For a Di2 bike I'd use the Quarq Elsa or Riken, not the Red, due to its chainring spacing. Although it may make less difference than the manufacturers would like us to think. The Elsa, with the older Red chainrings that it comes with, shifts quite well on my 2012 Red bike, even though I'm supposed to use the new Red Quarq.


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## blairellis (Nov 9, 2012)

ericm979 said:


> Powertap doesn't measure each leg individually.
> 
> Stages always measures the left leg and assumes that the right is putting out the same power. Stages adds only 20g or so to the cranks, but only works on aluminium cranks, not carbon.
> Studies show that as at higher power outputs most people's L/R power becomes less unequal.
> ...


I have a Quarq Elsa (SRAM Red rings if I remember right) on my 2013 Ultegra bike that I just picked up and it plays really nice with it. Can't speak for the electronic shifting but mechanical gets along great. Quick and responsive shifts. I'm sure the electronic ones would be even better.

I've got an itch to upgrade to ui2 components, so if you end up going this route, please be sure to post here. I'm interested in your review.


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## the mayor (Jul 8, 2004)

Despite how hard you guys try to make it....cranks are cranks ( with a few odd exceptions)
I have a Cannondale EVO Ui2 that came with the Hollowgram compact.
I use a SRM Dura Ace now with a Wheels MFG adapter and 39/53 rings.
I have also used a Quarq Sram unit.
A little tweak of the front derailluer is all it takes.


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