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PostPosted: Mon Jul 23, 2012 3:02 am 
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Location: NZ
Thanks gospastic :beerchug:

If I add,say, 100g for an English BB that works out at 688g, which compares to my old Red at 730g. So about 42g (give or take) less.

Which isn't quite as good as I was hoping. Had my fingers crossed for more like 100g, being somewhere in between old Red and the light weight crowd (THM, Zipp, Lightning etc). The plan was to save a decent chunk of weight without taking on the unreliability (IMHE) of the lighter stuff.

:(

Oh well, maybe M3's would suit.... but nearly 3x the cost....

GJ


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Posted: Mon Jul 23, 2012 3:02 am 


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PostPosted: Mon Jul 23, 2012 3:18 am 
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Honest question: did you read the thread at all?

That would give you an indication why people are getting sub-600g total weight on their cranksets.
Even if you bought the M3's, you would need to buy chainrings, no?

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PostPosted: Tue Jul 24, 2012 3:37 am 
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Curt or Prendrefeu,
Can you take a Q-factor measurement of the new Red. Curt your easiest way is to measure to a point on the frame from each arm.
Pren, I am guessing if you haven't installed yet you can just take the measurement on the bench.


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PostPosted: Tue Jul 24, 2012 9:15 am 
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I just put the new Red cranks on my bike today. The old FC-R700 came off (762 g.) and the Red went on (576g.). The new BB86 GXP press-fit BB is 92g. compared to the Shimano's BB at 72g. Darn. The GXP BB does have noticeably less friction than the Shimano's. Total weight saved is 166g. I probably will keep the stock rings for now. In the future I plan to upgrade to Di2 and I will need a stiff large ring for the front shifting to work properly.

The rings on the Red are about 3mm further out from the BB as compared to the FC-R700. This makes it a bit less ideal chain line when I'm using the 34x27 climbing gear. I don't know about the difference on the Q factors between the two.

I also got the new aero link brakes. Off came the BR-7700 (314g.) and on went the Red (253g.) The 2012 brakes are a work of art.

Tomorrow I'll be taking on a maiden voyage with these new parts. Hopefully they will function as good as their jaw-dropping looks :beerchug:


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PostPosted: Tue Jul 24, 2012 10:13 am 
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Prendrefeu,

Sorry, I'm being a little slow today. I don't follow your point. I've been following this thread since the beginning and after reading your post but not seeing your point, I went back and re-read the whole thread again. Still don't get it.

Apologies for the double post of my question (which I won't restate here, so as to avoid a triple post ;) however I don't think anyone has yet answered it, other than a suggestion that Bikerumour might have said 588g.

Very sorry.

GJ


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PostPosted: Tue Jul 24, 2012 4:14 pm 
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Ah - so let me help then! :mrgreen:

Competitive Cyclist provides "actual weights" - your standard GXP crank will come to 586g.
Now let's ditch the heavy SRAM chainrings, see earlier in this thread. Minus 150g for the 53t, minus 33g for the 39t.
Add Praxis rings (remove pin, rotate both rings in alignment one arm) - 39t (31g) + 53t (97gr)

Now you're going to need a BB.
Using HSC's BB you're looking at 80g (minus unnecessary plastic bit)
Using Reset Racing you're looking at 70g (again, minus the unnecessary stuff)

Total?
601g or 611g, all in.

If we do the same with BikeTiresDirect "actual weight" of 613g w/o BB, subtracting chainrings, adding new ones, which you'll do anyway with M3's, adding a good BB,
you'll come out with 628g or 638g, all in.

If your old set up was 730g, you're looking at least 100g in savings.

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PostPosted: Tue Jul 24, 2012 4:37 pm 
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timzcat,

Haven't installed mine yet, I'm already making modifications. :twisted:
Most sites are claiming a Q-factor of 156mm.

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PostPosted: Wed Jul 25, 2012 5:23 am 
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Ouch! I haven't measured but that is a lot more then my Hollowgrams.


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PostPosted: Wed Jul 25, 2012 6:00 am 
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I'm hoping an actual measurement would reveal a different number, and someone on here will be able to supply that.
It will be at least 1.5 weeks for me with an upcoming work & travel schedule. :?

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PostPosted: Wed Jul 25, 2012 3:53 pm 
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I'll measure the Q factor on my bike here today.


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PostPosted: Wed Jul 25, 2012 5:41 pm 
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From the seat of the pants the Q is slightly more than the Shimano R-700 I had. I didn't measure the Q on the R-700 so I cannot say what the difference is. I don't know how to measure the Q anyway :lol:

Here's a brief ride report on my new compact Red GXP.

The first thing I noticed is how smooth and friction-free the new SRAM BB is. There's a noticeable difference to my barely one-month old Shimano press-fit BB. The Shimano has a lot of seal drag. I never thought BB could make that much of a difference to pedaling efficiency, but now I could really appreciate it with the new SRAM BB.

The second surprise is the vibration damping nature of the crank. Perhaps it's due to the hollow arms with no aluminum skeleton to transfer vibrations. The crank does improve the ride quality since your feet are two of five body contacts to the bicycle.

Last but not least I could feel the reduction in rotational weight. This is a major contributor to higher bike performance. Not only will you be able to climb faster due to static weight reduction but you will feel the reduced effort in accelerating the bike due to less rotational weight. I never thought I could feel a difference in bike acceleration as a result of a crank change but I'm pleasantly surprised :D

Shifting is spot on although I did have to adjust the front derailleur due to the larger Q factor.

I absolutely love my new crank and this along with the new Red brake set is converting me from a long-time Shimano fan into a SRAM fan :beerchug:

Regarding the heavy large ring....there's been talk about swapping it with Praxis. I looked up the Praxis rings and I noticed nothing special about them other than they're forged. From what I studied in college the stiffness of any material is determined by it's young's modulus of elasticity with everything else being equal. So forging itself won't make a ring stiffer as compared to a heavier ring. So my take is that by going to Praxis you will give up in stiffness. This may be fine for someone who doesn't power shift (myself included). I just want to clarify this so people don't get the impression that Praxis will work as well as the stock ring in all conditions.


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PostPosted: Wed Jul 25, 2012 7:44 pm 
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timzcat wrote:
Curt or Prendrefeu,
Can you take a Q-factor measurement of the new Red. Curt your easiest way is to measure to a point on the frame from each arm.
Pren, I am guessing if you haven't installed yet you can just take the measurement on the bench.



This is my first time measuring q factor... but I do know my way around measuring devices! :smartass:


I come up with 146 mm Q factor on my BB30 exogram. Take it for what it's worth :)


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PostPosted: Wed Jul 25, 2012 7:51 pm 
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Thanks Prend, very helpful.

Like you, I look forward to some actual weights, photo on scales.

:beerchug:

GJ


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PostPosted: Thu Jul 26, 2012 2:15 pm 
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Here's my 50-34 bb30 before and after the change with Extralite 94g octramp rc2


Attachments:
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20120725_1722362.JPG [ 72.45 KiB | Viewed 768 times ]
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Posted: Thu Jul 26, 2012 2:15 pm 


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PostPosted: Fri Jul 27, 2012 4:07 pm 
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The Q factor on my exogram bb30 50-34 is 146 mm.


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