Crank arms for DA7900 rings

Discuss light weight issues concerning road bikes & parts.
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hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

Guys,

I just purchased a set of DA 7900 rings for my bike to replace my DA 7800
rings. I was going to use my 7800 arms but it looks like crap.

Image

I would also like to shed some weight and am looking for crank arms that would fit
a 130BCD, I would like carbon for the look and weight. Any advice? I purchased
these over a lighter ring/crank package because i still want smooth shifting and
stiff rings.

Any advice would be appreciated.

Regards
:D

by Weenie


Mackers
Posts: 484
Joined: Wed Sep 05, 2007 2:02 pm

by Mackers

Image

hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

oh yeah, those are great. But if I'm going to spend that much i would
rather look at something a bit more exotic.

Hanzo
:D

WeightySteve
Posts: 293
Joined: Wed Jun 09, 2010 10:44 am

by WeightySteve

Mackers wrote:Image


They just 7800 cranks in Carbon, and it would look just as bad fitted with 7900 rings.

Also, the ring picture in the first post is not a 7900 big ring, so maybe this thread is misleading anyway.

Anyway, the only way 7900 rings look right is on 7900 cranks, and indeed part of the lateral stiffness of the crank/ring system (important for front shifting) is due to the design, because the oversized hollow big ring mates up with the oversized spider arm which counteracts the the bending force as the mech moves the chain. (I know oversized is probably the wrong terminology here).

SRM's design for their 7800/7900 hybrid power meter is probably the best out there for 7900 rings if you don't want 7900 cranks :)

hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

WeightySteve wrote:
Mackers wrote:Image


They just 7800 cranks in Carbon, and it would look just as bad fitted with 7900 rings.

Yes, they would look silly, Yes I know that.

Also, the ring picture in the first post is not a 7900 big ring, so maybe this thread is misleading anyway.

No, You are mistaken as they say Dura Ace 7900 on them and they are "big" rings; hence they are DA 7900 rings. :idea:



Anyway, the only way 7900 rings look right is on 7900 cranks, and indeed part of the lateral stiffness of the crank/ring system (important for front shifting) is due to the design, because the oversized hollow big ring mates up with the oversized spider arm which counteracts the the bending force as the mech moves the chain. (I know oversized is probably the wrong terminology here).


???


SRM's design for their 7800/7900 hybrid power meter is probably the best out there for 7900 rings if you don't want 7900 cranks :)



No, I'm not interested in a power meter.

Thanks
:D

User avatar
toiyuet
Posts: 172
Joined: Wed Dec 14, 2011 2:47 pm
Location: Hong Kong

by toiyuet

This is not a 7900 chainwheel, it is a Yumeya YM-FC91 for 7800.

It looks much weaker than 7900 chainwheel when pair with Di2.

Image

hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

toiyuet wrote:This is not a 7900 chainwheel, it is a Yumeya YM-FC91 for 7800.

It looks much weaker than 7900 chainwheel when pair with Di2.

Image




I must have the only Yumeya 7900 chain ring on earth then because it is NOT a 7800 ring,
Please assume that people other than yourselves can read, and are smart enough to know what
they are spending their money on.

FYI: please reffer to the first picture which states "7900" :smartass:
Image
Image
Image

Now can someone recommend a set of crank arms? I was thinking of an Extralite QRC2 crank set
but am not sure if they work with 130 rings?

Regards

Hanzo
:D

User avatar
Dov
Posts: 233
Joined: Sun Oct 17, 2010 8:45 pm
Location: London

by Dov

This thread is LOLs
Felt F1 DA Di2
Cinelli Supercorsa
De Rosa Nuovo Classico
Cielo Classic Sportif
Concorde Town Bike
Specilaized Rockhopper Kidmobile
Nagasawa Fixie Skid Machine
Cannondale CAAD 10 Track [custom]

Employee of Rapha
Strava

Watziznehm
Posts: 2
Joined: Mon Apr 30, 2012 12:45 am

by Watziznehm

Well, they may not be carbon but they sure are stiff and lightweight: Cannondale Hollowgram SL.

hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

Sorry its so funny :D

I was thinking of the hollowgrams, I will check them out


Thanks

Hanzo
:D

RussellS
Posts: 783
Joined: Wed Feb 03, 2010 1:31 am

by RussellS

hanzo111 wrote:
WeightySteve wrote:Also, the ring picture in the first post is not a 7900 big ring, so maybe this thread is misleading anyway.

No, You are mistaken as they say Dura Ace 7900 on them and they are "big" rings; hence they are DA 7900 rings. :idea:
[/color]


Lost track of the replies and counter replies. But as stated, the rings in your original picture are most definitely not 7900 rings. Dura Ace 7900 rings DO NOT have a hole all the way through them. The outer chainring is the nut for the crank bolt. The outer chainring is threaded for the bolt to screw into. Look at a picture of a 7900 crankset and you will see the bolt is not visible. The bolt is hidden.

http://www.nashbar.com/bikes/Product_10 ... 1___202430

denzity
Posts: 96
Joined: Sun Mar 27, 2011 10:01 pm

by denzity

I just swapped my 7900 rings for Q-rings. I am sitting here looking at them right now and can confirm that they look NOTHING like the ones the OP posted.

OP: what rings ARE they?

User avatar
toiyuet
Posts: 172
Joined: Wed Dec 14, 2011 2:47 pm
Location: Hong Kong

by toiyuet

YM-FC91 7800用フロントチェーンリング YUMEYA(夢屋) (Y0Y998040)【shimano】

http://www.flickr.com/photos/shino_soba/4331091041/

Limited wdition machined cut with 10g weight reduction....for 7800, also 7900 compactable.

http://www.shimano-yumeya.com/7800.swf

jsinclair
Posts: 397
Joined: Sat Aug 27, 2011 3:26 am
Location: Sydney, Australia

by jsinclair

Hanzo, please refer to your own first picture where it says "compatible with 7900". This is quite different to them actually being 7900 series rings. It's probably important to have this distinction clear in your own head before you start jumping down people's throats. We did assume you could read and knew what you were blowing money on. Obviously we were all mistaken in this respect.

by Weenie


hanzo111
Posts: 37
Joined: Sat Mar 24, 2012 5:40 pm

by hanzo111

Sooooo I called Shimano today. :oops:

I was wrong and I was right:
Wrong_they are 7800 rings_not hollow
right_they are have the ramps an profiles of the 7900 rings
right_they are not yumeya rings and weigh in at 102.3 grams where the yumeya rings are 90??? grams

Oh well, I will use them and research more next time


Kind regards

Hanzo
:D

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