SRAM goes electric....(almost official) Has Landed

Discuss light weight issues concerning road bikes & parts.
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sawyer
Posts: 4472
Joined: Fri Dec 15, 2006 7:45 pm
Location: Natovi Landing

by sawyer

nameless wrote:
NiFTY wrote:How often does anyone actually shift front and rear simultaneously? I am curious as I never do that currently. As for sequential, even with electronic shifting it is slower to shift the front then the rear, and not as smooth. I would still prefer to know when an FD shift was coming.


Happens quite often if the grade slowly changes from flat to uphill. For example, suppose you have 50-34 front / 11-28 rear (11,12,13,14,16,18,20,22,25,28). You're on a flat in 50/18 gear (19.5 mph @ 90 rpm). As the grade increases, you downshift to 50/20 (17.6 mph), then to 50/22 (16.0 mph). What do you do next? Any further in the back and you'll be cross-chaining. If you shift in front, 34/22 is 10.9 mph and that may be slower than you want. So you downshift in front and at the same time upshift in the rear twice, to 34/18 (13.3 mph @ 90 rpm).

More generally, the problem is that 50-34 gap in front is equivalent to 3 to 4 gear gaps in the rear, especially with a tight cassette and lots of cogs (up to 5 gaps if you have a 12-25 11-speed cassette) so you often have to compensate for the front shift with one or more shifts in the opposite direction in the rear. The problem is lessened with 53-39 in front but it's still there.



That is a good description nameless, though in reality it's easy to have a slightly too high or too low cadence for a second or two and shift the front and rear sequentially rather than simultaneously.

I think that's what most good riders do to minimise chain drop risk.

So in your situation I would shift up at the back (22 to the 20), then shift down at the front (34/20), and then shift up again at the back to whatever sprocket gave the right cadence
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Stiff, Light, Aero - Pick Three!! :thumbup:

BmanX
Posts: 3844
Joined: Thu Nov 10, 2005 5:31 pm

by BmanX

I have to agree that I use both at the same time a fair bit. Yes it might be the wrong way to ride but I do it. Will I learn not to do it when I go wireless. YES!
BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5960g/13.13 lbs

by Weenie


Imaking20
Posts: 1483
Joined: Fri Nov 18, 2011 5:19 am

by Imaking20

^this. Thank you!

It doesn't have to be for everyone. Di2 isn't for everyone. Campy sure as hell isn't for everyone.
Current:
T2

Retired:
Blue | Project C6.0 | Felt AR FRD | Colnago C59 NERO | 2014 S-Works Tarmac | S-Works Venge | Wilier Cento Uno SL | Tarmac SL2

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toiyuet
Posts: 167
Joined: Wed Dec 14, 2011 2:47 pm
Location: Hong Kong

by toiyuet

We learned to shift both derailleur delsimultaneously the first day be a MTBer in 1992.
If you are fast you realy need this skill.
Matching Di2 with this skill just perfect.

deek
Posts: 406
Joined: Fri Aug 31, 2012 6:32 pm

by deek

So you can't shift front and rear at the exact same time...big deal. Just start the front shift and then immediately hit one of the other buttons to shift the rear. Can you double click a mouse? How long does that take in between clicks, 0.1 seconds? In reality, your rear shift will probably still complete before your front shift. It doesn't really sound like something to be worried about.

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rmerka
Posts: 618
Joined: Wed Mar 06, 2013 4:23 pm
Location: Austin, TX

by rmerka

There's also the possibility there will be satellite shifters (which wireless I imagine you could put anywhere!) that could make a simultaneous shift possible.

SinPhi
Posts: 1
Joined: Thu Aug 28, 2014 6:49 pm

by SinPhi

This has me wondering if the possible function of a front gear change also changes a few cogs in the rear to do just what you would with a mech group, seems to make sense that it would. I now I change both at the same time for nearly every front shift. Would end up being a sort of hybrid between sequential and manual.

Zigmeister
Posts: 921
Joined: Mon Jan 24, 2011 8:09 pm

by Zigmeister

Isn't Shimano building this into the new Di2 MTB stuff to do cadence/ratio matching on the fly? Basically 1 button shifting?

So if you jump to the small ring on the front, it knows by the cogs/cassette to maintain the same rpm approximately, and shifts the rear down smaller 1/2 cogs?

For example, I do this with simultaneous shifting now when on the big ring, entering a climb, start to slow cadence, then drop it into the small ring, but to maintain the near same rpm, I drop the rear cassette once/twice often and go from there. Nearly exact button pushing I perform. Hopefully Shimano gets this logic built into the 9070 Di2 in a firmware update to enable and utilize this.

MisterNoChain
Posts: 122
Joined: Sun Nov 13, 2011 9:29 pm
Location: Belgium

by MisterNoChain

Yes, XTR di2 can be used with one shifter. If you're on your 11 and you shift up it goes to the big ring and shifts to a lower gear at the back.

Butcher
Shop Owner
Posts: 829
Joined: Sun Jan 03, 2010 4:58 am

by Butcher

The SRAM shifting uses the same buttons to shift the front and the rear. I have not used it and neither has most of us, but shifting front and rear the same time would be difficult [assuming that what you have to do is based on fact].

Yes, it does not bother many of you, but I have used it with the Campy 11 mechanical and when done right, it's like shifting up/down one cog. EPS, that's a different animal but it's ok [but not as good].
Last edited by Butcher on Fri Aug 29, 2014 4:12 am, edited 1 time in total.

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mellowJohnny
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Location: YYZ

by mellowJohnny

Eventually maybe we won't need to shift at all - given all the onboard data available today (cadence, power, incline, heart rate, etc) we likely aren't too far off from being able to select an "automatic transmission" mode. CPU knows my cadence, all I need to do is tell it which cassette I'm running + chain ring sizes to give it my gear ratios and the CPU does the rest. Detect a cadence / power drop? Shift for me, I'm getting tired. Detect a sprint? Keep shifting for me until my power / cadence top out.

The average week-end warrior would probably love it, and Pros could just turn it off.

Big data comes to the bike, think about the possibilities...

maxxevv
Posts: 1952
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

Shimano had an experimental lab prototype of that commissioned some 15 years ago using Mektronic and an SRM.

I'm just waiting for them to release that as a complete system package when they release their powermeter. ( Which there was a patent filed just recently, this year in fact )

Krackor
Posts: 260
Joined: Tue May 31, 2011 9:48 pm

by Krackor

sawyer wrote:That is a good description nameless, though in reality it's easy to have a slightly too high or too low cadence for a second or two and shift the front and rear sequentially rather than simultaneously.

I think that's what most good riders do to minimise chain drop risk.


I've been riding Red22 this season with the Sram chain spotter. I couldn't drop the chain if I tried, at least it certainly hasn't happened to me this season. I do probably 75% of my front shifts with simultaneous rear shifts.

Satellite shifters would solve the problem entirely, imo. Even without them, I'd consider going wireless despite losing simultaneous shifting. Not ever having to run or adjust derailleur cables ever again is just too attractive.

nameless
Posts: 18
Joined: Sat Aug 16, 2014 8:40 pm

by nameless

sawyer wrote:
That is a good description nameless, though in reality it's easy to have a slightly too high or too low cadence for a second or two and shift the front and rear sequentially rather than simultaneously.

I think that's what most good riders do to minimise chain drop risk.

So in your situation I would shift up at the back (22 to the 20), then shift down at the front (34/20), and then shift up again at the back to whatever sprocket gave the right cadence


I have Di2 (6770) and it has no problems whatsoever shifting front & rear simultaneously.

The only reason for SRAM's design is their desire to get things working with only two buttons instead of four. In other words, tradition.

mattr
Posts: 3456
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

nameless wrote:In other words, tradition.
It's probably to avoid patent infringement!!

by Weenie


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