Ogsarg

If you weren't aware of it already, you can setup semi-synchro shifting so that it shifts the rear and the front at the same time to lessen the gear difference. I have my hood buttons programmed for this purpose; left one shifts the FD to the small ring and the rear ring to the next smaller cog. Right hood is the reverse.

I only use the small ring for climbing. Once that is over, I switch back to the big ring and use the rear cogs as needed. The only time I ever wanted a small ring/small cog combo was when my Di2 battery died and went into limp mode and I was 15 miles from home.

rm -rf

Shift 3 with a long press
Back in 2014, my 6850 came with the default "shift all cogs" with a long press. That's never useful.

My setting is "shift 3 cogs with a long press" of a rear shifter button. That's holding the button for 1/2 second or longer.

At the base of a hill: hold both bottom buttons to get the small chainring and 3 smaller cogs. Nice, no thinking required, and no auto chainring shifting.
Over the crest of the hill: hold both top buttons, to get the big ring and 3 larger cogs.

That works great with my 11-32. I think there's a "shift 2 cogs" setting also.
I ride lots of small rolling terrain, so this is used quite often. I can decide which climbs are small enough to just power over on the big ring cross chained, or if shifting the front is better.

choddo

I guess it depends on your experience and fitness but I agree, big ring on anything below orange on the Garmin Climb Pro.

That automated “shift 3 cogs” sounds great. I need to get me some Di2 one day.

Iride01 

Why doesn't it make sense? It's what the Total Capacity limit is for the RD. However in the case of Di2, they are fudging that by allowing you to run bigger rear cogs by not letting you use the smaller cogs.

A limit due to cross chaining is what would make no sense. Why would cross chaining in the small/smalls be any worse for a cassette with a larger rear cog such as my current 11-30 than it would be for those cassettes with smaller large cogs like the 11-26 which is allowed to go into the two smallest cogs?

Perhaps it's my use of the term slack. But that's how I describe less tension. And in those gear combos when the chain is at greater angle between the front and back, less tension on the bottom run of the chain can result in poor shifting performance.

seypat

Dang, OP just asked if it could be done. He didn't need all the "you're a stupid SOB for even thinking that way" responses. He's probably going back to his mechanical group.

Mojo31

Yep, post 3 was the winner and provided him with all the information he sought.

Bald Paul

I have my Di2 set to a semi-automatic mode. I control the shifts front and rear, but when changing from the big to small chainring or small to big chainring the RD will shift 2 gears up or down automatically so I don't feel that big jump in gears. It's pretty seamless, and eliminates the temptation of cross-chaining just because I'm otherwise too lazy to make a FD change and compensate with two RD changes.

Iride01 

Were are you seeing anyone calling the other stupid? Much less an SOB.

Don't think that because people have differing opinions that they don't have respect for the other.

Turnin_Wrenches

The prevention of cross-chaining is exactly why those two gears are restricted when in the small ring...

Gear Position Control

So what is Gear Position Control, exactly? Basically, it is Shimano’s way to prevent cross chaining when in the small ring. They do this for two reasons:

• Prevent a chain line that would lower the chain tension too much
• To accommodate modern disc bikes with shorter chain stays that don’t work well with extreme cross chaining

source: https://bettershifting.com/di2-cant-...ng-adjust-gpc/

Iride01 

Essentially that boils down to what I've been saying. Except to me when people use the term cross-chaining, they are thinking only of the chain rub on the FD cage and excessive wear on the cogs and chain from the more extreme angle.

The less tension on the chain which is what I've been saying is the reason in the first bullet point.

So it seems we actually agree but just don't realize it because we don't see cross-chaining in the same way.

I haven't been into the newer version of e-tube project. I still use the old version prior to the version that had some issues back in 2020. There wasn't a Gear Position Control Enable/Disable option. However you could, as I have said, simply change the rear cassette size to be 11-26 or maybe it was 11-27 and it would happily shift to those two lower cogs on my 8000 series 11 speed Di2 even though the cassette was actually 11-30 or even a lower cog (more teeth).

mschwett 

As an aside, i find it interesting that on 12 speed di2, the default out of the box behavior prevents cross chaining little-little on dura ace but NOT on ultegra! They’re so similar otherwise…

Iride01 

Total capacity on the Ultegra RD-R8150 is 39 teeth and the DuraAce RD-R9250 is 37 teeth.

When the total capacity is exceeded, that's where the chain will chain tension will start to diminish all other things about the bike being equal. So that's going happen sooner on a bike with a DuraAce 12 speed RD than it is a Ultegra RD as the range from small to big cog on the rear increases.

Polaris OBark

If you have the charging brick, you can do it from a computer. If you have a PC, install the etube software and attach your usb cable and plug in the bike.

If you have a mac, you can run this in a virtual enviroment, but it might be easier to borrow someone's PC.

I "solved" the problem by not doing any firmware updates, because, like you, the idea annoyed me. I've had this for almost 10 years, and was only recently bitten by a bad shift. I was in the smallest cog and the large chainring, and dropped to the small chainring first, and backpedaled or something stupid, and stuff jammed up. I'm sure it isnt the first time I shifted like that, but it is the first time I got bit.

I should note that I am exceeding the capacity of the rear derailleur with a 30T front.

So, if you do go back, be careful of cross-chaining. I always wondered why it let you go into big-big without issue. I guess that is less of a problem.

Atlas Shrugged

My understand and like everyone else is nothing but bike shop rumours and generalized unsubstantiated gossip is that modern systems are good with cross chaining and the taboo is a legacy from the old days due to poor chains which had very little side play unlike modern chains.

The issue with small/small on a short chain stay bike with a compact, when on the small chainring the chain will rub on the larger chainring.

mschwett 

hmmm. that’s interesting. both my 12 speed di2 Ultegra and DA bikes have 52-36 up front and 11-34 in the back. (52+34)-(36+11)=39. i wonder if DA ONLY locks out little little when you have a cassette/chainring configuration that exceed the 37 tooth spread? the DA bike came with the 11-30, which would drop the spread down to 35, but it was configured electronically for the cassette. perhaps when you do that it changes the shift limits.

sfrider 

It allows running a 2t longer chain since the maximum slack (at small-small) that the rear cage has to pick up is reduced. This in turn allows use of a 32t or even 34t in the rear; I think for most of us this is a good trade-off... Before allowing the smallest cogs on the small ring, make sure your chain length and rear cassette will work with the rear cage.

TerryDi2C

As far as I know - and I should definitely update the GPC page linked above - one of the main reasons for restricting small x small is because on some bikes, and with certain chain rings, you risk getting the chain caught on the big ring's shift ramps (when cross chaining small x small).

eduskator

But we like to discuss and argue on anything and everything. Welcome to our current society. That's the whole point of a forum, right?

datlas 

I have been on this forum for many years, so I have learned to not take such things personally.

I have also come to love this place because, despite personalities, there is a wealth of knowledge/information/experience.

Carry on.