Shimano Di2 steals 2 gears

Bruceonabike
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Shimano Di2 steals 2 gears

Postby Bruceonabike » Thu Nov 23, 2017 3:45 pm

Just took delivery of a new bike with Shimano Ultegra Di2 8050. With a 52/36 chainring fitted the Di2 system won't let you select the 2 smallest gears when you're in the small chain ring! After talking to the bike dealer, they were mystified but we eventually found clarification in the Shimano dealers manual - it's a design feature! Supposedly to prevent you from changing into a gear which would "lower the chain tension"! Sounds to me like they had an engineering problem and their solution was to turn an 11 speed drivetrain into a 9 speed! I've had a look at the 6870 dealers manual and there's no such reference so I'm assuming its an 8000 series thing! Suffice to say I'm feeling robbed!

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find_bruce
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Re: Shimano Di2 steals 2 gears

Postby find_bruce » Thu Nov 23, 2017 4:22 pm

What you are attempting to do is called cross-chaining & it is generally considered a bad idea.

If you want to visualise what is happening with your gears, this gear calculator may help - you actually have about 15 usable gears, not the 22 that 2 x 11 would suggest.

human909
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Re: Shimano Di2 steals 2 gears

Postby human909 » Thu Nov 23, 2017 4:35 pm

Cross chaining really isn't that terrible. Sure it should be avoided but briefly cross chaining shouldn't be an issue. The real issue as already mention is insufficient chain tension. If you have a short derailleur this IS an issue, so this is a feature not a bug.

Bruceonabike wrote:Suffice to say I'm feeling robbed!

Robbed of what? You haven't lost any gears.

36&[11or12] is pretty much equivalent to 52&17

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g-boaf
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Re: Shimano Di2 steals 2 gears

Postby g-boaf » Thu Nov 23, 2017 4:37 pm

Bruceonabike wrote:Just took delivery of a new bike with Shimano Ultegra Di2 8050. With a 52/36 chainring fitted the Di2 system won't let you select the 2 smallest gears when you're in the small chain ring! After talking to the bike dealer, they were mystified but we eventually found clarification in the Shimano dealers manual - it's a design feature! Supposedly to prevent you from changing into a gear which would "lower the chain tension"! Sounds to me like they had an engineering problem and their solution was to turn an 11 speed drivetrain into a 9 speed! I've had a look at the 6870 dealers manual and there's no such reference so I'm assuming its an 8000 series thing! Suffice to say I'm feeling robbed!


It's probably something that can be tuned.

But why wouldn't you just use the smaller chain ring?


I don't have an Ultegra 8xxx series Di2 so I can't verify it.

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Re: Shimano Di2 steals 2 gears

Postby biker jk » Thu Nov 23, 2017 4:53 pm

g-boaf wrote:
Bruceonabike wrote:Just took delivery of a new bike with Shimano Ultegra Di2 8050. With a 52/36 chainring fitted the Di2 system won't let you select the 2 smallest gears when you're in the small chain ring! After talking to the bike dealer, they were mystified but we eventually found clarification in the Shimano dealers manual - it's a design feature! Supposedly to prevent you from changing into a gear which would "lower the chain tension"! Sounds to me like they had an engineering problem and their solution was to turn an 11 speed drivetrain into a 9 speed! I've had a look at the 6870 dealers manual and there's no such reference so I'm assuming its an 8000 series thing! Suffice to say I'm feeling robbed!


It's probably something that can be tuned.

But why wouldn't you just use the smaller chain ring?


I don't have an Ultegra 8xxx series Di2 so I can't verify it.


He's on the smallest chain ring but can't change to the smallest or second smallest cog. You can't disable this "feature" on 52-36 or 50-34 chainrings.

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Re: Shimano Di2 steals 2 gears

Postby Derny Driver » Thu Nov 23, 2017 5:11 pm

Car makers are very good at catering for people who dont know how to drive. Alarms ring if the seatbelt isnt on, headlights come on automatically if it is dark outside, you cant remove the keys from the ignition if it isnt in Park, you cant start the car without a foot on the brake etc. Last car I drove ( a mates VW) had lane sensing technology which I had to sort of fight against when I changed lanes, and an orange blinker light on the wing mirrors would flash whenever I went past another car or if a car came up alongside me in the next lane. Mildly annoying is an understatement.

I guess bike makers will probably head the same way and assume that cyclists have no idea what they are doing and start implementing this sort of thing. Perhaps a warning light could flash if the rider is cross chaining. Or a computer generated voice could call out from inside the headtube saying "Get off the effing hoods" if a rider is cornering or going down a steep hill on the tops. Or some sort of buzzer rings if a rider chug chugs around at cadence 40 everywhere.

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Re: Shimano Di2 steals 2 gears

Postby g-boaf » Thu Nov 23, 2017 5:19 pm

biker jk wrote:
g-boaf wrote:
Bruceonabike wrote:Just took delivery of a new bike with Shimano Ultegra Di2 8050. With a 52/36 chainring fitted the Di2 system won't let you select the 2 smallest gears when you're in the small chain ring! After talking to the bike dealer, they were mystified but we eventually found clarification in the Shimano dealers manual - it's a design feature! Supposedly to prevent you from changing into a gear which would "lower the chain tension"! Sounds to me like they had an engineering problem and their solution was to turn an 11 speed drivetrain into a 9 speed! I've had a look at the 6870 dealers manual and there's no such reference so I'm assuming its an 8000 series thing! Suffice to say I'm feeling robbed!


It's probably something that can be tuned.

But why wouldn't you just use the smaller chain ring?


I don't have an Ultegra 8xxx series Di2 so I can't verify it.


He's on the smallest chain ring but can't change to the smallest or second smallest cog. You can't disable this "feature" on 52-36 or 50-34 chainrings.


Apologies- still unwell, half asleep. :(

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Duck!
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Re: Shimano Di2 steals 2 gears

Postby Duck! » Thu Nov 23, 2017 7:05 pm

The gear blocking in cross-chaining positions has been included in the 3x11 setup of the XTR Di2 group, but as far as I'm aware this is the first time it's moved outside that configuration.

The justification about chain tension is a bit weird, because the Shadow rear derailleur design of the R9100 Dura-Ace and R8000 Ultegra series is vastly more stable and better-tensioned than traditional derailleur designs. I wonder if it's actually more to do with the new systems' disc-brake compatibility, with wider-spaced chainrings and greater lateral chain flex over previous-generation, and more outboard cassette position on disc-braked bikes due to wider hubs. Which would also explain why it's only on the compact & mid-compact chainring options; the greater chainring difference is more prone to chain interference on the inside face of the big ring when using the smallest sprockets and small ring.

I suspect it can be tuned out by plugging into the E-Tube software, going to the Synchro setup and basically lying to the system about what chainring combination you're using......

Oh, and H909 said, you haven't lost any gears anyway; the gear ratios that are found at the cross-chained positions on both rings can be found elsewhere in the gearset anyway, which is what the Synchro function does for you, essentially working as a sequential gearbox. At certain points in the shift sequence, instead of grabbing the next sprocket it changes chainrings and corrects the ratio jump by shifting two at the back in the opposite direction, so you end up at the next ratio interval. By doing so it shuts out the duplicated ratios.
I had a thought, but it got run over as it crossed my mind.

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Re: Shimano Di2 steals 2 gears

Postby ironhanglider » Thu Nov 23, 2017 9:51 pm

My mechanical 10spd groupset is much the same, and was so even when the bike was 8spd, probably due to short chainstays.

Whilst I can physically put the bike in the small-small combination the chain grinds away against the big ring and snags the shifting pins which attempt but fail to change onto the big ring. The two smallest cogs are unusable in the small ring for me.

I once had the bolt that holds the cable onto the FD come loose (and eventually fall off) in the middle of a 100km stage of the Tour of Bright, leaving me with just the small ring available. It left me to ride with a top gear of 39x15 on the flat roads of the Ovens Valley with a tailwind for 30-40 km. I am still mentally scarred by it.

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lone rider
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Re: Shimano Di2 steals 2 gears

Postby lone rider » Fri Nov 24, 2017 1:33 pm

How does the system know you are using standard, mid-compact or compact rings?

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Duck!
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Re: Shimano Di2 steals 2 gears

Postby Duck! » Fri Nov 24, 2017 1:42 pm

To calculate the Synchro shift points the gearset information is entered via the E-Tube platform. The factory default setting is for 52/36 & 11/28 gearing. Changing the programmed gearset will recalibrate the shift maps to suit.

Hence why I said earlier if you lie to it about what gearset you're using (i.e. program it for 53/39 while you're actually using 52/36), you may be able to circumvent the gear blocking.
Last edited by Duck! on Fri Nov 24, 2017 10:09 pm, edited 1 time in total.
I had a thought, but it got run over as it crossed my mind.

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Derny Driver
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Re: Shimano Di2 steals 2 gears

Postby Derny Driver » Fri Nov 24, 2017 5:07 pm

ironhanglider wrote:I once had the bolt that holds the cable onto the FD come loose (and eventually fall off) in the middle of a 100km stage of the Tour of Bright, leaving me with just the small ring available. It left me to ride with a top gear of 39x15 on the flat roads of the Ovens Valley with a tailwind for 30-40 km. I am still mentally scarred by it.

A mate of mine WON the A grade ToB in the 90s and rode the whole first stage in the small ring. He's s good pedaller.

A few years back before 10 and 11 speed was available, my brother wanted a good climbing cassette for the Hotham stage. The night before the stage, we put it on. It was a Miche junior cassette, 16-17-18-19-21-23-25-27-29
He had to get to the bottom of Hotham in the 53-16 which sounds easy enough but it wasnt.
I'd like to say it was a master stroke and he won the stage but he didnt. :D

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Re: Shimano Di2 steals 2 gears

Postby madmacca » Sat Nov 25, 2017 10:50 am

Derny Driver wrote:Car makers are very good at catering for people who dont know how to drive. Alarms ring if the seatbelt isnt on, headlights come on automatically if it is dark outside, you cant remove the keys from the ignition if it isnt in Park, you cant start the car without a foot on the brake etc. Last car I drove ( a mates VW) had lane sensing technology which I had to sort of fight against when I changed lanes, and an orange blinker light on the wing mirrors would flash whenever I went past another car or if a car came up alongside me in the next lane. Mildly annoying is an understatement.

I guess bike makers will probably head the same way and assume that cyclists have no idea what they are doing and start implementing this sort of thing. Perhaps a warning light could flash if the rider is cross chaining. Or a computer generated voice could call out from inside the headtube saying "Get off the effing hoods" if a rider is cornering or going down a steep hill on the tops. Or some sort of buzzer rings if a rider chug chugs around at cadence 40 everywhere.


"Incorrect riding procedure" in a German-accented voice. :)

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Re: Shimano Di2 steals 2 gears

Postby Derny Driver » Sat Nov 25, 2017 4:05 pm

madmacca wrote:
"Incorrect riding procedure" in a German-accented voice. :)

:D :D :D

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ComradeSpear
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Re: Shimano Di2 steals 2 gears

Postby ComradeSpear » Fri Dec 01, 2017 12:48 am

I am actually experiencing the same thing after I swapped my 6870 RD to the 8050 RD. If it's cross chaining then it's allowing a larger chain ring to large cog combination. Shouldn't it not allow this combination if it's cross chaining?

I used eTube and configured synchro shifting and it's not bad actually. I'll test this weekend on a longer ride if the Melbourne forecast doesn't eventuate.

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Re: Shimano Di2 steals 2 gears

Postby g-boaf » Fri Dec 01, 2017 7:13 am

madmacca wrote:
Derny Driver wrote:Car makers are very good at catering for people who dont know how to drive. Alarms ring if the seatbelt isnt on, headlights come on automatically if it is dark outside, you cant remove the keys from the ignition if it isnt in Park, you cant start the car without a foot on the brake etc. Last car I drove ( a mates VW) had lane sensing technology which I had to sort of fight against when I changed lanes, and an orange blinker light on the wing mirrors would flash whenever I went past another car or if a car came up alongside me in the next lane. Mildly annoying is an understatement.

I guess bike makers will probably head the same way and assume that cyclists have no idea what they are doing and start implementing this sort of thing. Perhaps a warning light could flash if the rider is cross chaining. Or a computer generated voice could call out from inside the headtube saying "Get off the effing hoods" if a rider is cornering or going down a steep hill on the tops. Or some sort of buzzer rings if a rider chug chugs around at cadence 40 everywhere.


"Incorrect riding procedure" in a German-accented voice. :)


People see photos or videos of pro riders cornering or descending with hands on the hoods, so they figure it must be okay.

Same with pro riders chugging along at low cadence, there were a few of them around. Beats me how they do it.

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