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Ultegra 6800: 46/36 to 46/34?

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Ultegra 6800: 46/36 to 46/34?

Old 05-22-16, 11:08 AM
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KonaRider125
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Ultegra 6800: 46/36 to 46/34?

I just got a bike with a Ultegra 6800 46/36 crank, and I was wondering if I would have any issues swapping the 36 chainring for a 34 chainring.

Does anyone here have experience running this setup? Any shifting issues?
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Old 05-22-16, 11:38 AM
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Originally Posted by KonaRider125 View Post
I just got a bike with a Ultegra 6800 46/36 crank, and I was wondering if I would have any issues swapping the 36 chainring for a 34 chainring.

Does anyone here have experience running this setup? Any shifting issues?
I can't say that I've tried this with a 6800 crank, but I've changed both of my 46/36 cranks (a FSA Gossamer and a Shimano CX-50) to 46/34 with no issue. I can see no reason why you wouldn't have the same success.
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Old 05-22-16, 11:50 AM
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I only see one replacement 6800 46T ring for sale online, leading me to believe they use the same one with 36T or 34T inner rings. If it were otherwise, I'd expect to see separate "A" and "B" type rings for sale that were specific to 36T or 34T.
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Old 05-22-16, 11:51 AM
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Thanks for the comments. I figured if Shimano doesn't sell the 46/34 combo together there must be a reason for it.

Looking forward to hearing from someone who has a 6800 crank and FD with 46/34.
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Old 05-22-16, 11:56 AM
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I figured if Shimano doesn't sell the 46/34 combo together there must be a reason for it.
Oh wait -- perhaps I spoke too soon. Looking through the Universal Cycles page, I'm seeing that the 52T, 46T, and 36T are listed as "MB" type, the 50T and 34T are listed as "MA" type, and the 53T and 39T are listed as "MD" type. So it seems that 46/34 isn't an "approved" combination, but I would be somewhat surprised if it didn't still work.
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Old 05-22-16, 12:47 PM
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Provided you can bolt it up and it doesn't exceed your derailleurs' specs, it should work just fine. The innermost chainring doesn't need any pins to lift a chain from a smaller ring nor gates to facilitate shifting to a smaller ring, so any ol' ring -- even one without any special shift aids -- will work.
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Old 05-22-16, 07:41 PM
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Bump for the Sunday night crowd.

Thanks
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Old 05-23-16, 08:09 AM
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Originally Posted by KonaRider125 View Post
Thanks for the comments. I figured if Shimano doesn't sell the 46/34 combo together there must be a reason for it.

Looking forward to hearing from someone who has a 6800 crank and FD with 46/34.
Shimano doesn't sell a lot of things for no reason. They also tell you that you can't do a lot of stuff that because it won't work. But, in my experience at least, Shimano severely underestimates the ability of their equipment. Their whole "MB", "MA", "MD" thing is to get you to buy new components when you don't really need to. At the very least, I'd get a 34 tooth inner (you don't even need to use Shimano's rings at all) and try it. If it doesn't work, you're out a few bucks for the ring.
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Old 05-23-16, 08:14 AM
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Originally Posted by ThermionicScott View Post
Oh wait -- perhaps I spoke too soon. Looking through the Universal Cycles page, I'm seeing that the 52T, 46T, and 36T are listed as "MB" type, the 50T and 34T are listed as "MA" type, and the 53T and 39T are listed as "MD" type. So it seems that 46/34 isn't an "approved" combination, but I would be somewhat surprised if it didn't still work.
I swap my 36 and 34 all the time depending on where I'm going riding. I usually use a 50 as the large ring, so you're going to be fine with a 48. If you only swap the small ring, you don't even have to adjust the FD.

The quickest way is to drop the chain onto the BB, remove the 4 bolts from the back, remove the big ring, then carefully guide the inner ring past the arms and over the crank so you don't scratch anything. Reverse to put it back together. Make sure inner ring is facing the right way, there should be recesses where the bolt heads sit.

There are no shifting helper bits on these small rings, They're pretty much identical except for the tooth count.

I follow the Shimano engineering documents pretty closely, but find no problem ignoring the suggested marriage to the big ring.
Pro Teams are mixing and matching any combo of big ring and small ring also.

Last edited by andr0id; 05-23-16 at 08:20 AM.
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Old 05-23-16, 08:26 AM
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6800 cranks have a single bcd so all chain rings are interchangeable so you can swap 36 for 34. You have to use Shimano rings though.
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Old 05-23-16, 09:29 AM
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Thanks for the comments, I guess I'll order up a 34T chainring and give it a shot!
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Old 05-23-16, 09:51 AM
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Originally Posted by KonaRider125 View Post
Thanks for the comments, I guess I'll order up a 34T chainring and give it a shot!
At $10 for the chainring:

Shimano Ultegra FC-6800 11-SPD Chainring > Components > Drivetrain > Chainrings | Jenson USA

It's not an expensive experiment!
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Old 05-23-16, 10:22 AM
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Originally Posted by KonaRider125 View Post

Does anyone here have experience running this setup? Any shifting issues?
Yes, on my commuter bike. Shifts about as well as a 50/34 set. I never tried it in 46/36 actually

A friend runs 54/36 with DA9000 and that works about as well as the approved 52/36
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Old 05-23-16, 11:12 AM
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Originally Posted by rms13 View Post
6800 cranks have a single bcd so all chain rings are interchangeable so you can swap 36 for 34. You have to use Shimano rings though.
Any ring that fits and shifts well would work.
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Old 05-23-16, 01:03 PM
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Originally Posted by Leebo View Post
Any ring that fits and shifts well would work.
But since the 6800 crankset uses Shimano's irregular 4-bolt pattern, you're limited to Shimano rings for the most part.
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Old 05-23-16, 08:32 PM
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Originally Posted by dr_lha View Post
Ordered, needed to get some Stans sealant anyways!

I'll try to remember to report back on how shifting of the 46/34 is compared to the 46/36
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Old 05-26-16, 02:35 PM
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Update: Installed the 34T small chainring and went for a 3 hour hilly ride today. Shifting is perfect. The 46/34 combo in Ultegra 6800 works great.
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Old 05-27-16, 09:56 AM
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Awesome, always glad to hear of successful experiments.
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Old 05-27-16, 09:57 AM
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Originally Posted by KonaRider125 View Post
Update: Installed the 34T small chainring and went for a 3 hour hilly ride today. Shifting is perfect. The 46/34 combo in Ultegra 6800 works great.
Good job! Welcome to the 46/34 club, members: You and me.
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Old 08-30-17, 07:22 AM
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Jut got my 34T ring today

Will install it over the weekend and report.

Also replacing the stock 105 11-32 cassette with a SRAM PG-1170 11-36 cassette.
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