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PostPosted: Sun Jun 04, 2017 10:02 am 
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Posts: 68
Hi,

I'm looking to use a 6870 group I have lying around to build up a disc road bike. (with st-785 shifters)
However it doesn't look easy to keep weight down on a relative budget...
Switching to 140mm rotors saves 40gr. but costs a little sense of security (though I am 62kg). Tubular is also not my preference.

However i read that the old r785 calipers are essentialy rebranded MTB calipers. Does that mean that I can use XTR calipers as well?

Are there other options to reduce weight (Hope, Magura, Sram, etc.)?

For now it is just a thinking exercise, I want to have my build figured out before I get into buying...


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PostPosted: Sun Jun 04, 2017 11:20 am 
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AFAIK all the shimano calipers road/mtb are interchangeable. I think there were some differences generation to generation. But anything relatively recent and comparable should be plug, (bleed) and play.

So don't expect old 4 pot XTs or saints to work with current road levers.......... (but they still might work!)


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Posted: Sun Jun 04, 2017 11:20 am 


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PostPosted: Sun Jun 04, 2017 11:37 am 
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Thank you.
Guessing there are no flat mount MTB brakes though. Just thought it through more and adapters add weight as well.
The flat mount rs805 weighs 250gr. for a pair, while the M9000 weighs 182gr.
70gr. on bolt and adapters for a less clean look might be worth a reconsider...


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PostPosted: Sun Jun 04, 2017 11:38 am 
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Yeah, no flat mounts. Only PM or IS with an adaptor IIRC.


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PostPosted: Sun Jun 04, 2017 2:36 pm 
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Posts: 223
I run an XT on the front, no issues.


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PostPosted: Sun Jun 04, 2017 4:05 pm 
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I use XTR calipers with my 785 shifters- they work great.
Terrific power and modulation, less draggy than 785 calipers.

Use 160 rotors- get RT99 XTR rotors. This becomes a set it and forget it system.


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PostPosted: Sun Jun 04, 2017 8:02 pm 
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My wallet is considering it. If adapters are 25g each, and XTR calipers cost 83 euro each, that would mean 80 euro for 25g compared to rs805.
It'd be 186 euro for 85g compared to r785.

It might be to costly for me to do...

Buying r785 shifters already isn't cheap (and funny enough buying them without r785 calipers is currently more expensive than with).
Going the chinese/diy route is supposed to be a cost saving measure. My total build can't cost 3000 euro.

(Di2 shifters, cables, battery, junctions, cassete, chain, etc = 400 euro/ R785 shifters and calipers, RT99 rotos = 355 euro/ Chinese frameset and wheelset + shipping= 1000 euro/ stem, handlebar, seatpost, saddle, tires, tubes, pedals, bottle cages)


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PostPosted: Mon Jun 05, 2017 12:08 am 
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Posts: 363
mattr wrote:
AFAIK all the shimano calipers road/mtb are interchangeable. I think there were some differences generation to generation. But anything relatively recent and comparable should be plug, (bleed) and play.

So don't expect old 4 pot XTs or saints to work with current road levers.......... (but they still might work!)


Yep, they do. Currently running Zee's on my roadie with R685 levers (18+ months). No probs.

Have my new & unused RS785 calipers (that came with my levers) lying around looking for a new home.


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PostPosted: Mon Jun 05, 2017 2:42 am 
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Location: NZ
So the Zee's are better than RS785?


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PostPosted: Mon Jun 05, 2017 3:29 am 
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Location: Houston, Texas
I suspect the only difference of consequence is hydro hose routing, as the Zee still use the banjo on the outboard side of the caliper, while the RS785 uses the 'inline' style that is inboard of the mount for a better alignment of the hydro housing with the caliper.

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PostPosted: Mon Jun 05, 2017 3:31 am 
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Location: Krasnoyarsk, Russia
boots2000 wrote:
I use XTR calipers with my 785 shifters- they work great.
Terrific power and modulation, less draggy than 785 calipers.

Did you weight both calipers without pads? I'd like to know how much exactly br-m9000 calipers save compared to br-rs785 (post mount, no banjo).

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PostPosted: Mon Jun 05, 2017 9:58 am 
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Seems it differs on who weighs them. Rose has them for 284g a pair, while arts cyclery says 124g per caliper, and Crc at 262g for the pair. Bike24 at 248g/pair. All including (identical) pads. I wonder where these differences come from... On average, the banjostyle r785 seem to be a little lighter.

Shimano lists the rs785 as 284g and the r785 as 271g.


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PostPosted: Mon Jun 05, 2017 2:12 pm 
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I went through this a couple months ago building up a CX bike. Turns out, pretty much any XT/XTR caliper can be used with the Shimano hydraulic road levers so long as you use the BH59 hose kits according to the folks at Shimano.


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PostPosted: Tue Jun 06, 2017 12:38 am 
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Gearjunkie wrote:
So the Zee's are better than RS785?


I primarily went for the Zee's, as 'bigger is better (pad size and power) and I'm not a flyweight. The bigger pads last longer, and compared to a mate with full RS686/RS785 combo on a Trek Domane, lever feel is the same.

Also, with the bike that I have (Volagi Liscio), the routing of the hose and positioning works much better, both front and rear, where it exits the fork/frame and connects to the caliper.

With respect to weights, I did weigh them and have the numbers at home, and I think the difference is about 12g/caliper (including pads). Naturally the Zee is heavier.


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Posted: Tue Jun 06, 2017 12:38 am 


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PostPosted: Tue Jun 06, 2017 3:18 am 
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Location: Houston, Texas
Bhaalgorn wrote:
Turns out, pretty much any XT/XTR caliper can be used with the Shimano hydraulic road levers so long as you use the BH59 hose kits according to the folks at Shimano.

Curious, as I thought Shimano was now recommending the BH90 hose kit for road/cx hydraulic setups? We have two cross bikes with ST-R785 shifters and RS785 calipers. My bike was the guinea pig and uses BH59 hose kit and just recently converted my wifes bike from DA9000 with Juintech to the Di2 hydro setup with BH90 hose kit. While my levers have more modulation, her bike has, albeit less lever travel, a much stiffer feel, when squeezing to achieve brake lock, almost considering replacing my hoses with the BH90 kits.

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