Road Disc Brakes- Rotor Choice

Discuss light weight issues concerning road bikes & parts.
MichaelB
Posts: 474
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

MoPho wrote: Are you using the Zee calipers on a road bike? Disc naysayers often use lack of traction as an argument but I feel like I could use even more power in the dry, 4 piston brakes would be interesting. :twisted:


Yep, Volagi Liscio.

They work a treat, and actually gave better hose alignment when fitted, especially on the rear.

MoPho
Posts: 447
Joined: Sun Jul 10, 2011 7:48 pm
Location: NorCal/SoCal

by MoPho

MichaelB wrote:
Yep, Volagi Liscio.

They work a treat, and actually gave better hose alignment when fitted, especially on the rear.


Fascinating... And they work with the Shimano road levers?


.

by Weenie


MichaelB
Posts: 474
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

@ MoPho - sure do. Been doing it for almost 2 years now.

The theory is they shouldn't due to the piston area differences between the 2 & 4 piston versions. I have a great lever feel and travel, and it's so damn similar (if not a bit better than a mate who had the R685 levers and 785 calipers) that I still have my new RS785 calipers sitting in the box they came in.

MTB'ers have been using the 4 piston calipers with 2 piston levers for years, so was pretty confident that it'd work fine.

The Saint/Zee pads are a bit taller and much longer than the 785's, so last better as well, and with an additional side benefit of having additional thermal mass. Great all round !!

ooo
Posts: 600
Joined: Sat May 21, 2016 12:59 pm

by ooo

Shimano released 4-piston XT caliper BR-M8020
http://bike.shimano.com/content/sac-bike/en/home/news-and-info/news/shimano-introduces-deore-xt-4-piston-hydraulic-brake-caliper-and.html
https://www.youtube.com/watch?v=24BP4si4vUg

In press release they say that it is 100% compatible with 2 piston brake lever BL-M8000
looking at picture we can see that it is almost the same caliper as BR-M820/BR-M640

That means ST-R785/RS685 that was made for BR-R785 should work with all 4 piston calipers
(because BR-R785 ≈ BR-M785 ≈ BR-M8000, so ST-R785/RS685 specs ≈ BL-M8000 specs)
'

MichaelB
Posts: 474
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

ooo wrote: ....In press release they say that it is 100% compatible with 2 piston brake lever BL-M8000
.....


Yep, they officially acknowledge that the calipers are 'swappable', something that has been done for ages !! I honestly was surprised by this, especially for Shimano.

Looking fwd to the next Gen 4 piston caliper, as it has been a while

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Lewn777
Posts: 338
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

R685 levers, Saint caliper, disk version of your current fork and disk wheel. All on current rim-brake bike?
Weight weenie maximum stopping power to minimum weight? Doable? Safe?

I just feel that running a rear hydraulic disk brake and all that cabling isn't worth the weight. Am I crazy? I know I'll end up with a frankenbike, but I always believe form should follow function. Also anyone done it already?

MichaelB
Posts: 474
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

Hi Lewn777,

I sort of did it when I 1st tried discs. Put a CX-ish alloy disc fork on my 2007 Argon18 Platinum with BB7 caliper, and left the rear rim brake.

That convinced me of discs, since then went the whole hog.

Do what you wish, it's your bike, but if you do it, do it properly.

joejack951
Posts: 434
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

I did the same thing as MichaelB on my commuter bike based on a cyclocross frame. At the time I built it in 2009, the Pedal Force CX1 was the lightest frame I could find that had rack and fender mounts, but it did not have a rear disc mount. I mostly brake on the front anyway so I used a Winwood full carbon disc fork and Avid BB7 Road brake up there. Served me well for many thousands of miles and I still use that bike (with something like 25,000 miles on it now). Similarly convinced of discs, my latest road bike is disc front and rear (Hongfu FM079-F).

Even though I rarely touch the rear brake, I could not see leaving it off entirely which is what you (Lewn777) seem to be suggesting. Are there hydro rim brakes you could use for the rear? Or maybe just deal with two different levers so you can run a regular cable brake on the rear.

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Lewn777
Posts: 338
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

MichaelB wrote:Hi Lewn777,

I sort of did it when I 1st tried discs. Put a CX-ish alloy disc fork on my 2007 Argon18 Platinum with BB7 caliper, and left the rear rim brake.

That convinced me of discs, since then went the whole hog.

Do what you wish, it's your bike, but if you do it, do it properly.

There is a disk version of my bike which is a Fuji SL. So I could order a disk fork from Fuji. Same colour. Then I already have a disk front wheel and rotor from my CX/bikepacking bike and then order a Zee or Saint caliper and a R685 lever and bleed them together.

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Lewn777
Posts: 338
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

joejack951 wrote:I did the same thing as MichaelB on my commuter bike based on a cyclocross frame. At the time I built it in 2009, the Pedal Force CX1 was the lightest frame I could find that had rack and fender mounts, but it did not have a rear disc mount. I mostly brake on the front anyway so I used a Winwood full carbon disc fork and Avid BB7 Road brake up there. Served me well for many thousands of miles and I still use that bike (with something like 25,000 miles on it now). Similarly convinced of discs, my latest road bike is disc front and rear (Hongfu FM079-F).

Even though I rarely touch the rear brake, I could not see leaving it off entirely which is what you (Lewn777) seem to be suggesting. Are there hydro rim brakes you could use for the rear? Or maybe just deal with two different levers so you can run a regular cable brake on the rear.

Well my thoughts are run a 105 5800 left hand lever with conventional cables with a conventional 105 rim brake on the rear (moto style). Then run a R685 right hand lever with a Saint caliper and replacement disk version of my fork from the original manufacturer. I've found Shimano levers to be fairly similar

I'm not convinced by having a rear disk brake as I think the weight, complications and maintenance isn't worth it. Like you I do nearly all my braking on the front.

CallumRD1
Posts: 129
Joined: Mon Apr 03, 2017 2:54 pm

by CallumRD1

The 5800 lever and the 685 lever are vastly different sizes and shapes. I would find it very difficult to ride with one of each.

MichaelB
Posts: 474
Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

Lewn777 wrote: ...... So I could order a disk fork from Fuji. Same colour. .....


I have often seen that just because they are fitted to a bike (i.e. they obviously make them), actually getting one is either, really hard, or REALLY expensive.

If you really want to go disc, it may just be as cost effective and a whole lot easier to get a new full disc bike from the outset.

All the bits and pieces add up pretty quick.

Good luck, and let us know how you go.

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Lewn777
Posts: 338
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

CallumRD1 wrote:The 5800 lever and the 685 lever are vastly different sizes and shapes. I would find it very difficult to ride with one of each.

Image
Image

I thought they looked somewhat similar. although you'd need them on your bike to really understand the differences obviously.

CallumRD1
Posts: 129
Joined: Mon Apr 03, 2017 2:54 pm

by CallumRD1

They do look similar but feel very different. My 2011 Scott CR1 had 5800 shifters and when I bought my Felt F3X it ha 685 shifters. The 685 shifters are much deeper from the clamp to where my hand rests and at least a centimeter taller. It took me the better part of a month to get used to the feel of the 685 hoods.

ooo
Posts: 600
Joined: Sat May 21, 2016 12:59 pm

by ooo

For disc + rim brake may be better to to use good mechanical disc brakes, like TRP Spyre

Shimano tried to make same design for new ultegra,
but r8020+r8000 doesn't look similar,
di2 r8050+r8070 is ok to combine rim + hydro disc sti
'

by Weenie


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