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PostPosted: Fri Mar 17, 2017 3:02 am 
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I'm trying to quantify the weight benefit of running a disc brake bike on very light carbon rims or a rim brake bike running on very light alloy rims - all components considered.

Has anyone given this some thought?

1. Frame - are the brake mounts adding a lot of weight?
2. Modern disc brake calipers compared to modern rim brake, difference?
3. Hydraulic vs wire - weight penalty?
4. Cables and housings - weight penalty?
5. Shifters (if hydraulic) - how much extra weight are we talking about?
6. Tubular carbon disc brake wheelset vs a clincher alloy rim brake wheelset - advantage? (hubs are heavier obviously vs rim weight)
7. Two modern disc brake rotors and screws?
8. Carbon tubular rims with vs. without brake track... how low can you go? :D
9. How well do mechanical disc brake calipers work with common shifters levers? Is it a problem?

Anyone have weight figures on for example Cervelo S3 vs Cervelo S3 Disc?

What do you think? Thanks for reading...
/a

Edit: Side discussion: Apart from being ugly, has anyone ever thought of switching to a lighter fork and going disc brake in front only? Is that a smart compromise?


Last edited by alcatraz on Fri Mar 17, 2017 6:39 am, edited 3 times in total.

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PostPosted: Fri Mar 17, 2017 3:30 am 
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Subscribed. Wish I had something to add

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Posted: Fri Mar 17, 2017 3:30 am 


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PostPosted: Fri Mar 17, 2017 6:37 am 
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Side note.... aside from the weight penalty of thru axles, rotors, calipers and hydro shifters + fluid, watch out for the steel reinforced dropouts on many carbon disc frames. Most manufacturers do not mention these on spec sheets but I was surprised to find they are really common.


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PostPosted: Fri Mar 17, 2017 6:41 am 
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toshi wrote:
Side note.... aside from the weight penalty of thru axles, rotors, calipers and hydro shifters + fluid, watch out for the steel reinforced dropouts on many carbon disc frames. Most manufacturers do not mention these on spec sheets but I was surprised to find they are really common.


Are thru axles a must? Is brake rub too common on disc brakes?

What about mechanical disc brakes. Maybe they are less prone to brake rub from running common dropout frame/wheels.


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PostPosted: Fri Mar 17, 2017 7:39 am 
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2. BR-RS785 disc brake caliper is 111g for a piece. 222g for a pair + 22g per 4pcs of steel caliper bolts (12g for titanium bolts). BR-R9100 is about 320g per pair.


Attachments:
BR-R785.jpg
BR-R785.jpg [ 119.13 KiB | Viewed 1832 times ]
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PostPosted: Fri Mar 17, 2017 12:32 pm 
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Kristinka wrote:
2. BR-RS785 disc brake caliper is 111g for a piece. 222g for a pair + 22g per 4pcs of steel caliper bolts (12g for titanium bolts). BR-R9100 is about 320g per pair.


Hey! Thanks. Does the weight Include brake pads?

/a


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PostPosted: Fri Mar 17, 2017 12:46 pm 
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IIRC (before Dura Ace / Red HRD was released) "equivalent" (eg Ultegra Rim) was ~400g less all in between disc version and rim version ultegra bikes.


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PostPosted: Fri Mar 17, 2017 2:03 pm 
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That sounds about right. I think @Madcow of Fairwheel Bikes did quite an extensive analysis and came up with "about a pound" as the answer. That coincides with what @jeffy just said above. If you narrowed your search criteria you could probably find @Madcow's analysis.

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PostPosted: Fri Mar 17, 2017 3:07 pm 
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Not an apples-to-apples comparison,

2014 Scott Solace Premium built with DA 9070 shifters, derailleurs, brakes, Ultegra CS-6800 12-25 cassette, Enve 12-cm stem, bar, and seat post, leather bar wrap, Fizik Kurve Snake carbon, Zipp 303 FC built on DT 240S SP hubs, Vittoria Corsa G+ 700x28, Michelin latex tubes, Jagwire brake cable sets, and KMC X11SL DLC weighed in at ~15.6.

2016 Scott Solace 10 Disc with Shimano ST-R785, BR-R785 calipers, ICetech 140mm rotors, DA 9070 derail;eurs, Edco Monblock 12-27 cassette, Enve 11-cm stem, 40cm bars, and seat post, leather bar wrap, Fizik Kurve Snake carbon, Nox Composites Falkor 36D rims built on DT 240S SP 24-hole CL hubs, Vittoria Corsa G+ 700x28, Vittoria latex, Shimano hydraulic hoses, and KMC X11SL DLC weighs in at ~16.9.

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PostPosted: Fri Mar 17, 2017 5:45 pm 
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This is a force 22 rear hydraulic shifter and flat mount caliper:

Image

Image

I think the weight difference is more than a pound when you are talking about sub 13lb builds or at least it becomes a lot harder to get to sub 13.

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PostPosted: Fri Mar 17, 2017 6:13 pm 
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Just some official info about the new shimano groupsets. This is a quite old PR document, but they claim that there is a 338g weight penalty for the Di2 (9150 vs 9170) and 348g for the mechanical groupsets (9100 vs 9120). If you cut the brake cables and housing and also account for the hydraulic fluid, that will give the rim brake version some extra edge.

Obviously there is some weight penalty also for the frame and wheels. You will probably indeed end up with around 1 pound extra.

Link to the pdf: https://media.dcrainmaker.com/images/20 ... eights.pdf

Image


Attachments:
rimvsdisc.jpg
rimvsdisc.jpg [ 9.7 KiB | Viewed 1583 times ]
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PostPosted: Fri Mar 17, 2017 7:09 pm 
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^ this was outdated info. for example, BR-R9170 updated weight from catalog is 255g/pair
(shimano still list 515g/pair on some of their websites, but you only need to look at catalog)

current catalog weights:

ST-R9100 - 365g/pair
ST-R9120 - 505g/pair
ST-R9150 - 230g/pair
ST-R9170 - 360g/pair

shifters: hydro vs non-hydro = +140g/pair
shifters: hydro di2 vs non-hydro di2 = +130g/pair

BR-R9170 - 255g/pair
BR-R9100 - 326g/pair
BR-R9110 - 150g+139g

calipers: hydro vs non-hydro standard = -71g/pair
calipers: hydro vs non-hydro directmount = -34g/pair

total disc brake penalty for calipers + shifters (per pair, without housing/wheels/rotos):

di2 disc hydro vs non-hydro di2 normal rim brake = +59g/pair
di2 disc hydro vs non-hydro di2 directmount rim brake = +96g/pair
non-di2 disc hydro vs non-hydro normal rim brake = +69g/pair
non-di2 disc hydro vs non-hydro directmount rim brake = +106g/pair


there is one interesting option to run front disc brake, rear rim brake - saves weight and $$$ on rear wheel
i have tried this on flat bar bike, and it works wonderful on 40mm tires for medium loaded touring

shimano tried to use similar form for R9100/20/50/70 shifters, but after looking at them I found that:
different form used for ST-R9100 vs ST-R9120 (mechanical non-hydro vs mechanical hydro)
similar form used for ST-R9150 vs ST-R9150 (di2 non-hydro vs di2 hydro)
so, for di2 setup it may be possible to mix hydro and non-hydro brakes

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PostPosted: Sat Mar 18, 2017 2:40 am 
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ooo wrote:
^ this was outdated info. for example, BR-R9170 updated weight from catalog is 255g/pair
(shimano still list 515g/pair on some of their websites, but you only need to look at catalog)


I just rechecked the specification. I believe that the table counts the rotors (160 mm) and lock rings included in the brakes weight. While the calipers might be lighter than the rim brake versions but the rotors and small parts add ~220-260g to the setup based on size. Let's say if you go with 140mm rotors front/rear your weight penalty for the groupset will be around 300g.

So I'd say 1 pound weight penalty overall (groupset, frame, wheels) sounds about right if you go high-end on everything.


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PostPosted: Sat Mar 18, 2017 8:57 am 
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if you use 160mm rotors with flatmount you need to add 140-to-160mm flatmount adapters too:
SM-MA-R160D/D (ISMMAR160DDA) ≈ 12gr each (24g/pair)

140mm rotors+dura-ace brakes+lockrings = 255+96*2+9= 456g (per pair, without STI/housing)
140mm rotors+dura-ace brakes+lockrings+di2 STI = 816g
140mm rotors+dura-ace brakes+lockrings+mech STI = 961g

160mm rotors+dura-ace brakes+lockrings+flatmount adapters=255+118*2+9+12*2= 524g (per pair, without STI/housing)
160mm rotors+dura-ace brakes+lockrings+flatmount adapters+di2 STI = 884g
160mm rotors+dura-ace brakes+lockrings+flatmount adapters+mech STI = 1029g

standard rim brake+di2 STI=326+230=556g (from this to 140 disc penalty=260g, to 160 disc penalty=328g)
standard rim brake+mech STI=326+365=691g (from this to 140 disc penalty=270g, to 160 disc penalty=338g)
directmount rim brake+di2 STI=150+139+230=519g (from this to 140 disc penalty=297g, to 160 disc penalty=365g)
directmount rim brake+mech STI=150+139+365=654g (from this to 140 disc penalty=307g, to 160 disc penalty=375g)

this is not counting wheel weight difference

some info (I think its not including qr/axle weights)

Sram 45mm wheel set comparison (cx-ray, 18/24 spokes, 24/24 spokes)
Zipp 303 Firecrest Tubular rim brake front=605g rear=785g set=1390g
Zipp 303 Firecrest Tubular disc brake front=640g rear=760g set=1400g

Shimano 37mm tubular wheel comparison (R9100 vs R9170)
weight info is not accurate, expected difference 25g per wheel (+50g per set)


Attachments:
sm-ma-r160-d-d.jpg
sm-ma-r160-d-d.jpg [ 3.4 KiB | Viewed 1365 times ]
flatmount-160.jpg
flatmount-160.jpg [ 59.09 KiB | Viewed 1365 times ]

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Last edited by ooo on Sat Mar 18, 2017 9:29 am, edited 1 time in total.
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PostPosted: Sat Mar 18, 2017 9:19 am 
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My Cervelo R3D came in at 7,900g as standard in a 56.

Not sure what the rim brake R3 weighs in the same size?

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Posted: Sat Mar 18, 2017 9:19 am 


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