## Adding a front disc to a road bike !! And Now Hydro!

Nobody
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### Re: Adding a front disc to a road bike !! And Now Hydro!

bosvit wrote:If this is the case how can a 140 place more stress on the hub than a 160? According to the physics I am aware of the bigger the disc (attached to the same hubs with the same bolt positions) the higher the torsional stress on the hubs for the same amount of braking pressure on the hand brake.
This is the leverage ratio of tyre tread to axle over pad to axle. This is different to below.

The distance of the pad from the axle matters as the wheel becomes a lever with the pivot point at the pad (when braking). This is the leverage ratio of tyre tread to pad (radially) over pad to axle. As the disc gets smaller, the pad (pivot) gets closer to the axle and the leverage on the axle gets bigger. Not only are you increasing the distance from tyre to pad but at the same time you are reducing the distance from pad to axle. So the difference in leverage between 185 and 140 is significant. How this affects the quick release is it provides a huge amount of sudden force which moves the quick release when braking, then the quick release relaxes after braking and moves back. This causes it to slowly unwind.

Assume diameter of wheel with tyre is 68cm, then:

For 185mm disc
(34 - 9.25) / 9.25 = 2.68

For 140mm disc
(34 - 7) / 7 = 3.86

Percentage difference:
3.86 / 2.68 X 100 = 144%

So my basic calculations show the force at the axle is 44% higher with a 140 than a 185.
Last edited by Nobody on Fri Jul 27, 2012 10:29 pm, edited 2 times in total.

baabaa
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### Re: Adding a front disc to a road bike !! And Now Hydro!

This causes it to slowly unwind.

This is misleading. May cause it...
Again good skewers and adjustment will override any issues ( of which I have had none whatsoever across three different types of skewer)

Nobody
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### Re: Adding a front disc to a road bike !! And Now Hydro!

I had already made the assumption of explaining something that actually happens, which can be seen by the context. It would be misleading if it never happened to anyone. I know it happens to one of my bikes.

Crittski
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Mate, that would represent a dodgy setup then if it can be setup so that there is not a problem...
Santa Cruz Blur TRc XTR
Volagi Liscio Ultegra

Nobody
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Yeah, that's me. Misleading everyone with my dodgy setup.

baabaa
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### Re: Adding a front disc to a road bike !! And Now Hydro!

(AT) nobody, so why haven’t you changed the setup on your bike with 160mm rotors which loosen skewers to larger rotors which will not?

bosvit
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Location: Port Lincoln

### Re: Adding a front disc to a road bike !! And Now Hydro!

Apart from the fact that you have your torsional forces backwards, fair enough.

A larger disc will place more leverage against the bolts that attach it to a hub than a shorter one with the same amount of friction/braking force used against it. It is basic year 10 physics.

So correct me if I have misunderstood you but you are basically saying that a 1.4m pole will have more leverage than a 1.85m pole?

Nobody
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### Re: Adding a front disc to a road bike !! And Now Hydro!

bosvit wrote:Apart from the fact that you have your torsional forces backwards, fair enough.
The resultant force acts perpendicular to a line which bisects both axle and pad as viewed from the side. In most cases this would be downward (or close to downward) as the disc caliper is usually on the back of the fork leg. So it tries to push the wheel out of (near) vertical fork dropouts with more force than your body weight applies downward in heavy braking. See the article on page 39 for more specifics.

bosvit wrote:A larger disc will place more leverage against the bolts that attach it to a hub than a shorter one with the same amount of friction/braking force used against it. It is basic year 10 physics.
Yes. However not directly related to what I was trying to explain.

bosvit wrote:So correct me if I have misunderstood you but you are basically saying that a 1.4m pole will have more leverage than a 1.85m pole?
The lever ("pole") is the same length, just the fulcrum is in a different position. Reading the article (again) may help visualise it.

MichaelB
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Oooh, ooooh, oooh, seems like TRP have a few new products coming out.

4 piston hydo calipers and dual piston mechanical brakes.

http://www.bikerumor.com/2012/07/24/prototype-trp-four-piston-disc-brakes-new-cyclocross-brakes-coming/

Hangdog98
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Joined: Mon Jun 13, 2011 11:54 pm
Location: Sydney, the REAL capital

### Re: Adding a front disc to a road bike !! And Now Hydro!

The likelihood of an axel being displaced as a result of disc brake use is directly related to the direction of force applied. Calliper position in relation to dropout opening is the key factor. I have a bike with a 160mm rotor that tries to pop the axel out even with moderate force on the lever. My solution after trying many MANY QR skewers was to retro-fit a solid bolt-up axel and use track nuts and a big spanner to tighten them up...TIGHT. This was a rigid fork made for heavy duty use and disc specific. The design worked fine with a 205mm rotor but was dangerous with a 160mm rotor because of the different calliper position. This is why some road-disc forks have forward facing drop-outs. The axel presses against the metal of the drop-out instead of the opening. In my experience, the wheel doesn't fall out but instead causes the tire to rub against the fork leg alerting you to the dropped axel shortly before locking up and vaulting you over the handlebars.

A friend on a mountain bike put his QR skewer in the fork with the lever on the drive side. The brake twisting forces loosened the QR and when he popped up over a jump, the wheel dropped and the resulting crash nearly got us a free helicopter ride to the hospital.

Disc brake calliper positioning is critical for safety for the reasons mentioned in 'Nobody's' post and even production forks can have this problem.

I begin building a new disc brake roadie in the next few weeks. This design factor will be given critical importance.

cobba
Posts: 283
Joined: Sun Feb 22, 2009 1:36 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

Re. moving axles from braking forces.

http://cotic.co.uk/geek/
Last edited by cobba on Thu Aug 02, 2012 11:30 pm, edited 1 time in total.

jasonc
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Hangdog98 wrote:I begin building a new disc brake roadie in the next few weeks. This design factor will be given critical importance.

doing a build blog?

Mulger bill
Super Mod
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### Re: Adding a front disc to a road bike !! And Now Hydro!

jasonc wrote:
Hangdog98 wrote:I begin building a new disc brake roadie in the next few weeks. This design factor will be given critical importance.

doing a build blog?

Hope so, looking forward to the result.
...whatever the road rules, self-preservation is the absolute priority for a cyclist when mixing it with motorised traffic.
London Boy 29/12/2011

Hangdog98
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### Re: Adding a front disc to a road bike !! And Now Hydro!

I unpacked my last set of callipers today and I'm setting up for the build and creating the project schedule. I'll post pics along the way. I still have to finish off my tandem Tag-a-long bike for the spring rides with my two kids.

MichaelB
Posts: 8819
Joined: Tue Feb 20, 2007 9:29 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

Hangdog98 wrote:I unpacked my last set of callipers today and I'm setting up for the build and creating the project schedule. I'll post pics along the way. I still have to finish off my tandem Tag-a-long bike for the spring rides with my two kids.

Please do tell us more. Don't leave us hanging ..... (pardon the pun)

On a side note, rediscovered this site

http://www.dbikes.de/

They make some reasonable priced disc roadies (and a disc TT bike as well !!), primarily using a cable/hydraulic converter. There is even one version weighing in at 5.1kg !!!!

They sell F&F modules as well

6.5kg, SRAM Red equipped steed

780g Road frame (forks are 520g)

Hangdog98
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Location: Sydney, the REAL capital

### Re: Adding a front disc to a road bike !! And Now Hydro!

This is the thing I have to finish over the next couple of weeks, then I can start the disc roadie. It's a tandem Tag-a-long. Code name "Double-O-Delta". Almost done.

MichaelB
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Looks good Hangdog, but hurry up !!

Re the Dbikes frames. Had an email back from them, and the 780g frame is for rim brakes only, so the disc enthusiasts have to stick with the 1,100g version.

Shipping of a set of wheels or F&F was quoted at 50 Euro (pretty good), but waiting on some more feedback re the VAT position and payment methods.

Will post them up when I find out.

Also, the frames were tested by Tour magazine as part of their large frame test shootouts, and here are the specs

Our frame set "DISC RACE" was measured from technical Center of the bike journal TOUR (see TOUR 11/2010)
The following date were obtained:

Standard Weight frame set: 1.675 kg
Stiffness Fork: 60N/mm
Stiffness bottom braket: 61 N/mm

cobba
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### Re: Adding a front disc to a road bike !! And Now Hydro!

Crittski
Posts: 392
Joined: Sat Oct 02, 2010 7:06 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

New 7.3kg aero racing bike from Culprit cycles with disc brakes.
Santa Cruz Blur TRc XTR
Volagi Liscio Ultegra

MichaelB
Posts: 8819
Joined: Tue Feb 20, 2007 9:29 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

New 7.3kg aero racing bike from Culprit cycles with disc brakes.

Looks good in terms of tech, but the name and graphics are a bit, ahem ...

No mention of cost. I reckon \$8 - 10k easily

MichaelB
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Joined: Tue Feb 20, 2007 9:29 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

You could call it good McGyvering ........ but it's a bit rough.

Mind you, it works .....

Home made conversion on the tri spokes as well ....

MichaelB
Posts: 8819
Joined: Tue Feb 20, 2007 9:29 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

Some more carbon double disc frames coming out there !!!

Foundry have the Riveter (tube to tube carbon, race geometry road bike, 1060g frame and internal cabling) - F&F is \$2199 and also available as a full bike, and then the Thresher (monocoque carbon, endurance road, 1200g frame) - F&F is \$1800 and also available as a full bike.

The Salsa Colossal is available as a Ti or Steel frame.

Nobody
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Location: Sydney

### Re: Adding a front disc to a road bike !! And Now Hydro!

Good explanation by Zinn about why hydros are better than mechanical currently.
http://velonews.competitor.com/2012/08/ ... kes_235280

I think much of his commentary about aero and weight issues only really applies to racers and WWs.

MichaelB
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Joined: Tue Feb 20, 2007 9:29 am

### Re: Adding a front disc to a road bike !! And Now Hydro!

And there are solutions to the issues he raises.

A degree of common sense is required to see through that stuff and realise that cable discs can still operate really well, but given a bit more development, will be even better

Nobody
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Location: Sydney

### Re: Adding a front disc to a road bike !! And Now Hydro!

One of the comments below the article got me thinking about some better cables (like below). I might give them a try in the future now I know my current brake cables are a compromise.
http://www.yokozunausa.com/prbrcaandhok.html