Disk brakes on steel road frames - design considerations and traps?
 

I was asked a question by someone in my ride group about designing a custom steel frame that would be fit for disk brakes. This came up in relation to a discussion about the upcoming SRAM road hydralic disk brakes for Red and Force. I don't have any idea, so I thought I'd ask the experts!

Is it a simple matter of just putting the relevant mount on the triangle at the back end of the bike (presume that fork will be carbon/off the shelf), or is there more to consider (road 'race' frames often being lighter than touring or MTB frames)?

- Extra bracing? Mounting side only or both?
- Choice of tubing? Avoid certain things?
- any geometry concerns (turkey wobble) from disks that you can get?


Details:
- cable routing?
- braze on types? Hydraulic lines need those open style (ie clip or cable tie on later)?

Most steel frames seem to need bracing or some extra beef at the dropouts
Note if the brake needs ISO or lighter-weight post mounts.
Chainstay mounting is used on touring bike to clear the rack mounts. This puts the cable route under the BB but many brakes have a poor cable angle for this location.

I don't think anyone sells ISO brakes any more, but they all ship with ISO adapters.

Low-mount brakes don't require bracing, mounting behind the seat stay makes a brace from the seat stay to the chain stay a really good idea.

The only non-obvious thing (to me anyway) about putting discs on a road frame is the fork.

Group; While I admire innovation, I have to wonder. I honestly have to admit I have never heard a real road racer give a hard whine that they didn't have enough brake. Sounds more like a solution looking for a requirement (aka; Amateur folks with more money that they know what to do with...). Thoughts?

ksisler: "Sounds more like a solution looking for a requirement (aka; Amateur folks with more money that they know what to do with...)"

+1 :thumb:

Brian

Ok, so real road racers aside... what about big guys who weigh 220lb and live in areas with huge hills? What about rainy conditions (disc brakes lose a lot less grip in the rain than rim brakes)?

As a bigger guy who's spent quite a bit of time adjusting brakes professionally, I can tell you that there are situations where having disc brakes on a road bike would be nice for me. It's not that I'd die if I didn't have them, but it's nice to always have the range between "a little slower" and "flying through the air sans bike" available, and not have that high end diminish a lot in some situations. Granted, there are situations where the reverse is true (brake fade dragging the brake on long descents), but since I don't ride a paceline, I can scrub speed in bursts. Even in a paceline, I think this worry can be a bit exaggerated (really depends on how crazy long your descents are).

That being said, if you are bigger and want a stronger brake, but don't want as much special design consideration or the wory of brake fade, sram is making some hydro rim brakes (like the old rim-crushers, but prettier). Again, I'm not saying that this is something most people need, but it can be nice to have an over-abundance of braking power if you're a big guy who goes down steep hills.

Sure, they're going to market all of this stuff to people who don't really need it... but there are upsides even for lighter folk. Disc pads need less replacement, less adjustment (on hydro setups), and have an awesome lever feel that makes me smile. The braking surface is replaceable, so the wheel itself will theoretically last longer if you wear through rims (again, fringe problem but I see it happen). Plus, if you decide to do some touring, it could come in handy way loaded down.


NOTE: I only have disc on my cargo bike right now, so I'm not trying to justify a purchase ;-)

bike equipment goes through cycles, and it's road disc brakes time in the limelight. Far be it from me to try to stop a moving train

Having just built a road bike with disk brakes I'll rejoin with "Don't diss it until you've tried it". I love discs. Loooooove them.

I'm not a "real road racer" but then neither are 99% of cyclists. Real road racers get paid to ride, the rest of us do it for enjoyment.

I'm fairly big (185 cm, almost 90 kg) and perhaps oddly for someone my size I love climbing but that inevitably means coming down again. I'm now faster down the hills because I have so much more confidence.

Two of the guys in the beer-inspired conversation were on the big side of 90kg/200lb (as am i), so there was a certain extra element there. We all also ride in hilly areas. One guy has ridden disk equipped CX bikes before and thought it a huge improvement. I suppose the main usage would be for a bike suited to audax/sportif events.

Mounting locations - as Unterhausen mentioned.
I guess that now that I think about it most MTB put them up on the top of the seat stay. The stays are thicker and heavier (and shorter) than a road bike.
Many of the CX and commuter bikes I've seen photos of seem to have them inside the triangle on a bracket that connects the chain stay and seat stay, presumably acting as a significant brace as well as putting the mount in the right place.

I have pondered this myself...given it is near impossible to add disk brakes to an existing frame without welding, I'm now looking to a fork swap for front disks. Practical? Meh, but its a low end bike and disk brakes are pretty pimp...at least I find them so. The key is to find something that is close so my bike doesn't look too "frankensteinish".

Mounting the caliper inside the rear triangle does make things tidy and adds a measure of protection in a fall. It also is easier to mount racks & fenders with the caliper out of the way. The downside is awkward access for initial set up and pad removal later. The seat stay gets in the way of ratchets & torque wrench when tightening the rear mount bolt, and reaching the inboard pad adjuster on BB7s with short fingers and wide hands is a challenge at that angle. This location can also limit the size of the rear rotor; a slotted bracket mount and arcing stay can fix that issue.

Mounting the caliper on the rear of the stay places the caliper in easy reach. Note the rear drop-out on the white bike incorporates the ISO mount.

There are options for steel forks and disc brakes. I doesn't have to be an unyielding metal monolith to provide adequate support.

Werkin, are those forks your builds? If so what size/wall thickness and maker are the blades?

thanks, Brian

http://www.bikeforums.net/attachment...4&d=1337557615

I'm not the builder. They are off-the-shelf from Traitor Cycles http://www.traitorcycles.com/NotBike...431F607C9BBF48 The black fork is Continental Oval spec 28mm x 20mm on the large dimension, probably could be found at Nova.

If you shop well you can likely find a new bike with disks already installed that is in the net equation better than the existing bike and for about what the conversion of the old bike would cost. They you can flip the old bike for travel money or to fund bling, lights, etc.
/K

Not examples you want to emulate...looks like they did everything you don't want to do for a disc fork.

I don't see most real racers using discs on road bikes, maybe a wet day, and mountain option. For cyclo bikes it could be the coming thing. And for touring bikes it isn't silly. Personally, I would mount the front one only for road uses. Rear braking power is really not that dependant on it being a disc or not. Mounting on the front fork and using a commercial fork makes a lot of sense weight, stopping power, and liability wise. Not my fork, for the most part. On tandem weight set ups I prefer a set of cantis or pedersens, + a disc up front.

Disc brakes are not all about power. The main advantage disc brakes have over rim brakes is improved modulation. Rim brake modulation can be improved upon, and inversely disc brake modulation can be ruined, depending on component choices, but in general disc brakes have the better starting platform. The ability to hold the rear brake at the threshold of lock-up and finesse changes with low lever effort is equally important on the rear as at the front of the bike. Good rear brake modulation is extra beneficial on a single user bike in instances where the road tilts downward and the rear goes light.

Kinda...when I say low end, I mean I picked it from the dump. I could sell it, but to find another one like it retail or 2nd hand would be hard with disk brakes...meanwhile, how many Free Spirits have disk brakes? I'm guessing none, especially now they don't sell them anymore. Sounds cool to me.

I read some place (and darned if I can remember where) that there are heat dissipation issues with disc breaks on road bikes and long, fast down hills and this is limiting adoption for road bikes.

For me, the advantages of disc brakes are that (1) the rim can be made lighter with no sacrifice in strength because no sacrificial material needs to be designed in, and (2) the rim and tire stay MUCH cleaner from wet conditions because you're not grinding the rim away every time you hit the brakes. Those two alone are worth it, regardless of whether their performance is better or the same.

Are these advantages you expect with road use? I have read where folks running cross bikes are finding all kind of ways of using discs to improve downhill performance. But I am not so much expecting that in road use. I figure a lot of folks there are more concerned with learning to run the downhill with as little use of the brakes as possible. But I don't really get memos from any of these camps. Certainly from the clyde side of things, I can have a problems stopping the bike in rain.

Salsa Vaya. steel road bike frame (although is more touring I guess). Discs front and rear. Rear is tucked in so that any fender/rack mounts are clear. Front blocks some mounts but can be worked around.

Improved modulation is an advantage I experience first hand, in road use.

I think it was BikeRumor. Guy had a CX bike and he tested it down a significant steep road. Cooked the brakes and he ended up in the ditch with busted ribs.

Found it - http://www.bikerumor.com/2012/02/14/...ill-they-work/

Lightweight discs not really suited to the job?



But he felt no brake fade with the new SRAM set up...

http://www.bikerumor.com/2013/04/15/...s-first-rides/

Unfortunately this second article won't go as viral as the first "we're all going to die" article did. It's cool that SRAM is pushing forward with road discs and I look forward to trying some.

I think the real key to generating sales will be getting riders to fully understand that the advantage of any wet brake (and discs in particular) is one of feel and modulation. Car and motorcycle enthusiasts have been thinking about this for a long time and have gotten past the "the wheels will lock - how much more do you need?" question. The ability to bring the wheel right up to the edge of skidding/locking but not have it go past that............and to do this time after time and in all weather conditions is the real deal IMO.

It's one thing to explain the difference between power and modulation and another to feel it. Riders will need to feel it.

Thanks for posting the links.


Dave