Disc brakes and cx frames

[JuanGrande]

So what are folks doing to accommodate disc brakes on their cx frames... Specifically I am curious about the following;

1) in terms of the rear disc mount, do folks use heavier duty chain stays? Seat stays? Add a brace at the rear dropout tying the chain stay and seat stay together (I have used the Paragon mounts that have the disc tab intregrated into the dropout.... And have skipped using the brace. Curious about thoughts on this - seems to work fine on my bike)?

2) switching to the front end, are folks building lugged forks with disc tabs? I had talked with the guys at Nova during the handbuilt bike show and they mentioned a fork blade that they thought would work. Curious about thoughts on this?

3) do folks use different non-drive side tubes (fork blade, chain stay, seat stay) vs. drive side to address added stress imposed by disc brakes?

Thanks for advice.

JC

[GrayJay]

So what are folks doing to accommodate disc brakes on their cx frames... Specifically I am curious about the following;

2) switching to the front end, are folks building lugged forks with disc tabs? I had talked with the guys at Nova during the handbuilt bike show and they mentioned a fork blade that they thought would work. Curious about thoughts on this?
JC

I built a (cantilever) CX fork for myself using Nova blades;
NOVA CRMO ROAD OVAL 1.0 x 24 Oval (28/20)

I can attest that these blades are very stout (and heavy) in comparison to thier standard .9/.6 fork blades. Wall thickness at the bottom end of the 1.0mm blade is 1.8mm, should hold up to disk torque.

[Kumo Cycles]

So what are folks doing to accommodate disc brakes on their cx frames... Specifically I am curious about the following;

1) in terms of the rear disc mount, do folks use heavier duty chain stays? Seat stays? Add a brace at the rear dropout tying the chain stay and seat stay together (I have used the Paragon mounts that have the disc tab intregrated into the dropout.... And have skipped using the brace. Curious about thoughts on this - seems to work fine on my bike)?

I have not been in the game as long as the other cats here, so take my advice as such:

I use thicker chainstays and seatstays, plus used a brace between the two, using Paragon slider dropouts. Better safe than sorry.

This was also after a post by someone with more experience than me (wish I could remember who it was, peacock groove maybe??) where he mentioned that a couple of paragon slider frames developed small cracks after a long time without the braces

[Dornbox]

I use the Paragon low mount dropouts with no brace on thin chain stays and 12mm seat stays without any issues after a year to include a race season. I have however started using 16mm seat stays but only because I also bumped up the seat tube to a 31.8. I still punt on the forks and buy themhere are a few good option now.

[JuanGrande]

Thanks guys, I really appreciate the feedback. Since it is for my own bike, I will give it a try and race it this cross season. Will report back.

JC

[ineff]

I was going to post a new thread on this, but the above conversation directly pertains to what I was going to ask....

Recently I had a conversation with Richard Schwinn (we sell a lot of Gunnar's at the shop I manage) about disc brakes, TA and what the results are to the ride quality of a steel bike. To be honest it sounded to me like he had never thought about what the results of slapping a disc mount on a frame are. That said, its not that they aren't using strong enough tubing, as a matter of fact, it might be doing just the opposite.
Part of my line of questioning for Richard had to do with a custom CX frame they built for me last year. It is a disc frame with sliding dropouts. I find the bike to be particularly...um "uncomplaint". Basically it rides very, very stiffly. Not at all like the plethora of other steel bikes I have owned (none with discs). He said this is due to how beefy the tubeset is (probably also why it weighs like 30lbs)
My main questions for all of you here, how light can you go with a tubeset when using discs? And, can a TA help with the strain that a disc brake puts on a frame? How can you best balance the durability needed when using a disc brake and ride comfort?

[steve garro]

I was going to post a new thread on this, but the above conversation directly pertains to what I was going to ask....

Recently I had a conversation with Richard Schwinn (we sell a lot of Gunnar's at the shop I manage) about disc brakes, TA and what the results are to the ride quality of a steel bike. To be honest it sounded to me like he had never thought about what the results of slapping a disc mount on a frame are. That said, its not that they aren't using strong enough tubing, as a matter of fact, it might be doing just the opposite.
Part of my line of questioning for Richard had to do with a custom CX frame they built for me last year. It is a disc frame with sliding dropouts. I find the bike to be particularly...um "uncomplaint". Basically it rides very, very stiffly. Not at all like the plethora of other steel bikes I have owned (none with discs). He said this is due to how beefy the tubeset is (probably also why it weighs like 30lbs)
My main questions for all of you here, how light can you go with a tubeset when using discs? And, can a TA help with the strain that a disc brake puts on a frame? How can you best balance the durability needed when using a disc brake and ride comfort?

Wow, I know an Isaac Neff since they were tiny, now a big metalworker in FLG, far out……….

Short answer is that the disc needs to be braced - sufficient bracing and you can run pretty thin tubes - or, use a dropout with an integral mount and run about anything.

I of course would be smart and not spec a pencil thin 14mm double taper or such, be smart and use a good 16mm at least and brace, brace brace.

I would use this & feel good about it with the precautions I mention above:

http://www.cycle-frames.com/bicycle-...0mm-Round.html

- Garro.

[Will Neide]

With no data to support my impressions, and simply going on theory, it doesn't take much material to do the job of a seat stay. Seems like most of the forces are in compression, which a steel tube handles really really well, even thin ones. For a CX bike, if you want to go with thin stays, I'd either add some wall thickness to account for impacts, or go thin walled and accept the fate of dings. When Cannondale went from canti's to discs on the Super X, they talked about how they could lighten up their seat stays because the braking forces weren't happening way up the stays.

Ironically, I'm building myself a CX bike with double taper 14mm stays to see how un-smart of a choice it really is. No bridges for seat or chainstays and thru axle rear end. I'm not a big guy, and don't crash all that much....so time will tell. :)

[ineff]

Thanks for the replies guys!
I was specifically interested when talking with Richard if you could (in theory) go with slightly lighter and more compliant seat stays if using a thru axle with discs mounted on the chainstays. He said no... you still need super beefy chain and seat stays.

[Crowemagnon]

i too subscribe to the theory mr Neide begins discusing. but im not a pro and i dont build commercially ; grains of salt included.

i have a franken-cross-bike with 14mm double taper stays, paragon "low-mount" dropouts,these chainstays (CHAINSTAYS FX3510). it has a small chainstay bridge (investment cast pre-mitred type) , and a seatstay bridge which i cant imagine helping distribute braking force in any significant way. (made from a sindle strip of 14x1mm flat stock bent into a curve to follow the tyre profile) no additional reinforcement or bracing. 9mm qr wheel with a 160mm rotor.

im 75kg and and race cross on this bike.
this bike was raced (and crashed) at the qiansen trophy this year and gave no issue but otherwise its pretty new, follow my signature for an update if anything breaks.

[steve garro]

Ultimately all engineering failures are due to the lack of suitable redundancy - or, in other words, bikes need to last more then a year or two - time will tell.

- Garro.