A Better, More Thorough Technical Explanation of 3T’s Disc Cyclocross Fork Design

In our never ending quest to get answers and quell your (and our) insatiable appetite for cycling tech, armchair speculation and road/trail side discussions, we reached out to 3T a little more.

After reading it, we got to thinking. Many of the comments on the previous two posts (first look / followup #1) do voice legitimate concerns, but from our experience, ‘cross doesn’t typically involve a lot of things brushing up against the legs of a fork like it would in mountain biking (brush, rocks, etc.), and so we came up with the professional rendering above that offers another reason why the cable placement is OK on the outside: In what scenario will the side of the fork ever directly impact the ground? If you’re falling directly on a raised surface like a barricade, you’ve probably got bigger problems. The lower edge of the fork has no cable on it, and by the time the cable meets the caliper it’s no more exposed than those on a mountain bike. Anywhoo, just food for thought.

Here’s the explanation of the design of their forthcoming Luteus disc brake specific cyclocross fork, directly from their technical director Richard McAinsh:

When we saw the UCI rule change allowing discs for cyclocross we were already starting to scheme a composite MTB fork.  After consulting with a few CX and MTB riders, (we sponsor the MIG Team for example), it was clear from the start that this, (an MTB style solution) would not be the answer for CX.  The road bike geometry of the CX bike does not allow us the luxury of the massive axle to crown lengths possible with an MTB frame. Tire clearance under the crown is much tighter. Current CX forks with cantilever brakes outside the wheel envelope do not encroach on the tire clearance under the crown.  A cable or hydraulic hose coming up the fork leg would be difficult to accommodate and the decision to take it up the outside of the leg was taken pretty early on.  We wanted to keep the underside of the crown as clean as possible and not provide any trigger, or key, for mud to start collecting and to cling onto, if the hose or cable was inside the leg it would end up encased in mud being dragged around by the wheel or grabbed by hands trying to clear the mud out.  We figured on a CX bike it would be way more vulnerable on the inside than on the outside to be honest.

Continued…

As for damaging the hose or cable if the bike falls it’s a possibility but actually very remote.  There are cables or hoses external all over the frame and if there’s a shunt there’s nothing to legislate which part might take an impact.  A hydraulic hose is pretty robust as you’ll know if you’ve ever tried to cut one to length.  The fork leg is composite, if you lay the hose against the fork leg and try and bash a hole in it with a rock I think you’ll find the composite gives up first!  It’s just not a good argument for not putting the hose or cable where we have.

As for the appearance we debated long and hard about that and it seems it might be quite a polarising feature.  We could have not put anything and shown the fork ‘clean’ but I think the feature itself will eventually prove its worth once riders start to build the first CX bikes to the new regulations.  This is the first stab at getting something for the early adopters to try; I am pretty sure there will be lots of development going forward.

As for the tie wraps I think there will be more issues with the disc on that side in terms of handling and carrying the bike, I think most riders will trim the ends and tuck them around the hose so as not to offer a sharp edge anyway.  They also mean there is nothing external to the fork, no hooks, or riveted clips that could catch and break off allowing the hose to come unattached.

The good news is, our enthusiasm on the matter has us on the list for one of these forks to test out when they become available in mid-spring! One thing we’re curious about is how easy it’ll be to trim/hide the zip tie ends, per his last paragraph.

Personally, I’m (Tylercan’t speak for the other contributors) more concerned about whether frame manufacturers are going to build disc cyclocross frames with 130mm (road) or 135mm (MTB) rear hub spacing. My vote is for 135 as there are a million disc hubs already ready to go into action, making one less major component that needs to be rejiggered to take your ‘cross bike into the future.

Comments

Andrew - 02/11/11 - 12:30pm

Wouldn’t 130mm disc wheels end up being not very stiff?

Also has 3T mentioned yet what the price of this fork will be.

Tyler (Editor) - 02/11/11 - 1:29pm

I’ve been talking a few manufacturers, both components and frames, and it seems like it’s leaning toward 135mm for that reason and others (frame/rotor clearance, etc.). Fingers crossed…as you could pretty much use any 29er disc wheel right out of the gate, and there are some pretty lightweight tubeless ones out there.

John Caletti - 02/11/11 - 1:42pm

The trick with a 135mm rear end is that road parts (crankset, front der.) are made for a chainline that results from 130mm spacing. Probably with the longer chainstay length helping out, things will be okay, but it might have a hard time with the front shifts. Also, what if you want to run Campagnolo? You can’t put a Campy cassette on a mtb hub/wheel. I think the future will see the big component manufacturers getting in there and maybe making a cx specific group, although it would be great to see discs on the road bikes too. Once there is a superlight minimal Dura Ace hydro disc brake we’ll have reached the tipping point.

ZachOverholt - 02/11/11 - 1:47pm

My vote: 135mm rear for sure. 135 spacing seems to work fine for narrow q factor double MTB cranks, and the current availability of 135 spaced hubs and wheels make it a no brainer. New frames and hubs will be needed anyways to accommodate discs, so there is nothing extra forced by going 135.

apsbiker - 02/11/11 - 2:01pm

The one topic that still hasn’t been covered by 3T is the fact that the cleanest disc forks (like the Niner carbon forks) run the cable down the back side of the leg. Any chance you guys can get an answer to that? I’d imagine that would be just as easy, and less polarizing, as running the cable on the outside of the leg.

Nick Burklow - 02/11/11 - 4:12pm

John Caletti, I’ with you. It’s only a matter of time until the major component Manufacturers start pumping out the CX specific group sets. And, I can’t wait to see what hydraulic break solutions they come up with.

AnonymousChris - 02/11/11 - 5:40pm

My commuter is a 130mm spaced Lemond Poprad Disc.

I still run the stock Bontrager hubs (with a better rim/spoke built around it) because almost nobody makes 130mm disc hubs; Phil Wood and Velocity are the only two who explicitly make them. Based on the specs, it looks like King’s tandem hub could be converted to 130mm, but I’ve never been able to get anyone to confirm “yes, that hub config will work on a 130mm spaced ‘cross bike.” However, a have gotten a “no way” from several companies.

Hopefully this new rule will get more hub manufacturers on board, but if it doesn’t, then frame builders really have no choice but to build at 135mm and try to make the chainline work.

Matthew - 02/12/11 - 12:51am

@Andrew: The original post on the fork had an update that stated MSRP was $595.

As for stiffness of a 130mm OLD, I have a 2007 Trek Portland with a pair of Bontrager Select Disc wheels (the OEM for the bike). They’re not bad as long as you’re in a straight, clean line. But as soon as you start going over bumps or going through turns, you can feel the wheel flexing and hear the disc singing against the pads. It’s not bad, but the wheels would not be suitable for an entire cross campaign, and the stiffness isn’t good for racing. Plus, as mentioned above, it’s nearly impossible to find aftermarket disc hubs to replace the stock hubs if they break. I don’t even think that you can buy the wheels from Bontrager or Trek (a quick search of their online store indicates this to be true… an actual Trek dealer should be able to chime in on this).

With regards to John’s comment about Campy for CX… I can truthfully say that up here in the Pacific Northwest, almost no one is running Campy on their race bikes. You’ve got one or two kooks here and there, but even with Campy’s attempted push into cross this year, it’s just not happening. I don’t see the market for Campy in cross.

Overall, put me in the 135mm camp.

AnonymousChris - 02/12/11 - 3:25pm

Hey Matthew; my day job is at a Trek dealer and looked that up for you. They make a modified version, available aftermarket, called the Bontrager SSR Disc Road. It’s a $400 wheelset:

* New Balanced lacing pattern combined with a disc specific, 700c rim for the ultimate value in urban commuter or cyclocross performance
* Cromoly axle with polished, ground races and forged hub shell for highly durable and easily serviceable hubs
* 24 spokes with low profile rim make for a very durable, quick wheelset
* 130mm and 135mm Over Locknut Dimension (OLD) hub options makes these wheels usable on road or cyclocross frames

Tom Boonen - 02/12/11 - 11:03pm

135 is the way to go… Get a steel frame, and spread your legs!

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