Tuesday, January 21, 2014

Road Disc-Brake Wheel Build

As part of my series on building up a road disc bike (part 1 and part 2), I figured I would devote a post to the wheels.  Like all things road-disc-brake, disc wheels are still pretty niche. At least the standard seems to have settled down on 135mm rear hub spacing.   But there aren't a ton of factory options out there.  And I will admit that I love deep & wide carbon clinchers -- not so much for the speed (I'm sure there are a few mph tenths there) as much as the stiff road feel, the lack of any side-to-side flex, the cornering (wide rims), the sound, and the aesthetics.  I know that there are disc-brake clinchers made by the big brands: Zipp, Reynolds, Enve, Roval (Specialized), Vision (Cannondale), etc.  But the cheapest of these retail for $1800 and that's about $1000 more than I'm willing to spend on wheels.  (And most are 24-spoke,  which makes me a little nervous with disc brakes.)  November makes a disc verison of their Rail available, but it's still somewhere north of $1400.  I bought a Saab 900 for that price.  Yeah, I really couldn't justify spending more than $800 on these.  Even that feels pretty extravagant.  But this isn't exactly a project born of necessity.

I've some experience with Chinese carbon clinchers from Farsports (50mm deep x 24mm wide); I bought those as wheels (not just rims) and the lesson I took away was that I should have built these myself. The main issue you read about with carbon clinchers -- and the main reason I would go with a reputable brand -- is braking surface.  Not only is the braking performance inferior to alloy rims,  but you also run the risk of delamination under heavy braking -- e.g. down a hill -- and you might die.  (The Farsports rims had a high-temperature braking surface which mitigated this concern, though I probably still would have reconsidered riding them down mountains.)

But for this project braking surface is irrelevant and I saw little reason to spend 3-4x the price for a set of wheels that have superior thermal properties.  So, in short, I decided to build my own wheels using carbon hoops from China and budget hubs.  

The Rims

For this project I decided upon the 45mm U-shaped rims from Light-Bicycle.  These get good forum reviews; there was apparently a production run that had issues with clearcoat over the braking surface, but it sounds like customer service was good and the problem was resolved -- and, again, I could care less about braking surface.  I worked with Nancy on the order, which went extremely smoothly.  I ordered 28h rims with 3k matte finish and no braking surface.  I received the rims within a couple weeks and the quality of the finish was fantastic -- almost flawless.

I wasn't sure about the 3k, but I like the result.

The beads are very straight/smooth with a good bead hook.

The only flaw I could find was this wrinkle/seam in the superficial layup.
I measured the rims; the ERD I measured matched exactly the 554mm manufacturer-claimed ERD.  The weights were also very close to claimed weights, with one rim weighing 449g and  the other weighing 454g (claimed weight 450g).  This may be a placebo, but the tight tolerances leave one with a good feeling about the manufacturing process and quality control.

The Hubs

I have used BHS hubs for many of my recent wheel builds, but for this project, I decided to try out Novatec hubs w/ Japanese EZO bearings.  The hub geometry looked attractive; the prices and weights were reasonably good; there is a front hub (the XD711SB) that has interchangeable hub/axle options; and the freehub bodies include an "anti-bite guard" technology (looks like a steel reinforcement on one of the splines) to keep cassettes from gouging up the freehub.   I went with the D712SB-10 rear hub, figuring that I didn't need 11-speed yet on this bike.  In retrospect, I should have paid the extra $20 and used a spacer, since the hub geometry is the same.

Originally my intent was to run these with 15mm thru-axle, planning to replace the fork that came with my frame with a Whisky No 9 road (disc) fork.  Upon further consideration, I decided to save some (a lot) of money and just use the fork I already had :)  So I decided to run a 9mm thru-bolt instead; the XD711SB hubs also support this option, so I ordered these end caps and had them from Taiwan in jjust a few business days.  My goal was to prevent side-to-side flex that I do experience with my QR front disc hubs on my commuter.  Well, the 9mm thru-bolt appears to have done just fine; I cannot make the rotors rub in out-of-saddle climbs or hard sprints with this wheelset.  Success.

Actual weight for rear hub was 279g (published weight was 269g).  Actual weight for front hub and the 15mm end caps was 142g (published weight was 139g w/o end caps).

XD712SB-10 with "anti-bite guard" freehub body.

XD711SB with 15mm end caps.

The Build

I built these with 28 spokes front & rear.  The idea of under-building the front wheel doesn't make sense to me with disc brakes, given that is where the bulk of the braking force is applied (especially with larger 160mm rotors up front).  I have been  running 28-hole front wheels on my commuter for the past year; I did break a front spoke after ~6k miles, but I attribute that to my build technique rather than something inherent in spoke/rim/hub configuration.  I retensioned the wheel and the last ~4k have been smooth sailing.

I chose Sapim CX Ray spokes since they are light, are disc-approved (unlike Lasers), and seem appropriate for deep carbon wheels.  I used 2x front and rear.  I could have gone 3x, I suppose, but I like the way 2x looks -- and it should be relatively inconsequential.  I did the Shimano (etc.) recommended lacing with outer spokes setup leading on the NDS to resist rotor torque.  This probably doesn't matter a whole lot, but it's what I've always done.

And 14mm alloy nipples because I wanted something  that was deep enough to protrude through the 4mm-thick rim bed and I see no reason not to use alloy nipples.  I've had alloy nipples fail me during builds in the past, breaking in half when spoke threads were insufficiently lubricated or rim bed was rough.  I use Sapim Polyax nipple washers now to provide consistent interface (and help spread the load a little)  -- tensioning has been noticeably easier with washers.  I also used regular motor oil this time, instead of boiled linseed oil, as per suggestion of Roger Musson in his wheel building book.  This was my first time  building with carbon rims; it worked out just fine.  It is a credit to these rims that they built up true with very even tensions.

Final build weight was 727g/869g front/rear for a 1596g wheelset.  Not bad!
Front wheel in 15mm thru-axle configuration

XD711SB front hub

D712SB-10 rear hub

Rear wheel

The Ride

I have only had these out on one 15-mile ride at this point.  It's very hard to compare these to other wheels since it's also a new bike, but the ride had many of the familiar characteristics of my other carbon clinchers -- confident cornering, the wind-tunnel noise at speed, and on the gusty day I took them out they got blown around a bit more than my alloy rims.  So I enjoyed building these and it looks like I'll enjoy riding them even more.

Update: a few months later

I have ridden the wheels a little over 1,000 miles now and I've been extremely happy with them.  Recently I rode them on the Diabolical Double (mountainous double metric) ride and loved that I could ride carbon rims without worrying about the braking (down the mountains in the rain).  I haven't had any issues with trueness or tension, which is what I'd expect when I'm building with bladed spokes and able to avoid any windup issues.  I've smacked them pretty hard into a few potholes without any problems.  I did notice that I've managed to add a few superficial scratches in the carbon, but the scratches are hard to see; the finish still looks great.  So, very happy with these so far.  Looking forward to many thousands of miles more.