May 20, 2008 5 Comments
(1) Wood rims are drilled for a specific pattern. The holes are precisely aimed. The rims want a X3 pattern, you can stick a nipple into any hole and it will tell you unequivocally where the spoke needs to originate
Don't worry about artistic and unique spoking patterns. Wood wheels deliver a knockout visual and the pattern really takes back seat.
Notice also, that the Cermenati's are not obsessive about valve hole placement. That's a mania from the modern era. Most of the time the hole will be placed between spokes that are angled away from it, affording maximum access to the valve. Sometimes, however, the valve won't be in such a space. I know you might not prefer this, but let's admit that valve access is still outstanding. It's only a cosmetic issue. Pretend the Cermenati's are your Zen wheel guides. Pretend they did this just to perturb you. Take a breath and relax. There you are. It's 1925 and the road beckons. Don't be distracted by valve hole drilling!
(2) Measure each rim with washers in place to determine ERD. These are made by hand and you must confirm the spoke diameter for each. Before spoking the wheel, push all the washers into place. The smooth sides face out. They're a snug fit. Just push them in carefully, pressing on one edge and then the other, with a blunt object, like a bladed screwdriver. They’re light gauge so don't hit one with a punch if it doesn't sit evenly. Take it out and try another. Striking it can make a deformed mess, as one edge of the washer can hang up on the wood.
(3) Wood rims prefer less tension, such as 50-60kgf. However, some builders use nearly modern tension on the Elegant and Sport models. Laminated hardwood is extremely rugged but not as stiff as aluminum. Part of the feel of wood rims is this deep strength combined with lower spoke tension; a formula that, unsurprisingly, is being seen more often these days with carbon fiber rims.
I received this comment from one of the most experienced builders I know, after he finished a set of Elegants:
I just completed one of the wood wheels with uniformity as good as any carbon wheel. I took time to carefully true the wheel initially then perfectly balance tension at 40kg. Next I checked tension and trued the wheel before winding up to 70kg in two stages. At 70kg I kept the wheel straight within 0.007 inch laterally and 0.014 radially. Spoke tension is uniform within 3-5% between spokes. The wheel is beautiful ! I think the 70kg number is a sweet spot for those rims.
(4) Wood rims respond to spoke tension more exactly than do aluminum rims. This means unevenness in tension that an aluminum rim might not reveal, can cause untrueness with wood. Since the rims breathe, responding to temperature and humidity, some retruing is necessary. Unequal tensions will reveal themselves, if not immediately, later as slight wobbles. So the more consistent you begin, the less truing over time.
(5) Wood rims have a several day to one-week period of settling in. After resting for this stage, during which you can be riding, they'll need some minor touchup. Even tension to start will minimize retruing, but some readjustment is inevitable. When I first learned to build, old timers said you should hang a custom wheel so it can settle. I tested that and came to believe it was superstition. Now, with wood, I can see where it originated. Aluminum is dead, 100% inert. Wood is dynamic. Even though the cells aren't metabolizing, the material is responding. It absorbs moisture on humid days (harmless) and listens to the forces around it. Also give a really lively, cheerful ride. These rims came from happy, carefree trees!
Pay as much attention to tension uniformity (pluck neighboring spokes to find inequalities) as you already do to trueness.
(6) After extended, hard riding, you may find tensions have gone down. Has the rim shrunk? Are the washers sitting deeper in their seats? Has the wood at each nipple settled, become more dense? Perhaps a little of each. If you notice your tensions are lower (with deflated tire) and it's been a few thousand miles, then add 1/2 - 1 full turn to each nipple. Few wood wheel owners ride long and hard on them to notice this. If you're one of us, great!
(7) Don't obsess over trueness, either in the initial build or later after riding. With aluminum rims, we've come to expect optically perfect rotation. This is possible because the rims are straight, thanks CNC brake surfaces, and stiff (more than wood). But such trueness is not important for your ride. Every tire is far less true and deforms continuously in use. Try and get your wood rims to +/- 1.0mm. This tolerance might be unacceptable for a high end, brand name aluminum wheel but it's just fine for wood. And as the miles go by, don't stop and retrue your wheels too often. Let them wander around like smart dogs. They won't stray far from home.
If you notice untrueness, take a moment to make a quick inspection. Pluck spokes in the area to be sure none are completely loose or broken. Just don't interrupt your ride for the sake of cosmetic trueness. Slip back into time, back before cell phones and stop lights.
(8) As with aluminum rims, some thread compound is highly recommended. I'm getting best results with Loctite 220, a lower strength version of the famous 290. Both of these are "after assembly" types, which means they wick into threads. Just put a fraction of a drop where the spoke disappears into the nipple. Loctite does the rest.
(9) Gluing tubulars is the same as with aluminum but the adhesive is protected from brake heat, so the chance of losing a tire in a corner is far smaller. Wood won’t absorb heat so the energy of braking can attack the brake shoe. But it won’t be able to migrate to the rim cement and soften it. Note, there's no need to sand the rims before applying glue. Make sure the surface is clean of oil and dirt, but no need to roughen the surface. Ghisallo tubular rims have a wonderful radius to support tires. There's abundant glue area. If you're ever reborn as a tubular tire, make sure to request a Ghisallo rim. It's tire heaven.
(10) The Sport clincher rim does not have “hooked” beads for the tire. Hooks appeared in the 1970’s to provide greater security at high pressures. The Sport is designed for no more than 4.5 bars (65 psi). Best results come from a generous sized tire (28-40C) with a light sidewall and wire bead. Folding tires are less dependable for bead diameter; I’d avoid them with wood. As far as riding a rims without bead hooks, don’t be skeptical. All automobile and motorcycle rims, for racing on and off road, have no hooks. If you mount your tire carefully, keeping the bead uniformly straight and making certain your inner tube is not pinched before inflation…then you’ll have great results.
(11) Wood consumes brake pads because it won't accept the heat that braking generates. The pad melts at contact and makes a mess of the rim. Best to use pads with cork, leather, or wood. These are heat resistant and will last. I'm partial to the cork pads offered with Bontrager, Zipp, and Mad Fiber carbon rims.
Second best pad choice would be Swisstop Yellow. These are tough enough to last but still deposit some material on the rim. Cork is best.
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