Rim Spoke-Hole Offset: Normal vs Reverse Rims and the Left-Drop / Right-Drop Rule

Why the same lacing can look wrong on two different rims — the hole-offset rule a workshop calls a trade secret, with links to the original posts.

Contents

What rim hole offset is
Normal rims vs reverse rims
The valve-straddle problem
Left-drop, right-drop: Italian vs JIS
The trade secret: asymmetric-cross builds flip the rule
Strongly-phased rims and how to read them

Two builders can lace the same pattern, the same way, and one wheel comes out clean while the other has the spokes crossing the valve hole. The difference is the rim's hole offset — something most riders never think about and most English wheel-building writing barely mentions. This guide lays out the rule one workshop openly calls a "trade secret," with links to the source. Throughout, "right" is the drive (freehub) side.

1. What rim hole offset is

Unless it's a deep section rim, a rim's spoke holes don't sit on the centreline — they alternate, drilled slightly left, slightly right, left, right, all the way round. That tiny side-to-side alternation is the hole offset, and it exists so each spoke pulls toward the flange it serves. It also means a rim has an orientation: which way the alternation runs, relative to the valve, is not arbitrary.

Source: Nomu Lab #122

2. Normal rims vs reverse rims

Put the valve hole at the top and look at the wheel. Take the spoke immediately to the right of the valve and ask which flange it comes from:

From the far flange → the workshop calls this a normal rim (Japanese sei-rim). This relationship holds even if you flip the wheel to view from the other side.
From the near flange → a reverse rim (gyaku-rim).

Almost every aftermarket hand-build rim is a normal rim, which is exactly why few people realise the distinction exists. The notable reverse-rim exceptions are factory wheels: Campagnolo and Fulcrum front wheels, and the Mavic Cosmic Carbon Ultimate. Some older Corima rims were reverse rims too. If you buy a rim to hand-build and assume it's normal, a reverse rim will catch you out.

Source: Nomu Lab #122

3. The valve-straddle problem

For radial lacing, the offset barely matters — mind the alternation and you're done. Tangential (crossed) lacing is where it bites. A crossed wheel is built from repeating units of four spokes (five units = 20H, six = 24H, seven = 28H, and so on). You do not want one of those four-spoke groups to sit astride the valve hole — it looks wrong and crowds the valve. So the question becomes: how do you start the lacing so no four-spoke group straddles the valve?

Source: Nomu Lab #122

4. Left-drop, right-drop: Italian vs JIS

The answer is which way you "drop" the first key spoke through the hub. Hang the first spoke parallel to the axle; the opposite flange's hole is offset in phase, so you choose to drop the spoke to the left or to the right. On a normal rim:

Drop direction	Lacing that avoids valve straddle
Left-drop	Italian
Right-drop	JIS

That's the baseline most builders internalise: left-drop Italian, right-drop JIS. On a reverse rim the phase shifts by one, so it flips — right-drop becomes Italian, left-drop becomes JIS. (For why you'd choose Italian over JIS in the first place — and what reverse-Italian is for — see the Italian vs JIS lacing guide.)

Source: Nomu Lab #122

5. The trade secret: asymmetric-cross builds flip the rule

Here is the part the workshop singles out as the thing that will trip you up. The "left-drop Italian" rule assumes both sides use the same cross count. To test a build, split the spoke holes with the line through the crossing point and the hub axis, and count the holes on one side: 4-cross gives 2, 6-cross gives 3, 8-cross gives 4. What matters is whether that number is even or odd.

Both sides even, or both sides odd (4&4, 6&6, 8&8) → the normal rule holds: left-drop Italian on a normal rim.
One even, one odd (4&6, 6&8) → the phase shifts, so on a normal rim you need right-drop for Italian — the opposite of the baseline.

So a 4:6 cross build laced Italian on an ordinary (normal) rim must be right-drop, not left-drop. This is precisely where someone copying an asymmetric build from a blog post will stumble once and not know why. (And on a reverse rim, the double negative cancels: reverse-rim Italian is left-drop again.)

Source: Nomu Lab #122

6. Strongly-phased rims and how to read them

Some rims have such strong, fixed hole phasing that you can't freely choose at all — most famously Mavic's aluminium-spoke wheels (Ksyrium and similar Zicral-spoke rims). Their tangential side carries a heavy fore-aft hole offset, so if you shift the phase even by one hole, the spoke's nipple threads simply won't line up. The non-drive (radial) side can be laced as a normal rim, but if you thread it without thinking, there's a 50/50 chance the drive side then won't go together.

On these rims, lace the non-drive side first to avoid the trap (on an R-SYS it's the freehub/tangential side instead). And read the factory marks: Mavic stamps two dots beside the valve on a rear rim (the two-dot side is the freehub side) and one dot on a front rim. A 1-hole phase error makes the wheel unbuildable; a 2-hole shift returns it to normal.

Source: Nomu Lab #1826 — On rims with strong hole offset

The detail that separates a clean build

Hole offset is invisible until it bites. It pairs directly with lacing choice — see the asymmetric rear wheel guide for the 4:6 build this rule applies to, and start from the Wheel Building Guide for the whole process. Every claim here links into the Nomu Lab Diary archive.