A customer left me a complete Shimano XT grade wheel set.
29-inch spec.
Both front and rear have 160mm rotors, but they look small.
The scale reference is just for size comparison and doesn't have any particular meaning.
The WH-M785 comes in three sizes—26-inch, 27.5-inch, and 29-inch—to match the segmentation of MTB wheel categories.
Furthermore, there are two axle hub specs:
quick release and through-axle.
(There is no through-axle rear wheel option for 26-inch)
This wheel set is 29-inch with front through-axle and rear quick release.
The customer suspected both wheels had axle drift issues, but in reality only the rear was off-center.
Apart from rim brake applications, the runout was so minimal you wouldn't notice it on the bike, so I corrected it.
The front wheel had perfect center and only minor runout, but it was obviously loose, so I did additional tightening separate from the truing work.
The fact that it was obviously loose is inconsistent with the rear wheel being fairly tensioned.
With a complete wheel set, it's rare that a single builder assembles both wheels in one continuous operation, so it's unavoidable.
The customer says they've been using it for about a year, but if the wheel had loosened from riding, the rear wheel would also show slackness. It was probably a loose unit from the start.
We have a WH-M785 29-inch front wheel quick release spec in the shop right now for a different job, and it's looser than this one by comparison.
Even if we rode that wheel hard for a year, I'd find it unlikely to become as loose as the front wheel we received.
The spokes' final crossing isn't woven, but due to the hub flange shape, they cross quite close together—as close as Shimano wheels typically get.
↑When you grip the crossing...
It flexes quite a bit.
The spokes had been flexing regularly during use, and the crossing points are worn from contact.
Round-section spokes, but with a section designed to be gripped by tools during nipple turning to prevent rotation of the spoke.
Due to needing to use restraint tools from the wheel's side, the flattened direction should theoretically be oriented as shown in the image, similar to aero spokes. However,
I observed the characteristic scattered orientation of the flattened sections typical of low-tension Shimano wheels, so I corrected them all.
When this wheel was built, the flattened sections should have been mostly aligned.
(Gripping in this direction is extremely difficult to work with)
Especially on the non-rotor side of the front wheel, which had particularly loose tension, most spokes had their flattened sections rotated every which way.
There's a possibility the spoke tension loosened from the original factory state, but in that case usually just one spoke loosens, which doesn't match the symptom of needing almost no truing work.
I think the loose wheel made the spokes rotate, but I don't think the rotation is what made the wheel loose. The tubeless nipples have coarse pitch threads due to material properties, and if they're threaded in this deep, vibration would almost never loosen them.
Since the spokes turned easily once I gripped the flattened section with tools, I suspect that during a buckling moment when tension released, the spokes rotated incrementally on their own.
If nipple threads aren't the cause of wheel slackness, the next consideration would be spoke stretching. However, that's a small factor and minimal.
Even if the rear wheel's spokes—which are reasonably tensioned—stretched to their maximum, they wouldn't slacken as much as the front wheel.
The front wheel was retensioned enough to feel the difference by hand, so I think spoke crossing contact will be less likely now.
I also told the customer that after aligning the flattened sections, the wear marks on the spoke crossings scattered all around.
These are round-section spokes, but considering only wear, I'm not sure whether it would have been better to leave them rotated as they were, given that they won't rotate further from this point on.
29-inch spec.
Both front and rear have 160mm rotors, but they look small.
The scale reference is just for size comparison and doesn't have any particular meaning.
The WH-M785 comes in three sizes—26-inch, 27.5-inch, and 29-inch—to match the segmentation of MTB wheel categories.
Furthermore, there are two axle hub specs:
quick release and through-axle.
(There is no through-axle rear wheel option for 26-inch)
This wheel set is 29-inch with front through-axle and rear quick release.
The customer suspected both wheels had axle drift issues, but in reality only the rear was off-center.
Apart from rim brake applications, the runout was so minimal you wouldn't notice it on the bike, so I corrected it.
The front wheel had perfect center and only minor runout, but it was obviously loose, so I did additional tightening separate from the truing work.
The fact that it was obviously loose is inconsistent with the rear wheel being fairly tensioned.
With a complete wheel set, it's rare that a single builder assembles both wheels in one continuous operation, so it's unavoidable.
The customer says they've been using it for about a year, but if the wheel had loosened from riding, the rear wheel would also show slackness. It was probably a loose unit from the start.
We have a WH-M785 29-inch front wheel quick release spec in the shop right now for a different job, and it's looser than this one by comparison.
Even if we rode that wheel hard for a year, I'd find it unlikely to become as loose as the front wheel we received.
The spokes' final crossing isn't woven, but due to the hub flange shape, they cross quite close together—as close as Shimano wheels typically get.
↑When you grip the crossing...
It flexes quite a bit.
The spokes had been flexing regularly during use, and the crossing points are worn from contact.
Round-section spokes, but with a section designed to be gripped by tools during nipple turning to prevent rotation of the spoke.
Due to needing to use restraint tools from the wheel's side, the flattened direction should theoretically be oriented as shown in the image, similar to aero spokes. However,
I observed the characteristic scattered orientation of the flattened sections typical of low-tension Shimano wheels, so I corrected them all.
When this wheel was built, the flattened sections should have been mostly aligned.
(Gripping in this direction is extremely difficult to work with)
Especially on the non-rotor side of the front wheel, which had particularly loose tension, most spokes had their flattened sections rotated every which way.
There's a possibility the spoke tension loosened from the original factory state, but in that case usually just one spoke loosens, which doesn't match the symptom of needing almost no truing work.
I think the loose wheel made the spokes rotate, but I don't think the rotation is what made the wheel loose. The tubeless nipples have coarse pitch threads due to material properties, and if they're threaded in this deep, vibration would almost never loosen them.
Since the spokes turned easily once I gripped the flattened section with tools, I suspect that during a buckling moment when tension released, the spokes rotated incrementally on their own.
If nipple threads aren't the cause of wheel slackness, the next consideration would be spoke stretching. However, that's a small factor and minimal.
Even if the rear wheel's spokes—which are reasonably tensioned—stretched to their maximum, they wouldn't slacken as much as the front wheel.
The front wheel was retensioned enough to feel the difference by hand, so I think spoke crossing contact will be less likely now.
I also told the customer that after aligning the flattened sections, the wear marks on the spoke crossings scattered all around.
These are round-section spokes, but considering only wear, I'm not sure whether it would have been better to leave them rotated as they were, given that they won't rotate further from this point on.