If you can tighten the nuts holding the wheel in the forks, then the threads must be ok. If the nut/s then loosen, the nut/s were not tightened enough. Tighten the nut/s to the recommended torque and if you want to, use some threadlock compound eg Loctite.
Chain adjusters will not prevent the wheel going out of line if the wheel nuts become loose. Bicycle manufacturers always fit nuts even when they fit chain adjusters
It's not as simple as that Robert.
As Tillson has said, he's already stripped the thread at the recommended torque figure, and Threadlock isn't convenient on a nut that will be routinely undone for maintenance purposes, there are better solutions than that.
I can assure you that chain adjusters most definitely prevent a wheel moving out of line if a wheel nut starts to slacken, and I say that from trade experience of the days when bicycle chain adjusters were commonplace and also from trade motorcycle experience where they still are routinely used.
Shimano changed the spindle on the Alfine, saying they'd made it stronger without specifying how. If it's very high tensile, the lack of "give" will not give the maintenance of grip that some elasticity gives. Since Tillson has only experienced the problem since changing to the Alfine, this hypothesis fits.
There's more than meets the eye where the tightness of wheel nuts in slot dropouts is concerned though. There is always a small degree of vertical tolerance in the fit of the spindle in the dropouts, and the effect of road shocks versus the bike and rider weight will always move the spindle up to take up that tolerance. The result is a fractional change in the area of grip of the nut on the two sides of the dropout, leaving less grip on the lower. This is exacerbated by the degree of compression (dishing) of the dropout material that nut tightening brings, since an upwards movement of the spindle forces the upper edge of the nut onto an undished section of the upper dropout, at the same time moving the lower half of the nut more into the dished area, lessening the lower grip.
The forward force of chain pull, multiplied when the chain transmits rider
and motor power as on these bikes, exerts a rotational force on the nut as the spindle tries to move forward. On the right hand side that rotational force undoes the nut due to that lower underside grip, on the left hand side the rotational force tightens the nut, and that's an additional reason why it's always the right that loosens.
In turn this is why chain adjusters additionally help, especially if the adjuster bolt has a locknut. That's because the forward chain pull is primarily opposed by the tightened chain adjuster, in turn removing the potential for rotational force being applied to the wheel nut.
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