Incidentally why (Haynes again) should my Bay window have a recommended 94 ft/lbs torque when the steel wheels,hubs,studs and nuts are the same as the T25/T3?
Simon's right, this is because the weight of the van is greater. This may sound either silly to some or obvious to others, but in reality, nuts and bolts are done up to clamp two or more parts together - the nut not coming off is taken for granted when torqued up to the correct figure, and is only much of a design a consideration in some cases, usually lightly clamped parts. Wheel nuts and recesses are tapered, so at anywhere near the correct torque figure, they're highly unlikely to loosen.
But the aim is firstly to provide a clamping force calculated as appropriate, and in cases of fluctuating and even reversing loads such as a wheel, the clamping force reduces the chance of fatigue failures by creating a high static-stress level (e.g. pre-loading). This is probably the case with wheel bolts and studs.
Between 1/2 and 2/3 of the torque figure frequently goes into friction in the threads and the bolt or nut bearing face, so as little as 1/3 produces the clamping force.
I too usually carry a powerbar and 19mm impact socket on board and use it much like Stuckin says.
Knowing that the threads are cleaned and lightlty lubed with anti-seize whenever they come off tp keep corrosion in check, and that the hub face and back of wheel is also checked and cleaned, I usually torque not much over 100 ft-lbs* on 15" steels on a Syncro, that can have at least a ton in the back from time to time. 133 is what Bentley says, so knowing that they're clean and the wheel's nicely flat against the hub, I expect I'm easily getting the minimum clamping force that VW hopes for under worst case conditions, doing them up in stages to get everything seated nicely.
Alloy wheels often have a larger and different tapered contact area to reduce local bearing stresses. You might follow the same thinking, that if the threads are well brushed clean, the tapers aren't knarled and corroded and the nuts run up nicely, you needn't go berserk with the powerbar or torque wrench. But done up to not come off,
isn't the only criterion! The clamping force should be much the same as with steels, so also make sure the backs of the wheels and hub faces are clean, flat and not corroded badly, do them up to 100 lb-ft and worry not. But be sure to tighten them in a star pattern in 2 or 3 stages, unequal torques are definitely a bad thing on fronts, due to the potentila for disc warping.
*
If you insist on lubricating lug threads, please be sparing and make sure to compensate for the increased torque likely to result. For example, one lubricant manufacturer recommends torquing nuts to only 85 percent of the factory specification when using their nickel-based anti-seize compound on threads.
from
http://www.volvoclub.org.uk/faq/WheelsT ... teelWheels
For more, see the link at the bottom of
Wiki on Torques
