Fox Wheel Spacer

stykthyn said:

If you have hubcentric spacers it should be enough. That focuses the clamping force into the hub. If you have the flat disc with holes drilled into them then you are putting all that stress onto the studs which will eventually fail. Maybe not with the wheel coming off, but you will have issues.

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• As long as the wheel, hub, and spacer are stiff enough to prevent flexing and loss of clamp force, the cause of most wheel stud failures is under tightened lug nuts (not enough clamping force) orover tightened lug nuts (the stud has been stretched past it's elastic limit, so the clamping force goes away). Therefore, properly installed wheel spacers are perfectly safe.
• The wheel stud applies a clamping force that holds the wheel to the hub. When the lug nuts are tightened, the wheel studs stretch elastically, like very stiff springs. The lug nuts should be tightened until the stud is at 90% of its elastic limit. This will provide the greatest possible force to hold the wheel to the hub.
• The amount of clamping force at a joint is important because of the coefficient of friction (Cf). The more clamping force applied to the joint (in this case the joint between the wheel and the hub), the more force required to make the wheel slip relative to the hub. Unless the wheel slips on the hub, there cannot be any bending load on the stud.
• Coefficient of friction -- There is friction between the wheel face and hub face. This friction can be measured, and it is called the "coefficient of friction". The coefficient of friction (Cf) is the ratio of normal force, at the intersection of two surfaces, to the lateral force required to slip the bodies relative to one another. As an example, good street tires have a Cf of 0.9. This means that if there is a 100-pound vertical force applied to the tire, the tire can generate 90 lbs. of cornering force before it slides.
• When the car starts moving, the stress applied to the stud does not change appreciably, unless one of two things happens:
  1. The vertical component of any external force applied to the wheel is so great that theclamping force is not sufficient to hold the wheel in place, and it slips on the hub. At this point the stud is loaded in bending and in shear, and may yield, or even break.
  2. Some portion of the clamped joint, wheel, or hub is not stiff enough to prevent flexing, and allows the tension load on the stud to drop to zero. With no tension load on the stud, the clamped joint is no longer tight. The wheel can then move relative to the hub, and place a bending load on the studs.
• Inserting a wheel spacer between the hub and wheel changes nothing about these physics.
• The hub center of a hubcentric spacer does not hold the spacer on the hub or reduce the chance of stud failure. There is never any load on the lip of the wheel spacer. For there to be a load on the lip, the friction force in the joint must have been completely overcome. The lip on a hubcentric wheel spacer serves only as an aid for wheel installation.
• Increasing the length of the wheel studs to use a wider wheel spacer has no appreciable effect.

Chuckman said:

all a hubcentric spacer does is center the spacer and wheel onto the hub, which considering most of the factory cars from this era (and most aftermarket wheels) are LUG centric, isnt that big of a deal unless your using one of the big 1" spacers with its own lug studs. a 1/4" spacer would be (and is) fine.

the "safe" rule says that a nut needs 1x diameters of full thread engagement for full strength. mustang studs are 1/2"-20 threads, and therefore need a minimum of 1/2" of FULL thread engagement (10 turns). looks like you'll need longer studs.

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