Wheel drive pin depth in wheel

[Mark H.]

Question… from an engineering perspective, drive pin depth using a wheel spacer would affect what? With all things being equal i.e…spinner torque, wheel still engaged and centered on hub, etc… comparing pin engagement either 1” or 1/2” in the wheel with a spacer; shear on the pin would the same, bending moment might increase on shorter pin depth , drive pin impact surface area in the wheel receiver hole would be increased? Went thru this discussion with a mechanical engineer and his take was without a complete analysis of materials, clearances, torque measurements, etc… he could not really give a definitive answer as to a failure. Was asked this question by a Cobra owner who wants to use wheel spacers.

 

[Lee Patterson]

Similar to the person that puts a spacer on a 5-lug wheel. The lugs (or pins) are there to center the wheel rotationally and resist the torque applied when driving and loads encountered from the mass of the car. The smaller they are, the more load that is applied over a shorter distance/smaller footprint. Imagine if your spacer was 7/8" - with 1/8" pin engagement. Would it support the car statically - yea, more than likely yes. Would you put driving loads on it - no. I certainly would not do what the cobra owner is asking - but I guarantee there are plenty of people that have done that with 5 stud wheels and a 1/2" spacer. (I believe the shear force would be distributed over a shorter piece of pin whlch makes it worse, not the same.

 

[Mark H.]

Thanks for the input Lee, but lug nuts on threaded studs are a different animal than smooth pins in a wheel reciever hole with circumference clearance sufficient for wheel mounting. Torqued lug nuts on threaded studs press the wheel to the hub creating friction, so threaded studs do not or should not be placed in shear. Like a single large lug nut, pressure applied to a "pin drive" wheel is from the center knock off spinner or center nut. So the pins, while called drive pins should not drive or be in shear. If the pins are preventing the wheel from rotating than the torque on the center knock off/nut is insufficient. Based on this reasoning, depth of the pins in the wheel should be relatively moot, whether 1/4", 1/2" or 1". If the pins are truly driving the wheel, I see that the further from the stud attachment point from the hub one gets (i.e from a spacer) the bending moment in the pin goes up and the tension in the pin/nut attachment threads at the hub may increase. I just can't see shearing drive pins base upon pin depth in the wheel. This takes me back to what is affected when drive pin depth in the wheel is reduced if a spacer is used?