69427
The Artist formerly known as Turbo84
Now that I'm back in the midwest and in the middle of some winter downtime, I'm trying to catch up on a few minor annoyances. One of the items is the rear hanger bolts. Due to the combination of a C3 batwing (and the attending low position of the spring mount) and C4 knuckles (with the high height of the hanger bolt "tab"), I need a damn long set of hanger bolts (12-13 inches, and the current multi-bolt setup I'm using is a bit too busy). The selection of bolts in the local hardware stores is pretty thin for bolts this length. I see McMaster Carr has bolts long enough, but they're all grade eight (which seems overkill), and are a bit expensive. Before I pull the trigger at M-C (along with the postage), I've got a technical question. The hardware store (half inch) bolts are grade two. According to a couple technical sources these bolts should have a tensile strength of 60-74 kPSI. The area of a half inch bolt is .196 square inches. This gives a max load capability of .196 x 60k = 11760 pounds. Cutting this maximum load in half to get far away from any yield issues gives us 5880 pounds. I'm estimating that each rear corner of my car is less than 750 pounds. Assuming I hit a good bump and the suspension bottoms (maximizing the spring compression) I would have an additional two inches of travel at 420# spring rate (adding 840 pounds of force to the bolt), resulting in a peak load of 750 + 840 =1590 pounds on each bolt. 5880/1590 = 3.7 safety factor (or 7.4 if I don't divide the bolt rating by two).
So, I need some help convincing myself that I'm not wasting money if I go for the Grade 8 bolts.
Thanks,
Mike
So, I need some help convincing myself that I'm not wasting money if I go for the Grade 8 bolts.
Thanks,
Mike