The distance between the plumb...
The distance between the plumb bob to the face of the rear brake drum (the area where the wheel bolts to) should be measured next. As you can see, this vehicle is under construction, and the axles aren't installed in the housing yet. At this point, though, the measurements won't change. Basically, this dimension determines the amount of room for the wheel (and tire) "face." See the text for details.
Yet another problem area can be the overall length of the wheelwell. The "length" of the wheelwell is critical, especially if you want to slip tall tires under your car. If you measure wheelwells, you'll find that many aren't really "long" enough to handle most big-diameter tires (including slicks, if that's your weekend cup of high-tech tea). This simply means that tall tires will sometimes rub on either the leading or trailing edges (occasionally both) of the outer wheelwell. The real solution is to create more length at the front or rear of the well. In order to accomplish this (and it's really beyond the scope of this article), the 90-degree lip at the leading (or trailing) edge of the well should be cut out, taking care not to remove the piece entirely. Next, a very small pie-shaped (approximately 11/2 inches wide) cut is made in the sheetmetal from the bottom up. Weld the works back in place, filling the pie-shaped cut.
In many late-models, this surgery isn't required at the rear of the outer well. If everything is welded correctly, only a small amount of plastic filler is needed to smooth the area. This trick is very subtle and it takes a very well-trained eye to spot the rework. If you follow these steps, you can stuff a 29.5- or 30-inch tall tire, (such as a drag slick), under a late-model car without tubs.
Armed with the dimensions gained from the above guidelines, you can then make a rational decision in regard to rolling stock. Just remember to measure the wheel backspace dimensions before you lay down the cash. Aside from wheelwell clearance (sheetmetal interference), the backspace dimension is the most critical of all wheel dimensions.
Measure the distance between...
Measure the distance between the plumb bob to the inside of the factory wheelwell or to any suspension component that "intrudes" into the well. In this case, the shock was closest component. Due to the OE wheelwell configuration, there can very well be several different dimensions. Use the smallest figure.
The Routine Goes Like This:
* Create a "plumb bob" from string and a weight (a lug nut works). Tape the plumb bob to the inner lip of the fender. This is your major point of reference.
* Measure the distance between the plumb bob to the face of the brake drum (the area where the wheel bolts to). Subtract 1/2- to 1 inch as a clearance figure. The final figure will give you the maximum "face" or curb-side wheel width you can handle.
* Measure the distance between the plumb bob to the inside of the fenderwell or to any suspension component that "intrudes" into the well. Due to the fenderwell shape, there can very well be several different dimensions. Use the smallest figure. This is the maximum backspace your car can handle.
* Take the tire "bulge" calculation you made earlier and subtract it from the above maximum backspace dimension. Subtract another 1/2- to 1 inch as a clearance dimension. This is the largest possible overall rear backspace figure that will fit into your existing fender-wheelwell opening.
* If you add the maximum face or curbside dimension (step 1) to the final figure in step 4, you'll end up with the widest possible wheel that can fit inside your stock wheelwell.