This subject seems to come up quite often as many feel it’s quite difficult to perform. If you have basic fabrication and welding skills, notching your rear frame rails for additional tire clearance can be easily done in your home garage for little money. I think it cost me about $30 in materials to do mine. First you need to figure out how your going cut the outer skin off the original frame. You can use a torch, a plasma cutter or even a 3″ abrasive cut-off tool (slow, but what I used). The first two cuts are made vertically in front and behind the tire. Leave about 3 or 4 inches clearance between this cut and the tire to allow for vertical tire movement and also to allow for a taller tire down the road if you happen to go taller. The next two cuts are the top and bottom of the frame rail, the length of the rail “hump” from the front vertical cut to the rear one. I suggest not going any deeper than 1″ cut from the outer skin. The original rail is about 2″ wide and you don’t want to make it weaker than you have to. Once the outer frame rail skin is removed, use a grinder to clean up your cuts and straighten the edge of the rail that is left. Next use a large piece of cardboard and trace the section of frame left to make a template to transfer to .090″ steel sheet. Once the template is done, cut out the steel sheet and test fit to the frame. Once your satisfied with the fit of the replacement outer skin, tack weld into place. The front and rear cuts will need two small pieces made to fill the gap where the rail now steps in. At this point, it’s time to carefully and slowly weld the new plates completely. Take your time and skip around as too much heat in one area can easily warp the rear frame section. I suggest skipping from side-to-side to minimize warpage. Keep an eye on your rear door gaps and trunk lid gaps as your welding as they will show tell-tale signs of warpage…listen for creeks as your weld too as the welds cool, they will begin to “pull”. Lastly, I chose to add a crossmember to help strengthen the frame. I used a piece of 1 1/4″ steel tubing and placed it between the coil spring and the shock. This cross tube is located as high as it could go and runs side-to-side in the inside of the original frame…welded in place and is welded to the inner side of the coil spring pocket for additional strength. With these mods made, you should now have approx. 14″ between the frame and the inner wheel well lip, assuming you’ve rolled the wheel lip up previously.
Courtesy of Todd Geisler
One mod that “should” be done with a frame notch is to “mini-tub” the inner wheel wells. This will provide the most usable room for a larger tire. You can either remove the stock inner wheel well and move it and replace the gap with a filler strip, or completely fabricate a new squared off inner wheel well. Both ways will accomplish the same goal, and both are acceptable ways. My inner wheel wells were rusted through where they met the trunk floor, so I chose to make all new inner wheel wells. With all this work completed, I was able to fit a 10.5 x 29.5 M/T ET Drag slick mounted on a 15 x 8.5 Centerline Convo Pro rim under the car. With careful measuring and back spacing selection, you should be able to fit a tire section width (sidewall buldge) of approx 12 1/2″ to 13″. Keep in mine when going to a 30″ tall tire, the front of the wheel opening usually needs to be moved forward (stretched) slighlty for tire growth. A 29″ tire seems to clear just fine, but a 30″ tall tire is a bit too close for comfort IMO. I stretched mine 1″. I simply took a pie cut out of the lower quarter panel from the body contour line down to the rocker.
Courtesy of Todd Geisler