'We're all slaves to traction. After all, what good is a 600hp thumper gonna do underhood if it just turns into tire smoke when you mash the honker pedal? Though suspension tuning can take you part of the way, real traction gains always come from increasing the contact patch via bigger meats. To fit the big rubber, you may need to narrow your rear axle.
To get the scoop on how it's done, we visited with Ed and Mando Sutton of Sutton Engineering. All they do is rear axle work of all kinds, and they have a special place in their hearts for guys working on a low budget. Big proponents of cutting and resplining stock axleshafts for use in narrowed axlehousings, they say they've seen hundreds of customer cars crank off 11-flats (automatic transmission) and 12-flats (stick cars) on reworked stock axleshafts. At about $140 a pair (plus shipping), it makes pretty good economic sense too.
Of course, the guys are quick to point out that the added cost of aftermarket axles is a small price to pay versus the potential consequences of breaking a stock axle and smacking the wall. So be smart and realistic when you choose your specific axle strategy. As for narrowing the axlehousing, the Suttons charge between $100 and $150 for the labor. Let's have a look at what it takes to get more rubber under any car.
The most critical step is fitting the fully inflated tires to the wheels you'll be using and taking careful measurements. If the car is under construction and has no rear axle, support the body and place the wheels and tires under it for your measurements. If the rear axle is still in the car, support the car on the axle so the ride height is accurate, then make note of where the sidewalls contact the body. On this '63 Dart, the Radir 10.00-15 piecrust slicks (12.5-inch bulge width) and Cragar 15x7 wheels (3 1/4-inch backspacing) just barely fit. We need to gain 1 inch of fender clearance for safe street and strip action. In case you were wondering, no, the slicks won't clear the Dart's stock leaf springs. We had to install an inboard spring relocation kit to get inboard clearance. That's another story for another time.
 The Dart's stock 7 1/4 rear...  The Dart's stock 7 1/4 rear axle measures 57.5 inches from drum to drum. We know that we need to reduce this total width to 55.5 inches for sidewall clearance. Also, because there will soon be an infusion of 440 big-block power, this weakling axle goes into the scrap bin. |  To cope with the 440, we scored...  To cope with the 440, we scored an 8 1/4 rear from a '68 Dodge A100 van in the junkyard. The bare housing measures a whopping 56.5 inches-not including brakes and axles. We need to narrow it 6 inches to arrive at a 50.5-inch width. Once the axleshafts and drum brakes are installed, the drum-to-drum dimension will be 55.5 inches, just what we want. The fingers point out the two close-spaced differential studs that indicate the top of the Mopar 831/44 housing. By contrast, Ed and Mando Sutton point out that the Ford 8-inch housing has no up or down thanks to its symmetrical differential bolt pattern. |  Mando Sutton used a plasma...  Mando Sutton used a plasma cutter to remove all traces of the A100's useless shock-absorber mounting brackets and spring perches. They get in the way of the cutting and welding operations and aren't compatible with passenger-car mounting strategies. |