If you’ve spent more than five minutes scrolling through C10 forums or checking out builds at Dino’s Git Down, you’ve heard the numbers. 4/6. It’s basically the "golden ratio" for the 1973–1987 Chevrolet C10. While some guys want to lay frame on air bags and others prefer a mild leveling kit, the 4 6 C10 drop is that sweet spot where the truck actually looks like a custom machine without requiring you to cut your bed floor into pieces.
Honestly, it’s about the rake.
Most of these old trucks came from the factory with a "stinkbug" stance—the rear sat way higher than the front to accommodate a payload that most modern owners will never actually haul. When you drop the front four inches and the rear six, you aren't just lowering the truck; you’re leveling the body lines with the pavement. It changes the entire silhouette. Suddenly, that slab-sided Square Body looks long, lean, and aggressive.
What Does a 4/6 Drop Actually Consist Of?
Getting a front-end down four inches isn't as simple as heating up your springs with a torch—please, for the love of all things holy, don't do that. You’ve basically got two paths here. Most builders lean toward a combination of 2-inch drop spindles and 2-inch drop springs.
Why the mix? If you do all four inches with just springs, your lower control arms are going to be scraping the pavement, and your suspension geometry will be so out of whack you'll eat through tires every 5,000 miles. Spindles keep your steering geometry closer to factory specs while tucked up inside the wheel.
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The rear is where the "6" comes in. To get six inches of drop in the back of a C10, you’re almost certainly looking at a flip kit. This moves the rear axle from underneath the leaf springs to on top of them. That move alone usually nets you about five inches. To get that final inch and really dial in the level look, most kits include a shackle or a hanger adjustment.
The C-Notch Necessity
Here is where a lot of guys try to cut corners, and it’s a massive mistake. At a six-inch rear drop, your axle is going to be incredibly close to the frame rail. If you hit a pothole—or even a decent-sized pebble—without a C-notch, you’re going to hear a bone-jarring "thud" as metal hits metal.
You have to notch the frame.
Basically, you’re cutting a semi-circle out of the frame rail above the axle and reinforcing it with a steel plate (the notch kit). It gives the axle room to travel upward. I’ve seen people try to skip this by running air shocks or super stiff springs, but the ride quality becomes absolute garbage. If you're going for a 4 6 C10 drop, just buy the notch. Your lower back will thank you.
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Wheels, Tires, and the Rubbing Reality
Lowering a truck this far changes the math on wheel fitment. You can't just throw a massive offset wheel on there and hope for the best. With a 4-inch front drop, a 20x8.5 wheel with about 5 or 5.25 inches of backspacing is usually the "safe" zone.
Tire height matters too. If you run a tire that's too tall, you’ll be rubbing the inner fenders every time you turn into a gas station. A 245/45R20 is a common choice for the front, while the rear can handle a bit more meat, like a 275/40R20 or even a 295 if your backspacing is perfect.
Keep in mind that every truck is slightly different. These frames were stamped in the 70s and 80s; tolerances weren't exactly "aerospace grade" back then. One guy’s truck might clear 20s easily, while yours might need a little "clearancing" with a rubber mallet.
Real World Living: Is it Too Low?
It depends on where you live. If your daily commute involves dirt roads or the cratered streets of the Rust Belt, a 4 6 C10 drop is going to be a workout. You’ll become an expert at "the angle"—that diagonal crawl you have to do to get over speed bumps or into steep driveways.
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But on the highway? It’s surprisingly good. Because you’ve lowered the center of gravity, the truck feels much more planted. The "boat-like" swaying of the factory suspension disappears. Companies like Belltech, McGaughys, and IHC Suspension have spent decades refining these kits so they don't feel like a pogo stick.
Common Misconceptions and Pitfalls
A lot of people think they can just "bolt and go." You can't. When you drop the rear six inches, your pinion angle changes. This can lead to nasty vibrations in the driveshaft. Most high-quality flip kits come with angled shims to tip the differential back into the correct alignment, but it's something you have to check.
Then there’s the shock absorber issue. Your factory shocks are way too long for a lowered truck. They will bottom out immediately. You need "drop shocks" which have a shorter body and specific valving for the decreased travel.
Essential Parts Checklist:
- Front: 2-inch Drop Spindles + 2-inch Drop Springs.
- Rear: Axle Flip Kit + 1-inch Lifting Shackles (to get to 6" total).
- Frame: Under-bed C-Notch kit.
- Hardware: Shorter shocks, new U-bolts, and possibly a panhard bar relocation bracket if you have a later model with a coil-spring rear (though most 4/6 talk refers to leaf spring trucks).
Actionable Steps for Your Build
If you’re ready to pull the trigger on a 4 6 C10 drop, don't just buy the cheapest kit on an auction site. Quality of steel matters when it's holding your axle to your truck.
- Measure your current height. Measure from the center of the wheel to the fender lip on all four corners. Old leaf springs sag over time, so you might already be "lower" than factory, which affects your final result.
- Order a complete kit. Mixing brands can sometimes lead to headaches. Stick with a reputable manufacturer like Belltech or McGaughys for the main components.
- Inspect your bushings. If you’re pulling the front suspension apart anyway, spend the extra $100 to replace your 40-year-old control arm bushings and ball joints. It’s the difference between a truck that drives like new and one that wanders all over the lane.
- Get a professional alignment. This is non-negotiable. Your toe-in and camber will be completely wrong after the install. You’ll ruin a new set of tires in a weekend if you skip the alignment shop.
- Check your brake lines. Sometimes lowering the truck puts tension on the flexible rubber brake lines. Make sure they have plenty of slack throughout the full range of steering.
The 4/6 stance is popular for a reason. It's the point where a C10 stops looking like a farm implement and starts looking like a classic muscle truck. It takes some work, and you'll definitely have to cut your frame, but the first time you see that reflection in a store window, you'll know it was worth the effort.