Most derbies limit body modifications to safety-related items such as reinforcing the driver's door. Seldom are you allowed to reinforce frames, bumpers, or bodies. The tips outlined below are legal where I run my cars.

Tires
Tires are the second most important factor in motorsports, although maybe not so much in demolition derbies. Most people are tempted to get the biggest, ugliest tires they can find, but this isn't always the best strategy. I wouldn't go any bigger than 235-75R15 since bigger tires will invariably end up causing interference problems with the fenders. Also, when you're stuck up against another car, the big tires with the deep lugs just dig themselves into a hole real quick, and then you're toast. A less aggressive tire will allow you time to try to rock yourself out, or maybe hang in long enough until someone else hits you free. So what's the best tire? One with a moderately aggressive all-season tread that has about 1/3 of its tread-depth remaining.

The real tip for tires, however, is to install tubes in each tire. Car bumpers are at the perfect level for nailing tires and knocking them off their beads. Without tubes, the tire goes flat and you have a serious handicap. With tubes, the tire can stay inflated for a little while and buy you some precious time.

Other tips I've heard for tires: Cut the beads off a slightly smaller tire and place it inside the main tire to add a little support. Some people also add screws through the rim into the bead to help hold it on. I've never tried either of these, mainly because I'm too lazy.

Bumpers
Cars from the 60s and 70s had huge chrome bumpers with ends that curled right around the sides of the car. These ends are great for getting caught in other cars and getting you stuck. Take a cutting torch and nip the ends off.

Next, get some heavy chain (don't use Bowser's for this) and wrap it around the bumpers and the sturdiest looking sheetmetal you can find in the vicinity. Bumpers are easily ripped off and left dangling, and the chain will help prevent them from getting wedged under your car.

Gas Tanks
In the interests of safety, all derbies require you to remove the stock gas tank and install a marine-type tank where the back seat used to be. Make sure you get the hoses hooked up right. Older cars need only one line going to the fuel pump, but newer ones also require a return line. Use good quality neoprene lines and stainless steel clamps. I use a 3 gallon marine tank filled before each race, and I have never used more than a gallon of gas during a race.

Fenders
As your car gets scrunched up, the fenders will start to get intimate with your tires, often cutting them or locking them up altogether and causing them to drag. Depending on your local rules, cut out as much of the fenders, especially behind the back tires, as you can. Don't forget the inner fenders as well.

Hoods
Most derbies make you cut a hole above the carburetor to allow safety workers to extinguish engine fires. But really, you can do away with the entire hood if you wish. It adds virtually no structural support, and its removal will help keep the engine cool. In addition, if your front end gets hit a lot, the hood will often buckle up and obscure your view.

If you do keep your hood, a couple of tips: First, for cars that have a cable operated hood release mechanism be sure to cut the cable off about a foot from the latch and let it dangle. Once the front end is hit it is virtually impossible to release the hood using the release inside the car. Second, remove those little adjustable rubber stops near the front of the fenders that help vertically align the hood when closed. Their removal lets the hood drop deeper into the fenders and add a bit of side-to-side support.

The sharp eyed among you will note that I didn't remove the hoods on any of my cars. I guess I just place too much value on all that sheetmetal as a canvas for painting my designs.

Trunks
If you're running a sedan or coupe, you may want to cut two or three 8-10 inch holes in the trunk to allow you to see backwards in case the trunk pops up or gets folded up.

For both hoods and trunks, you must fasten them very securely to the rest of the body. The best method is to use multiple loops of a heavy guage farmer's wire run through the strongest parts of the fenders. (I reject welding because it cracks easily, and chain can never be tied tight enough.) Feed the wire through your holes somewhat loosely and then place a big crow bar in the loop and twist, you will have a very strong joint.

Windshields and Backlights
Without a doubt, the biggest pain in the ass when prepping your car is removing the windshield and backlight (rear window). Especially on newer cars, where they use some kind of Shwarzenegger-strength urethane compound to glue the glass so securely that it actually becomes an integral part of the car's structure. So how do you get them out? There's basically four ways.

• The least graceful method: smash-and-vacuum. When all else fails, you can depend on this. For the backlight you may want to cover both sides of the glass with packaging tape to minimize the fragment scatter.
• The recumbent position: a firm but gentle push. Leave the car in direct sunlight on a warm day for a few hours to soften the glue. Then get inside and use your feet to gently push the edges of the window away from the frame. I've had about a 50% success rate with windshields using this method, 0% with backlights. It also helps to have a trusted friend cut the glue with a carpet knife as you push on the window.
• Using tools, like men were meant to: a wire. Get a strong wire such as a piano wire or the wire cable from your hood latch. Work it through a convenient spot on the edge of the glass and make handles on both ends using vise grips or bolts. Now saw back and forth. A friend on the inside of the car helps here, as does sitting the car in a hot sun. I've never tried this before, but I've been told that the wire gets very hot so go easy and be careful in case it snaps.
• Like the pros: specialty knife. There are knives made specifically for this task that are basically heavy duty carpet knives with a 90 degree bend in the blade that lets it cut under the glass. This is how they do it in the glass shops, and is highly recommended. It'll be the best $15.00 you've ever spent.