Dodging a falling door:: Reversing this equation gives us x=gt^2/2 as the fallen distance x for a given time t. How much time would you have to dodge a falling door if the spring were to suddenly break at the top of travel? Let us assume you are 5.5 feet tall, so the door will hit your head after falling 2 feet from its 7.5 foot fully-raised height. This 2-foot fall takes sqrt(2*2/32.2) = 0.35 seconds (350 milliseconds). The quickest human response time is about 200 milliseconds, so even if you are alert to the hazard, this leaves you only about 150 milliseconds to accelerate and move your noggin out of the way. If you are an Olympic gold medalist in the 100 meter dash, you can accelerate (horizontally) about 10 feet/second^2, and your 150 milliseconds of wide-eyed panic will move you all of 10*0.15^2/2 = 0.11 foot = 1.35 inch.
Current data from real estate firms throughout the country show that replacing the garage door raises the value of a home by an average of $2,810, according to Remodeling Magazine's report. Based on the average cost of $3,304, this means that replacing a garage door is expected to return 85 percent of the job’s cost, nationally. When replacing a garage door in the Western U.S., however, the return is predicted to be 110.8 percent of your investment.
Although the door weight and drum size determine the maximum torque (termed MIP, maximum inch-pounds) needed from the fully-wound spring(s), the spring selection for a given door can still be varied to adjust the cycling stresses. A heavier wire on a larger diameter or longer length will produce the same torque as a lighter wire on a smaller diameter or shorter length, while undergoing less stress and therefore increasing expected cycle lifetime. The heavier spring will cost more but last longer, so this is another design trade-off. Calculating these spring sizes in the field is done using a book of tables (or the software equivalent) that we cannot provide here, although you will find the formulas to estimate spring properties below. If you can accurately provide the weight of the door, or the size(s) of the old spring(s) (assuming they were well-matched to balance the door), then a spring dealer should be able to tell you which spring sizes will work for you.
If your garage door is opening slowly or making a lot of noise, the problem may not be your opener. So before you buy a new one, check for broken or wobbly rollers and brackets. But don’t replace the bottom roller bracket yourself—the cable attached to it is under extreme tension. You’ll need to call a pro. If you’re replacing the rollers, get nylon rollers. They operate quieter than steel rollers and cost only a few bucks more. Next, check the torsion spring (mounted on the header above the door opening) to see if it’s broken. When one breaks, you’ll see a gap in the coils. You’ll need a pro to replace a broken spring.