when weighing a vehicle for springs you need to take away an amount for the unsprung weight of the rear end and suspension
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when weighing a vehicle for springs you need to take away an amount for the unsprung weight of the rear end and suspension
Interesting that that never appeared in any of the research I've done, and the QA1 tech didn't mention it, either.
At least he told you about the mounting angle
I placed a follow-up call to QA1, and was told that their recommendation is based on the actual weight at the wheel, NOT unsprung weight, so that's the weight to use when ordering parts. I'm not arguing that there's no difference, I'm reporting what number to use based on the shock manufacturer's recommendation and what they'll expect when you call.
My main point, however, was to not guess at the weight, but to actually weight your vehicle. For years, I had read estimates for a vehicle like mine ranging from 1250 to 1450 lb. at the rear, which is why I had 200 lb./in. springs to begin with. I learned the hard way that using someone else's numbers is a mistake, and I'm passing that along.
It's in the manufacturer's best interest to ask the right questions which lead to the right solution, and thus happy customers. They don't expect their customers to know sufficient mechanical engineering to divide the required spring rate by the sine of the mounting angle to determine which spring to order, but most of us can compute or measure the angle ourselves.
If someone would like to contribute design criteria based on unsprung weight rather than wheel weight, we'd all like to hear it. It would be especially valuable to provide a formula that derives the necessary spring rate for a given unsprung weight.
No formula or anything, but I weigh the rear end all assembled prior to putting it in the car...Deduct it's weight from the scale weight of the car with the rear end installed... I usually run to the soft side on springs by a few pounds, but I also have ballast in the car when I weigh it so the fuel and fluids, plus driver weight is all dialed in on the equasion.... My reason for going soft on the springs, seems most manufacturers' spring selections are too harsh of a ride and don't leave enough compression for the shocks to do their job correctly.... Like I said, no real formula or math----just a lot of trial and error....
Oh yeah--"your results may vary"--- Not all of us want the same rate springs, seen lots of cars that barely have room for an inch of movement on the tires before contacting something,,,,so they crank up the coilover spring height, and kill the shock action....
I haven looked at one of there catologes for a couple of years but if I remember right---QA 1 had about the best presentation in there about springs and shocks---mounting angle, rates relative to arm length, unsprung weight,etc
of course when I did my first pro stocker, had problems---but when checking the springs themselves they were all over the place ---ended up with a pair of evry type of spring---probably still have 30 or so of them------
It's still a problem, Jerry.... Being an old circle burner, I still have a coil spring checker around.... I've had 120 pound springs test anywhere from 85 pounds to 150 pounds---- the difference in rate from one manufacturer to another is huge!!!! Tru-coil and AFCO seem to be about the closest to matching the advertised spec for pressure at height.....Quote:
Originally Posted by jerry clayton