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Coil Spring WTF?

M

monkeystash

Active Member
I have 2 sets of coils for my '65. 480# 1" drop from NPD, and 620# 1" drop from Laurel Mtn. It seems funny to me that the 620# are taller, thinner, and coiled looser. I can even compress them easier by hand. The 480# are 12.5" high uncompressed, and the 620# are 14". The 480# are .712" thick while the #620 are only .600". Somebody give me a lesson on why this seems backward???

 

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are the black ones possibly progressive rate springs? may just be the shadowing in the pic, but the coils look smaller at the top (actually the bottom in the pic). if not, my only guess is they used chinese math for a chinese spring??? :shrug
 
Were the 620's actually advertised as 620 pound springs or just "620s"? Common misconception is that 620 springs are the spring rate when in reality they are the spring diameter. Typical 620 springs are around 500lb spring rates. If you can compress the spring an inch with less than 500lbs, then they are likely just stock replacement springs (which I'm guessing) and likely rate at 260ish or so.

Those 480 springs have a much thicker coil that I thought they would, but then again the spacing between coils is much smaller.
 
"buening" said:
Were the 620's actually advertised as 620 pound springs or just "620s"? Common misconception is that 620 springs are the spring rate when in reality they are the spring diameter. Typical 620 springs are around 500lb spring rates. If you can compress the spring an inch with less than 500lbs, then they are likely just stock replacement springs (which I'm guessing) and likely rate at 260ish or so.

Those 480 springs have a much thicker coil that I thought they would, but then again the spacing between coils is much smaller.
Click to expand...

Here is how the 620s are advertised, and I attached a picture of the box they came in.

THESE ARE THE 1'' LOWERING FRONT COIL SPRINGS FOR ALL 65-66 MUSTANGS WITH 289 (OR 302) ENGINES, 1 PAIR
FIRMER THAN STOCK 620 RATE BUT NOT TO FIRM FOR A SMOOTH COMFORTABLE RIDE WITH IMPROVED HANDLING.
BLACK POWDER COATED

This is how the NPD 480s are listed:

COIL SPRING SET, HIGH RATE, GRAY POWDER COAT FINISH, 480 LBS RATE, 1 INCH LOWERING HEIGHT MAY VARY DUE TO OPTIONS (A/C, HEADERS, HOODS, ETC), US-MADE
 

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Since the stock springs were not 620 lbs, I think the earlier explanation is dead on. The listing language of both ads fits with the explanation given.

I, by the way, have those same 480's and would love to see a pic of final ride height when you get there.
 
"Horseplay" said:
Since the stock springs were not 620 lbs, I think the earlier explanation is dead on. The listing language of both ads fits with the explanation given.

I, by the way, have those same 480's and would love to see a pic of final ride height when you get there.
Click to expand...

I should have the 480s in soon, but there will be no engine weight for a while.

I think you just nailed it, these aren't 620s. I originally read the description as this (adding commas):

FIRMER THAN STOCK, 620 RATE, BUT NOT TO FIRM FOR A SMOOTH COMFORTABLE RIDE WITH IMPROVED HANDLING.

What is probably really means:

FIRMER THAN STOCK 260 RATE (as buening said) BUT NOT TO FIRM FOR A SMOOTH COMFORTABLE RIDE WITH IMPROVED HANDLING.
 
I've got the 550lb. 1" drop from NPD for my '67 and they were 12" high if that comparison helps any. I'd be interested to see if there is any descernable difference between your car with 480's and mine with 550's. That is if either of us can get our cars back on the road... :peter
I really liked the ride/ response from the 550's when I drove it stock for a yr. before teardown. Not soft and not jarring with GR2's.
Jon
 
I am under the impression that the 620's that most people talk about are describing the thickness of the coil: .620 inch

I'm pretty sure I read that somewhere awhile back.
 
This is a simple coil spring rate calculator...
http://www.proshocks.com/calcs/coilsprate.htm

According to thier calculator,
The tall black ones, .600 wire dia, 8.25 active coils come out to 259#.
The .712 diameter springs come out to 555#.

Coil springs are like sway bars, the longer or thiner they are, the easier it is is to twist or compress them.

Thinner springs need to have more free length so that they don't collapse too much when the initial load is placed on them. Thicker wire springs, don't compress as much, so the free length doesn't need to be as tall... As an example.... If your front end wieghs 1000#, the 260 springs will need to compress about 4" to support the #1000. The 555# springs will only need to compress about 2" to support the 1000#. It's actually a little more technical when you factor in the motion ratio of the upper A arms, but the concept is basically the same...
 
Thanks Stangg, great info there!

Got one side done today:

53-160511203158-8110459.jpeg
 
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