Front Suspension Spring Rate

[Ed Price]

I finally got around to measuring the spring rate for my Amphi front coil
springs. I also measured the rate for a new Maeco PK22K1 coil-over shock
(available from Surplus Center at $20 each). Here's the results:

For 1 inch of compression:
Original Amphi Front Spring #1: 172 pounds
Original Amphi Front Spring #2: 145 pounds
Maeco PK22K1 Shock & Spring: 180 pounds

For 2 inches of compression:
Original Amphi Front Spring #1: 350 pounds
Original Amphi Front Spring #2: 304 pounds
Maeco PK22K1 Shock & Spring: 310 pounds

Averaged out, the spring rates for each are:
Original Amphi Front Spring #1: 175 pounds per inch
Original Amphi Front Spring #2: 152 pounds per inch
Maeco PK22K1 Shock & Spring: 155 pounds per inch

I conclude that one of my front springs is a bit weaker than the other. I also
see that the Maeco is very similar to the original Amphi springs. So, I'm going
to follow Ken Chambers advice and use the pair of new Maecos on the front of my
Amphi.

BTW, the Amphi shocks have an extended length of 13" and a stroke of 3.5". The
Maeco shock has an extended length of 13.25", and a stroke of 3.5". This is so
close as to be identical.

Rear spring data maybe next month.

Ed
El Cajon
67 Rust Guppy


[Non-text portions of this message have been removed]

 

[rogtwo@aol.com]

Ed, you say:

"For 1 inch of compression:
Original Amphi Front Spring #1: 172 pounds
Original Amphi Front Spring #2: 145 pounds
Maeco PK22K1 Shock & Spring: 180 pounds"

Is this one inch of compression from the free length of the SPRING or one
inch of compression from the full extension length of the SHOCK? Based on the 2
inch compression forces you give, I suspect its the latter. The rest of this
post is based on the assumption that the 1 inch forces you list are based on 1
inch of SHOCK compression. If this is wrong, then so is much of what I have
written below.

Based on your numbers, this question is not important for the original
springs. This is because, as you said previously, the original springs are
about
slack when the shock is fully extended.

But, the same does not seem to be true for the Maeco shock. Here if you
subtract the 1-inch force from the 2-inch force (310 -180) you get a 130 pound
difference for 1 inch of travel. Thus, the spring rate for the Maeco shock is
around 130 pounds per inch.

Applying this rate we see that at full shock extension (one inch longer than
at the 180 pound length), the spring would have about a 50 pound preload (180
- 130 = 50). This preload is not likely to cause any undesirable effects when
you use these shocks.

Also of interest though is the fully compressed force. With a 130 pound
spring rate, 3.5 inches of travel, and a 50 pound preload, the fully compressed
force of the Maeco shock will be around 505 pounds (130 X 3.5 + 50 = 505). This
assumes the spring is not a variable rate spring (i.e., the spring coils do
not stack significantly when the shock is fully compressed).

Using the same methods as above, I get the following numbers for your
original springs:

Spring 1

Rate - 178 lb/in*
Preload - negative 6 pounds** (i.e., the spring has a little space to rattle
when the shock is fully extended)
Force when shock is fully compressed - 617 (i.e., 178 X 3.5 - 6)

Spring 2

Rate 159 lb/in*
Preload negative 14 pounds** (this spring has a bit more slack when the shock
is fully extended).
Force when shock is fully compressed - 543 (i.e., 159 X 3.5 - 14)

So, it would take a total force of 1160 pounds to compress both front shocks
fully.*** Two Maeco shocks would require 1010 pounds to fully compress them.
This is 150 pounds less than the original shocks.

Is this 150 pound reduced load significant? I doubt it. We took our Amphi
on a camping trip this summer. I had the trunk packed very - very tightly with
food, tent, dishes, stove, cloths, sleeping bags, etc. I carefully packed
things in every crevice of the trunk. We had so much stuff that in addition to
filling 2/3 of the back seat (my daughter got the other 1/3), I even had to
build a little shelf UNDER the rear seat to hold the tent poles! My point?
Even with this load, and even though I drove on some gravel roads and a rocky
beach at the time, I don't remember there being a problem with the front shocks
bottoming out. I don't think the 150 pound reduction will be a problem.

* These rates are so close to the ones you calculated that the difference is
not significant.
** In actuality, the spring may or may not have room to rattle when the shock
is fully extended. The accuracy of these numbers is probably not really good
enough to predict if there is a 0.08 inch gap or not.
*** These fully compressed forces only apply to the static condition. That
is (minus the front weight of the car), this is roughly the load that you would
have to add to the trunk to fully compress the front shocks. During normal
use, the shocks only fully compress due to hitting a large bump, not because
you put 800 pounds in the trunk. Hitting a bump is a dynamic situation and in
addition to the spring capacity, the damping of the shock absorber makes a big
difference in whether the shock actually bottoms out or not.

Roger
White '63
Seattle

PS - Are any of the Maeco shocks still available? Who woul'd I contact?


[Non-text portions of this message have been removed]

 

[Randy Bograd]

Ed,
The Maeco shocks you describe require no modification and will bolt
right in?

Randy

--- In amphicar-lovers@yahoogroups.com, "Ed Price" <wb6wsn@c...>
wrote:
> I finally got around to measuring the spring rate for my Amphi
front coil springs. I also measured the rate for a new Maeco PK22K1
coil-over shock (available from Surplus Center at $20 each). Here's
the results:
>
> For 1 inch of compression:
> Original Amphi Front Spring #1: 172 pounds
> Original Amphi Front Spring #2: 145 pounds
> Maeco PK22K1 Shock & Spring: 180 pounds
>
> For 2 inches of compression:
> Original Amphi Front Spring #1: 350 pounds
> Original Amphi Front Spring #2: 304 pounds
> Maeco PK22K1 Shock & Spring: 310 pounds
>
> Averaged out, the spring rates for each are:
> Original Amphi Front Spring #1: 175 pounds per inch
> Original Amphi Front Spring #2: 152 pounds per inch
> Maeco PK22K1 Shock & Spring: 155 pounds per inch
>
> I conclude that one of my front springs is a bit weaker than the
other. I also see that the Maeco is very similar to the original
Amphi springs. So, I'm going to follow Ken Chambers advice and use
the pair of new Maecos on the front of my Amphi.
>
> BTW, the Amphi shocks have an extended length of 13" and a stroke
of 3.5". The Maeco shock has an extended length of 13.25", and a
stroke of 3.5". This is so close as to be identical.
>
> Rear spring data maybe next month.
>
> Ed
> El Cajon
> 67 Rust Guppy
>
>
> [Non-text portions of this message have been removed]