Very confused

[jpaulus53]

I removed my original rear springs from my 77 and they measured 18 inches.
I bought a set of 16 inch 125 lb springs , i wanted to lower the car even though
i was a little afraid that a 2 inch shorter spring would be to much.
I test fit the new springs (no shocks). Hmmmm. it looks exactly the same to me!!
What am i missing.

original spring
https://dl.dropboxusercontent.com/u/217 ... spring.png
original spring in car
https://dl.dropboxusercontent.com/u/217 ... spring.png
New 16 inch spring in car
https://dl.dropboxusercontent.com/u/217 ... spring.png

[djape1977]

drive it for a couple humdred miles and see if it sets down. your original sprngs have gome mushy over the years and new harder springs despite being shorter keep the car sitting higher than old ones. if they don't se down, take em out and cut off couple rounds

[jpaulus53]

I ordered these specifically because i did not want to cut the springs. I know many people do but
Spring manufacturers say that only Tangential springs should be cut. The spider has square end springs,
so instead of just cutting what i already own, i bought springs 2 inches shorter.
Hope your right about the car settling.

[FiatMac]

Using the spring specifications from the Fiat Factory Manual, I did the following calculations:

Per the Fiat Factory Shop Manual the rear springs are to have a length of 11.61 inches under a load of 628 +/-29 lbs. If the free length is 18 inches then this equals a deflection of 18 minus 11.61 or 6.39 inches. The stock spring rate is then obtained by dividing the load by the deflection under the load or,

628 (+/- 29) lbs/6.39 inches = 93.9 to 102.8 lbs per inch of deflection

The manual also states that the minimum permissible load to produce an 11.61 inch length is 589 lbs. This results in a spring rate of 92.18 lbs/inch. (weakest spring allowed per Fiat).

So, the stock rear spring can have a spring rate ranging from 92.18 to 102.8 lbs/inch.

The Fiat 124 curb weight is 2250 lbs, and the weight distribution is 55/45; therefore, each rear wheel supports 506.3 lbs.(2250/2 x 45% ). Calculating the deflection of the spring for this load we get,

503.6/93.9 = 5.36 inches max.
503.6/102.8 = 4.9 inches min.

503.6/92.18 = 5.46 inches for the weakest spring allowed

The springs you purchased are 16 inches long and have a rate of 125 lbs/inch of deflection. Under the above curb weight load the calculated deflection is,

503.6/125 = 4.03 inches.

However, your springs start out 2 inches shorter than the stock spring, so we add this to the deflection number and we get,

4.03 + 2 = 6.03.

The difference between the stock spring deflection and your spring deflection plus the 2 inch shorter length is the curb height difference.

6.03 – 5.46 = 0.57 inches stock spring just barely met Fiat spec.
6.03 – 5.36 = 0.67 inches stock spring at the normal bottom end of the Fiat spec.
6.03 – 4.9 = 1.13 inches stock Fiat spring at the top end of the Fiat spec.

I would guess that your stock springs were on the low end of the Fiat specification.

[jpaulus53]

Wow thanks. That's a fantastic explanation.

So The stock spring is 11.61 inches under load

and my new 16 inch spring has 4.03 +2 = 6.03 inches of compression So

16 inches minus 6.03 = 10.91 inches (spring under load)


So the car is 11.61 - 10.97 = .64 or .64 inches lower.

and that looks like what i,m seeing , about a half inch lower


Thanks for the reply!

[djape1977]

there you go. that's exactly why i never liked maths but was good at shop class

cutt off A round, not two.