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Have you modified the rear spring cups to use these springs? The springs that I have seen advertised are a different diameter from the ones used in Alfa Spiders.also speedway motors have springs.. any rates and 39.95-59.954 each..

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I know about the front springs but it is the rears that I am interested in. It looks to me that Speedway Motors do not sell a spring that is the same diameter as the Alfa rear. How did you install the Speedway springs in the rear?the speedway front springs that you want are 5.5"

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Which ones have you used? They sell 125 lb/in with 16" free length. That sounds promising for a Spider5" diameter spring will work just fine... trust me I sell cars

if you have access to a spring tester then thats pretty easy , obviously but if you don't the math works like this :

(G x D x D x D x D ) ( thats D to the 4th ) / ( 8 x N x M x M x M)

G is the the torsional modulous of the material is presumed to be 11.25 x 10 to the 6th or 11,250,000

D is the wire diameter measured with a micrometer to three decimal places

N is the number of ACTIVE coils ... the coils that touch the seat on flat end springs don't count

M is the center line diameter of the spring called the mean. arrived at by subtracting one wire dia from the overall dia.

"8" is a derived constant

so... its 11,250,000 times wire dia to the 4th divided by the quantity 8 times the number of active coils times the mean dia cubed .

so this gives you the actual spring rate, known as K , in pounds per inch for what is actually on your car. now... nothing keeps you from doing that same calculation on your new springs and determining is they are stiffer softer or what. if the rate calculates the same and they are the same free height then the ride height must be the same... stiffer and same free height and the car will be higher, softer and it will be lower.

now... a word about the number of coils and why it matters...

a spring is nothing more than a sway bar that has been wound into a spiral . the " spring " action comes from each " section " or slice of the wire twisting like a sway bar relative to the section next to it... so... a spring that has one coil gets its entire rate by twisting one section a long way while a spring with 10 coils twists 10 sections a much shorter way ( the same as a short sway bar of a given dia will be stiffer than a long bar of the same dia ) ... why is this important ?

elastic limit . all materials have a strain ( deflection ) limit to where it can be " bent or twisted " and still return undamaged to its original shape. once a material is deflected beyond its elastic limit it permanently deforms ( yields ) and never goes back. a spring with too few coils twists its sections beyond the elastic limit of the material and basically is killed as a spring at that point a spring with a lot of coils has more capability for large deflections. thats where all the design elements come into play ... only have room for a very short spring with only a few coils ? use big wire at a large dia. have a lot of room for a tall spring but no side clearence ? use smaller wire at a smaller dia with a lot of coils .

i read these posts and begin to onder if these cars had all manner of spring rates for different years and that centerline is trying a " one size fits all approach " it will be easy to know... either measure one and do the math or stick one on a spring checker along with the one you are taking off the car.

there shouldn't be as wildly varying results are as posted here . this is pretty basic stuff and hard quantifiable answers should be easy to find

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There is a post somewhere that lists the spring rate for standard Alfa springs and many aftermarket springs. I have a copy of it in an Excel file.

My standard rear springs are 70 lb/in, both calculated and measured with a bathroom scale and a yard stick. Most aftermarket "sport" springs are about 180 lb/in. Bianch1 has pointed out that there are more options with springs from Speedway Motors.

A friend who has a fast Giulia super race car uses rear springs from 125 to about 200. Shankle sold springs that were 114 and 134 lb/in.

there are lots of calculators online where you just dump in the data and they give you the rate... i have to say that i find those numbers staggeringly light. im not doubting them because i don't have shred of real data but with those kind of numbers the weight distribution of the car would have to be hugely forward... never the less , i find the bizzare results posted in the first three pages inconsistant with what should be a straight up deal. something is going on somewhere and i think some math might go a long way towards explaining it... i mean really... gigem took springs off , put new springs on that are supposed to be performance springs at the same free length and you lose 2" of ride height ? ... what can possibly do that except impossibly light rates ? i can't even imagine a street car with 80 lb rear springs. a full tank of gas would lower the car a 1/2 inch never mind passengers..... a spitfire that weighs 1400 lbs in street trim had transverse leaf spring that was 300 which is 150/side straight onto the uprights...

There is a post somewhere that lists the spring rate for standard Alfa springs and many aftermarket springs. I have a copy of it in an Excel file.

My standard rear springs are 70 lb/in, both calculated and measured with a bathroom scale and a yard stick. Most aftermarket "sport" springs are about 180 lb/in. Bianch1 has pointed out that there are more options with springs from Speedway Motors.

A friend who has a fast Giulia super race car uses rear springs from 125 to about 200. Shankle sold springs that were 114 and 134 lb/in.

it all seems very wierd to me at first blush...

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