[Formulabruce]

If you opted for F-41 in 70 you got stiffer T/A springs and the 15 inch wheels/ tires . USUALLY, however the 15 could be ordered separately. This subject was beat bad last year, do a search. .
IMHO, after researching this I do not recommend Eaton 70-72 springs with different ratings per side.
The 73 model made both sides equal. This allowed for better handling tuning with the newer " crowned" roads AND radials. Hence RTS advertising shows up in 73.
Also if you buy new Eatons, select a lower rating than you think, or select a drop spring.

[Ramairnacho]

Originally Posted by Formulabruce

If you opted for F-41 in 70 you got stiffer T/A springs and the 15 inch wheels/ tires . USUALLY, however the 15 could be ordered separately. This subject was beat bad last year, do a search. .
IMHO, after researching this I do not recommend Eaton 70-72 springs with different ratings per side.
The 73 model made both sides equal. This allowed for better handling tuning with the newer " crowned" roads AND radials. Hence RTS advertising shows up in 73.
Also if you buy new Eatons, select a lower rating than you think, or select a drop spring.

My car came with 14 inch steel rims then i.got formula leaf springs. Can you school us on the stiffness? What's that mean?

[Formulabruce]

Originally Posted by Ramairnacho

My car came with 14 inch steel rims then i.got formula leaf springs. Can you school us on the stiffness? What's that mean?

Many folks forget that in most all GM V-8 cars ( not wagons, trucks or 6 cyl cars)
the tire height goal is 26 inches as they want just under 800 revs per mile.
This is true for new Vettes and 1970 Firebirds.
So, if you use 14" stock size tire, you get Same tire height as the 15, ( 26 inches) and Better Ride than the 15" as you have more sidewall to take the shock out of the road. This is a bit of a compromise on Handling though, but same fuel economy if width is the same.
Formula leaf springs are just a tiny bit higher rate, and the anti sway bar will help with roll just as the higher rate spring does. ( If the sway bar can move, many dont move much at all, either due to age and rubber, or someone cranked the mounts and drop link).
Eaton seems to have a problem with Deflection and rate at that higher deflection. Members here have had to have new Eaton springs " De Arched" .
Eaton now offers their factory springs in a 1-2 inch drop, which it isnt really.
If I was ordering a set today ( probably will be for a buddies 1970 that's in 4wd mode with new Eaton springs) , I would order the Esprit rear springs for 73 with the 1 inch drop. that would get you about 1 inch below level and a soft enough ride to enjoy and still have a sway bar for handling.
iF YOU WANT SCCA racing OR Drag racing, you can find a lot of "harsh riding" options out there.
1972 > Y99 got you slightly higher spring rates, bigger bars, but same height.
hope this helps..
In 1970 the Chevy F41 suspension package was used on the T/A and a separate option on the formulas. ( this probably has a few pages of discussion, and Im not sure there is a full agreement.) There are cars with F41 and 14 " tires and 15" tire Formulas without the F41.
F41 dates back to the 67 Z28 in Chevrolet as I recall. Chevy installed it in some 6 cylinder stick Camaros with Z stripes to sell during Indy as "Pace setter" sale Camaros... ..