Hey my car is too stiff:
Yellow Konis all around.
21 mm front bars
150 lbs rear that are about 10-inches long
Is stock?
19 mm front
100 lb rear?
If so I think that'll be a good thing to try.
What is the stock rear spring length?
And anyone have a stock spring set they'd like to sell??
Thanks!
Full Version: 1974 stock spring rate ?
Stock front torsion bar is 17.9 on a four and 18.8 on a six.
Stock rear springs were around 50 lbs and about 60lbs on a six.
It's easy to get to harsh, especially on the front. A mid 80's 911 Carrera only has 19mm front torsion bars and it's a 2700 lb car.
The formula for calculating spring rate is: k=d^4G where k=spring rate, d=diameter, G=modulus of elasticity (constant for steel)so ignoring the constant:
% increase in stiffness = ( (d2^4)- (d1^4) ) / (d1^4) * 100
where d2 is new diameter and d1 is original diameter
Stock Front = 18.8 increase to 21 mm = 55.7 % increase in spring rate.
Going from 17.9 to 21mm = 87.5% increase in spring rate
Stock rear springs were around 50 lbs and about 60lbs on a six.
It's easy to get to harsh, especially on the front. A mid 80's 911 Carrera only has 19mm front torsion bars and it's a 2700 lb car.
The formula for calculating spring rate is: k=d^4G where k=spring rate, d=diameter, G=modulus of elasticity (constant for steel)so ignoring the constant:
% increase in stiffness = ( (d2^4)- (d1^4) ) / (d1^4) * 100
where d2 is new diameter and d1 is original diameter
Stock Front = 18.8 increase to 21 mm = 55.7 % increase in spring rate.
Going from 17.9 to 21mm = 87.5% increase in spring rate
Thanks very much. Super helpful. I found a set of 17.9 front bars that I will try.
Do you happen to know the length of a stock rear spring?
Stock front torsion bar is 17.9 on a four and 18.8 on a six.
Stock rear springs were around 50 lbs and about 60lbs on a six.
It's easy to get to harsh, especially on the front. A mid 80's 911 Carrera only has 19mm front torsion bars and it's a 2700 lb car.
The formula for calculating spring rate is: k=d^4G where k=spring rate, d=diameter, G=modulus of elasticity (constant for steel)so ignoring the constant:
% increase in stiffness = ( (d2^4)- (d1^4) ) / (d1^4) * 100
where d2 is new diameter and d1 is original diameter
Stock Front = 18.8 increase to 21 mm = 55.7 % increase in spring rate.
Going from 17.9 to 21mm = 87.5% increase in spring rate
Do you happen to know the length of a stock rear spring?
QUOTE(mepstein @ Nov 24 2019, 09:31 PM) 
Stock front torsion bar is 17.9 on a four and 18.8 on a six.
Stock rear springs were around 50 lbs and about 60lbs on a six.
It's easy to get to harsh, especially on the front. A mid 80's 911 Carrera only has 19mm front torsion bars and it's a 2700 lb car.
The formula for calculating spring rate is: k=d^4G where k=spring rate, d=diameter, G=modulus of elasticity (constant for steel)so ignoring the constant:
% increase in stiffness = ( (d2^4)- (d1^4) ) / (d1^4) * 100
where d2 is new diameter and d1 is original diameter
Stock Front = 18.8 increase to 21 mm = 55.7 % increase in spring rate.
Going from 17.9 to 21mm = 87.5% increase in spring rate
I always thought rear spring rate was closer to 70# on a 4 and 90# on a /6...
QUOTE(Racer @ Nov 25 2019, 07:06 AM)
I always thought rear spring rate was closer to 70# on a 4 and 90# on a /6...
The factory service manual lists spring rates that are in line with what Mark posted once you do the math (50ish for the four).
QUOTE(bbrock @ Nov 25 2019, 09:33 AM)
QUOTE(Racer @ Nov 25 2019, 07:06 AM)
I always thought rear spring rate was closer to 70# on a 4 and 90# on a /6...
The factory service manual lists spring rates that are in line with what Mark posted once you do the math (50ish for the four).
math? I own a 914.. I don't do math
Found this:
http://www.914world.com/bbs2/index.php?showtopic=95741 (scroll to post #14)
and it had this:
https://members.rennlist.com/chuxter/914CoilSprings.htm
i can't vouch for validity, just my ability to google stuff..
In testing for production of our springs we found the spring rates were in th3 64 -68# range for the 4's We optimized the the spring at 100# as the geometry and loading suggested that the 100 was the best, We also made the 140/160 progressive springs for a more sporty ride.
Sorry I stand corrected it has been awhile we were in the 54-58 range. They were old springs but that's about where they were for most tested (10 sets if I recall correctly).
Sorry I stand corrected it has been awhile we were in the 54-58 range. They were old springs but that's about where they were for most tested (10 sets if I recall correctly).
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