 1974 stock spring rate ?, 1974 stock spring rate ???? |
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| lweb19 |
 Nov 24 2019, 08:21 PM
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#1
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Newbie  Group: Members Posts: 2 Joined: 14-November 19 From: Ann Arbor Member No.: 23,642 Region Association: None  |
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! |
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| mepstein |
Nov 24 2019, 08:31 PM
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#2
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914-6 GT in waiting Group: Members Posts: 19,268 Joined: 19-September 09 From: Landenberg, PA/Wilmington, DE Member No.: 10,825 Region Association: MidAtlantic Region 
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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 (IMG:style_emoticons/default/welcome.png) |
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| lweb19 |
Nov 25 2019, 05:30 AM
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#3
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Newbie Group: Members Posts: 2 Joined: 14-November 19 From: Ann Arbor Member No.: 23,642 Region Association: None |
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? 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 (IMG:style_emoticons/default/welcome.png) |
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| Racer |
Nov 25 2019, 08:06 AM
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#4
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Senior Member Group: Members Posts: 787 Joined: 25-August 03 From: Northern Virginia Member No.: 1,073 Region Association: MidAtlantic Region |
I always thought rear spring rate was closer to 70# on a 4 and 90# on a /6...
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| bbrock |
Nov 25 2019, 08:33 AM
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#5
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains
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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). |
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| Racer |
Nov 25 2019, 10:14 AM
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#6
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Senior Member Group: Members Posts: 787 Joined: 25-August 03 From: Northern Virginia Member No.: 1,073 Region Association: MidAtlantic Region |
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 (IMG:style_emoticons/default/wink.gif) 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.. |
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| Mikey914 |
Nov 25 2019, 11:02 AM
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#7
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The rubber man Group: Members Posts: 12,661 Joined: 27-December 04 From: Hillsboro, OR Member No.: 3,348 Region Association: None
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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). |
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