spring rate and math question
Joined: Jan 2011
Posts: 5,651
Likes: 104
From: Mt. ________
Tire size is not factored in - the motion ratio is to the center of the contact patch. No matter how wide your tires are the centerline is in the same place, assuming the same wheel width/offset.
Unfortunately because of how offset is measured if you have a different width wheel/tire with the same offset, it actually moves the centerline of the wheel slightly. so I guess technically width does matter. but not actually because of the width change itself, just because the way offset is measured it's dependent on the width.
Anyway this is really just mental masturbation - in practice offset and width only change the motion ratio by a very small amount so most people ignore it. The reason you put a higher spring rate up front if you have wider tires up front is not because of motion ratios, it's because of something completely different (the fact that you can now load the front tires more).
Unfortunately because of how offset is measured if you have a different width wheel/tire with the same offset, it actually moves the centerline of the wheel slightly. so I guess technically width does matter. but not actually because of the width change itself, just because the way offset is measured it's dependent on the width.
Anyway this is really just mental masturbation - in practice offset and width only change the motion ratio by a very small amount so most people ignore it. The reason you put a higher spring rate up front if you have wider tires up front is not because of motion ratios, it's because of something completely different (the fact that you can now load the front tires more).
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Joined: May 2005
Posts: 472
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From: WLA
8inch=203mm
6inch=152mm
800lb=14kg/mm
900lb=16kg/mm
S2000's unspring weight
NOTE: when you do adjust coil over, always use weigh at spring which is NOT a corner weight. Corner weight includes unsprung weight.
Ft:390kg (appx860lb)
Rr:390kg
How much spring compress at 1G
390/16=24
390/14=18(17.8)
24-18=6mm
Spring free length difference
203-152=51mm
You are changing spring rate to softer spring, you need raise spring parch 6mm to keep the same ride height.
And you are changing spring free length to shorter length one, And to adjust the free length difference, LOWER your spring parch for 45mm(appx 1.8inch) from where it the spring parch was initially set. then you should get same ride height with different spring rate and free length.
NOTE: I am talking with coilover with NON-full length adjustable type.
6inch=152mm
800lb=14kg/mm
900lb=16kg/mm
S2000's unspring weight
NOTE: when you do adjust coil over, always use weigh at spring which is NOT a corner weight. Corner weight includes unsprung weight.
Ft:390kg (appx860lb)
Rr:390kg
How much spring compress at 1G
390/16=24
390/14=18(17.8)
24-18=6mm
Spring free length difference
203-152=51mm
You are changing spring rate to softer spring, you need raise spring parch 6mm to keep the same ride height.
And you are changing spring free length to shorter length one, And to adjust the free length difference, LOWER your spring parch for 45mm(appx 1.8inch) from where it the spring parch was initially set. then you should get same ride height with different spring rate and free length.
NOTE: I am talking with coilover with NON-full length adjustable type.
Joined: Apr 2012
Posts: 450
Likes: 13
8inch=203mm
6inch=152mm
800lb=14kg/mm
900lb=16kg/mm
S2000's unspring weight
NOTE: when you do adjust coil over, always use weigh at spring which is NOT a corner weight. Corner weight includes unsprung weight.
Ft:390kg (appx860lb)
Rr:390kg
How much spring compress at 1G
390/16=24
390/14=18(17.8)
24-18=6mm
Spring free length difference
203-152=51mm
You are changing spring rate to softer spring, you need raise spring parch 6mm to keep the same ride height.
And you are changing spring free length to shorter length one, And to adjust the free length difference, LOWER your spring parch for 45mm(appx 1.8inch) from where it the spring parch was initially set. then you should get same ride height with different spring rate and free length.
NOTE: I am talking with coilover with NON-full length adjustable type.
6inch=152mm
800lb=14kg/mm
900lb=16kg/mm
S2000's unspring weight
NOTE: when you do adjust coil over, always use weigh at spring which is NOT a corner weight. Corner weight includes unsprung weight.
Ft:390kg (appx860lb)
Rr:390kg
How much spring compress at 1G
390/16=24
390/14=18(17.8)
24-18=6mm
Spring free length difference
203-152=51mm
You are changing spring rate to softer spring, you need raise spring parch 6mm to keep the same ride height.
And you are changing spring free length to shorter length one, And to adjust the free length difference, LOWER your spring parch for 45mm(appx 1.8inch) from where it the spring parch was initially set. then you should get same ride height with different spring rate and free length.
NOTE: I am talking with coilover with NON-full length adjustable type.
650# corner weight - 75# unsprung = 575lb
575# / .7 motion ratio = 821 pounds acting on spring
821/900 = old spring compressed .91"
821/800 = new spring compressed 1.026"
difference of .116"
so you need to raise the perch by 2.116"
As far as the rest of you post, you made several errors.
First, I'm not sure were you came up with your 390kg number (although it is close to the number I came up with).
Second, you have a lot of conversions and rounding which are introducing some error since there are so many.
Third, you say: 390/14=18(17.8) --> but this is not true, it is 27.85
Finally, you say he needs to lower the perch for a shorter spring? That is backwards.
Thread Starter
Registered User
Joined: Jun 2009
Posts: 4,340
Likes: 0
From: Frankfort, KY
yea thanks guys! I'm going to order springs friday when I get paid. Anyone got any 2.25" x 6" 600 lbs hypercoil springs they want to sell?
I've never taken to tophats off and spring myself, it's always been at SRP, hopefully its easy to do?
I've never taken to tophats off and spring myself, it's always been at SRP, hopefully its easy to do?
Joined: Apr 2012
Posts: 450
Likes: 13
Very easy if your shaft has a place to hold it from spinning. Just remove the spring preload first so you don't get a spring or bolt in your face.
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boyguan
S2000 Racing and Competition
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Aug 3, 2013 11:42 PM