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Author Topic: Cutting front springs  (Read 17408 times)

///digitalme

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Cutting front springs
« Reply #15 on: January 29, 2010, 11:27:26 PM »
i bought a 89 cabrio once it had cut springs on the front the ride was rough and it didnt feel better than stock....and it made so much noise...
i recently bought a 318is and it has h&r lowering springs and honestly i wouldnt go lower than this i have trouble with the pan it scrapes occasionally
i wouldnt go too low....at the end its your decision :)


its lower than it seems cause it has tiny tires


and this thing had cut springs and driving it sucked!
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dwtaylorpdx

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Cutting front springs
« Reply #16 on: January 30, 2010, 12:35:51 AM »
If the coils are evenly spaced the spring rate is constant per inch of compression regardless of length.

If they are a progressive rate spring, IE have tight coils at one end and loose coils at the other the rate goes DOWN if you cut a tight coil and UP if you cut a loose coil.

Stock BMW ti springs are progressive. The Race springs from H&R are not.

Just my little old free opinion...

BTW if you cut the springs the cap coil will not grip the perch as well unless you re-bend the coil to fit correctly.
Remember this is a strut not you 62 Impala with big buckets for the spring to sit in...

Dave
« Last Edit: January 30, 2010, 12:39:20 AM by dwtaylorpdx »
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Chalino

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Cutting front springs
« Reply #17 on: January 30, 2010, 12:50:20 AM »
Quote from: dwtaylorpdx;86135
If the coils are evenly spaced the spring rate is constant per inch of compression regardless of length.

If they are a progressive rate spring, IE have tight coils at one end and loose coils at the other the rate goes DOWN if you cut a tight coil and UP if you cut a loose coil.

Stock BMW ti springs are progressive. The Race springs from H&R are not.

Just my little old free opinion...

BTW if you cut the springs the cap coil will not grip the perch as well unless you re-bend the coil to fit correctly.
Remember this is a strut not you 62 Impala with big buckets for the spring to sit in...

Dave


This was my concern; it seems like it wouldn't be way off but it probably wouldn't sit correctly as you stated.
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1991 318is
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flyinglizard

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Cutting front springs
« Reply #18 on: January 30, 2010, 12:34:04 PM »
You cant decrease spring rate by cutting coils. That is not correct info.  
 Think of it like this. Place one end of a 4ft rod in a vise. Twist the  free end with a  pair of visegrips. Moves real easy. Now twist it at the 3 ft mark,much harder to twist.
 Go to 2ft, 1 ft etc.  At 6in the rod will twist very hard and depending onthe actual size of the rod, maybe not at all.
 A coil spring is a twisting rod of steel. Cut off some of it and it will twist less , with
 the same force.  That just how it is.
 For the actual calculations please see ;http://www.eatonsprings.com/atqCuttingCoilSpringsCalculations.htm  TIA. MM
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dvmotorsports

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Cutting front springs
« Reply #19 on: January 31, 2010, 12:07:01 AM »
That would just be leverage exerted at the fulcrum.

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dvmotorsports

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Cutting front springs
« Reply #20 on: January 31, 2010, 12:20:58 AM »
From your link....

Quote
The longer the wire is the lower the spring rate. As the wire get shorter, such as when cutting the coil, the spring rate increases.

This is true on a piece of straight rebar for example. But only due to the lack of leverage that can be exerted. Not because the bar is magically stronger.

Take the same bar and crush it flat with a hydraulic press. It doesn't matter if the rod is an inch or a foot long. It will take the same pressure to flatten the bar.


Maybe those years I spent engineering for race teams I was wrong all along. Glad nobody got killed.
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dvmotorsports

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Cutting front springs
« Reply #21 on: January 31, 2010, 12:26:59 AM »
And allow me to quote one of the greatest suspension engineers/experts in the world and a mentor to me, Allan Staniforth

Quote
Spring rate is meaningless as it is totally modified by two things: the sprung weight of the vehicle and the leverage exerted by the suspension.

In the end, it's the OP's decision.

I'm done here.
« Last Edit: January 31, 2010, 01:33:55 PM by dvmotorsports »
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dwtaylorpdx

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Cutting front springs
« Reply #22 on: January 31, 2010, 02:35:23 AM »
My spring dyno doesn't lie.... :) Usually.....

I've ruined a bunch of springs screwing around and according to my tester I'm right.

Progressive springs have a rising rate per inch as they are compressed, linear springs dont. Taking the stiff end off makes a softer spring at full compression, cutting the soft end off makes a harder spring at full compression.

I agree with the last post though, its the whole package that affects handling as much as the spring rate ,, within reason..

Dave
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Chalino

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Cutting front springs
« Reply #23 on: January 31, 2010, 02:48:01 AM »
Sounds like you guys know what you're talking about. My initial thought was to cut ONE coil and live with the "shitty" ride but now I'm wondering if it's safe...it probably is, right?
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1991 318is
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"Now, me and the mad scientist got to rip apart the block... and replace the piston rings you fried."

tjts1

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Cutting front springs
« Reply #24 on: February 02, 2010, 10:59:55 AM »
If you put an E30 M3 spring next to a 318i spring, you'll realize that the M3 spring is identical, minus 1 coil. Same wire thickness, same coil spacing. Go ahead and cut 1 coil. You'll basically end up with stock M3 springs. The whole cut springs = bad myth starte with ricers that cut their springs in half to get that special-ed slammed look. Cutting 1 coil won't hurt a thing and the spring will be slightly stiffer.
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Chalino

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Cutting front springs
« Reply #25 on: February 02, 2010, 11:30:32 AM »
tjts, you make a good point. I'm cutting mine this weekend.
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1991 318is
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"Now, me and the mad scientist got to rip apart the block... and replace the piston rings you fried."

4banger

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Cutting front springs
« Reply #26 on: February 02, 2010, 12:31:03 PM »
tj as allways you cut thru the bullshit. good on you man! im gonna hack up a pair of junkyard coils this weekend. if nothing else spring steel is great to forge drifts and punches out of :)
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Genjinn

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Cutting front springs
« Reply #27 on: February 04, 2010, 06:22:16 PM »
o and on that note dont buy h & r racing springs they are crazy low i snap a pic of how low my 318is is i belive its close to a 3" drop....speed bumps put great fear in my heart....o and funny ass quote 4 banger!
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rac3r

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Cutting front springs
« Reply #28 on: May 25, 2011, 10:23:56 PM »
I would like to chime in too, hopefully without sounding like an arrogant know-it-all. On Efunda.com, they lay out the equation for calculating spring rate.

k = spring rate
G = shear modulus
d = diameter of the wire
D = diameter of the entire coil
na = number of active coils

k = (G*d^4)/(8*D^3*na)

Ignoring the complicated stuff, the bottom line is that spring rate (k) increases as the number of coils (na) decreases.
« Last Edit: May 25, 2011, 11:02:03 PM by rac3r »
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carlos318is

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Cutting front springs
« Reply #29 on: May 27, 2011, 01:34:51 PM »
I cut mine and have had no problems and I am well happy with the ride height and the handling
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