Top 3-5 cost efficient ways to decrease body roll? - Page 7 - PeachParts Mercedes-Benz Forum

#91 01-14-2011, 05:06 PM

Quote:

Originally Posted by moon161

Wrong.

Shear does not accumulate like displacement through the length of the spring. If it did, there would be no reaction at one of the supports- either the spring perch or the LCA.

Viewing each coil as a free body is useful, and spring body connects the equal and opposite (in a static case) forces at the spring perch and LCA via shear.

Consider the spring again 10" 10 coils, 100lb/inch. For a 100lb load, each coil sees 100lb, and deflects .1". The spring constant of each coil is the force over the deflection, or 100/.1 = 1000lb/in.

Cut a coil off, 100lb load, deflection is 9x.1" or .9". To achieve 1" deflection, each coil deflects 1/9" = .111", the reaction is 1000*.111=111 lb. The new spring constant is 111 lb/in.

Another way to look at it is each coil being in series w/ the next.

http://en.wikipedia.org/wiki/Hooke%27s_law#Multiple_springs

Springs in series add like resistors in parallel:
If added in series, 1/k = Sum(1/k1 + 1/k2 ....)

10 coils 1/k = 10 * 1/1000 =.01
k = 1/.01 = 100

9 coils 1/k = 9 * 1/1000 = .009
k = 1/.009 = 111

I believe you are correct. Based on a free body diagram approach, each coil will be exposed to the full load and will respond accordantly, therefore the spring with the greater number of coils will have more total deflection than the spring with fewer coils for the same load.

Sorry, I confused myself trying to do statics in my head. My previous post is incorrect because I didn't recognize that each coil will respond to the full load on the spring, not just a portion of the load. Good catch.

leathermang · #92 01-14-2011, 05:06 PM

Ours are SPECIAL coils..... can be used by seeing impaired as 'guide springs'....

leathermang · #93 01-14-2011, 05:10 PM

Quote:

Originally Posted by Craig

Sorry, I confused myself trying to do statics in my head. My previous post is incorrect because I didn't recognize that each coil will respond to the full load on the spring, not just a portion of the load. Good catch.

Each coil in the spring will respond to its PORTION of the full load on the spring.. even his math agrees with that..
Each coil does not ' see' the 100 lbs... but only ( in the 10 coil example ) one tenth of the 100 lb load...

#94 01-14-2011, 05:19 PM

Quote:

Originally Posted by leathermang

Each coil in the spring will respond to its PORTION of the full load on the spring.. even his math agrees with that..
Each coil does not ' see' the 100 lbs... but only ( in the 10 coil example ) one tenth of the 100 lb load...

That was my mistake too, if you think of the system as 10 small springs stacked on top of each other, each one has to transmit the full load from the section above to the section below. Each spring section will be displaced a specific amount due to the total load, not just 1/10 of the load. That is consistent with the equation for springs in series (1/k = Sum(1/k1 + 1/k2 ....)), which you can look up anyplace.

English Bulldog · #95 01-14-2011, 05:22 PM

I was stopped at a red light in front of a freeway on ramp. From behind i hear this rumbling, and i look in the rear view mirror. I have been told my car is slow and I did not want to get run over from behind...so I hit the pedal firmly.....To my surprise I pull away and after 100 yards I look in my rear view mirror and he is 60 feet behind and pushing hard, but I am pulling away. Wow, my first kill in my 300 diesel.

Now i just have to figure out how to paint a small picture of a UPS truck on the side of my car.

moon161 · #96 01-14-2011, 05:27 PM

Quote:

Originally Posted by leathermang

Each coil in the spring will respond to its PORTION of the full load on the spring.. even his math agrees with that..
Each coil does not ' see' the 100 lbs... but only ( in the 10 coil example ) one tenth of the 100 lb load...

Consider a series of sewer pipes, placed end to end, with sewage flowing through it at a constant rate, higher at one end than the other. The decrease in sewage height (head loss) due to friction is cumulative from one end to the other- (Ref. First Law of Civil Engineering). The head loss is distributed evenly between sections, but the full amount of sewage goes through each pipe. The principal is the same- loss is distributed through serial elements, load is distributed through parallel elements.

leathermang · #97 01-14-2011, 05:29 PM

Quote:

Originally Posted by Craig

That was my mistake too, if you think of the system as 10 small springs stacked on top of each other, each one has to transmit the full load from the section above to the section below. Each spring section will be displaced a specific amount due to the total load, not just 1/10 of the load. That is consistent with the equation for springs in series (1/k = Sum(1/k1 + 1/k2 ....)), which you can look up anyplace.

HIS MATH shows springs with a deflection of one inch per 100 lbs..
HIS MATH figures that at .1 inch deflection.
The total load ...100 lbs... is spread between the 10 coils ..thus causing each to bend .1 inch... his example set the deflection rate of one inch per coil per 100 lbs load..
Don't give up so fast on your initial judgment..

leathermang · #98 01-14-2011, 05:31 PM

Sewer pipes have nothing to do with this ' feeling stiffer' spring question.

EDBSO · #99 01-14-2011, 05:54 PM

Quote:

Originally Posted by English Bulldog

What are the steps to do this.

What is a budget to do this.

Good article here double up sway bars article

I purchased my sway bars from a wrecker for about $50 for both front and rear sway bars. Bushings are extra.

Too cold and too much snow to play with doubling up before spring.

The front end result should look something like this.

another full thread

leathermang · #**100** 01-14-2011, 06:01 PM

OK. That double sway bar url clears up a lot... They are not trying a full hookup of two bars.. which I could not visualize as having room to do..
but are ' doubling up' on the interior length of the bars... and cutting the attachment ends off the originals...

English Bulldog · #**101** 01-14-2011, 06:07 PM

Quote:

Originally Posted by EDBSO

Good article here double up sway bars article

I purchased my sway bars from a wrecker for about $50 for both front and rear sway bars. Bushings are extra.

Too cold and too much snow to play with doubling up before spring.

The front end result should look something like this.

another full thread

Hey, was waiting for your reply.

So this is done without the 20 hours of labor or is it done as an external add on without removing the battery etc.???

You have to take the front and rear sway out to do this???

English Bulldog · #**102** 01-14-2011, 08:43 PM

As i understand this better, this is unofficial but more detail.

1. BBS RS 7 x 16 Nexen N3000 205 50 16 ET 24 Diameter =24.1
2. BBS RS 8 x 16 Nexen N3000 245 45 16 ET 11 staggered set D = 24.6
3. OEM oil pan protector
4. KMAC Camber adjuster rear
5. front 3 inch spring cut
6 rear 3.5 inch spring cut

1. Revalve Bilstein Comforts to HDs at Bilstein Poway CA $65 each plus urethane bushings.
2. Cut existing springs so if i make a mistake i can buy new ones.
3. Replace rubber bushings but dont know which.
4. Adjust height of car with 1-4 nub spring donuts.
5. Wait for group buy perfect sway bars front and rear.

#**103** 01-14-2011, 08:57 PM

Quote:

Originally Posted by leathermang

HIS MATH shows springs with a deflection of one inch per 100 lbs..
HIS MATH figures that at .1 inch deflection.
The total load ...100 lbs... is spread between the 10 coils ..thus causing each to bend .1 inch... his example set the deflection rate of one inch per coil per 100 lbs load..
Don't give up so fast on your initial judgment..

I wasn't basing my correction on the details of his math, I made a conceptual error; I just needed to think about it some more.

The more important point is that making the springs 10% shorter and 10% stiffer isn't going to accomplish anything useful; they will just make the car lower and bottom out easier. If you really want to affect handling, you need higher rate springs anyway.

leathermang · #**104** 01-14-2011, 09:30 PM

Quote:

Originally Posted by Craig

The more important point is that making the springs 10% shorter and 10% stiffer isn't going to accomplish anything useful; they will just make the car lower and bottom out easier. If you really want to affect handling, you need higher rate springs anyway.

Agreed.

I was just addressing the misconception that cutting off a coil had any way to ' stiffen' the spring..
only using larger wire size will do that.

t walgamuth · #**105** 01-14-2011, 10:16 PM

I still disagree. Moon161, who posted formulas disagrees too. My basis is from conventional wisdom heard from many sources, and a limited understanding of springs.