side loading?

[Rennen]

OK, I was at the parts counter of my local Nissan dealership the other day and they had an ad for the new Maxima. In this ad they had a pic of the rear suspension. I noticed it because the shock was outside of the spring:confused: This struck me as odd. The ad said it allowed each component to "do it's job better." I instantly claimed bull****. and I discussed this with a friend of mine who had also seen the ad. He didn't have a real good answer either, and wrote in to Nissan Performance Mag.

This was his answer:

http://www.nissanperformancemag.com/october03/ask_sarah/

:confused:

What is spring induced side loading?

It seems to me that the best place for a shock would be inside the spring. Because the only motion a suspension should see is in the direction that a spring compresses. Where would a load from the side come from?

Someone please explain side loading to me :aw:


-Matt:confused:

EDIT: eye spehl gud

[docrice]

What is spring induced side loading?

I think what they mean (my best guess based on her answer) is that "side loading" is putting horizontal pressure on the base of the shock, which would push the opposite side of the piston against the cylinder and cause friction/less efficient suspension. let's take a look at schitty diagram:(note: the `'s are because the forum messes up the diagram if you just use spaces, so they are nothing)

_______
|```|
|```|
|___| Effect: Pushes shaft/piston in <- that direction against
|`\`| cylinder, causing friction
|`\`|
|`\`|
|_\_|
``\
``\
``\
---- Cause: Pushing this mount in -> this direction (my guess of what side loading is)

[Rennen]

That's what I assumed as well, but where would this load come from inside the spring perch that it wouldn't elsewhere?

Correct me if I am wrong, but isn't most of the suspension's motion in the path of spring compression, and it would make sense to dampen that motion in a parallel direction. This makes the ideal place for a shock(damper) inside the spring.

The spring doesn't move perpendicular to its compression does it?

-Mat:confused:

[docrice]

Yeah, irregaurdless of what "spring induced side loading" really is, I don;t understand the purpose of moving the shock outside the spring....:loco:

[thx247]

she is saying that as a spring compresses it introduces lateral (side load) pressure on the piston inside the shock. This increased friction is not ideal because it adds increased wear and heat to the shock oil and internals.

Basically the piston in the shock is dragging on the inside of the shock as more sideload is introduced. Just because the piston is designed to move up and down only does not mean it cannot drag on the walls of the shock body.


Wether or not this is really worth the effort remains to be seen.

[s14slide]

to give youself a good idea of what/how a spring makes sideload, do this:

take apart a ball point pen like a bic
(the retractable kind, i.e. click-click),
take out the spring,
stretch it out slightly so the "coils" mimick and cars coils.
You will see that the spring will not compress straight no matter how hard you try when you only touch the top and bottom.








Now, a cars springs will do the same and when a shock is mounted in a spring as in a mcphereson strut situation where the strut itself holds the spring, this side loading by the spring causes the inner piston of the strut to press against the inside of its housing. This causes friction, and I believe (don't quote me) a scientific term for this is stiction. This heats the oil in the strut and also changes the rates of the struts because this friction is not accounted for in strut tuning as its almost completly unpredictable.
Hope this helps you understand a little better.

[Rennen]

Ah, I think I may have it figured out now, but first marvel at my drawing skilllz

http://www.imagestation.com/picture/sraid83/p58dffcf179ea9968550aab68e7aa153e/fae65539.jpg

OK, Mc Pherson strut design has the spring attached to the strut right? (I think this is the point I was missing before) and with this method there is a 3rd point in the middle of the shock that allows it to deflect side to side(pic 1) But this new fancy design takes away the attachment point in the middle of the spring, which will take away the side loading(pic 2).

still, this is inefficient packaging, the strut needs to be in the middle the spring, just not attached McPherson stylee. :D

-Matt

[thx247]

because space is usually at a premium in todays cars, I wonder if the spring is actually offset from the shock, of if the shock is a short body and the spring still sits around the shock, only not mounted to the shock but rather the A arm or whatever the hell they are using now.

[s14slide]

also note that moving the spring inboard changes the springrate at the wheel. Say an 8kg/mm spring on a coilover setup has a s/r of 6kg/mm at the wheel. Moving the spring inboard on the suspension (towards center of car) changes the effective spring rate (at the wheel), allowing you to use a higher rated spring w/ out the harshness of a spring over shock setup. It can get really really complicating really really fast. I don't have the paitence to to explain it on a forum. To much math that most probably wouldn't have a clue as to what's going on.

edit: I've added this diagram to help. Remember basic physics in highschool. About levers, fulcrums and work. Spring=work(3,4), arm to chassis=fulcrum(1), and the lever is the arm that all this is mounted to.

[s14slide]

diagram here

[Rennen]

Originally posted by s14slide
Moving the spring inboard on the suspension (towards center of car) changes the effective spring rate (at the wheel), allowing you to use a higher rated spring w/ out the harshness of a spring over shock setup.

There it is!

I kept wondering what the advatage was over a standard McPherson strut design. Less body roll due to higher (relative) spring rate, with the same dampening due to the longer travel of the strut. Thanks for explaining it all.

-Matt