Suspension Questions - with pic

[Pearce]

The questions relate to the movement of either spring or shock / strut assembly on a McPhersons(sp?) style front suspension vehicle.

Summary: Apart from up and down - does any "point" of the suspension move in a strictly non linear up down motion at any stage.

PICTURE 1. Bright Green lines - what I call the linear up / down motion.
Red Lines - Movement due to changes in "Castor / Camber" ( length of shock / spring under compression )

PICTURE 2. Red lines - Do either spring / bottom of the shock move under steering / bump conditions.

OR does the whole assembly stay exactly still apart from the UP / DOWN motion.???



thanks,
Pearce

[Pearce]

To save creating another thread:

How much is the Width of a spring likely to expand under full compression?

I know that depends on: Spring size, Tension etc.

However, is it likely the coils increase in diameter more than 5- 10mm each side ?

[wilbo666]

Just letting you know I can't see sweet FA in that pic (too small).

And I also have no idea what you are really asking...



Cheers
Wilbo

[Pearce]

Click the Link for a bigger pic -

Imagine a hollow metal tube sleeve put over the top of your strut and welded / fix in place - is the shock / spring combo going to hit the sides ?

[Dale]

I sort of understand the questions.. but I don't get why you're asking? Is it going to be an issue for some reason?

[Pearce]

If I tell people the reason, they wont reply because it sounds wankish...a la

Im looking to add small air bags between the suspension top perch and strut tower - empty they sit 45mm high, and 175mm when inflated - tho im only looking to use about 50 - 100mm.

The airbag / spring's top perch could be contained within a reinforced steel tube guide - but only if there was limited / no side ways movement.

It can be done cheaper than a decent audio get-up if your not after fancy bouncing crap. (or so i can figure so far.)

[RWDboy]

Yeah it will move 'sideways' a bit. The lower control arm is fixed length, and hence the point where the lower part of the strut (spring/shock assembly etc) meets the lower control arm will usually move in a radial motion (ie follow an arc as the length of the strut changes).

[oldcorollas]

Yeah it will move 'sideways' a bit. The lower control arm is fixed length, and hence the point where the lower part of the strut (spring/shock assembly etc) meets the lower control arm will usually move in a radial motion (ie follow an arc as the length of the strut changes).

yup, LCA will move strut in/out... but the radius rod is also attached, so that pulls the strut forward and back....

also if your steering arm pivot is not directly under the strut axis, this will also cause movement....


stick the head in and see wil be different for every suspension setup

[wagonist]

And if the bottom of the strut is not directly in line with the lower ball joint, then it will move in an arc while turning.

My suggestion.
Jack your car up & take the wheel off & watch it while someone else turns the wheel. You'll soon see.
Alternatively, drive up onto car ramps & have someone turn the steering wheel while you look from underneath. This is a better method becuase there is load on the wheel.

[Pearce]

Thanks to all who've replied. I understand now the bracket cant go past the top of the spring -

I have a rough sketch of what might be "do-able" - but engineers and such have yet to speak.

See Picture A


Only other hiccup maybe the lack of rigidity - where the strut top was bolted to the strut tower - now has a squishy mass of rubber - which is likely to drastically reduce the effectiveness of the spring / shock -

A plain solution here maybe to do away with having a spring as well and accept the poor quality ride of airbags alone.

The second solution here could be to build a spacer between the top of the strut and air bag - and have a locking "pin" inserted from the side of the bracket (an idea not too hard to belive if you can imagine)
But this adds even more height = shorter strut / higher resistance needed in the shock.

See Picture B

[RisingStar]

ok first question would be to ask exactly what you are trying to achieve?
there are currently McPherson struts on the market with the air bag section in them
most commonly used for vehicles that tow heavy trailers or carry large loads
when there is more load you pump up the air bags and effectively raise the height of the vehicle
i can't see any reason why this couldn't be used for the similar purpose that you are aiming for
also have the added bonus of not having to pay heaps for engineering
if there is not an aftermarket fitment for your vehicle try somewhere like pedders or midas
they may be able to make somethin up for you

[Pearce]

there are currently McPherson struts on the market

Any more information would be really appreciated.

FWIW, all I'm trying to achieve is follow an idea - wank factor or not, if my car has something that the next guy's doesnt its worth it.

I like low cars, but they're not pratical - this is my solution.

I wouldnt say its impossible. Just asking for a little advice.

[steve_t647]

OK there is an easy way for you to achieve what you want.

The tube has to be down over the spring when flat and have a slot in each side 4 quarter's but attached to the top of the strut the base fit's inside the tube but has 4 tab's going out of the slot's and attached to the top of the shock.

For a warrant in NZ the top section need's to not drop out of the bottom section this is achieved by 4 threaded rod's which run down parallel to the slot in the tube section for the same length and go through the tab's on the bottom section haveing a lock nut at the bottom. this setup can jump a car (it was on a bike when I saw it and it could jump don't ask and it wasn't mine) what you need is a compressor to fill a tank and then throw pressureised air at the bag's of they are in the tube and the pressure is not too high it will jump and not burst.

Hope this help's if you have any question's I will see if I can help

[Pearce]

Ahh I think i know what your trying to explain - thats a really good idea for the bracket, especially if it has to be sealed either end - that puts my locking pin idea to shame!
Saves some height too.


By having a "tongue and groove" effect bettween the top and bottom tubes, it cant really expand by more than double original height unless the top "tongues" run past the bottom tube.

I've tried to draw it - but unless its 3d and shaded it doesnt really make sense.

If you had a pic that'd be great - to see how far i've missed the point.... of course.