lower control arms

[STUMPY]

i'm planning a coil conversion at the moment and i'm wondering if many people are using an I section for the lower control arms. i often read of people bend the arms and reckon this would be a better solution.

i'd appreciate your thoughts, pros and cons.

cheers joel

[N*A*M]

i thought most times, the forces are in compression and stretch along the link. it's only sometimes that the link gets damaged on the rocks and bent. will this design hold up to the forces that occur 98% of the time, even if it can handle the other 2% better than round tube?

[Scott]

A square section of the same size would be stronger than the I-section. In the square you get two verticle pieces instead of one.

And I assume you'd have to fabricate the I-section, since I can't imagine you'd find something in the right size.

[elgordomuygrande]

from an engineering point it's got the flesh on the right places, very stiff in the longitudinal plane, which is good against bending them. resistance against movement/bendig sideways is lower, but with a panhard or y-link shouldn't be a problem. I-bars can relatively easy be twisted around their axis which can help increase flex. Of course right size of material is also important

Cheers

[Slunnie]

Thats along the design idea that is used for radius arms like in front ends. Can you use those in a modified state as a lower link?

[STUMPY]

from an engineering point it's got the flesh on the right places, very stiff in the longitudinal plane, which is good against bending them. resistance against movement/bendig sideways is lower, but with a panhard or y-link shouldn't be a problem. I-bars can relatively easy be twisted around their axis which can help increase flex. Of course right size of material is also important

Cheers

you say that resistance to side way bend (lattitudinal) would be less. it would be twice a stiff because it has 2 horizontal member. as for the movement sideways, it would flex in the bushes well before the arm ever would.[/b]

[Scott]

you say that resistance to side way bend (lattitudinal) would be less. it would be twice a stiff because it has 2 horizontal member. as for the movement sideways, it would flex in the bushes well before the arm ever would.[/b]

It would have greater bending resistance in the vertical direction rather than the sideways direction. The two flanges being a particular distance from the centre of the beam in the direction of bending is what achieves this. Not sure if that makes any sense.

[elgordomuygrande]

from an engineering point it's got the flesh on the right places, very stiff in the longitudinal plane, which is good against bending them. resistance against movement/bendig sideways is lower, but with a panhard or y-link shouldn't be a problem. I-bars can relatively easy be twisted around their axis which can help increase flex. Of course right size of material is also important

Cheers

you say that resistance to side way bend (lattitudinal) would be less. it would be twice a stiff because it has 2 horizontal member. as for the movement sideways, it would flex in the bushes well before the arm ever would.[/b]

Stiffness to sideway bend would definitely be weaker, for stiffness the material should be as far as possible from the center line to create a sturdy construction (e.g. large diameter driveshafts can be very thin material). I wouldn't make them from I bars myself without calculating all the forces and torques that it has to deal with and adjust the material to that, because i see no real advantage( As you mentioned bushes will help the flexing). just use tube or boxsection (manufacturers do that too), but a well engineered control arm from I-bars can do the trick just as good as any other.


bending control arms often means need for bigger meat

[JK]

As said above, if you are worried about bending by getting hung up on your control arms, use heavy wall SHS or RHS (box section).

Heavy wall resists being dented which will cause the arm to buckle under compression and the box section is more efficient than tube in bending i.e lighter section is stronger.

You can get grade 450 SHS off the shelf and is quite reasonably priced compared to high grade tube section.

The "I" section will get belted around a lot and the flanges (the horizontal plates) will get bent up along their length which will greatly reduce the strength of the section.