How much camber is too much?

So, should I put on a matching larger front bar? I plan to put Prodrive springs, but for now I'm running just the STI ones. I'm running stock dampers for now.
Click to expand...
Run the sweetness Hotckis setup that I am.. its very nice.. and yes go BIG on front and rear!

I may do the tein flex coilovers next year, not really sure.
Click to expand...

that may not be a good setup for you.

 
Lighter, and a hollow tube has less resistance to bending than a solid bar.
Click to expand...
Solid is better than hollow. A sway bar is a torsional member. If you're familiar with torsion in round members the further you get from the surface the less torsion force you experiance and the less material you really "need". A 25mm hollow bar is probably about the equivalent of a 23mm solid but at less weight. The idea being that since the surface does most of the work, hollow it out and make it lighter.

However, where ulimate stiffness is concerned solid is best by far. Personally I like to have a comfortable daily driver so the bigger the bar you can run the smaller spring ratio you can get away with (in the idea of comfort). If you're running something sort of comfy like the prodrives huge solid bars are what I'd run 1" or 1 1/8" at least. With that said running huge bars especially on the back with stock or close to stock spring rates is also a very bad idea, 3 wheeling in a scoob is not good.

 
This ought to get good.

Now I ain't no scientist, but I was always taught that a tube has more torsional rigidity, but when the threshhold is reached, it'll break instead of bending, like a solid bar would.

 
Oops

A hollow bar is stiffer than a solid bar.

More resistance to bending.
Click to expand...
No sir, that is 100% incorrect. You need a bigger hollow bar to be as stiff as a smaller solid bar. The material in the middle may not do much, but it still does something. Think about it a bit What is harder to twist a straw or a solid plastic rod?

The largest sway I can imagine fitting in the front of my car is the 27/29 that's up there now. If that same bar were offered and hollow it would be less rigid. You'd need something like a 32mm or so to make up for the missing material in the middle and you'll never fit one up there. Solid > Hollow....straight from the mouth of a BSME...you can take that to the bank.

default_redface.gif


 
This ought to get good.

Now I ain't no scientist, but I was always taught that a tube has more torsional rigidity, but when the threshhold is reached, it'll break instead of bending, like a solid bar would.
Click to expand...
Think about the polar moment for both a solid and tube member:

Solid:

J = pi/2 * r^4

Tube:

J = pi/2 * (ro^4-ri^4)

The two r's in the tube are the inner and outer diameter. If the outers could potentially be the same but with the pipe you still have to subtract the radius of the hole and put it to the fourth power. There's no way to get that back.

The highest shear stress in a torsional member is on the surface because in the equation tau = T * r / J the radius is the little r so you can see the highest shear stress will be at the furthest point out (it's in the numerator). The middle portions however due still experiance some shear stress.

You could perhaps use a different material in a hollow bar that had a higher shear modulus but I'm pretty sure most cost effective bars will be made from similar steels. Another interesting thing is that the smoothness of the bar surface is of the utmost importantance in a shear stress situation, dimples, imperfections and whatnot lead to stress concentrations at those areas and could lead to failures down the road.
default_redface.gif
:o

 
Ah, that makes a lot more sense :
default_redface.gif


Like I said, I'm not a scientist (apparently you are) What the hell is a BSME?

Now I remember. I thought a solid bar is better when it comes to twisting, but a tube is better when it comes to torsion. Hmmmm?

I'm not being a smart-ass, just curious.

 
<-----not an engineer, not even close.

But to play devil's advocate, and hijack this a bit.

Roll cages are made with hollow tubing. They don't deal with torsional stress. However, tubing is used rather than solid bar stock. Wonder why that decision was made ages ago. Ditto with bike frames etc.

As far as I understood it. The hollow sway bars were created for their light weight relative to their strength.

A hollow bar needs to have a larger diameter to be as strong as a solid one. Yet at equal strength, the hollow ones are lighter.

 
<-----not an engineer, not even close.

But to play devil's advocate, and hijack this a bit.

Roll cages are made with hollow tubing. They don't deal with torsional stress. However, tubing is used rather than solid bar stock. Wonder why that decision was made ages ago. Ditto with bike frames etc.

As far as I understood it. The hollow sway bars were created for their light weight relative to their strength.

A hollow bar needs to have a larger diameter to be as strong as a solid one. Yet at equal strength, the hollow ones are lighter.
Click to expand...
Cages are hollow because the cage would weigh more than the car if they were solid steel :-P Plus tubing can be manufactured relatively cheaply in sizes like that compared to solid bars. Tubing is better than flat bar because it is torsionally rigid and more resistant to torque than flat bar. And that last sentence you said nailed it.

If you're in bending the larger outer diameter is beneficial (think supported on both ends with a force applied in the middle). You can bend rebar if you're really rugged, but you cant bend a 2" diameter thin walled tube. 8)

 
Ah, that makes a lot more sense :
default_redface.gif


Like I said, I'm not a scientist (apparently you are) What the hell is a BSME?

Now I remember. I thought a solid bar is better when it comes to twisting, but a tube is better when it comes to torsion. Hmmmm?

I'm not being a smart-ass, just curious.
Click to expand...
At equal diameters the solid bar is stronger for everything. A BSME is a Bachelor Science in Mechanical Engineering. I've taken some advanced strength of materials classes and it was one of my favorite topics
default_redface.gif
Sick...but that's why I do what I do.

The benefits of tubing in general manufacturing is lighter weight and supremely less costs (due to the cost of steel in material weight).

 
See. Hollow bars are better
default_smile.png


Thanks a lot for clearing that up. In all my years I've been thinking the wrong thing.

 
Thanks a lot for clearing that up. In all my years I've been thinking the wrong thing.
Click to expand...
Hey no prob ;D When i ordered the big solid 27/29 from you it wasn't by mistake. I knew what i was doing.

And sorry for trying to add something to the forum. I'll be sure to post more about personal problems in my life and less about actual knowledge to keep with the forum guidelines
default_smile.png
;D

 
And sorry for trying to add something to the forum. I'll be sure to post more about personal problems in my life and less about actual knowledge to keep with the forum guidelines Wink Grin
Click to expand...
that's more like it ;D

 
You must log in or register to reply here.
Back
Top