Hope this is in the right forum... suspension and handling I'd think is correct. If not... please move.
Well... in short what do they do? Will they improve traction for drag racing? Does a car HAVE to be lowered to use them? Anything you guys can answer will be helpful. Thanks in advance!

 

no the car does not have to be lowered to benifit from them. the lower the rear lca mount the better the angle it has to push the front of the car up to get better traction. some say it might effect handeling by causing more flex but i didnt notice any more flex then i had.

 

That sounds like a reasonable explanation though I am obviously not a physics guru! I read an article in Chevy Hi Performance magazine where they relocated the control arms on a 3rd gen Z28 and pretty much explained it just how you did. They mentioned pushing the body up which means effectively planting the tires to the pavement. I was trying to visualize how that happens.
It seems to me the rear end would pull on the LCA's when launching on a drag strip... causing the body to "squat" from rear spring compression. Yes???
So the next question is... the LCA brackets will move the control arms more forward or directly parallel to the axle tubes???

 

There's a geometric construction that goes with this, and the anti-squat percentage can be calculated using it. But briefly, the greater the angle that the LCA's slope upward from the axle pivots to the chassis pivots the greater the anti-squat and the harder the tires are planted.

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It seems to me the rear end would pull on the LCA's when launching on a drag strip... causing the body to "squat" from rear spring compression. Yes???

No. When you are accelerating the LCA's are being compressed. IOW, pushed on by the axle. You can either view this as the LCA's pushing the car forward or pushing the axle back so the wheels remain in the wheel wells. In a torque arm rear suspension the axle is restrained against rotation by the torque arm, which is loaded in bending and shear, not tension. None of the axle locating parts are being pulled on under acceleration with this arrangement.

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So the next question is... the LCA brackets will move the control arms more forward or directly parallel to the axle tubes???

They move the axle end LCA pivot point downward.

And relocating the axle end pivots of the LCA's downward does one other thing - they make the car "loose", or more prone to oversteer, particularly under hard cornering conditions. This may or may not concern you, but you should be aware of this side effect before you decide that "if more's better, too much is just enough".


Norm

 

One of the reasons the car gets loose when you lower the LCA in relation to the axle is that it changes the axle roll steer characteristics from a toe-in condition to a toe-out condition.

 

Thanks guys for the explanation... it's starting to make sense though I need to study it a little more. I'll take a look around the net for diagrams... etc.

 

I'm plannng on picking up a set from Eric@DMS really soon so I'm glad you posted this. Do any of you have any pic of the install or the finshed product?

 

How does the axle roll steer get toe-in or toe-out on a solid axle?

 

It's more usual (dare I say conventional?) to term this rear stick axle effect roll steer rather than toe steer, which is more of an IRS parameter.

If the LCA's are not parallel to the ground, when the car rolls to (say) the left as you turn right one wheel will move slightly rearward and the other will move forward a little bit. Depending on whether the LCA's initially angle upward toward the chassis or down determines if the effect is vehicle oversteer or vehicle understeer respectively. And yes, this means that how the car is loaded will affect this roll steer. It's probably fortunate that more heavily loaded conditions change the roll steer in the direction of more understeer/less oversteer.

Has it really been over a year since relo brackets and roll steer were last discussed? Time flies, I guess.

Norm

 

Will they have an effect one way or another on axle hop on braking?

 

Nope I asked about relocation brackets being used in autoX a couple months ago. With my car lowered and the lca's pointing up on the axle end it has a lot of roll understeer. At the time I was trying to find out how the car would feel with them back at level. Sam Strano thinks the roll understeer helps.

 

That cleared it up pretty good.... thanks for the details.

 

Yes. LCA's that angle up toward the chassis give a higher SVIC. For any given TA length, a higher SVIC is associated with more anti-squat and more anti-lift (greater liklihood of brake hop) as well as less vehicle roll understeer/more vehicle roll oversteer. So running the LCA's downward toward the chassis provides a little extra margin against brake hop in addition to the previously mentioned roll understeer. The price for this is that it's somewhat easier to get wheelspin at the start and you will probably have to roll into the gas a little more smoothly while on course (so that you don't "get ahead of" the springs' reaction to rearward weight transfer).

Norm

 

In an effort to improve communication, could you provide the full term for which the acronym SVIC is used. I don't believe it was used previously in this post.

 

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