What's the ideal handling/traction angle for adjustable relocation bracket/LCA connection? I've had my LCA's on the lower bracket mount and the ride has been pretty harsh in the rear yet hooks very, very hard from a launch. I'm guessing you "give to get" in this area with a sweet spot like most of the other adjustable live axle suspension parts. I was acutely aware of the rearend movement at that extreme angle. I moved them to the top-most hole tonight and they are now angled ever so slightly downward to the rear axle. Haven't test drove her again yet but I'm guessing the ride/handling will improve substantially.

I'm done with suspension mods except for watts link, bracing and poly bushings on select parts. This weekend I will be doing some tuning and bumpsteer adjustments but the rear LCA's were done tonight.

 

I'll preface all of this by saying that this is the theory, in practice I drive a lowered car with no LCA angle correction, therefore my car exhibits rear axle roll understeer.

From a handling perspective, the idea is to get the LCAs as close to parallel to the ground as you can get them. This should impart the least amount of rollsteer to the car. In other words, as the car rolls in a turn the rear axle won't impart understeer or oversteer, but rather be neutral.

Generally speaking, rear axle rollsteer is to be avoided since we would really like the driver to be controlling the car (via steering, throttle and brakes) rather than the rear axle. But, if you cannot have the LCAs parallel to the ground, the general consensus is that they should be angled "up" toward the axle so that the rear axle will impart understeer in roll, rather than oversteer. Understeer is safer at the limit than oversteer.

All else being equal, the change you made should reduce oversteer/increase understeer at the limits of the car's handling. Whether it reduces oversteer or increases understeer depends on the car's handling characteristics (i.e. springs, bars, dampers) prior to the change.

As for traction, your change may reduce overall longitudinal grip from a standing start. That is why drag racers run with a lot of LCA angle. However, at a road course, it is much more important to have confidence in the car at the limits of traction than it is to have good grip from a standing start. Greater confidence leads to faster cornering speeds and earlier throttle application, both good things for lowering lap times.

 

Yeah i definately noticed the roll oversteer as soon as I installed my LCA brackets (I used the lower hole). I kind of like it b/c it creates a nice smooth oversteer condition when cornering hard rather than a power oversteer which is sometimes more abrupt. However, my driving is all <45 mph which makes it easy to catch and hold a slide. When tracking at higher speeds, I would probably remove the brackets to prevent high speed slides which are a little more risky.

 

I drove the car yesterday and the change of LCA angle had a pretty significant impact on rearend behavior. It's smoother now, not as jolting over large irreglarities and potholes and I do notice the oversteer change.

I haven't driven the car hard so that's all I can say at this point. They now angle downward from chassis to axle-side very slightly.

 

Chances are that none of the holes is drilled in quite the right place for hard cornering at speed, since relo brackets are primarily marketed as a drag-racing fix for improving launch grip.

When the LCAs run uphill toward the chassis, small bumps cause the rear wheels to move rearward a small amount. This rearward component of wheel movement takes some of the sting out of the bumps by delaying how fast the forces transmitted to the chassis are developed. This can be a good thing, as long as it doesn't make the car oversteerish to drive.

For computing roll steer, note that in addition to LCA inclination that the height of the PHB at its mid-length matters slightly (the LCAs do converge a little bit (I think about 22 feet behind the rear axle), so the rear suspension's own roll axis isn't precisely parallel to the LCAs). This also means that perfectly level LCAs should result in a relatively mild amount of roll oversteer.

You may end up wanting a set of holes a little higher than the topmost holes. Whether the LCA relo brackets in question will safely permit this is a separate issue that I have not evaluated for any make/model relo bracket.


Norm

 

Thats why you buy Steeda LCA brackets with multiple mounting holes ! The CHE are crap and the Bmr are better but they still lack additional mounting holes to get your LCA perfect !

 

Even the ones with multiple sets of holes have the holes drilled more with various amounts of launch traction in mind rather than handling, and even the top-most holes are still going to be a little too low for best handling up toward the limits of lateral grip unless the car has been lowered by about the same amount as the relo bracket holes drop the axle side pivot heights.


Norm

 

I did a bit of enthusiastic driving last night. My traction is NOTHING like it was on the lower holes. And it's still angled slightly downward towards the axle. It's definitely a tradeoff.

My BMRs have two holes, steeda's have three but the top-most hole requires drilling the axle bracket to use. So I'd be no better off with the Steedas. The BMR's are really beefy brackets. A guy bent his steeda bracket by trying to jack the rear of the car from it (yeah I know...crazy). I don't think these BMRs would bend .

 

I'm gonna be installing the BMR brackets and LCA very soon.

 

You're correct Norm. The axle-side mounting points do not allow the slight adjustment that mild lowering requires without drilling through the tabs (i.e. steedas top hole). The top-most holes on BMR's that I run are just below the mounting tabs on the axle side and usable. I think its a pretty good tradeoff for handling traits and traction. I was really amazed at how much traction I got on the lower holes though. Wow...it was great traction, but the rear end movement under load was harsh.