Yes,,Another LCA question!

[Mad Hatter]

Blacksheep-1 has me wondering about my suspension setup now...........I have the rear LCA on the lowest hole and the control arm angle is 6.3 degrees (got my accuRemote!).... I will be switching to a 18mm rear bar with 295/30-18 R7's next week. SHould I raise the rear a little and use a higher mounting hole?? I have the 3 hole BMR relo setup. I used to use the middle hole to avoid erratic braking, then I just lowered the rear more and went to the lower hole again. Is their a Ideal angle?? Or may better put... a range??

I let one of my instructors drive the car a few weeks ago and he spinned out on a tight curve..He said I have a very loose rear..... I took offense!! Maybe I got used to too much roll oversteer?

 

[Grant 302]

6.3º sounds like a lot. I'm using a 4" adjustment (I think that's the same) but my car is set really low in the back.

Maybe a pic would help to show your ride height and the LCA angle.

 

[Mad Hatter]

I'll see if I can get a better pick

 

[VoodooBoss]

Remember the Phoenix Mustang is a race car that never sees the street and has a professional driver, @ajaquilante , behind the wheel.

 

[Mad Hatter]

Remember the Phoenix Mustang is a race car that never sees the street and has a professional driver, @ajaquilante , behind the wheel.

Good point!

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[Fabman]

3 to 5 degrees seems to be a popular compromise between excessive roll steer and good antisquat.
I'm at about 1 1/2* and ready to add a little more for the forward bite, but let me tell you, roll steer is a biznitch.
Just like a hook and ladder truck, whatever the front does, the rear does the opposite.
There are times some roll steer is beneficial, like short tight tracks to help get around tight corners or to promote forward bite on high powered cars on corner exit but it comes at a cost.
The nice thing about coil over tube frame stock cars is that everything is so adjustable so you can try every adjustment under the sun and learn first hand what happens.
I would suggest you try every hole just to feel what happens when you do it.
There's no better classroom than the race track if you use the time well.

 

[Grant 302]

I would suggest you try every hole just to feel what happens when you do it.

??? That's what she said.

 

[Grant 302]

I'll see if I can get a better pick

She said that too.

Seriously, you could probably lower the car a bit in the back. Even if it is just for the track.

 

[Mad Hatter]

??? That's what she said. [emoji14]

Hmm... but I would have to do it in public...might not be legal in some States.

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[Grant 302]

Hmm... but I would have to do it in public...might not be legal in some States.

Everything is legal south of the equator, right? Just do it at the track.

 

[Mad Hatter]

Everything is legal south of the equator, right? Just do it at the track.

As long as you keep it below 95DB!!

 

[Fabman]

This measurement is for 27" tall tires. With 25.5" tall race tires use 4.0".

 

[Flyboygsxr]

Can anyone explain to me why in the Boss by putting the rear control arm in the lowest hole on my BMR relocation brackets it made the rear end feel stiffer (less bump stop contact) and I put the power down better out of corners too. I was ready to buy a new smaller sway bar but after lowering the control arm it completely changed the way the rear of the car hooked up and I no longer felt the need for the smaller sway bar.

Thrust angle, roll center???

 

[Mad Hatter]

This measurement is for 27" tall tires. With 25.5" tall race tires use 4.0".

I guess I am their already, I measured 4.5" with 26.5" tall street tires. Hmm that means with my 25" tall 295/30-15 tires I must be just below 4"

 

[Mad Hatter]

Can anyone explain to me why in the Boss by putting the rear control arm in the lowest hole on my BMR relocation brackets it made the rear end feel stiffer (less bump stop contact) and I put the power down better out of corners too. I was ready to buy a new smaller sway bar but after lowering the control arm it completely changed the way the rear of the car hooked up and I no longer felt the need for the smaller sway bar.

Thrust angle, roll center???

I think if you just look at Fabman's diagram above, you can see the force vectors of the coil over and the LCA with regards to the axle, are going to make the car less likely to squat. If the angle was a zero or less, you can see how the coil would have a hard time controlling the axle.

 

[Fabman]

This is anti squat.
Drag racers sometimes call it "Percentage of rise":



Re: Yes,,Another LCA question!


You can see how the leverage action of the arms converging up to the front would lift the body and add traction, but the side effect is that as the body rolls the arm moves up through an arc, the wheelbase gets longer on that side and shorter on the other side effectively steering the car from the rear as it rolls.
This is why its called "Roll steer". The more antisquat, the more straight line traction you have (to a point) and the more roll steer you have. So there must be a compromise.
This is one reason Torque Arms are so awesome.
You get that body lifting antisquat from the torque arm so you can use flatter control arms for less roll steer.


A side benefit is that unlike anti squat on a 3 link which tends to unload the suspension on braking, the torque arm is working to pull the body down against the track essentially giving you traction both on and off the throttle.

 

[Fabman]

Forget about what hole the bolt is in, that changes with ride height, the type of brackets you have an how tall the tire is.
What matters is the angle of the arm, however you get it.
Place a digital level on the arm at ride height to find the angle.
Or, if you don't have access to one, measure the front control arm bolt to the ground and the rear bolt to the ground and note the difference.
Start with the front bolt about 1/2" higher and see how you like it. Adjust as necessary.
You will probably find that just a few degrees is beneficial while much more than that causes the rear to be loose as the body rolls and then tighten up as the car flattens out.
As with many things, moderation is key. Too much of a good thing is....too much.

 

[Fabman]

I guess I am their already, I measured 4.5" with 26.5" tall street tires. Hmm that means with my 25" tall 295/30-15 tires I must be just below 4"

You have 15" tires? I think you mean 295/30/18.
4" is about as low as I would go, especially if you are still on a 3 link.


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[Mad Hatter]

Too right.... 18" oops! I am waiting too see how my buddies GT turns out with the Torque arm and watts link. End of the month my season starts again!.

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[Fabman]

Too right.... 18" oops! I am waiting too see how my buddies GT turns out with the Torque arm and watts link. End of the month my season starts again!.

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If you get the watts, start in the second hole from the bottom.


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