Roll Center Adapters (RCA)

[Z-Monster]

Guys,

 

I have been contemplating making a set of RCA's for my 1980 280zx to reduce bump steer in a lowered z. I have read somewhere in this site that RCA's were the way to go for lowered Z's but I dont seem to ba able to find the posting anymore. Anyways, I dont know how RCA's are going to help me my ride quality and reduce bumpsteer when my z is lowered to the extend that my lower arm is not level with the ground. I know from theory that thats the best set up anyone can ask for. So my big question is, should i go ahead and make RCA's anyways for the front or just to forget about it as its as good as it gets.

 

I'm happy with my ride height but I feel things can be improved. I race my z ofthen and am always to look into areas of improvement. Has anyone installed RCA's for the front of their 280zx? I am currently running adjustable coilovers and can easily increase the my ride hight to get more of an angle on my lower arm and increase travel but thats not going to make the car more stable.

 

input from yall is very much appreciated.

 

Kevin

[blueovalz]

The leveling out of the lower control arm through the use of the RCA or relocation of the inner pivot point can be used to correct what I would describe as excessive geometry from a severly lowered chassis. I've got my arm pivot point raised 1", along with a 1" thick RCA installed for a net gain of 2", and it barely gets the arms horizontal. There are many opinions on the correct configuration. With the ouside of the arms pointed at an upward angle, the roll center is so low that a heavier swaybar is required to perform as well as a smaller one with a higher roll center. If you get the roll center too high, then you risk the effects of "jacking". Also, I found I needed to modify my steering arm/tie-rod configuration to keep bump-steer at a minimum with all of this stuff done to the front.

[DHale_510]

The minimum RCA error occurs when the arm travels through horizontal at mid travel. If the arm sits angled up from the frame pivot at rest, then you have the problem. It's all a real world geometry problem. This is typical for a lowered strut suspension. Usually we settle for horizontal at rest, and this helps with the camber problem too.

510s use the same ball joint and steering arm spacing as the 280ZX and these parts are available for them that will fit. Generally they are 1". You will need the loger bolts to mount them.

The 240/60/80Z parts have a wider bolt space and spacers for them will not work on a 280ZX.

[Z-Monster]

dear guys,

 

this is the second time i am typing this as i lost the last post i submitted. thanx for you inputs. I have gathered that only good things are to come from installing RCA's for our cars. I have a few more quick questions before running off to the machine shop though.

 

1) i was going to make the RCA with a little bit of an angel on the mto get a natural camber from the car.. i will make them to one inch thick and have 2 degrees of camber dialed into them. would this compromise anything as i have notice most RCA's sold four our cars are neutral.

 

2) By adding a one RCA i would have to lower my shocks by another 1 inch to get the same ride height I have now. As it is i have already compressed the srpings by 1/4 of an inch and would compressing the springs another inch would it compromise my ride quality and performance?

 

this is all i have to find out before i go runnin gto the machine shop to get myself some RCA's!!! you guys make alot of sense to me and would really really appreciate your feedback on these last few issues.

 

thank you

Kevin

[BlackBeaut]

Check out the bump steer FAQ, rca's have no effect on reducing bump steer.

 

1) dunno

 

2) No need to change spring height as ride height isn't affected by rca as it sits below the wheel axis line. You could make a 5" thick rca an it would still have no effect on ride height - it would bugger up the geometry admittedly, so don't make one

 

Cheers,

Rob

[blueovalz]

Sometimes it's not as intuitive as one would think, but this piece will not change your ride height or spring/shock relationship. All the RCA does is lower the pivot point (ball joint), and thats all (BlackBeaut said it all).

 

Also, I'm confused on the camber issue. I cannot understand your description of how you'll achieve the camber change by using angles (also, what is mto?).

The spindle is solidlly joined to the strut tube. The installation of an RCA will increase the POSITIVE camber a slight amount, and the thicker the RCA, the greater the positive camber increase will be (this is because the lower arm's length is fixed, so if you lower the balljoint away from the tower mounting point, the spindle will move inboard a small amount as the arm's outer pivot point drops down - depending on current settings, it could be 1/8" or more). This issue can be resolved by machining the upper portion at an offset with the lower portion of the RCA, but then you'd need to have the fasteners be studs in the upper portion, and threaded holes in the lower portion. This piece is extremely critical to the integrity of the suspension, so I would not recommend that.

 

 

Study the RCA, roll center theory, and the Z suspension, and you'll see these issues.

[pcs]

There are two suppliers of these spacers available on Ebay.com (not the Oz site) I have bought the cheaper of the two and they appear to be very well made in 6061 alloy and anodised red. They are supplied with the correct length high quality bolts and fit nicely.

pcs

[johnc]

1) i was going to make the RCA with a little bit of an angel on the mto get a natural camber from the car.. i will make them to one inch thick and have 2 degrees of camber dialed into them. would this compromise anything as i have notice most RCA's sold four our cars are neutral.

 

Bad idea for two reasons

 

1. It won't work. RCA's have no affect on static camber, they just affect the realionship between the strut and the LCA.

2. The threaded bolt holes in the strut casting are parallel to the vertical axis of the strut tube.