Lowered Car - Does the angle of the steering rack require Bump Steer Correction Kit?
 

I own a 1994 RX-7. It is lowered on BC Racing Coilovers and has 18x10 XD-9 wheels.

The car tends to dance around when it hits bumps. Its pretty tough to keep it in a straight line. I've never bought a bump steer kit for any of my cars. Wanted to get your input to see if the angle on the steering rack is too steep and requires a bump steer correction kit. You can use the front sway bar has a reference.

The last picture shows how low the car is sitting.

Attachment 755108

Attachment 755109

Attachment 755110

Did you get the car aligned after you lowered it?

Yes got a full alignment done.

It sounds like you would have a different issue. My car is lowered on JIC Magic coils and I dont have any issues.

Side note, what are the specs on your wheels, I love the fitment!

what are the spring rates? Is the shock rebound adjustable?

i agree that its an alignment issue. possibly differences in castor (will make it pull strange if it is off from side to side).

my car is slammed and i have no bump steer issues.

the alignment could be statically accurate but dynamically off. there are two cam bolts for each lower control arm that can be adjusted independent of each other but still get the same static measurement. i would check to see that all 4 lower control arm cam bolts are lined up to the same hash mark.

18x10 +38 Front and a 5mm spacer to let it sit a bit more flush (essentially making it +33)
18x10 +18 Rear

10k Front
8k Rear

I will check up on that. Will also take a scan of my alignment to see if there is anything wrong.

You probably need more toe-in on the front.

You need bump steer correction when the wheels are moved outward I believe, not when the car is lowered. If it fits under the guards - chances are you don't need bump steer correction.
EDIT; iv also got BC coil overs, they are set about in the middle of the adjustment range (off the top of my head front are 14 clicks from soft, rear are 13 from soft)

lowering an FD does not change bump steer.

chattering over bumps is either too high a tire pressure (30 fr, 27 rear set cold), incorrect toe
(just under 1.8th toe in fr and zero toe rear) or too high shock setting or spring rate.

howard

There is the alignment sheet I received. Everything look okay?

One thing I wanted to point out is the car pulls to the right pretty heavily when the engine is not under load (off the gas).

Attachment 755096

You front camber is fucked up
They can do better

What about bumpsteer when using spacers to move the front wheels out for a more flush appearence?

Those are minimal spacers, they should not cause the bump steer.

Where you you recommend the camber should be? And would out of spec camber on both sides play a roll in the car feeling unstable at highway speeds?

i have blissfully forgotten about how degrees translates into inches as to toe but it appears you are toed out .7 of a degree.

if this is correct the car will hunt over bumps. your front should be toed in to form a self centering vector. about just less than 1/8th inch.

your camber should be 1.2 degrees negative at all four corners.

caster should be equal.

tire pressure should be accurately set and monitored and is very important. the FD likes
30 front 27 rear set cold.

proper settings can change your ride from hell to heaven.

do the above and if you have further problems let us know.

bump steer is about parallel arcs between the steering arm link and lower A arm. it is not an issue here.

good luck,

howard

Umm, down here at least, that's showing as toe-in at front.

There is another thread on here about the upper universal joint, which is staked by a pin through a hollow steering shaft (wall thickness ~2/3mm), that tends to wear. If that's loose, car will be very nervous over bumps, should be able to see if it's a problem, with someone moving the steering wheel from side to side and someone else checking free play on the lower shaft. Scrub radius with the dodgy offset and spacers won't be doing any favours either!