I have a dedicated autox/track s2k. The suspension consists of:

SPC adjustable balljoints in the front
TCDesign rear anti-bumpsteer kit
Saner front swaybar on middle setting
removed rear swaybar
Koni double-adjustables with valving by TrueChoice (supposedly capable of handling 700-1100ish spring rates on my ~2600lb car)
Ground-Control upper shock mounts (moves shock attachment point up by 1 inch), which should offset a car lowered by 1 inch and bring the shock piston back to a more 'centered' location -- in theory.
950lb springs front and rear.
255x4 Toyo R888's on 4 ap2 rear wheels (17x8.5) -- fronts use a 5mm spacer
Alignment: -3.5 camber, 6.8 caster, 0 toe front; -3 camber, 0.05 degrees total toe-in rear

The car is mostly used for autocross right now and I'm getting one peculiar behavior. On hard right turns after a hard braking zone, the back end wants to hop/bounce as it rotates through the corner. It may happen on left handers too, I just haven't been through a particularly tight left hander after a hard braking zone in either of my last 2 events. Both events where I noticed this were on asphalt, by the way. I chased this away at the last event by slowing down more for the corner, and making a couple of progressive shock changes: increased front rebound by 2/3rds of a turn, then decreased rear compression by a couple of clicks. The rebound changes put the front shocks nearly at full stiff, and the rear shocks have rebound already set very close to full soft.

I am wondering if what I am getting is 'wheel hop' and what the right way to correct it is. I'd also like to get the shocks a little further away from the 'extremes' of their adjust ability ranges so I still have 'room' to make a change, if needed.

Incidentally, I tried 1200F 950R a few events ago and the car was a little pushy, but still experienced this hop on tight corners. Also, before my left-front TCD control arm broke, I was running 700F, 800R without any of this hopping business. I freely admit to being a hack with respect to suspension tuning and I'm just basing everything on trial-and-error. My gut feel says I should change up the spring rates so I'm relying less on the adjustability of the shocks, and move back to rear-biased spring rates. So, I'm wondering what y'all think I should try next. Onhand, I have pairs of the following springs: 700lb, 800lb, 1200lb, 950lb (2 pairs). Aside from the hop, I'm very happy with how the car is handling.

Autocross run. Bouncing starts at the 42second mark:
[media]http://www.youtube.com/watch?v=S65G77YDLz4 [/media]

 

I've always increased rebound stiffness at the rear to stop rear wheel hop. Maybe totally wrong...but that's what has seemed to work for me in the past.

 

Where is this "hop" happening? Are you on throttle? Neutral throttle or still trailbraking? If it happens when you are at neutral throttle or on the throttle out of the corner, I would suspect you've run out of bump travel on the laden rear wheel and your bouncing off the bumpstop/tire sidewall. Put back in that rear sway or raise the rear and give it shot.

 

It's happening mid-corner to corner exit, while on-throttle.

My initial thought was that I may be bottoming out on a shock, but I never got that with the 700F/800R springs. I also forgot -- I added the ground-control upper shock mounts when I went to the 950/950's, which should give me an inch more bump travel than before. Ride height is only 0.75inches lowered from stock.

 

Is the car lowered? I ran across some new, scary info about the SPC ball joints.

 

Yes, about .75 inches below the minimum stock ride height as measured at the alignment bolts. Do share regarding the SPC's.

Added youtube video to the first post.

 

The front isn't so much a problem as the rear is but I'm pretty sure that the suspension can go in to a mechanically locking situation when using the SPC ball joints. They raise the upper control arm but the ball joint is limited in its range of motion. As the suspension compress the angle of the upper control arm could be so severe that it mechanically locks making it feel like the suspension is bottoming out before it should.

Next time you have the shock off I'd check to make sure that the front suspension is capable of freely moving all the way through it range of motion.


This is not a diagnosis of you issue but rather something I think you should investigate. I recently saw a failure related to these ball joints (broken rear upper control arm) and I'm 100% sure that's what happened.

 

I only have them installed on the front, and my front tires will rub before the shocks get to full compression, I'm sure.

In talking with some other folks and reading through Spaf's BSP setup, I'm going to drop my rear spring rates down to 700lb, which will give me 950F/700R and re-connect my rear bar. I'll give that a shot on Sunday and see how it feels.

 

Bryan...here's an interesting Honda-Tech post. Mind you the post's intent was probably drag racing, but the response is from CRX Lee (aka Lee Grimes, aka "The Shock Guy").

http://honda-tech.com/showthread.php?t=1607368

Lee Grimes was the Automotive and Motorsports Manager and is now the Street Aftermarket Sales Manager for KONI North America. He's also founder of a HPDE group called 100-speed.