Ride height/tire cupping problem

[BobMc]

The front tires have started cupping/feathering on the inside edges on my 91 5MT. Also, the steering is quite heavy, so I've been running the front tire pressure at 38 psi, rears at 40 psi. The car was aligned a year ago with new front oem Yokohama tires (15") at 66k miles. Now have 74k miles. Figured I'd go and get it aligned, and asked the mechanic to check the ride height first. Front height was 6.5" (spec is 6.7-7.1). Rear was 8" (spec is 8.4-8.9").

This seems normal for a 91, some sagging. Does this contribute to the cupping problem? Does running 38 psi cause problems? I'm thinking of replacing the springs/shocks with originals. Checking pricing and with a 25% discount, parts cost would be $928 for springs/shocks, or $1242 for the entire assemblies.

Your comments would be appreciated.

 

[mystican]

CHeck the following...I think you are on the right path...

1. Alignment...make it spec 1991 agressive alignment

2. shocks would be good for replacement...what are running now....

3. check the ball joints

4. check the way the YOKO tires were put on the car...they are rotational...

Tire pressures...go back to the factory settings...and the ride height should not cause the problems you are describing...

Do you have pictures of the cupping?

 

[dalybo]

cupping is caused by unbalanced tires

Bob Daly

 

[Larry Bastanza]

Bob,

Please provide your alignment settings. This will help alot for the discussion. I also have a 1991 and run 33/40psi with no issues. Cupping can be caused by poor shocks, but need to understand your toe settings first. Not sure I would go with the stock replacements though. There are alot of alternatives, like Bilstiens to consider. Also the spring choices are extensive too.

Regards,
LarryB

 

[dalybo]

I agree with Larry that bad shocks can cause tire cupping too...essentially something is making your tires bounce a bit rather than a nice smooth rolling motion. I have 1996 and use 33/40psi tire pressue also.

Bob Daly

 

[BobMc]

Larry

The alignment settings are as follows, all in degrees:

Front:
Caster: 8.3L, 8.1R
Camber:-.2L, -.2R
Toe:-.13L, -.15R

Rear:
Camber: -1.5L, -1.4R
Toe: .15L, .13R

Total toe: -.3F, .3R

Bilsteins are a very good shock, although I've had them on a previous BMW 540 and thought they were too stiff. I would be nice to improve the handling on the NSX, but don't want something too stiff. :smile:

I thought about reducing the caster to reduce the steering effort, maybe 6-7 degrees, is that too low?

 

[Larry Bastanza]

I think you may sacrafice the crispness of the turn in if you reduce the caster, but certainly you can experiment and see if you are OK with the handling. One thing about alignment is you can always go back to how it was. Not sure what exact Bilsteins you had on the M5, so it is hard for me to compare. I have not found the Bilsteins to be too stiff, at least the versions on the NSX, but for sure this is personal preference.

Certainly you will return the car to "original" handling quality if you replace the shocks and springs with new stock verisons.

Also your alignment looks fine to me.