Jim:
One source of bump steer is installing wheels with a non-stock offset.
To
minimize bump steer the steering axis normally must pass through the center of
the tire patch (there are some exceptions). This is referred to as "zero scrub
radius".
You mentioned your "old steel wheels" so I am wondering if your new
wheels
have the factory correct offset - if not they may be the source of at least
some of your rough road syndrome.
Wide tires have issues with "tram lining" where the car wants to follow
the
wear pattern in the asphalt on a worn road. My Corvette was TERRIBLE for this,
but the tires were much wider than the TR6. They were 255/50-ZR16 so they were
a full 2" wider than the TR6 rubber. It was so scary at times I had to drive
the 'vette at the very edge of the lane on some roads, so that the tires were
riding on unworn portions of the road surface. I noticed other performance
cars would often do the same on the affected stretch of highway (Mercedes AMG,
BMW M3, etc).
I am assuming that tram lining is NOT what you are referring to. Tram
lining
has little if any feel through the wheel, rather the car simply has a mind of
its own and wanders back and forth without any steering input. Bump steer is
felt as a series of sharp tugs through the steering wheel as each wheel
encounters a bump or pothole in the road surface. For a car without power
steering, it is essential that the correct wheel offset be observed, otherwise
bump steering effects will increase, potentially becoming quite severe.
Cheers,
Vance
Vance Navarrette
Cogito Ergo Zoom
I think, therefore I go fast
-----Original Message-----
From: 6pack-bounces@autox.team.net [mailto:6pack-bounces@autox.team.net] On
Behalf Of Jim Jones
Sent: Friday, October 02, 2009 6:38 AM
To: 6pack List; Kendall Larsen
Subject: Re: [6pack] New tires and wheels
Kendall:
Let us know how the car steers after you mount them. I have 205/65-15's on my
car, and it tends to wander badly on rough roads. I'm going to have my
alignment check, however. I'm thinking about having my old steel wheels
refurbished and getting a set of redline tires in the stock size to use for
show. I'm thinking that might reduce the dartiness of the steering.
Jim
--- On Fri, 10/2/09, Kendall Larsen <mailkendall@sbcglobal.net> wrote:
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