File in Section:

Service Bulletin

Bulletin No.:
Date:

PI0512A
September, 2012

PRELIMINARY INFORMATION
Subject:

Characteristics of Wide Low Aspect Ratio Tires, Vehicle Pulls Left or Right, Wanders,
Follows Depressions in Road Surface, Tramlining

Models:

2009-2013 Cadillac CTS, CTS-V
2005-2013 Chevrolet Corvette
2010-2013 Chevrolet Camaro
2006-2010 Pontiac Solstice
2008-2009 Pontiac G8
2007-2010 Saturn SKY

This PI is being revised to add the 2013 model year and update information under Driving
Characteristics and Alignment sections. Please discard PI0512.

Some customers may comment about their vehicle having a tendency to pull left or right depending on road
conditions. Typical descriptions may refer to the vehicle not tracking properly or that the car wanders. Additional
comments may include that the car follows grooves or inconsistencies in the road to the extent that the vehicle must
be steered or directed with additional force to overcome these roadway characteristics.
What is Tramlining?
"Tramlining" is an industry term used to describe a vehicle's tendency to follow the longitudinal ruts and/or grooves
present in the road. (Also called “trough wander”). The name comes from the feeling on a tram or trolley as the
vehicle follows along the tracks. Any vehicle can exhibit tramlining due to uneven pavement or severe rutting in the
roads surface. All vehicles tramline to some degree, however vehicles equipped with low aspect ratio, wide tires tend
to be more sensitive to this condition.
Turning the steering wheel left or right slightly may give a "scrubbing" feel like rubbing up against a curb (only not as
pronounced). Vehicles experiencing this condition can feel “pulled” in both directions depending on the positions of
the tires in the trough (ruts).

Driving Characteristics
A test drive with the customer to duplicate the concern and driving a comparably equipped vehicle over the same
roads may be beneficial before any repairs are attempted. For further information on diagnosing vehicle leads/pull
issues, refer to the latest version of Corporate Bulletin Number 05-03-07-009.
Note: Test driving over road surfaces, like smooth concrete, the vehicle may be less susceptible to pavement
inconsistencies due to the fact that concrete can be less susceptible to developing troughs and other variations in
the road surface. Additionally, since troughs may or may not be visible in a given lane, it is recommended to drive the
vehicle within the lane, but on each side of the lane to verify if the vehicle is reacting to the road surface variation due
to the steering precision of vehicles in this category.
If a similarly equipped vehicle experiences the same condition as the customer’s car, the customer’s car is most
likely experiencing tramlining, which is a normal characteristic of a car with low aspect ratio, wide tires.
Tires
Verify that all tire pressures are set to the specification listed on the vehicle’s tire placard prior to driving and verify
there is no uneven tire wear.
Note: Tire pressures should be maintained at the recommended pressures. Increasing tire pressures above the
recommended pressure will further stiffen the sidewall of the tire and may increase tramlining.
Swapping tires from a known good vehicle can be used to determine if the condition is tire related.
Verify that the tires and suspension setting have not been modified from the production standards. GM accessory
wheels and tires are an acceptable modification.

Alignment
While alignment may be thought to be a contributing factor, it has NOT been found to affect trough wander or
tramlining complaints and therefore a wheel alignment check is NOT recommended for the condition. Reference the
latest version of Corporate Bulletin Number 05-03-07-009 for GM corporate policy information on wheel alignment.