2008 Cadillac CTS: RWD vs. AWD Differences Revealed
March 02, 2009
Right out of the gate, the first respondent spotted the difference between our two 2008 Cadillac CTSeses, despite a self-admitted alcohol impairment at the time (at least we're assuming it was alcohol.)
The brake calipers on the RWD CTS (the red one) are located behind the front axle centerline, while those on the AWD/black CTS are situated ahead of the front axle centerline. But no one grasped the significance of this difference.
With respect to the front axle centerline, brake calipers are located opposite the steering arm and tie rods. This means the RWD CTS has a forward-mounted steering rack, while the AWD CTS has an aft-mounted one.
A forward-mounted steering rack is far superior when it comes to steering precision, so most serious RWD machines use this placement. Having the control point (the tie rod ball joints) ahead of the tire contact patch means that forces at the contact patch create smaller unwanted toe-changes. Positive control is also helped by having smaller angles in the steering shaft u-joints (a straighter shot from the rack to the steering wheel, if you will). The RWD CTS features a new ground-up front suspension design and GM incorporated the forward rack placement from the start.
But the AWD CTS uses a carry-over front drive sub-assembly from the AWD Cadillac STS, and that car has a rear-mounted steering rack. I drove this particular AWD CTS, a US-spec car, in Germany at a GM-sponsored event (yes, the photo was taken at the Nurburgring). Despite having the same all-season tires and FE2 level suspension as our red CTS, the AWD car's steering clearly felt less immediate and a bit more vague. There was more steering kickback, too.
Front wheel drive machines with a lateral engine and transmission layout have to use aft rack placement because there's no other choice. And some high performance machines with longitudinal engine and transmission placement (most notably our Nissan GT-R) use the less-favorable rear rack placement if the underhood packaging is particularly crowded.
Dan Edmunds, Director of Vehicle Testing