The E39 M5 was a groundbreaking car when it was released. Touted as the most powerful sedan in production, it certainly performed with more than 400 hp on tap from an individual throttle body-equipped V-8, coupled to a 6-speed manual gearbox in a RWD layout with clutch-type LSD. Fast-forward 11 years and, on paper, the E39 M5 doesn't look like anything special, but it most certainly is. With a traction control system that can be fully disabled with one button and an engine that makes its own noises without help from the stereo, there is definite beauty in its simplicity. It's fun to slide, comfortable to drive, and is quite the bargain these days.
When starting with a car of this caliber, most all of the components used are of very high quality, and it can be easy to go backward with "upgrades." Picking the right wheel/tire package for this car was a challenge. Many wheel designs don't suit the body and end up looking substandard compared to the stock wheels. Nineteen-inch BBS CHRs (19x9 +20 front, 19x10.5 +25 rear) with the appropriate 74.1mm hubcentric rings in Titanium Gunmetal set off the car perfectly. One issue that came up during installation is the inside of the rear tire touches the plastic inner fender liner with the suspension at full droop. The stock dampers have what I consider excessive droop travel, and this interference only ever becomes an issue when up in the air. The rear wheels are already nice and flush without any spacers, so a rear damper with less droop seems to be the best solution.
The right tire makes a huge difference in how a car of this caliber is enjoyed. I wanted something quiet and comfortable for long trips, but with good response and ultimate grip for spirited driving, all while offering excellent wet-weather traction. Some say you can't have it all, but I have been thoroughly impressed with the new Yokohama Advan Sport. Despite the shorter sidewalls on the 265/35R19 front and 285/30R19 rear, there was very little compromise to the ride quality.
The Advan Sport V105 uses a heap of technology to achieve such a well-balanced tire. The Matrix Rayon Body Ply incorporates lessons learned from Yokohama's race tire lineup and uses body plies constructed of lightweight, heat-resistant material turned up from the sidewall at a precise angle to provide increased rigidity and enhanced steering precision. This explains the excellent response the tire offers during hard cornering. A variable pitch tread design is used to reduce tire noise and most certainly does work to provide a quiet and comfortable ride. The Sport Compound 5S is composed of Orange Oil, Micro Silica, Silica dispersant, and chemically bonded polymer, all of which combine to offer excellent dry- and wet-weather grip. I've currently racked up about 3,000 miles on the tires, so I can't give a good indication on wear but have not seen anything unusual so far.
Sliding-type brake calipers are flexible by design and often create a vague pedal feel while being awkward to service, even if they aren't all seized. You can't beat a fixed, opposed piston caliper, and it's surprising a car like the M5 doesn't come factory equipped with such a setup. Fortunately, AP Racing has a bolt-on solution to address this.
We ordered up AP's 6-piston front kit and had them build up a custom 4-piston rear kit for our application. I requested the kits be fitted with Hawk HPS pads for excellent street manners, and installation was a straightforward bolt-on affair with complete, pre-assembled, two-piece rotor with aluminum center and Goodridge DOT-approved stainless braided brake lines. Unfortunately, the same can't be said for the rear. The caliper throat center did not line up with the rotor center, and I was unable to install the kit. It's a shame, as the rear kit is a really nice setup, maintaining the factory drum-type E brake.
Fortunately, AP designs the front kit to work as a standalone unit and it's fully compatible with the factory master cylinder and ABS system. I measured the piston sizes, and the total area is actually slightly smaller than the stock single piston. (Make sure to double the area of the single-piston slider when comparing to an opposed-piston-type caliper.) This all adds up to a firm pedal with slightly less travel and feels great on the road. Our before and after stopping tests recorded with an AIM SOLO did show a reduction in stopping distance of about 5 feet. But the biggest gains can be found after extended stops where the increased thermal mass of the brake package and fresh Gulf Competition RF1000 brake fluid can handle the heat better and maintain consistent stopping distances. They look great behind the BBS CHRs and fit without any clearance issues.
The upgrades installed on the M5 have improved performance without any drawbacks, which can be a rare find these days. The car now inspires confidence in the corners and puts down power well, all while maintaining a quiet, comfortable ride and looks great doing it.