325xit - Tyre selection

I have lately purchased a set of 4 Avon ZV5 tyres. The characteristics of the tyre are: 205/55R16 XL 94V. I can only but recommend this tyre, the car feels 100% different with great handling, a smooth ride and virtually no sound from the wheels.

The 2002 325xit can take one of the following tyre configurations:

• 205 55 R16 91V
  
• 225 50 R16 92W

The load index 91 means that each tyre can handle 615 kg (1356 pounds) of weight. 92 will load 630 kg (1389 pounds) and 94 will carry 670kg.

Here is an explanation of the speed rating:

M		81 mph	130 km/h
N		87 mph	140km/h	Temporary Spare Tires
P		93 mph	150 km/h
Q		99 mph	160 km/h	Studless & Studdable Winter Tires
R		106 mph	170 km/h	H.D. Light Truck Tires
S		112 mph	180 km/h	Family Sedans & Vans
T		118 mph	190 km/h	Family Sedans & Vans
U		124 mph	200 km/h
H		130 mph	210 km/h	Sport Sedans & Coupes
V		149 mph	240 km/h	Sport Sedans, Coupes & Sports Cars
W		168 mph	270 km/h	Exotic Sports Cars
Y		186 mph	300 km/h	Exotic Sports Cars

DSC, BRAKE, ABS Yellow light on the BMW325xit

I was surprised the other day while driving by a beep and the simultaneous yellow light appearing on the DSC, BRAKE and ABS symbols.

When I turned off the engine for a while the light would go out, but then after a few minutes of driving it would appear again.

The car was at the mechanic a week ago, and he was working on the front left wheel, he also disconnected the battery during his intervention. I did some research on the forums and read some instructions on how to reset this behavior (turning the wheel clockwise the counter-clockwise to the extreme, or opening and closing all doors) but it did not yield any results.

So I went to the car electrician in order to run the BMW on the scanner. The moment of truth revealed three alarms:

• Front left wheel speed meter.
• Brake pad.
• Power interruption.

He told me there was something broken which needed replacement but I insisted on clearing out the alarms. He did that and I then drove it and the symptoms did not appear for a week, then they started appearing again and more frequently. As a last shot before the mechanic, I decided to do it myself and check the sensor. I removed the wheel, checked it out, re-fitted the cable connector firmly and that was it. No more orange lights, problem solved every since!

I guess the lesson learned here is that I should buy a scanner and make sure I clear the alarms each time the battery is disconnected or some sort of sensor or electrical component is replaced or refitted.

Needless to say that I have tested the ABS and DSC functionality, it’s all working like a charm.

The X in the BMW 325xi

The BMW 325xi E46 has three differentials: one in the front, one in the middle and another one in the back.

The middle differential transfers power at a 32%/68% ratio favoring the back. This distribution, while providing a good grip to the car in wet conditions, favors the sporty driving experience in dry conditions by transferring more power to the back wheels.

The ratio is fixed mechanically and cannot be changed electronically like in other cars like Subaru or Saab.

The differentials are open and therefore do not have a Limited Slip Differential (LSD) mechanism. However the ADB-X (Active Differential Breaking) and DSC-X (Dynamic Stability Control) system, will enhance the grip of the vehicle by applying brakes and cutting off power to the wheels which are spinning. This system is controlled electronically via the central computer vs. the mechanical nature of LSD. It intervenes on each wheel individually to retain traction and is unoticeable to the driver.

The added AWD mechanism comes with a price. More than 100kg of weight which will make the vehicle stopping distance longer. However, it will make it start faster in normal conditions or get you off the snow in extreme weather.

The E90 models are fitted with the xDrive system, which is a bit more elaborated and designed to distribute the torque based on the road conditions.

To Disable DSC-X: Press the button once. To Disable ADB-X: Keep holding the button won't work on the 325 xit model, it is only supported on the non-X E46.