AS PHOTOS ATTACHED SHOW WE HAVE
HAD THE NEWEST BMW 328iX SERIES ALL WHEEL DRIVE SEDAN. WE
ALSO BOUGHT THE PREVIOUS GENERATION 3 SERIES WITH X DRIVE OR ALL WHEEL DRIVE.
THE PREVIOUS MODEL IS SLIGHTLY DIFFERENT WITH THE ALL-WHEEL-DRIVE SYSTEM AND
HAS RUN FLAT TIRES. RECENTLY WITH SO MUCH SNOW, RAIN, ICE QUESTIONS ARE BEING
ASKED ABOUT TIRES ON ALL-WHEEL-DRIVE VEHICLES.
Some “experts” state if tire has
less than 50% of tread all four tires need to be replaced for all-wheel-drive
to work properly.
So many Pot Holes in Detroit and
surrounding areas owners of all-wheel-drive cars are getting bad advice on replacement
of tires. Many tire dealers are recommending replacing all the tires. Acura,
BMW, Mercedes, Audi, Land Rover, Subaru recommend have dealer help determine if
all tires need to be replaced.
True all wheel drive vehicles
like those from Audi, BMW, Mercedes, Volkswagen, Land Rover/Range Rover,
Porsche and of course Subaru have very sophisticated systems. Part time all wheel drive like on 2014
MDX are not true off-road or all wheel drive vehicles. The MDX all wheel drive
like many of its competitors run in 2 wheel drive but can transfer power back
and forth when slippage is sensed by the traction control system.
Audi recommends that the tires remain within 4/32nds of one another in
tread depth, while Subaru recommends 2/32nds. But if your tires are outside
that range there’s still another option. Tire truing or shaving. While it’s
primarily used in racing, the same technique can be applied to a new tire to
get it within specification of the worn tires for about $25 – $35 per tire.
I talked to some of the experts
at BMW and they answered my questions as follows:
1. BMW all-wheel-drive X Drive
models have a 40 / 60 split?
BMW answered stating that the xDrive sends 38% of the torque to
the front axle and 62% to the rear axle under normal driving conditions. The
system can redirect up to 100% of the torque to any axle when low traction,
understeering or oversteering conditions are detected. The system is fast enough
to react and intervene in the middle of a corner when the vehicle starts to
understeer or oversteer.
2. 100% POWER/TORQUE CAN AUTOMATICALLY GO TO WHEEL THAT NEEDS IT?
· 100% of the torque can go to the front axle when there is no
traction available in the rear axle (i.e. both rear tires are over ice or mud)
and 100% of the torque can go to the rear axle under extreme understeering, or
during parking maneuvers at very low speeds. BMW’s DSC traction and stability
control system can then intervene and brake a slipping wheel on one axle to
redirect torque to the tire which has traction. The vehicle will have traction
even if only one wheel is over a surface which provides at least some degree of
friction.
3. DO ALL X MODELS HAVE SAME
DRIVE SYSTEM
· No, we have used different suppliers for drivetrain components
during xDrive’s history as a BMW technology. BMW’s first all wheel drive
vehicles had an x added to their model names (for example the 325ix), xDrive
became available when the first generation BMW X3 was launched and was the
first BMW intelligent all-wheel drive system, capable of varying the torque
split between the axles. Our previous all-wheel drive vehicles had a fixed
torque split between the axles.
4.RUN FLATS ON ALL X DRIVE
MODELS?
· No, the previous
generation of the X3, and the first generation of the X5 (which started to
offer xDrive from MY2004 onwards) used conventional tires.
5. IF ONE TIRE IS DESTROYED
DOES THIS REQUIRE ON X MODELS TO REPLACE ALL TIRES.
· As on all ABS and traction/stability control equipped vehicles,
correct tire circumference is critical to the operation of all functions based
on the measurement of the wheels
speed. The system allows minor deviations in tire circumference but significant
tire thread depth differences will cause error codes. Correct tire inflation
according to the vehicle’s load is also important. This is equally valid for
conventional and run flat tires.
Bruce Hubbard
Auto Advisor Group
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