Free Wheeling Hubs - Useful or sheer nonsense ?
by Takeo De Meter
What do free wheeling hubs REALLY do ? Not much. I mean they engage / disengage the half-shafts from the wheels, as if one would be taking the driving members off or putting them back on as needed.
So, considering your basic part-time 4x4 Land-Rover (like
a Series vehicle) without any free wheeling hubs, and you are driving
it on the road, you will -in principle- drive your vehicle in 2x4 mode,
i.e. with only the rear axle driving the vehicle. The front axle is then
disengaged from the driveline, it does not help in the transmitting the
traction effort to the road.
So what are these free wheeling hubs for then ? With the free wheeling hubs disengaged, the wheels are not able to drive the half shafts, differential and drive shaft, thus eliminating the friction therein. So your front axle gets disengaged twice; once at the gearbox and once at the wheels. (Not unlike pulling out a second plug in your bathtub after having pulled the first one and the tub is already empty). While this sounds good, (I can hear you think: eliminating friction = no wear and tear, fuel economy etc.) it is pure nonsense when you come to think of it. WHAT friction ? How much ? Is it worth it ?
One can safely say that the friction inside a non-driven 4x4 front axle can be neglected. The only frictions that get eliminated is the crown-and-pinion, bearing and satellite frictions (undriven). The order of magnitude falls well within the measuring error margin when the whole of the frictional resistance in a Land-Rover is considered. It is generally accepted that the whole of (driven !) drivetrain frictional losses in a motor vehicle is in the order of 15 %, since load is applied. Where free wheeling hubs eliminate undriven friction loss, this is only fractional and can be estimated at something like 25 - 50 Watts.
So what does this mean in terms of saved money, for instance ?
If you vehicle is using something like 50 Kilowatts (50,000 Watts) to happily potter along the freeway at 65 Mph (e.g. Series II), then your free wheeling hubs save like 50/50000 th of the total effort, or the same amount in fuel spent = 15 Mpg / 1000 = 0.015 Mpg. In other words, after burning 1,000 gallons of gasoline, you will have gotten 15 miles further. Now please explain to me why anyone would spend like £ 250 for a pair of these things ?
I also think that a radio antenna + a CB antenna + a couple of larger rear view mirrors cause more aerodynamic drag that free wheeling hubs would ever make up for.
Some claim improved handling using free wheeling hubs. Improved handling of WHAT ? Of their mobile phone ? If the front driveshaft is disconnected in normal 4x2 mode, how in the world could any steering backlash (or anything else) be generated since the connection with the front axle is completely severed ?
Moreover, free wheeling hubs can be (and have been !) downright dangerous to have. Imagine you are at a Landy meet with some off-roading involved. You are standing at the top of a looong very steep drop, ready to take the plunge. You tell your co-driver to shut up and hang on and you go for it. Using good driving practice, use let her drop against the engine brake in first low, only to find out that some obnoxious child has turned one (1) free wheeling hub loose when you were not watching your truck. Then you hit the bottom at 60 Mph, breaking your truck and some bones. In a comparable situation I saw the driver hit the brakes and rolling his truck. He was carried off later in a body bag.