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-   -   Do I Need 4 Wheel Drive? (https://www.airforums.com/forums/f240/do-i-need-4-wheel-drive-197489.html)

albret 08-11-2020 10:35 PM

I agree that you can drive over 30 mph, but like you said on ice and snow at 50 mph where the tires have some movement. Hard surfaces, making turns at a high speed, can cause a lose of control and wear out the tires. Straight down the road is no problem, but locking the front axial does not allow free movement of the tires in turns. Just my opinion.

SWH 08-12-2020 09:23 AM

Do I Need 4 Wheel Drive?
 
Quote:

Originally Posted by Amg (Post 2395579)
I have a 2020 Interstate 4x4 lounge. Never heard of limitation of speed while in 4x4. I know there is a limitation while in low range



My understanding is that the Sprinter ‘4WD’ system is identical to the full time 4MATIC AWD system used in Mercedes passenger cars, and thus no speed limitation whatsoever. The only difference is that it is selectable and not full time in the Sprinter.

See this link: https://media.daimler.com/marsMediaS...ml?oid=9362120

“Designed with the professional in mind, the all-wheel drive of the Sprinter 4x4 is based on the Mercedes-Benz 4ETS Electronic Traction System, a technology that is employed also in the Vito 4x4 and Viano 4Matic and which has proved highly effective in Mercedes-Benz passenger cars up to the ML-Class. In contrast to the permanent all-wheel drive in the Vito and Viano, however, the Sprinter's 4x4 drive is engageable in line with the van's exceptionally versatile operating environment. The all-wheel drive is engaged with the engine running and with the vehicle stationary or at low speeds up to 10 km/h. It involves an electric motor engaging a spur-gear pair on the transfer case.”

albret 08-12-2020 11:12 AM

Let's update my last post with the following information:

Back to the original question - "How fast can I drive in 4WD?". As fast as you like - none of the 4WD or AWD systems has any mechanical speed limitations. Speed will do no harm to the drive components.

There is one exception though. Owners of part time 4WD systems (the ones that let you chose between 2WD and 4WD) should be very cautious when using 4WD on slippery roads, because their handling is not as precise as full time 4WD and AWD.
For one, they should always shift back to 2WD when approaching dry surfaces (and back to 4WD on slippery stuff) because part time 4WD should never be used on dry surfaces. If you do, you can cause severe mechanical damage.
Also, when in part time 4WD neither ABS, traction control or stability control will work.
The faster you (accidentally) drive on hard surfaces in part time 4WD, the more likely it is that mechanical damage will occur.


If you own a vehicle with part time 4WD the need for different rpm front and rear represents a major problem. The transfer case will power the front and rear drive shafts with same rpm and is not able to satisfy the front axle's need for more rpm. Remember, the combined rpm of front wheels (A+B) is higher than the combined rpm of the rear wheels (C+D). Only full time 4WD systems are able to negotiate the needs of front and rear.
So, with part time 4WD engaged your front wheels are forced by good traction on the ground to rotate faster than the rear - but since the front drive shaft delivers only the same rpm as to the rear there is a fight between front wheels and rotational force coming from the front drive shaft. The front drive shaft in effect tries to slow down the front wheels. This results in very wide turns (understeer) and dangerous handling on pavement.
The name "part time" derives from its use. It can only be used part of the time - most of the time (for most uses) it has to remain in 2WD. Only "full time" - notice the name - can be used full time for all uses.
The fight between front wheels and transfer case also makes 4WD performance suffer - in a turn the front wheels are not pulling like they should. They are in effect hindered by the front drive shaft.
The slowing effect caused by front wheels stresses all components between wheels and the transfer case. It causes mechanical components to bind instead of moving freely - this situation is called "axle binding" ,"driveline binding" or "driveline wind up". First indicators while driving is a hard steering feel and the vehicle displaying jerky movement. Shifting back to 2WD will become impossible (gears and levers are extremely forced together). Continued 4WD use on dry surfaces will cause the weakest links to break (U-Joints, axles, differential gears, transfer case gears and chains, bearings, drive shafts).
When traveling with part time 4WD on high traction surfaces like asphalt, concrete, etc. handling of the vehicle will become unsafe (understeer) and the "driveline binding" will eventually cause component failures. Part time 4WD should not be used on high traction surfaces! Even when going straight most of the time, slight differences in tire pressure front to rear or vehicle load resulting in different axle speeds will cause "wind up" and eventually damage.
When traveling with part time 4WD on low traction surfaces like sand, gravel, mud, snow, etc. handling of the vehicle is unsafe (understeer) as well, but not as severe as on pavement. The slowed down front wheels simply skid a little on gravel, sand, snow, etc. during a turn. This in mind you should always approach difficult off-road obstacles in a straight line otherwise you might lose some of the much needed traction due to wheel slip on your front wheels.

Do not listen to guys who tell you it is OK to use part time 4WD on pavement! Severe damage will be the result.

SWH 08-12-2020 03:31 PM

Do I Need 4 Wheel Drive?
 
Quote:

Originally Posted by albret (Post 2396471)

For one, they should always shift back to 2WD when approaching dry surfaces (and back to 4WD on slippery stuff) because part time 4WD should never be used on dry surfaces. If you do, you can cause severe mechanical damage.

Also, when in part time 4WD neither ABS, traction control or stability control will work.

The name "part time" derives from its use. It can only be used part of the time - most of the time (for most uses) it has to remain in 2WD. Only "full time" - notice the name - can be used full time for all uses.

When traveling with part time 4WD on high traction surfaces like asphalt, concrete, etc. handling of the vehicle will become unsafe (understeer) and the "driveline binding" will eventually cause component failures. Part time 4WD should not be used on high traction surfaces! Even when going straight most of the time, slight differences in tire pressure front to rear or vehicle load resulting in different axle speeds will cause "wind up" and eventually damage.

Do not listen to guys who tell you it is OK to use part time 4WD on pavement! Severe damage will be the result.

What you say is true of vehicles with these types of systems, but to be clear and to avoid confusion, the vehicle we are talking about here is an Interstate/Sprinter 4WD, which is NOT the type of traditional part time 4WD system you describe above. Sprinters use an engageable AWD system. There is no driveline binding on dry surfaces because, as stated in the link I provided above: “In contrast to other systems of this type, the engageable all-wheel drive in the Sprinter does not result in a rigid through-drive. Power is transmitted variably; all elements of the standard-equipment ADAPTIVE ESP, including ASR acceleration skid control, remain operational while the all-wheel drive is engaged.”

Here is another link providing additional information about the Sprinter 4WD system (relevant excerpts below): https://ourkaravan.com/4x4_sprinter_and_transit_vans/

“Despite the “4×4” badge on the rear of the Sprinter, the system is based on the Mercedes-Benz 4Matic All Wheel Drive (AWD). Mercedes-Benz calls the Sprinter drive system “4ETS,” which stands for “Electronic Traction System.” In fact, Mercedes-Benz rightly calls the system “engagable all wheel drive,” because that’s what it is. It takes the 33/67 torque split AWD system from its line of cars and couples it with a button so the AWD can be turned off.

The advantage of using such a system is the van can be run in 2 wheel drive to save fuel. Additionally, 4 wheel drive can be engaged on pavement and not damage the drivetrain. 4Matic is permanently engaged in Mercedes-Benz cars so-equipped.”

nickclifford 08-12-2020 03:40 PM

Yes !! I love having 4wd as a backup plan ... unless you only plan on RV parks of course.


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