R KLASSE

I was wondering if there was a guru on here that was familiar with the Mercedes 4-Matic system, and could explain how it works? I recently drove up to an area this past weekend with the car that had gotten a fresh dumping of snow. Anyway most of the roads were plowed but after about a half hour of searching I found a neighborhood in a very hilly part of the area that had fresh un-plowed snow. I was a little apprehensive at first because as I got to the hilly section I stopped seeing cars, vans and average SUV's and more rugged stuff like big trucks and SUV's that were lifted, some with chains parked along the road. I kept going anyway, first off though I was amazed at how the R just tracked right through the slick stuff. I couldn't spin a wheel unless really I wanted to. I also found out the only way you could sucessfully do a doughnut in the snow is by turning the ESP off. With the ESP on it's virtually impossible to execute, you can hold your foot to the floor and the car will just do a perfectly composed circle. I wasn't trying to beat on my car, just see what it feels like in the slushy stuff and how I could expect it to react under certain circumstances in real life.

I found while climbing a steep driveway though it only really wanted to climb it well if the ESP was turned off, other wise it would just bog down for some reason. My question is if the 4-Matic is always in AWD or just when needed? Does the R-Class have any type of limited slip differential? Is the center diff a gear type or viscous type. Everything I ever heard about the MB 4-Matic system is that in all actuality is a pretty basic and simple setup. All and all this is a very secure feeling vehicle to drive in the snow, probably the best I've ever experienced. The only downside is ground clearance (I tried to drive through a snow drift or small snow bank) I can easily do this in my truck, the R gets hung up for a second then pulls through with no problem.

avlis

ESP is a hindrance at low speed. Or, more accurately, traction control (which ESP comprises) is a hindrance at low speed because the computer shuts down engine power whenever it senses wheel slip. When climbing that steep driveway, wheel slip is inevitable even when barely moving. Yet the computer still closes the throttle even though you actually need wheel slippage in order to get moving. That's why the ESP Off button is there in every car.

AFAIK, there is no proper limited slip differential (LSD). However, ESP will apply the brake to a slipping wheel which sorta serves the same function as an LSD.

R KLASSE

I see, that explains it all. I appreciate the response. The car does go a whole lot better in deeper, slicker snow with the button off. But I love how the car sort of gives you a huge cushion or sense of safety with it on.

JTReeves

I have Michelin Alpins on my R500. My wife and I helped out a family who were stuck in the parking lot of a BestBuy when their Explorer's starter died. This was early in the deluge of snow we recently got in the DC area. We piled the mom and three kids into the rear 4 seats and took off. They lived in an area that hadn't been plowed. Once off the main road, the only evidence of travel was tire ruts in the snow, the edges of which had frozen. We were able to maneuver along the higher levels of the ruts onto the final street where our evacuees lived. Their street hadn't had much traffic and there was lots of fresh snow to drive through. We were able to move with confidence and a feeling of security.

Because my wife was with me on the way home, I resisted the urge to apex the turns as we drove home. The laws of physics still apply (Number 1, that an object in motion tends to remain in motion unless acted upon by an outside force) and turning the steering wheel while proceeding through a turn as a means to corrent understeer will not always be successful if one's speed is too high to gain any traction. Nonetheless, I enjoyed driving the car immensely under those conditions.

JR

avlis

In that deep soft snow the tires need to spin in order to claw through the snow and find traction. As the tire spins the treads cake up with snow. If wheel speed is too slow the snow remains stuck in the treads reducing traction and you're stuck. Sometimes faster wheel speed will fling the snow out of the treads and allow the tire to take another bite. Traction control often prevents fast enough wheel speed to clear the treads or even move the vehicle.

melvinh

While my R was in service, I had ML as loaner. Drove into deep snow hill with it's 19 or 20 sports tires, almost got stuck. I can feel the 4 matic working hard while i try to get out of the deep snow. I saw many others such as CRV gave up and stuck there. I think with snow tires 4 matic probably will do much better.

avlis

You mention the CRV getting stuck. Prior to the R-Class we had a Honda Element which shares same platform as the CRV (which shares its platform with the Civic, oddly enough). Anyway, Honda's "Real Time" 4WD is really just front wheel drive most of the time. If the front wheels spin faster than the rear, a hydraulic pressure builds and engages a clutch that applies torque to the rear. Too much of this and the system overheats to protect itself and you're back to front wheel drive until it cools off. In practice I found this system a bit lacking but still better than 2WD.