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Originally posted by Kuan
Seems like the official Paris-Dakar site is not meant for us who don't know how to use a GPS!  Actually, the M-Class finished 2-3-4 in their class, 38-41-42 or something like that overall. They participated in the unmodified category. The Mitsubishis which won all competed in the super modified.
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Thanks for the info. So, the class that the M's competed in was what? Stock? I only pay attention to the three main classes - Trucks, 4wd cars, and motorcycles, and don't know too much about any of the other classes... Any url's you can point me to?
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ETS kicks in when the difference between tires is 3mph, 1.2mph at low range. Big tires won't affect the ABS, the ABS sensor only detects lockup and releases the piston when that happens. It's conditions which affect wheel lockup, not tire size. As far as traction is concerned, I don't see why ETS is any different from locked differentials. If you have no traction on one tire then you have no traction. The locked differentials allow one tire to keep spinning, ETS brakes the spinning tire. Either way you have traction on only one side so I don't see much difference.
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Some problems here:
Larger tires most definitely affect ABS. The computer that controls the ABS measures wheel speed (larger tires=slower rotation per distance traveled) and compares this to the speed it thinks the vehicle is going to determine when to use and not use the ABS. This, in turn, will affect the ETS system.
For example - w/stock tires you are travelling at 50mph and 3200 rpms. With larger tires, when you are ACTUALLY traveling at 50 mph (remember the speedo will still show 50mph=3200RPM, but in actuality at 3200 RPM you'll be doing a speed higher than 50mph, due to the larger tires) your engine revs may now only be 2900 RPM. So, you'll be farther down the engine's power and torque curve. THEN ADD TO THAT the fact that with a larger radius tire, a given torque at the axle shaft (produced by the motor at a given RPM) will produce less reactive force at the road, due to the fact that the road now has
a "longer lever" to work through in the larger tire radius (thanks Dave ;-)
The ETS will also be affected by the reduced reactive force.
As far as comparing ETS to locking differentials, there is no comparison. Here's a very simplified breakdown of how each works in one scenario:
Scenario - climbing a hill with moguls deep enough to cause extreme articulation - enough so that your front passenger side (PS) wheel and rear driver side (DS) wheel are in the air.
ETS - Without ETS, the two wheels that are hanging in the air will spin, as that is the path of least resistance for the differential. You will be stuck. Then, ETS kicks in and says "whoa! we've got wheel spin. Let's apply the brakes to those wheels that are spinning, and that will help distribute some of this unused power." The ABS braking system then activates and starts braking, which starts to distribute some of the power to the wheels with traction. The problem with this is that each wheel is not getting equal power, as some of that power is lost in the transfer via the braking and spinning.
The other problem with this is that you have already been stopped by the obstacle and have to get the hanging wheels spinning in order to activate the ETS.
LOCKERS - by equally distributing power between all four wheels at all times guarantees that any wheel with ground contact will be pushing the vehicle. You won't stop when those two wheels are airborne. It won't take wheel spin to activate the lockers. Your momentum and traction will not be lost.
Unless you have witnessed both on the same obstacle in person, you really can't get a picture of the difference. And the difference is truly amazing.