Crabbing
12-12-2019, 09:34 AM
#1
Junior Member
Thread Starter
Crabbing
I know this has been talked about a lot with the GLC, but I have noticed that I do get some crabbing on my 450, mainly with the wheels on full or near full lock and with cold tyres. Anyone else have this?
12-12-2019, 09:21 PM
#3
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2017 GLE350 4MATIC
Mainly the result of Ackerman geometry (error). Accentuated by tire and wheel selection, weather and drivetrain components (differentials and clutches).
I get some crabbing on a W166 GLE350 but not nearly as much as what seems to be reported on the GLC.
BMW X3 latest version also has it.
I get some crabbing on a W166 GLE350 but not nearly as much as what seems to be reported on the GLC.
BMW X3 latest version also has it.
12-13-2019, 10:30 AM
#4
MBWorld Fanatic!
Mainly the result of Ackerman geometry (error). Accentuated by tire and wheel selection, weather and drivetrain components (differentials and clutches).
I get some crabbing on a W166 GLE350 but not nearly as much as what seems to be reported on the GLC.
BMW X3 latest version also has it.
I get some crabbing on a W166 GLE350 but not nearly as much as what seems to be reported on the GLC.
BMW X3 latest version also has it.
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chassis (12-14-2019)
12-14-2019, 08:16 AM
#8
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2017 GLE350 4MATIC
Ackerman geometry error is the phenomenon where all four tires neither rotate at the same rotational velocity, nor translate with respect to the same (virtual) point. Google Ackerman geometry.
Rotation means the wheel and tire moving about the wheel bearing, or "spindle". Translation means moving in three dimensional space relative to a fixed reference frame on the ground.
Each wheel translates about a virtual point, as a vehicle turns at low speed with full steering lock. This is influenced by vehicle tread width and wheelbase. This creates a condition where tire contact patch stress evens itself out when the highest stress contact patch slips, or "crabs". When the high stress contact patch slips, the vehicle can lurch a small amount, a rubbing sound can be heard, and a vibration might be felt in the steering or floor. All of this is taking place at the tire-ground interface.
Each wheel rotates at its own rotational speed. This introduces driveline torque buildup, to a greater or lesser extent, depending on drivetrain design details such as clutches and couplings in the three differentials in the case of 4MATIC. One differential in the case of RWD.
Each front wheel has its own steer, or "cut", angle, and is a design choice by the manufacturer. The angular difference between the two wheels, when turning, is a compromise between high speed and low speed steering performance, cost, and the basic reality of available space in an area densely populated with components.
All of this is at the "worst" possible condition at full steering lock. In practical terms, full steering lock is only achievable at very low vehicle speed. So the phenomenon is perceived by humans during parking maneuvers, generally.
Rotation means the wheel and tire moving about the wheel bearing, or "spindle". Translation means moving in three dimensional space relative to a fixed reference frame on the ground.
Each wheel translates about a virtual point, as a vehicle turns at low speed with full steering lock. This is influenced by vehicle tread width and wheelbase. This creates a condition where tire contact patch stress evens itself out when the highest stress contact patch slips, or "crabs". When the high stress contact patch slips, the vehicle can lurch a small amount, a rubbing sound can be heard, and a vibration might be felt in the steering or floor. All of this is taking place at the tire-ground interface.
Each wheel rotates at its own rotational speed. This introduces driveline torque buildup, to a greater or lesser extent, depending on drivetrain design details such as clutches and couplings in the three differentials in the case of 4MATIC. One differential in the case of RWD.
Each front wheel has its own steer, or "cut", angle, and is a design choice by the manufacturer. The angular difference between the two wheels, when turning, is a compromise between high speed and low speed steering performance, cost, and the basic reality of available space in an area densely populated with components.
All of this is at the "worst" possible condition at full steering lock. In practical terms, full steering lock is only achievable at very low vehicle speed. So the phenomenon is perceived by humans during parking maneuvers, generally.
Last edited by chassis; 12-14-2019 at 08:26 AM.
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tiri (12-16-2019)
12-14-2019, 08:40 AM
#9
MBWorld Fanatic!
We all know about ackerman effect BUT on GLC it is because of wrong geometry on right hand drive cars as admitted by MB, hence they change the steering knuckles free of charge at a cost of over £1000.
Until you have driven a GLC 43 or 63 RHD car you don't know how bad it is, check the GLC forum.
