February 20, 20214 yr Hello to all people am new to this Fourm, I have X5 E70 Model now this car I’ve never had a problem until now. It’s 2011 plate with 80,000 full Bmw service had the car for 2 years now... I notice a small jerk when accelerating to 40 or above been told it’s got cheap tyres on so I need genuine tyres but I was thinking all that time the car was fine... what I’ve notice is the car won’t select in sport mode ? Any help please ?.. really appreciate it thanks.
February 22, 20214 yr Hi Mo Welcome to the Forum All AWD cars need the tyres front and rear to have the same rolling radius if they are mismatched then you will have all the conditions for transmission wind up to occur. Transmission wind up can and will kill Diffs, Transfer boxes and even Gearboxes very expensive. Are the tyres the correct sizes for the car. From your description you have the symptoms and have ignored them, if the front axel is turning at a different speed to the rear then the transfer case in the middle will be damaged. If you reverse in a tight circle slowly do you get a jerking? When you stop the car open the door or window as you turn off the engine do you hear clicking? As you already are experiencing no Sport mode my guess is the transfer case is damaged which could be way more expensive than a set of decent tyres. If your car is running 19" rims my guess is it runs a staggered set up tyres should be 255x50x19 Front 285x45x19 rear and originally run flats, though you can replace them with non run flat tyres At the very least the tyres should be replace as a set and all from the same manufacturer at the same time. A set of decent tyres will cost around £800 a new transfer case 3 x that Sorry if that's bad news Dave
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