Faz-Faz

Hi this is the situation..the cars temperture is at optimum temperature. so i have just shifted into 2nd gear i put my foot all the way down and the car jerks violently as if you are double clutching..this only happens somethimes..i took it to lexus and showed it to their mechanic and it didnt jerk at all just random.. and this only happens in second gear at about 2000-4000revs. I have chekd the engin oil that is fine the car has just been serviced aswell and also this only started hapning after the service.. Could anyone advise me on what to check or what to do..

i bought some original lexus 18inch sport alloys.. and since i have bought them they have been nothing but a pain.. when i put the alloys on i had the wheels balanced and the tracking done i took it onto the motorway doing bout 70-80 and the car is shaking, not the steering wheel but the car.. so i took it back to a garage and had the wheels balanced again and this time the mechanic said i need two new tyres as one is getin bald from the side from the pulling to oneside issue and the other tyre has a flat spot.. so i had it changed, balanced the wheels hoping that it wouldnt vibrate and still it is.. i dont know what to do now. any suggestions plz.. thanks

Can i change from 16inch alloys to 18 inch alloys, without damaging the car?