I have a 2003 BMW. After the car has been sittng idle for around 4 days, I’ve noticed that it shakes at 45 mph, like the wheels need to be balanced, for the first 20 minutes of driving. It doesn’t start to behave like this again unless it sits around again for a few days.
Check the tires for a possible separation (maybe one tire is causing the shake).
Any growling noise from wheel bearings when this happens?
I like roadrunner’s response but I might suggest moving the front wheels to the back and back to front. Now if that made a difference, not fixing it but changed the feel, then you have eliminated everything except the tyres and wheels.
Verify air pressure in tires is proper. Given the time of the year(eg its colder) and that the car sits I am guessing your tires are susceptible to flatspotting. Basically a flat spot forms from sitting and then works it way out after your tires warm up.
Its tire specific on which ones do it. My current car with low profile performance tires does the same thing albiet for about 5 minutes although I get to highway speed in 3 mins after driving so they heat up quickly.
Visual inspection does not show any tire seperation, but I’m not sure what to look for. I’ll try moving the tires around.
Exactly, what brand and type of tires are on the car? Do they, by chance, have a nylon “cap ply”? Check the fine print on the sidewall.