Cant work this one out

[Zedhed]

Had a kind of jerking on acceleration the other day and closer inspection the rear drivers tyre had only about 20psi in it,but thought surely thats nothing to do with it.anyway fitted the brand new wheels and tyres and problem is now totally gone.can anyone understand this,i thought it was drivetrain related.

[X5Sport]

Different rolling diameter due to pressure differences so the transmission will feel wrong.  Surprised that you didn’t get a warning?

[Zedhed]

Already have 4x4 light on and brake pad light anyway.