I suppose it depends on which side of the Atlantic you are on I suppose. They are still arguing over Tomatoes and Potatoes.

No doubt! It is definitely beemer to me. Bimmer? Rhymes with simmer and glimmer. ;)

And I should add, in response to Fische, which side of the Atlantic is Malaysia on anyway? Malaysian English may be British originally, but Americanisms are creeping in all over.

So which is the British-English version: Beemer or Bimmer?

Bimmer - proper accepted slang for BMW cars. Most people don't know this.
Beamer/Beemer - proper accepted slang for BMW motorcycles.
You will hear this term used incorrectly by many people. So just why is a BMW car called a bimmer not a beemer or beamer? The answer in part lies in knowing some BMW history and what came first.
All real BMW enthusiasts know that BMW got a big start on two wheels, what many call the real BMWs.
In those days, BMW motorcycles were quite active in racing, and one of their competitors at the track was often the BSA bikes. Well as things would have it, a track slang developed, and the BMWs were usually referred to as 'beemers' and the BSAs were referred to as 'beesers'.

So, of course for any true enthusiast, there is no way that a BMW car could be called a 'beemer', so they were called 'bimmers'.

Source from: BMW car club of British Columbia