Change of nm > nw is more frequent than assimilation of nm > mm, so maybe menwa. But this sounds plausible to me.

+Paul Strack menwa could equally work

And then: *immenwa/immemma "automobile"? ☺️

(1) PE19:96 says that nm > nw occurs usually when the stem ended in n + m suffix, so this is our case.
(2) A couple of years ago somebody suggested a word immolendo for an automobile (it might be you, Tamas). I feel ok with it.

+Ицхак Пензев I think it was me, yes. Not sure about the lendo component, though.

Let one also not forget the perfectly usable attested items at https://www.elfdict.com/w/cart or the verbal stem lev- "to move" (intr.). I also wonder what JRRT's mind on the root KEL became after he thought up celvar..

By the way, the Finnish counterpart that's actually being used is not *kuljin (kulkime-) or even *kuljetin (kuljettime-), but kulku+peli, kulku+neuvo, ajo+neuvo — whereas in standard Estonian one does find the 'vehiculum'-type formation https://en.wiktionary.org/wiki/s%C3%B5iduk .

+Tamas Ferencz *immemma 'selfie'? :-)

+Björn Fromén indeed.

In my opinion, raxa works okay for ‘car'. Or, at least, not worse than other variants. I didn't know this word earlier.
P.S. And lunca for ‘truck’/‘lorry’.

+Ицхак Пензев Bjorn has been using raxa for "sleigh, sled" as the root implies dragging, pulling.

lunca could also work for "train"

+Tamas Ferencz in Elfling #27189 you suggested tungwa for 'train'. It makes more sense than Helge's tungwë for 'tax'.
Is not raxa too close to raxë 'danger'? It may be confusing. In my attempts of "conversational Quenya" two years ago I tried norollë, but I don't like it as a very early word.

+Ицхак Пензев well those are all variations on the same theme, aren't they: a root meaning 'pull, drag, draw', and a noun derived from it. So we can use one for one meaning, the other for another one...
Norolle is perfectly fine I think because the verb nor- is well attested in later periods.
And I am not really bothered by raxa being close to raxe...

+Tamas Ferencz I agree with you 100%. As for lunca, I thought it was somehow connected to lunga 'heavy'. Now I read an entry in Eldamo and saw I was mistaken.

I based my use of raxa for 'sleigh' on the gloss "a drag" in PE 17:28. Per OED "drag" can mean, i.a., "an overland conveyance without wheels; a rough kind of sledge".

norolle is only known from GL, where nor- is associated with rolling and wheels. There is no trace of that sense in late sources.

+Björn Fromén I feel frustrated in my search of consensus.