We can e.g. say that talta- does not necessarily have to carry a "downward" sense and can mean 'slide, glide' in general (see the etymology of E slide at https://www.etymonline.com/word/slide).

Following that, a noun derivate could be *talatmá > *talanwa/talanwe "sled, sleigh"

etymonline.com - slide | Origin and meaning of slide by Online Etymology Dictionary

I've used raxa 'a drag' (PE 17:28) for 'sleigh'.

I think 'down' is an essential part of the meaning of talta-, as shown by Atalante "the Downfallen".

+Björn Fromén raxa seems great for "sled". That would still leave "slide" unresolved though🙄

Those who don't like neologisms may consider using an already known verb á la Icelandic : https://en.wiktionary.org/wiki/renna#Etymology_2_2

For those who can live with them: The root (!)LEKH [http://eldamo.org/content/words/word-685899825.html] which also resembles PIE *(s)leh₂b- seems like the most plausible starting point for creating the verb (at least to a Finnish-speaker..). Would a simple root stem be understood as intransitive? Compare lah- "kick" from LAKH (the root having the same meaning as the verb).

+ܤܡܝ ܦܠܕܢܝܘܤ‏do you mean extending the meaning of, say, kelu or sir-?

Sorry for the mess in my comment, your RTL username confuses my G+ app.

This may have been little more than a passing thought, but in PE22 page 150 Tolkien considered redefining √KIR to 'shave; skim (surface), slip along, glide quickly' with kirya as an adjective 'swift gliding'.
eldamo.org - Eldamo : Primitive Elvish : KIR

+Tamas Ferencz Whatever one deems the most logical candidate. "To ski", "to skate" or "to go by sled, sleigh" would be good — if translations from any period were documented somewhere.

+Robert Reynolds that would actually make a lot of sense