Gearing for highway?

I know you can go up to a 16 on the front, I don't know how small on the rear. If I go dual sporting with my GS buddies, I need highway speed without blowing up. What's the tallest gearing sprocket on the rear one can get? Does chain length prevent the largest front and smallest rear sprocket? Why not just shorten the chain?

Thanks.

I am running 15t/45t set up at the moment, but feel I could still run 15/43 and pull to redline ok. 15/45 still feels ok for single track, with a bit of clutch abuse for real slow going...

15/48 was too short for my taste,
so I dug thu my collection of sprockets and came up with 15/42

don't know about stock
mine is mostly uncorked
and 15/42 is fine for pavement and forestry service roads

Its a compromise, but Ive got 15/46 on mine at the moment and pulls 170 km/h with a bit to go. Uncorked/ T4 pipe and rejetted.

Will probably change to 14/48 and keep the other sprockets and chain for when want to do a road trip...its an easy change anyway

HTH
Sean

I've put 15 & 49 on. Gearing-wise I also ride roads (gravel) & need to keep up with GS's, and even in technical stuff (no genuine footup trial work mind) it's fine.
However, pls note the odd choice - 15 and 49, odd numbers I mean. This will prohibit 'even' wear on the sprockets, obviously caused by the chain's links which are always the same per sprocket-tooth. Not with this setup, and therefore it will last quite a bit longer due to all teeth wearing same.

Plenty of go on the highways. cruising speed at 75mph.

forest roads in 1st and 2nd all day long.

i put a 108 chain on with 15/42.

if your doing any tight tracks then 15/43 would be better.