Some corrections from the start: you cannot fit a 120/80 or 90 without serious mod to the fender.
A 110/80 might fit, but I haven't found any model in 17".
You may live in flat land, and not have gnarly roads, but there is mud everywhere.
This below is not my experience but only my research as of today:
-TKC80 sucks for mileage (rear) and vibration (front). Not on the list at all for me.
-Shinko 805 (rear) (not 705! it's no typo) beats TKC80 in all but 1 aspect: it may slide a bit sideways.
-I have the k60 scout 150/70. I have not had any issue with the hydroplanning, but albeit the mileage, it squares and it has no grip to climb/brake unless you are leaning. It may be a bit useful in very soft terrain like mud of sand if the damn strip can be less of a factor. I don't like mine anymore.
-I have the heidenau k73 in front. Fair in packed dirt. Sucks big time on steel bridges and meaningless in mud (too small threads).
-If it wasn't from wanting more mud/sand grip, I would go for the mitas e-07 (rear). rounder, silent and good mileage.
-I will get a 150/70 Metzeller karoo3. it is like shinko 805 but even better mileage.
-I will get a shinko 705 as 120/70 front. It has a fair side grip judging by the threads shape. It is the only choice for front (I wouldn't bother with the pirelli MT60, I cannot get it and it's not getting good reviews.)
Last edited by dddd; 02-06-2017 at 06:40 PM.