Lio,
235/85R16s are only an inch larger in diameter than 31/10.50R16s and
-subjectively- are a little narrow for an 80 series. As Darrin mentioned
they do have the singular advantage of being similar in size to a 7.50x16
tyre so reputedly being easy to replace anywhere in Africa, if this is an
important consideration to you.
I ran 255/85R16 mud terrains on my 80 for three years and my impression was
that they suited the car well - no driveline problems at all and even the
early (90-92) brakes coped fine with the increased diameter (nominally just
over 33"). The stock Toyota driveline components appear to be easily up to
the task. Coincidentally these tyres put my speedo pretty much bang on when
checked against GPS.
I didn't notice any great difference in noise on tarmac between 265/75 BFG
AT's and the 255/85s though they did possibly make a small difference to the
handling. Whether this was because of size, tread pattern, or a combination
of the two, I don't know, but it certainly wasn't a problem - I'd go for the
255/85s again if I hadn't gone up to 35" tyres.
YMMV, but my experience is that you gain far more off road with an MT vs an
AT, than you lose on road. If you never encounter mud on your travels then
this may not hold true. Either way bigger diameter always helps off road,
bigger width generally doesn't.
Best of luck,
Toby
1990 HDJ80
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