Will it work?

Hey moose, have a look at your tubes. My spare tubes are printed with the tyre sizes which are acceptable.

The internal "circumference" of the 285/75 cross section is only about 5% bigger than that of the 275/70. I think I'd use the tubes in an emergency, but not for general use.

Cheers

John

I was exactly in the same dilemma a couple of years ago.
Went to buy a bigger tube at a tyre shop owned by a friend and he said my current tubes can easily be used for the bigger size - they expand a fair bit.

So I do what you are proposing and taking a 275/70 tube as spares for my 285's.

Cheers
Phil

Moose,
As said the size should be ok but check that they are in good condition. I always blow them up before a big trip and the last time I found they showed cracking at the creases when at pressure . They were 3 years old and according to the tyre place I buy from they find this is common with some of the cheaper tubes that are around. Make sure they are stored out of the sunlight. They advised that the Michelin tubes are the best available but often hard to get in certain sizes.

I always carry an old tube as well so if I get a bad cut I can put a piece inside as a sleeve. Only had to do it once in 40 years but I often use bits for other purposes anyway so like fencing wire it is just good to have stuffed into one of those little nooks.

cheers