Question about bigget A/T tires

[kopfjaegger]

Hi all,

I looked around to see if there was a post that answered this question, but found all kinds of different answers and got a bit confused so I'll just go ahead and ask:

I came accross a set of A/T 275/65R18's for free, no rims. They were used for like 6 months. My 70 Chevy K20 uses 16's and it needs tires. I left the suspension alone but installed a 3 inch body lift. I may do a suspension lift in the future, but I'm leaving it alone for now.

I came accross a $200 set of Pro Comp Xtreme rims that would fit the truck and tires. My question is; is there a drawback to switching to a bigger tire like that in terms of safety, fuel consumption, and the like? How hard or easy is it to alter the speedometer to give a true reading?

I mocked the tires on and they seem to clear all around so that is not a concern. Are there any other concerns I should look at? I know that 18's will be more expensive as far as replacement costs. The tires are just collecting dust in my garage and I would like to use them if it is beneficial. If not, I need to get rid of them before they rot in place. The truck will be used as a working truck with occasional use for light off road type applications, and maybe a highway trip here and there... not mudding or rockcrawling. I'll still have the 16 in rims, so I can go back to that size tire if necessary, but I would like to know the pros and cons.

I think I covered everything, any help anyone can give will be much appreciated.

Thank you in advance.

K