[SirKeats]

So I have my Metro's for commuting and they're great. This question isn't about them. It's about my beast of a truck I use for camping, towing, etc.

I'm thinking getting a slightly wider tire and am trying to find something that will tell me how much it will affect my fuel economy. It's already bad enough in the truck, I'd like to impact it as little as possible since it's our only truely reliable rig for long-distance travel (the geo's are just for in-town commuting).

Anyway, I'm thinking of jumping from 245/75R17's to 265/70R17's... so the diameter will be the same but the width would be about .5" more.

Any thoughts on how great an impact this would have on fuel economy?