235 70's were offered as an option on the blazer. when i bought my blazer it had 235 70's on it. it will change your speedometer but only by 1.9 mph. http://www.1010tires.com/TireSizeCal...?action=submit

 

How does swapping tires affect braking? And typically how much does it cost to have your speedo / etc recalibrated for new tires?
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I thought I ansewered the braking question. Depends on how you drive. In most cases the tire change mentioned in this thread wont have any noticeable effect on braking.

How do you get it recalibrated? Go to the dealer, call them and ask. Around here its .7 of an hour labor rate, about $60. Or you could by a programmer for $350 and do it yourself.