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After putting the 235's on my sportage, I have dropped to about 20-21 mpg instead of the 24 I was getting before. At miata.net there is a tire calculater that says your speedo is now 6.5% too slow. When your speedo says 60mph, you are actually going 63.9mph. Also, check your tire pressure. It will make more difference on the bigger tires. The tire shop put my tires @32psi, but the max psi is 50. I run them at about 46-48 and I can feel the difference, besides at the pump. The ride is a little rougher, but I drive a 50 mile commute, so less rolling resistance, the better.


You will find that your speedo was already slow to begin with. adding the 235's brings it up to about right (+/- 2 or 3%).

Check the sidewall of the tire for the maximum inflation pressure and subtract 5 psi from that as your max inflation pressure.

Over inflating is poor economics anyway as the center of the tread wears out much quicker making replacement of all 4 tires more frequent (within 20K miles from new depending on the tire)


2002 Sporty , Ironman 2.5" spring, 2" body, 15 x 7 ROH wheels, K&N, 15 x 10.5 Simex Centipedes, Powerchip 91.

"Never argue with an idiot. They will bring you down to their level then beat you with experience!"