gas mileage decreased with new tires??

I have a 96 Honda Passport DX (manual) with 197,871 miles. I usually get 22mpg but sometimes close to 24mpg on the highway. I recently got my tires replaced and my gas mileage has dropped to about 19mpg (20 on a good day!). I have BFGoodrich Radial Long Trails (the same as I had before). The only difference in the tires is I now have P225/75R16 and I had P235/70R16 (I think it was 70) so that shouldn't be the cause. My muffler is somewhat detached and slides. I have a power steering fluid leak and a small oil leak (that's been there for 3+years). I recently got a new thermostat because my car was overheating on long trips (after 7 hours of driving) and it still runs a little hot but not much more than before. I keep the tire pressure the same as before (around 40, equal in all tires). I replaced my air filter recently. Any ideas on what could be causing the decreased gas mileage? Thanks for your help!

dont know much but i was having the same problem with my vehicle and turns out after a while the car starts to get old and tune up and oil chages are ue more often, so i did a full tune up and started pumping "good" gasoline and even added octane busters to help it, i also changed the transmision oil, and all spark plugs and wires, so i pretty much did a full tune up, and it help i went back up to 29 mpg

I've had an oil change since then and it hasn't seemed to help it. I'll try the better gas thing. I definitely need a tune up because I'm not sure if I've ever gotten one. lol. I guess 20 isn't bad considering it's 13 years old and some new SUVs don't even get that!!

Do a tune up, but most importantly check your tire pressure again, if theres a small bead leak you might be low.

check air filters, clean the intake manifolds, tune it up, better mileage for you bud

" I am too facing the same problem and I am quite disturbed". Yeah! I too think, the problem is in air filters and intake manifold.