The rims are 18x7.5, and my cousin said that 235/40 would be the best fits. What are decently prices brand names to buy and from where, which web sites are reliable to deal with and have good reputations to buy tires from?

Thanks for all the feedbacks.

 

The Tire Rack and Discount Tire Direct

 

I heard that 40's were too small for maximas, oh well, you be the judge.

 

Got to the TIRERACK.COM
It reaaly kinda depends on where you live.
Your ride will be harsher (but still ok)with such a low profile so you could go higher in profile to a 235/45.
Take it easy on the pot holes as to not dent those 18" rims.

 

235/40/18's are the correct tire size. EricGP has them, and you can't tell a difference in ride quality from my 17's. Plus, we live in OKC, which is rated in the top 5 for worst roads in the country.

 

I put 225/40/18 on my 18x7.5. No problems here. Someone I live with has 225/40/18 on 18x8. No problems there either.