I'm ok with 17"s, but imo they look just a bit small on a such large car. The 18's look much nicer, but need taller tires than the OEM 225/45/18.
When it's time to replace tires, I would go with the tallest overall tires/wheels I can fit. Some say that 225/55/18 (which is almost 20 mm taller!!!) fits with no issues and if so, I'd go 235/55/17.

 

When it's time to replace tires, I would go with the tallest overall tires/wheels I can fit. Some say that 225/55/18 (which is almost 20 mm taller!!!) fits with no issues and if so, I'd go 235/55/17.

Based on all the tire brand/size input provided by this forum over the years my next set will be Pirelli P7 in 225/50/18. The tire has been reported to handle very well in wet and dry, it's quiet, apparently rides marginally softer than OEM tires and that size corrects our (18" wheel, I don't know about the 17s) speedometer error within about half a percent ending the constant math conversion while driving. When it comes to tires I'll go with function over form every time.

Cheers!

 

(anyone motocrossed their Avalon lately?)

Cheers

Not exactly but I drive very curvy roads regularly and did notice a difference between the 17" and 18" tires on the Avalon when test driving. The extra sidewall makes a big difference in the amount of wallow you get going through the curves. My Av with the 18's handles pretty good relative to the type of car it is...large and FWD. I wouldn't want to give up anything in that department on the roads I frequent.