Can I get comfort out of 235/40/18's ..... or should I go with the 225/50/17's..... any other suggestions .....

 

just to be safe, go with the 225 tire.. better for gas mileage, and wont screw around with your speedo either.

 

Of course 17" will give you a smoother ride.

 

How wide should the rims be for the 225's? Or should we go to 235's? ( does it make a difference)

 

With the same tire model, the lower the tire profile (sidewall thickness), the rougher the ride.

Wider and/or lower profile tires also need wider width rims. First pick a tire brand and model, then go to Tirerack's individual brand page and look at the tire specs. There you'll find the minimum rim width recommended by the respective tire manufacturer for the particular tire size.

 

225s will fit inside the fenders on a gen2 TL
235 will require cutting a plastic tab in the fenderwell, and if dropped much, some massaging of the fender lip-edge profile will be in order~

On my 2001 TL 18x8 inch wide rims 235-40-18 General Exclaims and Tein SS drop 1.75 inches, the ride and handling is great, the wife enjoys the ride and the tires are way better than the OE mickyslips In My Opinion

tirerack has a conversion page for speedo differance
Going from stock 16s to this setup was a very small rotational distance change, actually it cured the 2mph fast reading at 70