i am looking at that i am unsure of is a set of TRD 18" wheels and tires. my questions are, how do they affect the tire pressure sensor, will they still work ? what about the speedo, will it still read accurately ?probably my biggest question is, with these wheels, being a toyota product, will they affect my factory and extended warranties, as well as my service contract ?

I understand the BBS are what Toyota is installing on some of the TCH's at the port. However if the BBS wheels you are looking at are an older model wheel than they are currently installing then you may have a problem with the valve leaking on the TPMS. A good wheel installer should be able to look at that and tell you.

There is a current thread hrer with two links to a tire size calculator. Wheel dealers should also do this but I would want to know before I approached them as they will sell you what they have and say it's only off a little. A 205/50R18 will give you the closest accuracy, but it's a tad more narrow (good for rain?) I'd probably go with the 215/50R18 as it is only off from the OEM by 1.75mph at 65 and from what we've all found our TCH is off by 1.5 mph at that speed so what you have is a "more accurate" reading than the stock OEM tire.

I don't see where tires / wheels would affect the warranty UNLESS you went LARGE and caused premature wearing of parts that you wanted replaced. Since the dealers are installing 18" TRD BBS wheels as an option I would feel comfortable with that size.