I want wider tires and wheels but want to stay with 17". Does anyone know how wide of a tire will fit under a stock CT and what size wheel I would need?

 

You should be able to do 17x8.5 +35 to +40 all day long with tires as wide as 235. Hit up Jason from GetYourWheels on this forum as they have done a lot of CT's in the past including mine.

 

My current setup is...

Wheels: 5-100 17x7.5 +42 72.6mm>54.1mm
Weight: 16.4lbs.
Tires: Michelin Pilot Sport A/S 3 Ultra High Performance All-Season
Size: 225/45ZR17 91Y

On the next set of tires I plan to go 235/45-17 primarily so I correct the speedometer to match GPS units. If you ever did a test on stock tires you'll see that you are easily off by at least 4-5 MPH when cruising at 80. With my existing set of tires, I think I am still off by 1-2 MPH.

//Rant ON
From personal experience, Lexus (as well as Acura) is very conservative in MPH readings as well as estimated gallons left in the tank (aka they think the driver is dumb and will lie to you). With my other car (Mercedes), the speedometer matches my GPS units EXACTLY as well as correctly representing the gas gauge in that 1 tick = 1 gallon. In this scenario, if they tell you, "you are out of gas", by turning on the low gas light they mean it!
//Rant OFF

 

Thanks, but not sure what the +35 +40 after the wheel size designates.
Also, a 245/40 is the same diam. as a 215/45. Will the 245/40 fit?

 

...looks like you need to do a bit more homework before blindly asking.
http://www.discounttire.com/dtcs/infoWheelSize.do

...on what wheel? Besides, if you carefully read my post above, you'd find that you don't actually want to stay with the stock diameter size.

 

Wow, harsh. Thought this was a friendly forum.

I have not chosen a wheel, I thought I would start with finding the widest 17" tire that will fit under my car.

And I do want to stay with the same diameter, as my speedometer is accurate.

 

This may help you - http://www.discounttire.com/dtcs/infoTireMath.do