currently have 245 40 20 tires on my awd ls 460 , anyone see any issues with going to 245 45 20 ? got an insane deal on a new set of 245 45 20 and feel like they may feel a bit softer than the 40 series

 

I believe the change in aspect ratio will change the accuracy of the speedometer. I imagine it can be adjusted with Techstream or at the dealer.

 

Well the only issue is with the new tires when your speedometer reads 60 mph, you will actually be going 62.2 mph. You can use this handy calculator - https://tiresize.com/calculator/

I would be curious if this could be adjusted by Techstream or a dealer.

 

No, not possible. Only approved sizes are 235/50/R18 and 245/45/R19 (which calculate to same outer circumference and diameter). Those are hardcoded into everything. I don't think 2mph discrepancy is going to affect anything (I'm sure there's wear tolerances etc), but everything beyond that is uncharted territory.

 

Good to know the speedo can't be adjusted. I wouldn't let a small inaccuracy stop me from a good deal on tires either.

 

I agree, the slight inaccuracy wouldn't deter me. For many years my wife drove an Infiniti J30t and then later a Jaguar S-Type, both rear wheel drive cars. So I always got snow tires mounted on a separate set of wheels. Using that tire calculator I always got one or two narrower size widths in order to improve traction and yet keep the diameter as close as stock as possible. For tens of thousands of miles on both cars there was never a problem.