Recently my dislike for my low profile tires made me at least try to go from 40 to 45. Other drivers have done it and said it made a difference. I can attest that it made a difference and I like them. I went with Michelin Cross Climate 2 tires. They look different but the drive very nice and because I am into function over form these days, I'm good with it.

My question is this, going up a bit on the sidewall makes a bit of a larger diameter, do I need to get the computer updated so my speedometer / odometer is correct?

 

you didn't metion which size wheel (I'm assuming 18s as the 235/40-18 is a common size) but you can use a site like Tire Rack or wheel-size.com to see the diameter or revs per mile to compare. going up one size is generally around a 2-3% difference so figure your Speedo will read 1 to 1.5 mph slower at 60 mph with the taller tires. That would also influence your miles (ie drive 100 miles will indicate 98 on the odometer). To note, most cars don't read the exact road speed - most read slightly higher than true (except my VW which indicates 70 when the GPS says I'm doing 65...). I never bothered to ask if the dealer could recalibrate or not.

 

Ooops I forgot but yes 18 inch wheels.

Last spring I was considering going to a smaller wheel and larger tire (wife's Peripheral neuropathy pain doesn't like low profile). I called a dealer and it was around $100 to do the computer update for new wheels.

 

Going from 235/40/18 to 235/45/18
If my speedometer reads 65 MPH I am going about 67.4 mph.
https://www.discounttire.com/learn/tire-size-calculator

Called my local dealer and said I have gone up in tire diameter, just a bit, do you think I should get the computer adjusted. Their response was, "we only have software to upgrade if you change the wheel size."


QUOTE=mt6127;532249]you didn't metion which size wheel (I'm assuming 18s as the 235/40-18 is a common size) but you can use a site like Tire Rack or wheel-size.com to see the diameter or revs per mile to compare. going up one size is generally around a 2-3% difference so figure your Speedo will read 1 to 1.5 mph slower at 60 mph with the taller tires. That would also influence your miles (ie drive 100 miles will indicate 98 on the odometer). To note, most cars don't read the exact road speed - most read slightly higher than true (except my VW which indicates 70 when the GPS says I'm doing 65...). I never bothered to ask if the dealer could recalibrate or not.[/QUOTE]