255/35/19 vs 245/40/18 for OEM sizes - why not 255/40/18?

[samps]

I did a search for this but couldn't find what I was looking for. Having said that, maybe this already exists and has been discussed?

My S-Line Competition package came with 245/40/18. I wanted the 19's that came with 255/35/19 but whatever...

I'm wondering why the 18" size isn't 255/40/18? This matches more closely with 255/35/19. Or by that same token why aren't the 19" 245/35/19?

Seems odd the tire sizes don't match with respect to circumference.

This also leads me to question whether there is a VCDS setting to specify which tire diameter you have?

Any insights?

[JDillon15]

Coming form the B7 section, so forgive me with model specifics.

are your 18's 8.5" or 8" width? IMO, 255 on a 8" wheel is pretty wide (quite a bit of shoulder).

Also, I've never heard of VCDS telling your car a wheel size. I'm pretty sure your car doesn't care WHAT the circumference is as long as the circumference on all 4 wheels is +/- 3% or EACHOTHER (IIRC)

Really, you can do pretty much whatever you want (within reason) in terms of tires. willtheyfit.com is a good resource to check sizes as well.

[samps]

^ forgot about the wheel width. Mine are 8" which explains the 245. However, this still doesn't explain why Audi didn't match the different tire size options in terms of circumference. I still find that odd.

255/35/19 = 255/40/18
245/35/19 = 245/40/18

I know it likely doesn't matter I'm more curious than anything.

[oshwi]

Im pretty sure the stock 19's are x8.5 thats why they can run 255 on 19's