Tyre width vs profile 18s

[shibby!]

Hello,

My tyres are pretty much dead, i have the contientals on, and lets face it... they are terrible!

So off to camskill to order up a set of pilot super sports!

However!!!

The question i have is regarding width vs profile!

Now the standard sizes are 225/45/18 and 255/40/18, however when i ran an M3, the chat was that we could run wider tyres no problems, ie 235 and 265, we have to reduce the sidewall side as the sidewall size is actually in proportion to the width and was not an absolute size.
I have done a few searches and found that people here were just upsizing the width to 235 and 265, but keeping the same sidewall profile the same. ie. 235/45/18 and 265/40/18.

So my question is, should i buy the 235/40/18 and 265/35/18 or stick with 235/45/18 and 255/40/18. I figured with the 45 and 40 profile on the upsized tyres there would be speedo over reading issues, and the tyre would actually be a little bigger (bigger profile)

Just a query, as the pilot spots seem to be a fairly good chunk of change cheaper on the upsized sizes, and should also be grippier!!

Or just stick to the OEM sizes?

Whats the story guys?

[The_Dude]

Try this link. Has helped me lots over the years when altering wheels and tyres.

http://www.1010tires.com/Tools/Tire-Size-Calculator

[mmm-five]

Staying with the same profile (i.e. 45/40) with slightly wider (i.e. 235/265) keeps the overall ratio closer to original than going for a lower profile (i.e. 40/35) with those same widths.

You'd have to go up an inch in diameter to make up for the difference in going to a 5% lower profile (as you do when you put CSLs on).

[shibby!]

Excellent. Decision made.

Nice link, I need to remember that one.