Tire sizing...

[ValveFloat]

For A4 VW, the OD (Outer diameter) of the tire is about 25"
So: for 18 inch wheel, 225-40-18, OD = 25.1"
17 inch wheel, I think stock size is 225-45-17, OD = 24.97"
For winter tires I run 205-50-17, OD = 25.1"
For autocross I have 245-40-17, OD = 24.7" (on an 8" wheel)
More:
235-45-17 = 25.3"
235-40-17 = 24.4"
235-40-18 = 25.4"
235-35-18 = 24.5"

[Mikewire]

I like this site to give a visual and some numbers to compare tire sizes:

http://www.miata.net/garage/tirecalc.html

Stock steelies are 195/65/15 and I run my summer setup 225/40/18 and there is a little variation in diameter, but not enough to cause problems.

The last set of tires I bought are 205/65/15 which are considered "+1" because they are one size bigger in diameter than stock. If you want to get a "bigger" tire then you want to do a +1 or +2.

Wade, Any reason you want to go with a bigger tire?

[Mill3niumThr33]

I have been looking at the KDW2's which have both sizes I am looking at which were 225/45/17 and 235/40/17 . They are priced pretty well at 145 a pop. They are ranked 5th on the Ultra high performance summers and have good treadwear, great dry and really good wet traction. My roomate has had a set on both of his cars and they both lasted long and faired well.

As far as the larger size goes, a little more rubber on the road and....well i just like the wider tire look . I really hate the stretched look and am sick of running around with undersized tires .

[Mikewire]

Cool - refresh my memory on what wheels you are running these on.

[Mill3niumThr33]

Mille Milgia Spiders 17 x 7.5 . I would like to get a new set and have been looking to get a set of 18x8 or 18x8.5 OZ Ultraleggeras down the road but for now I will stick with the Mille Miligas.

[Roadhog]

Im confused.. Did a post get deleted?

[Mikewire]

Spence... nah -- Joe moved this from the shoutbox to a thread. I kinda threadjacked this to ask Wade a question.

Well, Wade I don't think you would visually notice much of a size difference between a 225 vs. a 235, or even a 245. They would be taller, but not wider. I don't think a bigger tire would handle any better either, but I could be wrong. If you want a wider tire then you need to go with a wider wheel, or go with a set of spacers to give it a wider stance.

Unless I am misunderstanding what you are looking for I think the best looking and handling option on a 7.5" width wheel would to be go with the 225/45, which would match stock diameter.

[Mill3niumThr33]

See thats why I ask questions before I go buy the entirely wrong set of tires . So the general consensus is 225/45/17 or 235/40/17?

[ValveFloat]

The width difference between a 225 and a 245 is noticable, and I believe the grip difference is also. I went from 225-40-18s on my stock 18x7.5 to 245-40-17s on a 17x8, so .5" wider wheel, .75" wider tire, same tire brand and model, and the difference is noticable.

So the general consensus is 225/45/17 or 235/40/17?

I would say so, yea.

[Mikewire]

So, educate me a little Joe - how noticeable are the size differences in a 7.5" wheel? The difference between a 225 and a 235 is .3" and comparatively to a 245 is .6" which I would say is negligible - esp because that's in diameter a.k.a sidewall height. Is there a grip difference too - like is there more rubber on the road because of the increase in diameter? Is there a minor increase in width too?

Not being a smarta$$ at all, I really would like to know if there is a difference - you have swapped out more set of wheels and tires than I have, so I am leeching your experience .
I try to visualize the stuff in my head, but sometimes I can't wrap my head around the concept.

I can tell a major difference between my 7.5" stockers and 8" alloys in traction, which I attribute to .5" gain in width.