Grip level of 245 versus 225?
 

Now I know 245s offer more grip than 225s, but does anyone know about how much? Though the 245s are close to 10% wider, I suspect they won't offer 10% more grip as tire and grip doesn't scale like that since the contact patch area doesn't change; the extra grip is from the lower slip angles generated by the 245s. Thanks.

I suspect that the brand one choses will have a much larger impact that the small change in width.
Another part of the equation is the steering response because a 245-40 on an 8" rim won't respond to steering input like a 225-45 on an 8" rim.

A bigger contact patch will always be better, but to calculate, I'm not sure. I'm running 245's currently on stocker rims.

That's not true at all, if you are running a tire that's is too big for the wheel then you will have very sloppy steering feel and response. That's why you see many people running a 235 race tire on a 9" wheel for the best results.

245s are the correct tire size for the car on 8'' rim IMHO.

Would steering feel really be affected by moving from 225 to 245 on the OEM wheels? I'm primarly concerned with the handling differences. It seems that most people are switching to 245s, but I have heard little about tracking experiences from these people. I have a feeling Mazda choose 225 for a reason...

I'm looking at new tires and can't finalize my decision.

FS

would they also choose a 225 tire with a 140 treadware rating and wears out after 20k so you have to buy another set from the dealer really quickly.

Yeah they do things for a reason, but its not always reasons to benefit the consumer.

Sadly, many people just throw away their money.

I'm looking at the 615s, but can't decide what size. This is my compromise for now until I get ahold of another set of rims.

FS

my plan is to get 615s in a 245 width.. but not for a few months. Seems like the wider tire will at least look nicer. I am hoping that the handling feel will only improve over OEM.

I'd bet nobody would be able to exercise the 'more' grip a 255 gives over a 245 (within tire brand) on any road.

He's comparing against 225, a tad more substantial.

245/40 615s on for 10k. I'm getting great wear and the ride is awesome! The only thing I hear on the highway is wind noise. With the stockers, I could feel the tires melt and whither when I hit the boost. Now I just goeeeeeeeeees!

Righto - even still - 20MM? What's that? Less than 1" at each tire?

In absolute terms yes, less than 1". However, that's about 10% and if someone told you your grip can increase from 0.9 gs to 1.0 gs, I'm sure you can feel it. The question is, since grip doesn't increase like that, how much of a quantative increase are we really looking at?

personally, i think switching to a sticker compound tire will have more effect on grip than putting on wider tires of the same brand/model/type

the obvious answer is if its the same tire then wider will offer more grip, if it's a different tire its hard to compare.

Too a point for instance alot of B-stock auto x guys run the kuhmo v710 in 245 not 285 because at 285 on a 8'' rim you have issue with sidewall flex etc.....

I wouldn't do any more than 245 on a 8'' rim, and at that 245 is pretty much the perfect fit.

In my original statement i meant stock rims. I agree with your statement, 245 is a perfect fit for the stockers.

But calculating the actual tire size, 255/40/18 is much closer to the stock diameter than 245.
On the other hand, I'm really not sure if 255 on the stock rims is a good idea or if it won't rub etc.

i still think 9" wide wheels would be better suited for 245 tires. even with the well-known stiff sidewalls of the RT615, when i had them in 245 width i still felt it was a bit more squishy than stock width of the Dunlop, and now that I'm back in a set of 225's, my feelings are verified, 225 on stock 8" rims give you sharper steering feedback, even with tires with a softer sidewall

what tires are you running at 225 on stock rims?

it's not much closer, it's barely closer. 245/40/18 is 1.0% off, 255 is 0.2% off. 1.0% off is pretty minor.

Thanks ZoomZoomH, that's the closest thing to what I wanted so far. I'm well aware that tire compounds have a lot to do with grip, but my query is on similar tires, what is the quantative (not relative) effect of switching to 245s.

Falken FK452 225/45/18 on stock rims

i shall have report back for these tires on the track in couple weeks :)

but for now, let me just say, these bad boys are quiet! and for 'street driving' they are gripping just fine :D:

is the sharpness of feedback any different?

I love grip, but above all, I love sharp feedback...