225/45/18 versus 245/40/18
 

For my next tire change. Thinking about this size. While going up in width (245 versus 225) will make tire larger, by reducing aspect ratio (40 versus 45 ) size will add width without diameter. Not compromising wheel well.

Tire Size Comparison Calculator


Size 1
225 / 45R 18

Size 2
245 / 40R 18

Compare

Size 1 Size 2

Diameter 26" to 25.7" A -1.2% reduction.

Width 8.9" versus 9.6" A +7.9% gain

Sidewall 4" versus 3.9" A -2.5% reduction

Circumference. 81.6" versus 80.7" A -1.2% reduction.

Revs/Mile 777 versus 785 A +1.2% increase


Because adding width (245 versus 225) while keeping the stock aspect ratio (45) would render tire too big.


Tire Size Comparison Calculator

Size 1

225 / 45R 18

Size 2

245 / 45R 18

Compare

Size 1 Size 2

Diameter 26" versus 26.7" A +2.7% gain

Width 8.9" versus 9.6" A +7.9% gain

Sidewall 4" versus 4.3" A +7.5% gain

Circumference. 81.6" versus 83.8" A +2.7% gain

Revs / Mile 777 versus 756 A -2.7% reduction.

Anyone tried this 245/40/18 on stock wheels ?

I run the 19" equivalent (245/35/19) on my R3, and I really like them. They grip well, look great, and protect the wheels better than 225s. My steering feels maybe a tiny bit less nimble, but I think that's due more to the characteristics of the exact tire I chose (Pole Positions -- they're heavy tires) and less to do with the 245 width.

Hi.

Seems like a good choice.

In the case of the 18's. Same added width is achieved with 245/45 and 245/40

But the 40 aspect ratio keeps sidewall and circumference almost identical, negligible difference.

The 45 aspect ratio adds too much sidewall and hence circumference which could cause problems.

Definitely will change to these 245/40/18 soon.

alot of us use that size

search bar and google are your friend
https://www.rx8club.com/series-i-whe...-flush-195496/

I run that size on my stock rims. Works perfectly, protects the rim from curb rash, speedometer reads correctly. No issues at all with it.

OK. About to order a set. Any brands prefered ?

Factory tires are Bridgestone Potenza RE040. Seems those are flat run tires.

Expensive tires. I think I am not getting flat run tires.

Saw Bridgestone Potenza S04.

Any suggestions ?

One of my tires is in very good shape ...( last one I changed, my tire got a hole on sidewall and it was not reparable Will get an extra factory wheel and use it as spare. )

Pole Position S-04s come pretty highly recommended here and on tirerack. I'm happy with mine, though I'm only about 1,300 miles into them. I plan to autocross and do a track day next year, but I've only driven on the street so far. They're definitely a step up from the run-flat all-season stock rubber, but I can't speak first-hand about how they compare to the Continental DW or Michelin Pilot Super Sport.

According to tire rack, the Michelin is a little better, but much more expensive, and probably not worth the additional cost. The S-04 and the DW are neck and neck with the S-04 having slightly better feel and response, and the DW having slightly better maximum grip (if I remember correctly). The S-04 and the DW are, at least on tirerack, the clear leaders in their category and price point. You probably can't go wrong with either one.

Cool.

Just ordered 4 Bridgestone Potenza Pole Position S04. 245/40/18

Tire Rack. As soon as I get them will get them installed.

Now I need to get a spare wheel. The only tire in good shape (from my current set) will become my spare. Spent some big bucks on this tire set. If anyone has a spare wheel, let me know.

Today tires arrived from Tire Rack.
https://cimg7.ibsrv.net/gimg/www.rx8...8fbd61e5fc.jpg

https://cimg8.ibsrv.net/gimg/www.rx8...4b3108597c.jpg

sex

Installed !

Feels very stable. Nimble. Softer as well.

New tires.
https://cimg3.ibsrv.net/gimg/www.rx8...ccb30c0c05.jpg

https://cimg4.ibsrv.net/gimg/www.rx8...a7dadce774.jpg