Jeffjett

How much wider is the 245 tire than the stock 225 tire? How wide can you go with the stick 8 inch wide rims?

Thanks.

Jeffjett

Sorry, ment stock 8 inch rim. :D

legokcen

The 245 is 20mm wider than stock. That's 0.7874 inches. I believe that's the widest recommended tire on an 8 inch wheel. If I'm wrong, please let me know. My next tires will be 245 40 18's. You should go a little narrower on the aspect ratio (45 to 40) to keep as accurate a speedo as possible.

I think someone on the list put wider AUTOCROSS tires on the stock rim. 255's I think.

Omicron

The 245s fit fine. Slight sidewall bulge, just enough to protect the rims from being "curbed" quite so easily.

RobDickinson

As said 245 is probably the widest recomended tyre.

Tyre width is in millimitres , 20mm is 2cm, 3cm is about an inch. Get metric sometime ...

One forum member autox's on 275 hoosiers on the stock rims.

f1michel

300 cm is a foot (just about) go from there and you will be almost correct.

legokcen

304.8 cm is a foot. I'm going to get flamed for this

RotorManiac

i disagree. i know 1 metre is about 3 feet so one foot is 30.48cm or 304.8mm!
cheers

ranger4277

WTF. 2.54 Cm per Inch. mmkay?

Twin 8s!

Here's a good page you can use to compare tire sizes.

http://www.bridgestone-usa.com/dpp/

Here's is a page that describes different terms for you.

http://www.tireguides.com/tip10.html


In comparing the Bridgestone 225/45/18 to the 245/40/18 I note that the 245 is .3 inches smaller in circumference. This means that the car speedometer will read faster than it is really going. Also, the odometer will be farther off than already noted.

Jeffjett

Thanks Twin 8's, and to all. I am thinking of going with 245 45 18's. I know they are larger in diameter than the stock wheels, and will affect the speedo, et.al., but I would like slightly higher gearing when on the freeway, and larger diameter tires will help a little.

What do you think?

Rotary Nut

245's fit just fine

These are 245/40WR18 Sumitomo HTR+ Ultra high performance all season radials I mounted last winter.

I think they fit better than stock.

RotorManiac

I can assume you have 245/40 in the front too, right?
So how do you find steering? Isn't 245 too much? Notice any differences from stock?

DjGO

nah i have Bf Goodridge G force KDW2 245 40 they are amazing. Turning responce, handling, road noise everything is great. The only bad thing is that ..............oh wait nothin is bad .

Jeffjett

Anybody use 245 45's?

Thanks.

Rotary Nut

Yes I amd running the same size at all four corners. No rubbing steering is actually better due to the greater width and there is less noise and harshness in these tires than stock. Plus the treadwear ia 360 with AA temp rating. much better than stock.

RotorManiac

sorry, but i don't know what the treadwear is so i can't understand this phrase of yours... can you explain it to me please?

Rotary Nut

Check this site:

UTQG ratings

RotorManiac

cool, thanks

Katchoo

Good discussion. My question is this: Does the change in size affect any of the other gizmos that the car has like traction control, etc.?

I am planning on going with the Pirelli PZero Nero M&S 245/40R18 on stock rims. I don't think the diameter size difference between the two tires would be a problem (Bridgestone: Diameter - 25.9" Rev per mile - 804...Pirelli: Diameter - 25.7" Rev per mile - 810) but ya never know!

shelleys_man_06

Putting a larger tire is going to affect the performance of the car. The contact patch is wider on a 245 than a 225; you may or may not have better acceleration. It depends on how much power you are putting to the wheels. IMO, it's important to match tire sizes with how much power you are making, well at least for street purposes. Since your tires are the only thing touching the ground, it's best to choose the right one. If you, for example, put a 335 tire with the stock horsepower (238), you may actually accelerate slower than stock. Mounting a skinny tire, such as a 195, will create significant traction problems; there's not much tire the surface can grab onto compared to the 225. 245 is actually fine, though. As for the tire changes affecting your TCS, DSC, etc., I'm sure the PCM wouldn't even notice. If the difference is 20mm v. stock, then your electronics shouldn't be compromised. Katchoo, did you need a wheel spacer to fit the 245?

Sputnik

As for simple ABS and TCS, they don't sense grip levels, they sense wheel spin. Even with stock tires, there is a huge difference in grip levels between a dry and wet surface, and the ABS/TCS systems don't really care what the grip level is, only if there is spin. So they should be unaffected. Even with a staggered setup, the ABS will probably not be able to adjust so that you have balanced braking, but it will operate.

As far as DSC, those systems vary greatly between cars. But again, for the RX8, the DSC doesn't care about grip levels, it cares about roll, pitch, and yaw. And so it to should work fine with just wider tires. With a staggered setup, it might not be as effective, but it will still work.

---jps

PUR NRG

Keep in mind that a 245/40-18 tire has a different contact patch based on what width rim it's mounted on. So the same tire on an 8" rim isn't as wide as if it's on an 8.5" rim. Check TireRack's technical articles for more in-depth explanation of all this.
________
black Cam

Katchoo

I have not yet gotten the tires but from what I have gathered from other postings in this forum a wheel spacer is not required and the 245's fit just fine with no clearance problems.

According to the Pirelli website, the 245 will fit on the stock 8" rim, but that is the narrowest rim recommended.

I don't think the tire diameter difference (and roll-out) are that much different than stock so I don't anticipate much affect on my overall performance. I actually drive the car pretty subdued compared to the rest of you I think.

shelleys_man_06

Are you implying I'm an insane driver :D?