What tire size is recommended for better grip? I have the stock 18" rims with 225/45 right now, I remember seeing a post before recommending sizes but can't seem to find it; tried the search and came up with a lot of nothing.

 

245/40x18 will fit on the stock wheel. The diameter is about the same, so your speedometer will still be correct.

 

I run 245/40-18 Eagle GT's and my speedo is optimistic by 4%
They fit easily with a lot of room to spare.

 

Same size have good grip anyway.

 

Got it, thanks!

 

Actually, monchie is mostly right. On the track, I found the standard size to be just as fast. Your not gaining that much section width with the plus size tire. For everyday driving, you are increasing your rolling resistance which will reduce your gas mileage. I have found speedometer to read 4% high with the standard tire size. This was measured by radar and gps.
Other than for looks, there isn't any point to do it on a street car.

 

^

 

225-->245 is a modest increase, but overall I find that the wider the tire is, the more unpleasant to drive on the street. As the contact patch gets wider and shorter, road imperfections tend to steer the car around more and hydroplaning gets worse. Cornering power may be better at the limits with a "race" alignment, but that will take a toll on tire life for everyday driving. MPG's will likely suffer; it's no accident that hybrids use rather prosaic narrow tire sizes like the P195/65R15 on the Prius.

 

Eh...I disagree with above statement. Hybrids use a narrower tire for less friction against the road and less rotating weight, thus better mpg, not because of a more pleasant drive. A wider tire will IMO and experience give better grip, better traction, better driving experience contrast to a narrow tire. You have more contact patch to absorb the imperfections of the road, the less the more prone it is to sending that "feedback" directly to the suspension and thus your buttocks.

If one wants to argue MPG sufferings with a wider tire well, buy set and try them. I actually got slightly better overall MPG with my 255's running more negative camber than the OEM setup on 225's and both are virtually the same circumference and both tire/wheel setup weigh the same. I will say if you do run more of a "race alignment" tire life will "some", to what extent it depends on multiple factors but from what I've experienced that's about the brute of it.

 

@vlaze: I was making 2 seperate points. A common misconception is that a wide tire has a bigger contact patch then a narrow one. For a given air pressure and with slight variations due to sidewall stiffness, rubber compound, etc, the area of the patch is essentially the same. Your observation that the wider tire with more negative camber got better mpg is consistent with the "narrow tire" hypothesis; by tilting the tire, one lifts the outer edge causing the contact patch to get narrower and longer on the inner edge. This will also keep the tread of the outside tires flatter during hard cornering, aiding handling, but potentially not a plus for tire life. Energy-saver tires do not reduce rolling resistance so much by reducing friction with road surface as by reducing the deformation the tire undergoes as it rolls (which may have the undesirable result of reducing adhesion to the road via harder compounding.) The narrower tire also has less air resistence. The fact that a narrow tire is more resistant to hydroplaning is well established (and is what largely determines the shape of aircraft tires). Generally, there's agreement as well that snow tires should be narrow. "In my exerience" is in my experience which may vary from yours. In general, by fave cruising cars were older Audi's and Benzes with their older style tires. I find the wider the tire, the "busier" the steering wheel gets over rough surfaces. Additionally, the wide tires come increasingly with bigger, heavier wheels, lower aspect ratios, harsher ride, and much higher replacement costs. The gains come with braking and cornering on dry, clean surfaces. While I have no desire to go back to P195/75x14, the wide low tire trend, IMHO, has gone rather too far. YMMV.