Wider tires on stock wheels
 

I have looked through tons of threads before deciding to post this questions to the fine folks here. I am looking to put some new rubber on the stock wheels and was looking to hear some input on the pros and cons of going to a wider tread in terms of handling characteristics, fitment, etc.

After looking at a lot of feedback between RS3's, Pilot Super Sports, Rivals, and ZII's I think I am leaning towards the Dunlops.

However, I an torn between tires widths. I have seen that the Dunlops have a naturally wider tread due to not tapering the way the stock Primacys do, but what about going wider? 225/45 17 or even 245/40 17 which is almost a full inch wider?

If I chose the 245/40 is there a problem installing them on a rim as narrow as the 7" stock? And, what does that do to sidewall deflection under load?

I am looking to get into AutoX and some track time this year (first time ever in my 44 years on this planet) and I am just looking for a little guidance.

Thanks in advance.

I've seen 225/45R17 Super Sports on the stock wheels. They fit very well. Not too beefy at all. They fit very nice and proper.

maybe @Racecomp Engineering or @CSG Mike can give you a good answer on this?

use 215. Any wider and you're gonna lose a lot of tire feel. 215 is the widest Z2 that is specified as being usable on a 7" rim.

Most 225/45-17 (ZII included) are OK on 7" - 8.5" http://www.tirerack.com/tires/tires....el=Direzza+ZII

I'd probably still go 215/45-17 though for reasons stated above, and also 2 lb. lighter, and the 225/45's are taller (slightly worse gearing, slightly higher c.g.). But could go either way. 245/40-17 definitely not a good idea...

Thanks for the great info guys. 215/45 it is. It is always good to get second and third opinions, especially from more seasoned users.

I have a 245/40/17 on the back of my car fits on the rim easily and looks very chunky.

fits in the guard easily too, since then i upgraded and have a 255/35/18 now still fits in the guard with plenty of room

I have 225/45/17 PSS on stock wheels and love them!

My winter tires are 225/45x17 on stock rims. They handle better than stock.

I think 225 is the right width for this car. Looks good and works better than stock 215.

Wider rim would make the tire a bit sharper in turn in and a bit harder riding.

17x7.5 is ideal wheel size. 17x8 will also work with 225 section.

Just by the by, 10 mm is about a third of an inch and that's nominal. Actual tire section is likely hardly different between 215 and 225. This 10 mm is divided between the inside and outside tread edges. 5 mm each....

not all 215 are made equal. You guys are not doing your research like the OP is. He is planning on running a tire that runs wide. His 215 Z2 is wider than a 225 winter tire or PSS.

Just because someone mounted it on a 7" wheel doesn't mean it FITS. Minimum wheel width for that tire is 8". Bad idea to spoon it onto a stock 7"...

How much of a difference in grip is there between a 215 and 225? Basically I'm trying to weigh if the overall grip outweighs the loss in steering feel.

Did a little research on Tire Rack on sizing:

(all XXX/45R17 sizing)

TIRE / SECT WIDTH / TREAD WIDTH
OEM Primacy / 8.4 / 7.5
MPSS 215 / 8.4 / 7.7
MPSS 225 / 8.9 / 8.2
RS3 215 / 8.4 / 7.9
RS3 225 / 8.9 / 8
ZII 215 / 8.4 / 8
ZII 225 / 8.9 / 8.2

Both on 7" wheels? Probably not as much difference as most people would think. Width does generally increase lateral grip, but not necessarily for the reasons most people assume. Contact patch area will be about the same for both, but the 225's will be a little wider and shorter. But this effect will be reduced a bit with both on the same 7" wheel.

Figure the improvement will almost certainly be less than the ratio of widths suggests, so less than 5%. Nothing you'd feel, and any improvement in laptimes from increase lateral grip will be offset to some degree by increased weight and slightly worse gearing from taller tires. Conceivable that 225/45-17 could be *slower*.