phatboyc

When my tires are up I’ll be looking to get wider tires up front. Don’t like the look of the side wall going in instead of a nice 90 degree like the back. The tire looks like it's to small for the rim. Also it might help in cornering grip. Perhaps 235/40/18? It's only .2 inches higher vs stock. What do you think? Also could it mess with the VDIM sensors since they where not calibrated for this setup?

al503

I don't think you'll have any issues. There are guys using rear tires that have a smaller overall diameter than the fronts and they're claiming no issues.

Losing .2 or .3" of the front to rear overall diameter stagger will be fine.

flipside909

The wider the tires you put in the front, the larger your turning radius increases.

al503

Can you explain? I'm trying to figure this out by imagining why a tire the width of a bicycle tire would decrease the turning radius compared to a 'normal' sized tire barring any slip/traction issues.

Payam

I was actually thinking of getting some wider tires up front as well. The stock setup looks way to stretched out to me.
Even if you lose a little bit of turning radius which wouldn't be much at all, I think you'll be ok. The turning radius is phenominal on this car.

jezza

As long as you don't go so big in front that you're rubbing, you're not going to lose any appreciable amount of steering lock. You will probably notice a heavier steering effort though, which may not be a bad thing in the IS.

I think I'll probably go to at least a 235 in front... more grip up front would be a good thing for this car.

4TehNguyen

iTrader: (1)

by increasing the traction of the front relative to the back you are inducing more oversteer (probably not that much of an increase)

al503

It may be more correct to characterize this as reducing the understeer. Going 10mm wider will make a difference but I doubt it will make the IS even close to neutral let alone oversteer.

ff_

More correctly stated: in regards to the IS, you're reducing the gross amount of understeer. You don't induce oversteer until you have more traction in front, which the IS is nowhere close to. From a "bad-driver" standpoint, this can be a bad thing, which is why carmakers dial in understeer. It's safer. But for a trained driver, a more neutral setup is desireable.

jezza

The two previous posters already responded as I would have. The IS pushes pretty badly. It's nowhere near having too much front grip relative to the rear, so more tire in front will go a ways towards alleviating that.

al503

Yup. I was honestly thinking about going 255/35/18's in the front with 265/40's in the rear. I put my wheels on and estimated the width of the 255's and it didn't look like I would have enough clearance with the spindle so I ended up going with 235's.

I don't know if it's more of the tire (PS2's) I replaced the original dunlops or the additional 10 mm (or both) but it has made a noticeable difference.

Pittdawg

Does anyone know the max tire size dimensions or overall diameter we can get away with without rubbing on the stock 18 inch wheels? Thanks.

Gernby

iTrader: (1)

Take a look here to see what people are getting away with. They will be aftermarket wheels and sizes, but you can figure out the outer diameter and width to compare. The important thing will be adjusting the offset of the stock wheels with the right width wheel spacer (5 mm , 10 mm, etc.).

Gernby

iTrader: (1)

It looks like you could get away with a 245/40-18 on the front, but you may have to use a 5 mm spacer. This is based on the fact that some of the people in the thread I posted above are using 245/35-19s with +38 offsets with minor rubbing. The 245/40-18 has .8" less tread width and a .1" smaller diameter, and adding the 5 mm spacer will give a resulting offset of +40. That would have a lot less rubbing potential.

phatboyc

Hi al503, Would you have pictures of your front 235/40/18 and back 265/40/18 by any chance? I would love to see the fit of the tire sidewall on our rim’s!