This was a response in another thread, but I figured I would make a new post for those looking to get mor grip at the front end. I am referring to the stock 265/35 18 rear tire size here.

Regarding the 265's, I ran the rear wheels with both 265 PS2's and the stock conti's on front to verify clearances before I ordered my HRE's. Both tires measure out about the same on the 18X9 wheel. The end of my driveway pitches back up to the road creating a drainage area. I hit this at enough speed to make the bottom rub strip hit the ground and bottom the suspension. I saw no rubbing. I did this while turning both ways as well and saw no rubbing. I measured about 3mm of clearance between the inside of the tire and the suspension upright. The upright travels with the tire so this will not change. Without a way to lower the car to the point of bottoming it is impossible to measure wheel to fender clearance accurately. However, with some straight edges and some figuring I came to the conclusion that the stock 39mm offset puts the wheel pretty centered in the available space. It should be noted the brake clearance is slightly higher and the wheel/tire does stick out a bit further than stock. After working with all the numbers I could find I figure that 35 or 36 mm offset is about as far as you can go before you risk wheel to fender problems. I ordered my wheels with a 38mm offset(18x9).

With the rear tires on the front there are two differences I noticed. The car feels quicker to make a transition and the car looses a bit of its straight line stability on the highway. The stability thing is very minor. Most would not even be able to tell. I did not notice an appreciable difference in steering effort.

To sum this up, 265/35 18 tires (continentals, pilot sport PS'2s and anything else that measures within a few mm of those tires) should be ok on on a 18x9 et39 to a 18x9 et37. A 18x9et36 or 35 will be getting close. Do not get an offset higher than 39mm.

 

I run 40mm in front and it just clears fine... I am going back to 255 though as my new front rims will be ET35, so I need a little more clearance.

As always, tire manufacturer and models makes a big difference (I noticed that even among the major manufacturers, the sizes vary widely). So some people may get away with ET42 in front on 265 if the tire is narrower or has round shoulders, or even smaller diameter.

-s-

 

All true. At ET40 you would still have about 2mm clearance with the two tires I tried. ET42 is going to put the tires I tried against the upright. Even if you could find a slightly smaller tire you still leave no room for deflection.

Here are pics of the rear wheels on the front.

 

would an 19x9 255/35 or 30's ????/19 work on the front? and stick with default 19x9 275/30/19 on the rears


also would 19x9 285's work on the rear?

 

There are people running 255/35 19's without problems. There is no compelling reason to using a 9 inch wheel (the 8.5 inch normally used would be lighter) with that tire unless you are trying to make the lip bigger. Even then I can't imagine you could get a noticeable difference and still maintain adequate brake clearance. I didn't measure the rear suspension clearance as I am using 275's in back so it's not an issue. If you do a search though you will likely find that answer. People tend to push the limit in back before they worry about the front. Someone has probably already mounted 285's on the stock wheels.

 

285/35R18 on 9" wide rims is not a good idea for most manufacturers... I have 285/35R18 on 9.5" wheels and if the offset were around 38, it would be perfect.

-s-

 

To be more clear about this, while it will fit OK, the tire will bulge from the wheel. This will force the tire to wear quicker in the center. I have run 295's on a 9 inch wheel on my Corvette before for years at a time (even track use). They bulged from the rim but on that car it looked good and helped fill out the wheel well. I didn't see any dramatic wear problems. On the MB I personally cannot imagine a reason not to use a 275 though. Keep this in mind as well. As you go wider with the same aspect ratio (the 35) the tire gets taller.

 

I just realised, scorchie and I are talking about 18 inch rears and you are talking about a 19x9 rear. A 285 would be even less advisable on a 19 inch wheel with a 30 ratio than it would on an 18 so draw your own conclusions.

 

The main problem you have in running tires with rims too narrow for the width is the reduction in sidewall stiffness. You will trade off greater contact patch for less sidewall stiffness and more roll-over, especially when tracking the car. I run 275 width tires with 10" rims on my track-car, which is about optimal in terms of handling and tread wear.

 

FYI:
I run on Factory in the front and 285/35R/18 on the rear.
This set-up is great.

Regards,
Manuel