sleeper408

iTrader: (6)

I was just wondering when running 19" or 20" wheels and low profile tires, why is it common to have 35 series up front and 30 series tires in the rear? Does it have anything to do with the weight of the engine? My previous car was a Cobra and you would usually run the meatier tire in the rear. I'm just trying to understand the concept for low profile tires. 30 series tires sounds scary especially when you live out here in the Bay Area, CA like me.

RMMGS4

iTrader: (5)

Utilizing a different series front/rear has nothing to do with weight, only matching up overall tire diameters when having a staggered set up where wider tires are utilized out back, but you want to maintain the same overall diameter front & rear.

To accomplish this, you need to go lower profile in back if you DO have meatier tires in the rear. A typical set up for 20's is 245/35 front and 285/30 out back. The profile is a lower number in the rear because the width is much larger, so if you do the math the fronts and rears actually come out to have almost the same section height front(3.375") and rear (3.366").

bee0818

iTrader: (4)

I also noticed on tirerack's website that they list optional 20" sizes at:
Front 245/30 and Rear 275/30

From what I've seen on here, it seems like a lot of people run 245/35 front and 275/30 in the rear. Is 285 in the rear better?

RMMGS4

iTrader: (5)

If you look up the tire specs listed by the TireRack, you will see that the overall tire diameter of the 245/35 is actually larger than a 275/30, meaning the front tires are slightly larger in diameter than the rears. So "Technically" the 285/30 is a better match.

A trained eye would notice this difference on our cars, but the difference is very minimal.

I'm thinking the main reason why you see a 275 recommendation is because some tire manufacturers do not offer the 285 size.

For any brand that did offer the 285, I would opt for that size over the 275. I also think a 285 fits quite well on a 10" wide rim versus a 275 which is a bit stretched and it doesn't fill the GS wheel well as good, but I am being pretty nit-picky when I say that.

On my old set up I had 285 and then I had to switch to 275 on my next set. I could tell the change quite easily, which is why I have made these observations and can point out these differences.

Neo

iTrader: (3)

RMMGS4 has covered some of the whys; but just in case, a review.

The "series" designation is a percentage (of the tire width) and not a hard measurement. The result of the percentage ((series/100) * width) is the sidewall height. Since the staggered setups have bigger widths in the back, you need a smaller percentage (i.e. 30 instead of 35) to accommodate the extra width in the rear.

This way, the sidewall heights are the same (or close) which translates to the overall wheel diameter being the same (or close).

jwin

iTrader: (16)

i thought it had a lot to do with rubbing beacause of the rear fender cut is smaller than the front so if i get a 255/35/20 for the rear instead of a 255/30/20 would it be a big difference in tire height will it rub i am running a 20x9.5 rim in the back with a 35 offset and a 20x8.5 in the front with a 32 offset... and i am running a 245/35/20 tire in the front

RMMGS4

iTrader: (5)

Your rubbing is affected by your offset, more so than it is by the tire size.

The 32 offset is a bit agressive but should clear with some inner lip shaving. A 35 offset would clear no problem. Yes the higher profile 255/35 will have a bit more chance to rub, but nothing that a proper offset wouldn't fix.

As far as your idea of using a 255/35-20 that is an awefully large diameter. Even a 285/30 is not as large in diameter as this. Your speedo will be off as well because of this oversize. Basically I don't know of any reason to go to this size. I don't know what would you accomplish by doing so.


As a point of reference, with the appropriate inner fender trimming modifications, a GS can fit a 20 x 11 rim with a 305 size tire and have absolutely no rubbing.

The proper offset and profile selection is the key to making these larger sizes fit.