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Discussion Starter #1
Like it says, I want to fit 225's for the traction, cornering, and because i think a little more offset will look pretty good on this car. So what offset is required to fit 225/45/18's without rubbing?
 

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Like it says, I want to fit 225's for the traction, cornering, and because i think a little more offset will look pretty good on this car. So what offset is required to fit 225/45/18's without rubbing?
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Depends on the width of the rim too, as the profile of the tire changes slightly depending on the rim width. Stock offset is 55mm, so any rim with 55mm OS would be guaranteed not to rub with 225/45s, whether using a 7", 7.5" or 8" wide rim. However, in general, something close to 50mm would be fine too. RX8 wheels are a good choice. Some people are running 235/40s on the RX8 rims without rubbing, while others have experienced some rubbing with the same size tire but of a different brand.

If going aftermarket, finding an offset larger than 48mm is very rare, but 48mm should be fine, if using 225/45s. However, there are variations between different brands and models of tires, ie. one mfgr's 225/45 could be wider than another's 225/45, so in some cases there could still be slight contact. Sorry for a less than definite answer, but other than sticking with stock offset or very close to stock OS there isn't any guarantee as there isn't a lot of room under the rear fenders.
 

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Discussion Starter #4
so a 18x7.5 in a 48 offset with 225/45/18's would or would not rub, I never figured out the offset crap in my head so forgive my ignorance....
 

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It's a crap shoot. It seems like two people can have the same wheels on the same type of car and even the same brand of tire and one person says they need to roll and the other will say no problem. I guess all it takes is a varience of a few mm's during the mfg of the car and you will rub. I think you just need to be prepared to have to roll your fenders with anything less than 48ET and if you don't it will be like xmas all over again.
 

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so a 18x7.5 in a 48 offset with 225/45/18's would or would not rub, I never figured out the offset crap in my head so forgive my ignorance....
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Offset is the distance the actual mounting surface of the wheel is from the virtual centerline of the wheel. 0 (zero) offset would be where the mounting surface of the wheel is in the exact same plane as the centerline. This means that there are equal amounts of wheel width to the inside and to the outside of where the wheel mounts to the hub.

Positive offset, which is the case of most modern cars, is where there is much more wheel width to the inside of the car than to the outside. On the MS6, the stock offset of 55mm means that the mounting surface of the wheel is 55mm closer to the outside face of the wheel, ie. the amount of wheel width to the inside is equal to "WheelWidth/2 + 55mm", while the amount of wheel width to the outside is equal to "WheelWidth/2 - 55mm".

A wheel with offset of 48mm would have wheel width to the outside of "WheelWidth/2 - 48mm". Obviously this would result in a larger amount since a smaller number is being subtracted, meaning the outside face of the wheel sticks out further, by 7mm (this is assuming wheels of the same width). 7mm may not sound like much, but when talking about hard metal edges, any overlap, even 0.1mm, will cause rubbing and result in problems. That's why a 48mm OS may be fine, but a 45mm OS will rub.

The severity of rubbing may not be as bad, but you'll hear it. In severe cases the end result is creased sheet metal as the rubber on the tire catches on the lip and bends it back out and/or damage to the tire sidewall.

There are sometimes car to car variations due to manufacturing tolerances. A certain wheel/tire combo may work on one car yet rub slightly on a different car of the exact same model. That's because it just clears on the first car, yet production variations between cars means the second one has a fender lip slightly closer, resulting in rubbing. In those cases a slight bit of "manipulation" of the fender profile usually clears it.

In your case, 48mm with 225/45s should clear. If there is rubbing it will be slight, say something that could be corrected by moving the fender lip upwards a few millimeters. This could be done fairly easily with a round wooden staff like a baseball bat, or by blows from a hard rubber mallet. You shouldn't be in the position of having to fold the fender lip flat, like a envelope flap, to clear the tire. Keep in mind that only the rear fenders have this issue. The fronts on Mazda6s have lots of clearance.
 

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People are running into problems with the rear passenger tire rubbing on the inside of the fender when running a 225/45/18. It is very close on my car with that set up and a 48 offset. One speed6 owner had to switch to 215's not because of the fender lip, but the bulge in the wheel well for the jack. Seems, like nothing is for sure on this issue.
 

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Discussion Starter #9
Bummer, so 225's in the rear are the issue, but of course 215/45/18 on a 48 offset would clear easily... 215's seem so wimpy after having 225's on my 160 HP ford probe GT... and this is so much more car!
 

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Bummer, so 225's in the rear are the issue, but of course 215/45/18 on a 48 offset would clear easily... 215's seem so wimpy after having 225's on my 160 HP ford probe GT... and this is so much more car!
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Hey BigBen, I would really recommend rolling the rear fender lips. It's not that much work, and there seem to be a few websites that have a process to rent and ship the tool. Then you can run a decent size tire as the car rightfully needs and deserves.

I don't know if you have a local 6 club where you are, but when we did ours we organized a group fender roll and split the cost. I also found a local guy that had the tool and was willing to rent to us.

You could also try and find a shop that will do it. People have varying degrees of success at this, as some shops don't want the liability issues if something happens with the roll.

Once it's rolled your wheel offest and tire width choices open up a lot. Members are using 225s on 42 offset wheels successfully (make sure the front edge of the fender is rolled down as far as possible), or run 235s on 48mm wheels. I did a partial roll on my MS6 and run 235/40s on RX8 wheels (50mm OS) with absolutely no problems.
 

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Why don't you just run a 225/40? The size is slightly off but not enough to make a big difference...

W/ a 18x7.5 -48 offset you should be able to run w/out a fender roll.

That is the exact setup I have and I am very close but not rubbing!
 

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Why don't you just run a 225/40? The size is slightly off but not enough to make a big difference...

W/ a 18x7.5 -48 offset you should be able to run w/out a fender roll.

That is the exact setup I have and I am very close but not rubbing!
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I agree that 40 series assures clearence, but looks bad on cars that aren't dropped. If you dont have plans to drop you car, IMHO avoid the 40s, the gap looks rediculous.
 

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Discussion Starter #13
That would work, I didnt want a smaller overall diameter but if it fits and gets me 225's....

Stock 215/45/18
Side wall 3.8
Radius 12.8
Circumference 80.5
Revs/Mile 787

225/40/18
Side wall 3.5
Radius 12.5
Circumference 78.8
Revs/Mile 804
Speedo would be off 2.1% slow

225/45/18
Side wall 4
Radius 13
Circumference 81.6
Revs/Mile 777
Speedo would be off 1.4% fast

O guess 225/40/18, if you guys dont think they will rub on a 48 offset, are my choice!
 

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I agree that 40 series assures clearence, but looks bad on cars that aren't dropped. If you dont have plans to drop you car, IMHO avoid the 40s, the gap looks rediculous.
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Ya that is true! You can live w/ it, but it looks 100times better w/ a drop...

That would work, I didnt want a smaller overall diameter but if it fits and gets me 225's....

Stock 215/45/18
Side wall 3.8
Radius 12.8
Circumference 80.5
Revs/Mile 787

225/40/18
Side wall 3.5
Radius 12.5
Circumference 78.8
Revs/Mile 804
Speedo would be off 2.1% slow

225/45/18
Side wall 4
Radius 13
Circumference 81.6
Revs/Mile 777
Speedo would be off 1.4% fast

O guess 225/40/18, if you guys dont think they will rub on a 48 offset, are my choice!
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Like I said, you 'should' be ok... As other people have said it's almost a hit or miss thing...
The tire might play a role in that as well, since the sizing isn't always exact.

But it would be your best bet!
 

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People are running into problems with the rear passenger tire rubbing on the inside of the fender when running a 225/45/18. It is very close on my car with that set up and a 48 offset. One speed6 owner had to switch to 215's not because of the fender lip, but the bulge in the wheel well for the jack. Seems, like nothing is for sure on this issue.
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Yup, that was me. I thought it would be clear of rubbing for sure but I lowered my car with Autoexe LD's and the 225/45/18's w/ +48 offset made the rear seats useless with two adults and and ice chest in the trunk. Major rubbing on the inside of the wheel well while shifting from 1st to 2nd gear from a standing stop.
 
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