Im looking at a set of wheels that are 18x8 if i use a 225-40-18 tire will they rub or do i have to use a 235? im really not sure, anyways any help is appreciated. thanks

Bruce
red03ecotec

they should clear and fit. what is the offset? also it looks like your confused on the tire sizing and what the numbers all mean. so ill give you a brief overview. the first number in the sizing in your case 225-40-18 the 225 represents the width of the tire the higher the number the wider the tire and smaller the number the smaller the width of the tire. the 40 represents the sidewall height or aspect ratio. the 40 in the sizing means that the sidewall height is going to be approx 40% of the width of the tire. so the height would be 40% of 225. And of course the last number is the diameter of the wheel in inches i hope that clears things up

Tyler, thanks man, but i understand the sizing, i just wasnt sure want would fit without rubbing the fenders, or the struts. Im pretty sure the offset is 42mm. Anyways main thing is will a 18x8 wheel with a 215 or 225 width with a 42mm offset tire fit without rubbing, i know for 18s the sideway is a 40, all i need to know for sure is what width i can go with so i know what size tires to buy. Thanks

Bruce
red03ecotec

is it a positive or negative offset is an important question aswell. the 225's may clear, but a 215 would be safer.

if you give me the full specifications on the tire, i can tell you how wide the tire will measure on the rim, take the offset into account and get a tape measurer out.

here is what i need to know.


what is the over all diameter of the tire you are looking at.?

ex 25.0"

what is the acceptable width range?

ex. 6.5" - 8.0"

what is the measured width on the recomended rim?

ex. 8.7" on a 7.0" wide rim

is it p-metric or eurometric?

ex. p-metric = P215/40R18
eurometric = 215/40R18

this seems like really stupid stuff, but trust me its really important. i will need all that information to calculate exactly how wide your tire will be on your rim and at what pressure you should run your tire at for it to handle properly and be safe.

also, im currently trying to write a guide on selecting aftermarket rims and tires, but there is just so much stuff, its taking a while to try and cover it all.

i'll try and check out some spec's so you can do some measuring, but dont take it for verbatim. the same size tire by 2 different brands can and will most likely measure out different on the exact same rim. anymore questions, just let me know.






Injection is nice but id rather be BLOWN!

Do they make a 215-40-18 that will fit an 8 inch wide wheel? As for what you asked i have no idea, i know the offset is 42. Doesnt the width have to change with a 8 inch wheel? Are you saying that any 215-40-18 size tire will work on both a 7 and 8 inch wide wheel?

Bruce
red03ecotec

yes, that is generaly what i am saying.

they way tires are designed, they can be mounted on certain rims. the wider the rim, the wider it will pull out the tire.

heres some examples for you.

for fun, we will look at the BFG G-Force Sport tire

the original tire diameter, for lets say, the 195/65R15 inch tire option on the j-bodies is 25".

now you want to keep as close as possible to the same overall diameter tire, so your best option is the 225/40R18 (25.1" overall diameter).

now this tire is able to be mounted on a 7.5" - 9.0" wide rim. you are using an 8" wide rim, which falls into the specs.

The tire mounted on the recomended rim width, which happens to be an 8" wide rim, measures out 9.1".

so this 225/40R18 tire will actually measure out to be a:

231/39R18

so, the tire that is said to have a 225mm width, actually has a 231mm width when mounted on an 8" wide rim.

now that you know the width of the tire on the rim, add that number to your offset and see if it will fit under your car.

just for fun, lets see how wide this tire would be if it was on a 9" rim, the maximum width the tire can be mounted on.

for every .5" in width you increase over the recomended rim width, wich was 8", you generaly add .2" in width.

so we are adding .4" in width mounting these on a 9" wide rim, because that is 2 x .5" width increases.

so we now have a 9.5" tread face, the size works out to be a:

241/37R18

so just by increasing the widthof rim a tire is mounted on, you can increase the width of the tire.






Injection is nice but id rather be BLOWN!

i have 225/40/18 on a 8' rim with a+45 offset and i clear fine

I'm runnig the 225/40 zr 18's as well and have zero issues with them fitting. And I'm dropped 2 inches. The 215's are too small and will throw the speedo off by a couple MPH. Always get a tire thats the same diameter is the original so the speedo stays correct. In this case the 225/40 18 is the correct size tire.




Semper Fi SAINT. May you rest in peace.

Shaun and Jackalope:

thats nice that you share the same tire size, but what size rims are they running on.

if the width of the rim is anything smaller than an 8" wide rim, than your input is kinda pointless. not saying anything bad, but like i said in my post before, ever 0.5" in rim width you increase, the tire will increase 0.2".

so like im saying, a 225/40R18 on a 7" wide will be smaller than on a 7.5" wide and even smaller than an 8" wide, etc.






Injection is nice but id rather be BLOWN!

18 x 8's And I think you ment to say for every 0.5" increase in width you DECREASE your overall tire diameter by 0.2". Or as we like to say around here NOT A WHOLE HELL OF ALOT !!! 0.2" in diameter is nothing! Geez! Thats like a couple months of drive time.
Hell different manufacturers with the same size tire are always off by a smidge. And 0.2" is a smidge! I'm not trying to come off like a dick but if yor worried about 0.2" worth of diameter then you must change your tires every other month. That must get expensive!




Semper Fi SAINT. May you rest in peace.

no, for every half inch you increase or decrease a rim, a tire can increase or decrease respectably by .2 of an inch. that .2 of an inch works out to about 5 mm or so.

so for example, increase the width of rim a specific tire is mounted on by a full inch, and you have bumped up the 225 to a 235.

now, certain brands rate their tires messed up too. i had a set of 205/60R15 michelin energy mxv+ on my stock steelies, and they measured out to either a 215 or a 225, cant remember.

and for the future jackalope, i do this for a living. i work in a tire shop, so when you have something to say on that topic do your research first.






Injection is nice but id rather be BLOWN!

Dude why are you biteing my head off? Why the hate man? And when you increase the width of the rim the center section of the tire isn't being bowed so the diameter would decrease not increase. When you stick a wide tire on a narrow rim the tread area bows outward makeing the diameter bigger. And for the record I used to work with tires everyday too. And of corse when you increase the width of the tire you need to increase the tire size. I think you and I are talking about the same thing but that we're both just wording it differently and thats whats messing us up.
Relax whitegoose I'm not starting with you.







Semper Fi SAINT. May you rest in peace.