Okay. So. I have a set of 18x9s in the mail. Now I'm looking at two different tires... One is a 215/35ZR18, the other is a 225/40ZR18. Will either (both?) of these fit the rims? What is the difference between the two as far as looks go? I talked to some tire shops and they all said they would look "funny" and "low profile"... But that's sort of what I want. :wtf: Somebody help, please.
Tire Sizes
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Well. I know almost nothing about tire sizes, but, I have 225/55/R16 on my 16x7.5 inch rims.. So these appear to be -smaller- than the ones I have now... But I don't know of any 18 inch rim that is less than 7.5" wide. :wtf: So why would they make 18" tires that won't fit the most popular width? :-?
OK, take a ruler, and measure the tread width of those 225 tires you have, or just do it with the metrics. .35X225=78.75" better really if you convert it to inches, then you can double it and add 18 for the wheel height. I think you would find that your wheel height would be less than your 16 inch rims with your 255/60/16 tires. What you need to do is get as close to your stock total tire height as possible, that way you don't throw off gear ratio or speedometer/odometer.
I don't mind if it throws off my speedo a little... What I'm primarily concerned with is: #1: If its "safe" to put either of those tire sizes on my rim. #2: That the tires don't look weird on the rim. Like, I saw a picture where a wider tire was used and it sort of bowed out. I only have found those two sizes... Which one would have better fitment and throw off the speedo less? It's raining so I don't want to go measure the tread. 
I really don't know, I would be afraid that a 225 with tire wouldn't seal right on a 9inch rim, other than that I guess it would be fine. IMHO it would definitely look weird though, just not wide enough for your rims. Go with at least a 245 or 255/40/18 for proper fit on that wide rim. Of the two sizes you mention a 225/40/18 is the taller and closer to stock tire height, but is still likely to be 1/2inch ot an inch shorter than stock.
I just found this really cool tool off google.
http://www.1010tires.com/tiresizecalculator.asp
It lets you enter the specs for two tires and it compare everything about them. According to this, the 225/40/ZR18 is only 2.8% difference in diameter than the 225/55/R16, and that's only a 1mph and +11 revolutions per mile difference. The 215/35/ZR18 is a 7.0% difference, which is 4mph. According to this the 225 is better, if any of them will actually fit on that wide of a rim. :-?
edit: And it says that the 215/35 will only fit a 7"-8.5" wide rim. But that the 225/40 will fit on a 7.5"-9".
http://www.1010tires.com/tiresizecalculator.asp
It lets you enter the specs for two tires and it compare everything about them. According to this, the 225/40/ZR18 is only 2.8% difference in diameter than the 225/55/R16, and that's only a 1mph and +11 revolutions per mile difference. The 215/35/ZR18 is a 7.0% difference, which is 4mph. According to this the 225 is better, if any of them will actually fit on that wide of a rim. :-?
edit: And it says that the 215/35 will only fit a 7"-8.5" wide rim. But that the 225/40 will fit on a 7.5"-9".
Before I bought those tires, I would look at the specs on tire sizes of mustangs that come with 18 inch tires like the S281 Saleen and see what size they come with, I really think that size tire is going to look silly looking on your car, but if its what you want, go for it, in my opinion the 245/45/17 looks sort of small on my GT.
I just checked for you. The saleen S 281 comes with the same size rims you have, the 18X9 five spoke saleens, they have Pirelli 255/35zr18 front tires and 265/35zr18rear tires, so that gives you sort of an idea how small 225/40 is going to look on your car.
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29 Posts
Stop!!!! Please listen to Rick and do NOT buy anything less than a 245 for those 9" rims!!!! 225 is extremely too narrow for a 9" rim!!!! Not to mention it would look funy as hel as its a smaller tire overall than you would want on a Stang!!!
When you go from one wheel size to another you're doing what is called a "Plus 1" fitment. 1 for 1 wheel size. So, going from 16s to 18s is a Plus 2 fitment. A good rule of thumb in Plus sizing is to increase width and decrease aspect ratio. This offsets the gain in wheel diameter and keeps overall circumference nearly the same. a 245/40R18 is .1" larger than a 225/55R16. A 275/35R18 is .5". This isn't enough difference to matter.
Remember, the tires hieght is dependant on the width and aspect ratio. A 225/40 has a height that is 40% of 225mm. So its a really short sidewall and relatively narrow tire.
But in any case with a 9" width on the rim, I wouldn't go below 245mm in a tire's width. Good luck finding a shop to even attempt to mount them.
Go back to yout tire calculator and comapre using a 245/40, a 255/40 and a 275/35R18. All are less than 1 mph difference on the speedo, less than 1" diff in circumference. The 245/40 is almost a perfect replacement in terms of overall size.
When you go from one wheel size to another you're doing what is called a "Plus 1" fitment. 1 for 1 wheel size. So, going from 16s to 18s is a Plus 2 fitment. A good rule of thumb in Plus sizing is to increase width and decrease aspect ratio. This offsets the gain in wheel diameter and keeps overall circumference nearly the same. a 245/40R18 is .1" larger than a 225/55R16. A 275/35R18 is .5". This isn't enough difference to matter.
Remember, the tires hieght is dependant on the width and aspect ratio. A 225/40 has a height that is 40% of 225mm. So its a really short sidewall and relatively narrow tire.
But in any case with a 9" width on the rim, I wouldn't go below 245mm in a tire's width. Good luck finding a shop to even attempt to mount them.
Go back to yout tire calculator and comapre using a 245/40, a 255/40 and a 275/35R18. All are less than 1 mph difference on the speedo, less than 1" diff in circumference. The 245/40 is almost a perfect replacement in terms of overall size.
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29 Posts
no, prob, you'd pretty much already covered eveerything. I just couldn't resist saying something! Sold tires for too many years...
Okay. I'm going to believe you guys that they won't fit. It just seems weird they only offer the 18" in sizes that are way too small to fit. Here are all the sizes:
245/55HR17
245/50HR17
245/45HR17
255/55HR17
255/50HR17
215/35ZR18
225/40/ZR18
They only make two 18" and they are all -smaller- than the 17" tires they make? :wtf: I just don't understand that.
245/55HR17
245/50HR17
245/45HR17
255/55HR17
255/50HR17
215/35ZR18
225/40/ZR18
They only make two 18" and they are all -smaller- than the 17" tires they make? :wtf: I just don't understand that.
What on earth brand of tire have you been looking at man? Look at some Kuhmo Ecstas, BFG, Bridgestone, Michelin, There are lots of good brands, apparently the ones you are looking at aren't. Those 17 sizes are mostly wierd, and all HRs??? 245/45 is the only common 17 inch size I see, the others are all oddball sizes.
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