If 17x9 fit why not 18x9?

ricgt88 · Apr 20, 2011

Hi,

I have a 1990 GT convertible and I am looking to buy new wheels for the summer.

Most of you (and even serious websites like allamericanmuscle ) say that 17x9 will fit under a fox with 245x45x17.

But what about 18 inches?

Using a tire calculator, I found out that 245x40x18 have numbers similar to a 245x45x17.

Do you guys think that the 18s would rub?

Thanks in advance

Zapp109 · Apr 20, 2011

I use to run cobra rs 17x10 in the rear.. with 275/40/17 , 255/40/17 front with 17X9 .. From what i remember im not sure what you concern is here ? Are you worried bout it hitting the inner fenders ? Also mine was a hatch so im not sure if they are different?

ricgt88 · Apr 20, 2011

Did you have any problems with running 255x40x17 in the front?

I am just wondering if I use a tire size that is similar to one that does not rub, I should be ok right?

Does 245x45x17 = 245x40x18 ???

No one seems to have a straight answer when it comes to rubbing in the front...

Mustang5L5 · Apr 20, 2011

Depends more on the offset/backspacing vs the actual size of the wheel

you are right, the 18x9 with a smaller sidewall would have the same size as the 17x9....but is the offset/bs the same?

93project · Apr 20, 2011

I'm running 18x9 and 18x10 on a 93. Tires are 245/40 and 275/40. Nitto 555's. They don't rub at all and I'm using Ford racing B springs, 02 spindles, 02 Moog ball joints. And Monroe sensatrac struts and shocks. It rides incredibly well, doesn't rub. And doesn't have horrid bumpsteer from the 02 spindles.

93project · Apr 20, 2011

delete

Zapp109 · Apr 20, 2011

I had no issues with rubbing in the front. Only issue i had was in the rear i had to push my flowmaster exhaust over towards the center of the car on each side to keep it off the tires. .. go to tire rack and pick a tire.. here is a example

Kuhmo ecsta XS

245/45/17 = 25.7" tall

245/40/18 = 25.7" tall aswell according to this

Kumho Ecsta XS

But choose tire and work with that chart

newskool · Apr 20, 2011

18's are gonna need some fender rolling.

ricgt88 · Apr 20, 2011

And so would the 17s. I have never heard of anybody with 17s that had to roll their fenders...at least not with 245s...

Mustang5l5
I'm looking to buy 18 inch cobra R (4 bolts)
Here's a chart I found on the internet
Size Bolt Offset BS
16x8 4x4.25 +15 5.28
17x9 4x4.25 +24 5.95
17x10.5 4x4.25 +28 6.80
18x9 4x4.25 +18 5.95
20x8.5 4x4.25 +30 5.96
Offset on the 17x9 is bigger than on the 18x9
Backspacing is the same

Does that mean I would have more problems with 17x9 (if any) than with 18x9

Zapp109 · Apr 20, 2011

http://www.stangnet.com/mustang-forums/822622-17s-18s.html

here is something i found.. has some info

Mustang5L5 · Apr 20, 2011

ricgt88 said:
And so would the 17s. I have never heard of anybody with 17s that had to roll their fenders...at least not with 245s...

I did..with 245's. It was with SN95 disk brakes out back, so it was close since they stuck out

ricgt88 said:
Mustang5l5
I'm looking to buy 18 inch cobra R (4 bolts)
Here's a chart I found on the internet
Size Bolt Offset BS

17x9 4x4.25 +24 5.95

18x9 4x4.25 +18 5.95

Offset on the 17x9 is bigger than on the 18x9
Backspacing is the same

Does that mean I would have more problems with 17x9 (if any) than with 18x9

It means the 18" wheels will stick out 6mm more than the 17's. Other than that they are the same.

You *might* need to roll your rear fender lips

93project · Apr 20, 2011

18x9, 18x10 didn't roll any fender and used B springs

2000xp8 · Apr 20, 2011

93project said:
18x9, 18x10 didn't roll any fender and used B springs

Yours fits because you are using an 18x10 with a tire that could fit on an 18x8.5. The tire is probably stretched which lowers the profile even more and takes the corner off the tire giving even more room for movement.
Really no sense in buying a rim that wide to use a tire that narrow, unless of course that's the only width available.

Ricgt, wheel fitment is about more than rim size.
The tire you run, the offset, how low the car is are all variables that affect fitment.

ricgt88 · Apr 21, 2011

I thought I could use some 'logic' to try to figure out if it would fit or not

Car is not lowered so I figured it I used a wheel with the same radius as my current 15 inches it would fit. Of course, I know that 245 is larger than 225 but hey, 225 seem lost inside the fender...

anyone as offset and b/s for 15x7?

90limited · Apr 21, 2011

ricgt88 said:
And so would the 17s. I have never heard of anybody with 17s that had to roll their fenders...at least not with 245s...

I have 255/40/17 on 17x9 on all four corners. Front will rub at full lock but no other issues.

93project · Apr 21, 2011

2000xp8 said:
Yours fits because you are using an 18x10 with a tire that could fit on an 18x8.5. The tire is probably stretched which lowers the profile even more and takes the corner off the tire giving even more room for movement.
Really no sense in buying a rim that wide to use a tire that narrow, unless of course that's the only width available.

Ricgt, wheel fitment is about more than rim size.
The tire you run, the offset, how low the car is are all variables that affect fitment.

275/40 18's are too narrow for a 10" rim? Wow.
I have 245/40 in front. 275/40 in back.

j_lutter31 · Apr 21, 2011

Zapp109 said:
I had no issues with rubbing in the front. Only issue i had was in the rear i had to push my flowmaster exhaust over towards the center of the car on each side to keep it off the tires. .. go to tire rack and pick a tire.. here is a example

Kuhmo ecsta XS

245/45/17 = 25.7" tall

245/40/18 = 25.7" tall aswell according to this

Kumho Ecsta XS

But choose tire and work with that chart

Not sure who made that calculator but they sure like to round.......Might as well have just said they were 26" tall.

If you do the math

(2*(245 * 0.45))/25.4 + 17 = 25.681

(2*(245 * 0.40))/25.4 + 18 = 25.7165

This means the 18" tire is 0.13% taller, might not be much...but its not the same.......

2000xp8 · Apr 21, 2011

93project said:
275/40 18's are too narrow for a 10" rim? Wow.
I have 245/40 in front. 275/40 in back.

You can put 315's on a 10 inch wide rim.

This is why i tell people not to obsess over buying wider rims for their fox, doesn't do any good, you can't fit tires wide enough to necessitate them.

93project · Apr 21, 2011

I know I can fit larger but I only wanted 275's. They aren't stretched at all. They sit flush on the rim face. I bought them cuz I dig the deep dish look on a fox. Everyone here has cobra R's, or 03 chrome cobras....lame

Mustang5L5 · Apr 22, 2011

93project said:
275/40 18's are too narrow for a 10" rim? Wow.
I have 245/40 in front. 275/40 in back.

technically...yes.

You want tire size to be about 2" wider than rim size

275mm = 10.8"

Ideal rim size...8.8", or a 9" wide wheel

If 17x9 fit why not 18x9?

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