Wheel offset/305's on SRA car require rolled fenders?

svt_redf1re

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Hey guys, hopefully some of you who have been through this before will be able to help me out so I (hopefully) don't waste a bunch of money on wheels and tires that I can't use. I know this subject has probably been beaten to death, but my situation is semi particular-

Car is SRA swapped (99-04 sra i believe) and was in a driver's rear fender accident and has bondo on it, so rolling unfortunately isn't an option for me without expensive body work.

That being said, the wheel and tire setup I'm currently looking to use is 18/10.5 wheels with a 22mm offset, and 305/35/18's on them. My car has H&R race springs (04 cobra) up front, and H&R super sports (04 GT) springs in the back with MM adjustable LCA's.

Will I be able to run this setup without much issue, or am I asking for trouble? I've done enough research to know this will work perfectly fine without needing to roll fenders on an IRS car, but where I'm lost is with my solid axle. TIA
 

Roush6018

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the difference is the 99-04 SRA is 1" wider overall than the IRS. you are trying to use too big of a wheel without modifications. the SRA will only FIT a 18x10 rear wheel with no modifications. the IRS is narrower so it can use 18x10.5 wheels with some mods like the low-profile IRS bolt, and maybe wheel spacers.

then the issue of rolling the fender depends on what size tire you are running.

i have a 295-35r18 nitto NT05 on my 2004 18x10 roush rear wheels and they are on my IRS mustang and have 1/2 spacers on each side and i do not have my fenders rolled and they dont rub at all. if i did run a 305/35 or 315/30 then i would need to roll the fenders because they would rub.

basically you are running a SRA so you need to choose a wheel that was on those cars (99-04 GT) like 18x10 saleen wheels, 18x10 roush wheels and 18x10 fr500/bullitt wheels will work on your car and depending what size tire you run will determine how much the fenders will need to be rolled or cut/ grinded down..... i think you can fit a 305/35r18 on a 18x10 in the rear but it depends on the tire brand.

you can FOR SURE run a 295/35r18 on a 18x10 wheel on a SRA mustang with no fender mods.
 

svt_redf1re

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the difference is the 99-04 SRA is 1" wider overall than the IRS. you are trying to use too big of a wheel without modifications. the SRA will only FIT a 18x10 rear wheel with no modifications. the IRS is narrower so it can use 18x10.5 wheels with some mods like the low-profile IRS bolt, and maybe wheel spacers.

then the issue of rolling the fender depends on what size tire you are running.

i have a 295-35r18 nitto NT05 on my 2004 18x10 roush rear wheels and they are on my IRS mustang and have 1/2 spacers on each side and i do not have my fenders rolled and they dont rub at all. if i did run a 305/35 or 315/30 then i would need to roll the fenders because they would rub.

basically you are running a SRA so you need to choose a wheel that was on those cars (99-04 GT) like 18x10 saleen wheels, 18x10 roush wheels and 18x10 fr500/bullitt wheels will work on your car and depending what size tire you run will determine how much the fenders will need to be rolled or cut/ grinded down..... i think you can fit a 305/35r18 on a 18x10 in the rear but it depends on the tire brand.

you can FOR SURE run a 295/35r18 on a 18x10 wheel on a SRA mustang with no fender mods.
Thanks man, that answers a lot for me. I've been researching for a couple days now and can not find anything as to the width difference between 03/04 irs and 99-04 sra at the wheel mounting point. The SRA being an inch wider makes sense
 

98 svt

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I can say on my 98, I've had a MT 305 on 18x11 True Forged wheels. Those wheels were cut for the 03 IRS. I'm currently running the same MT 305 on Cosmis 18x10. No fender rubbing with either.
 

svt_redf1re

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I can say on my 98, I've had a MT 305 on 18x11 True Forged wheels. Those wheels were cut for the 03 IRS. I'm currently running the same MT 305 on Cosmis 18x10. No fender rubbing with

I can say on my 98, I've had a MT 305 on 18x11 True Forged wheels. Those wheels were cut for the 03 IRS. I'm currently running the same MT 305 on Cosmis 18x10. No fender rubbing with either.
I have found through my research that the SN95 irs is 1.5" total less width than the 03/04 irs, but what I can't find is an actual measurement between 99-04 sra and 03/04 irs
 

DCguy

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I have found through my research that the SN95 irs is 1.5" total less width than the 03/04 irs, but what I can't find is an actual measurement between 99-04 sra and 03/04 irs

Well I can tell you the SRA 94-98 axle lengths are 29, 31/32nds and the 99-04 are 30, 11/16ths. So you're basically looking at around 0.72in difference on each side. With that, you should be able to get an idea on the difference between a 99-04 SRA and an 03/04 IRS, given what you already know.

The thing to remember is, there are many factors at play here when considering clearance and if you need to roll fenders. The main variable is the wheel itself, particularly the offset. If you have a lower offset (+10 vs +20 for example) the +10 wheel will stick out farther toward the outside of the car, therefore it will be less likely to rub the inner liner under the shock mount. Wheel backspacing will help you determine how far the rim will extend past the wheel hub toward the inside of the car. That won't account for tire clearance, but you will be able to determine if the rim itself would contact any body panels or suspension components. If yes, then you need a wheel with less backspacing ie a lower offset ( a +10 instead of a +20 for example).

Another factor is spring rate. If you run stiffer springs your suspension will have less travel and will be less likely to contact the tire with the fender. Also the ride height or how low the car is dropped will factor into this.

Then you have to account for tire height and width. A taller tire with a fatter sidewall or an 18in vs a 17in wheel will obviously sit closer to the inner side of the fender and can bottom out on hard launches or in hard cornering if you run a soft spring rate or the car is dropped too low and the springs are not stiff enough.

The best thing to do is take a few measurements, determine backspacing and then test fit a couple wheels to get an idea on fitment. Once you have that you can figure out what tire you want and can run next. Everything is a compromise, but if you understand what's going on you can fit an 11.5in/12in wheel on these cars with the correct offset.
 
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01yellercobra

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I have found through my research that the SN95 irs is 1.5" total less width than the 03/04 irs, but what I can't find is an actual measurement between 99-04 sra and 03/04 irs
The SN95 (96-98) didn't come with an IRS. The IRS didn't show up until the 99 Cobra. And the width is the same 99-04.
 

DSG2003Mach1

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Keep in mind looking at ACTUAL tire width from the manufacturer too (can find it on their websites). Best example being the r888r that is quite a bit wider than other brands in what’s supposedly the same size.
 

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