305 vs 315

SouthSideStang

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Hello all, I have been going through countless threads and am down to two options. the 305/35/18 Nitto or the 315/35ZR17 Proxes R888 for the rear. I am on stock rims but i wan to go with the 17x10.5 (unless i can find an 18x10.5 replicas, which idk if mods would be required) in the rear. Which of these 2 offer better fitment without too many modifications? I understand i will have to install the low profile IRS bolts but would rather not have to roll fenders or lower/raise the suspension. I pretty much am just looking for a tire that hooks at 450-500WHP and looks nicer than stock size. Any help or other suggestions is greatly appreciated.
 

94slowbra1

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multiple tings to consider here. first you are talking about two different rim sizes. second the fitment has alot to do with the wheel specs, not just the tire. next it depends on what nitto you are talking about, the 555r runs narrow and the toyo r888 run wide.
the best thing for hooking is tire compound and sidewall. those two tire sizes have virtually the same size sidewall, 4.2" vs 4.3". the two tires will about an 1" different in height due to the rim diameter. if you arent lowered you will be fine. i tuck a 305 35 18 r888 on mine and im pretty low with rolled fenders. the r888 has a stiffer sidewall with a soft tread compound. the nitto 555r has a softer sidewall.
the 17 will fit better due to being shorter by an inch
 

94slowbra1

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multiple tings to consider here. first you are talking about two different rim sizes. second the fitment has alot to do with the wheel specs, not just the tire. next it depends on what nitto you are talking about, the 555r runs narrow and the toyo r888 run wide.
the best thing for hooking is tire compound and sidewall. those two tire sizes have virtually the same size sidewall, 4.2" vs 4.3". the two tires will about an 1" different in height due to the rim diameter. if you arent lowered you will be fine. i tuck a 305 35 18 r888 on mine and im pretty low with rolled fenders. the r888 has a stiffer sidewall with a soft tread compound. the nitto 555r has a softer sidewall.
the 17 will fit better due to being shorter by an inch
 

SouthSideStang

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Wow, thanks for all that info. Would i have to roll the fenders with the 315/35/17? i was referring to the Nitto 555r sorry i forgot to mention that. It looks like i will be sticking with the 17x10.5, i really want the wide look but dont want the height to require the rolled fenders. Will spacers be required with the 10.5?
 

GodStang

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Wow, thanks for all that info. Would i have to roll the fenders with the 315/35/17? i was referring to the Nitto 555r sorry i forgot to mention that. It looks like i will be sticking with the 17x10.5, i really want the wide look but dont want the height to require the rolled fenders. Will spacers be required with the 10.5?

I run M/T 315s on 17x10.5 and no rolled fenders or lowered. Fits just fine.
 

94slowbra1

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Most probably not. I'll leave it open by saying every car is different and these cars arent exactly known to be held to the tightest production standards. Stick with the 17, they are lighter, tires are cheaper and you wont have to buy front wheels.
No spacers will be needed as long as you buy wheels speced for your car. Most 03 10.5 reps are meant for 03 cobras with irs so you'll be fine
 

01yellercobra

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Not only is each car different so is each tire/rim combo. When I bought my 04 it was H&R race springs with Cobra reps. They were the 17x10.5" rim with Sumitomo tires. That set up didn't rub. I switched to my FR500's with 555R's and it started to rub over the bumps. So I rolled my fenders and have the bolt from MM. When I ran the Nitto G2's I needed to roll a little more because they're wider than the 555R's. I'm even lower on coilovers now, but only really have issues on big bumps.
 
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I'D WIN

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The Toyo R888R in a 315 is wider than you think. I would go to their website and check out the specs. I run the 305 on 11” rim that is actually 12” from edge to edge. Fenders are rolled and I am running low pro IRS bolts.


Sent from my iPhone using Tapatalk
 

SouthSideStang

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depends on your ride height, did you say you are stock height?
FYI I needed fenders rolled with r888 w/ 305/35/18 on- H&R race springs had an 18x10wheel

yes everything is stock except for the low profile bolts. I will be running the 17x10.5 from American muscle and hopefully the R888R
 

94slowbra1

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I wouldn't. If you need to run a wheel spacer I'd run them on both sides. The irs is know for not being centered. You can get a shim/spacer to help center it. It doesnt move it much but it may be enough to help you out. I believe FTBR has them.
 

SouthSideStang

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I wouldn't. If you need to run a wheel spacer I'd run them on both sides. The irs is know for not being centered. You can get a shim/spacer to help center it. It doesnt move it much but it may be enough to help you out. I believe FTBR has them.
What part would it be easier/safer to run ? Easier to install? Would 5mm spacers create enough clearance ?
 

94slowbra1

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Obviously a wheel spacer is going too be easier than shimming the irs cradle. How much spacer you need is going to be determined by what you need. You want the least amount of soacer to clear where its rubbing. Dont want it to push out too far and rub the fender
 

SouthSideStang

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Obviously a wheel spacer is going too be easier than shimming the irs cradle. How much spacer you need is going to be determined by what you need. You want the least amount of soacer to clear where its rubbing. Dont want it to push out too far and rub the fender
This wouldn’t be any alignment issue right? I will try to attach a picture of how much it rubs to see if you can help me choose a spacer size, I have never spaced any tires in my life. I appreciate the help
 

SouthSideStang

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Here is the tire rubbing
 

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94slowbra1

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Is that rubbing on the irs cradle or the sheet metal inner liner? If it's just the the inner liner ( the textured part) then just take a big ass hammer and massage it a little
 

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