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Discussion Starter · #1 ·
Stock 275/40R20 on 20x9.5 Dynamics Package wheels to 315/35R20 on 20x11 MRR M392 Replicas (+24mm offset)...

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Before/After (Note the inner and outer sidewall positions relative to the body):

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Rear 315 on 11s -vs- Front 275 on 9.5s (Note the sidewall bulge and amount of inner liner visible):
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Results, Context, and Important Details:
The 315s are the Ferrari spec Pzero variants with only 160 treadwear. They are very soft and extra wide (sidewall to sidewall) for what the industry calls a "315". Something cheaper like an Atturo are slightly narrower and should fit with no problem. I wager only a Michelin Pilot SuperSport or a real comp tire might be physically wider at the stated size.

My combination just lightly rubs the inner fender liners at the front formed ridges with the car on a lift and the wheels drooping. As you spin the wheels you can hear the design on the sidewall making a zipping noise on the liner. When you lower the car onto the ground the contact moves to the floppy curve in the rear of the liner (Easily trimmed or heated and reformed out of the way). Everything else clears even at skidpad turns and over speedbumps like a Duke boy. With my side mirrors pointed at them I could see the IRS rear just pulling the top of the tread inside the metal fender upon compression. This is obviously dependent on your alignment. I know mine is maxed right around -1.2 degrees camber.


The Effect:
I had the pressures a touch high and they peaked around 40psi when hot but in 87f weather it was able to stick the car on a WOT 1-2 shift with little more than a chirp. The stock tires would blow right off and start hopping in the same conditions. My little skidpad circle rub test was extra fun. For a moment there I couldn't tell if they would break loose or just flip the damn car.


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There. I ABSOLUTELY maxed it out without a roller, hammer, spacers, or flares. Now everyone can stop asking... right? 馃お

Now I just need to squeeze some 295s on those 20x9.5s up front to match that beefy sidewall shape.
 

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Night and day.
That's adding some hips to that lady!
 
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Thanks, did you go thru e bay to get your wheels or? Looking for a pair for my t/a then mount my nitto drag radials
 

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Discussion Starter · #7 ·
I ordered the MR392 wheels through Merrick Motorsports. Tires came from TireRack (I'm not sure they're available anymore. Mine were manufactured a year ago.)
 

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2021 JEEP Wrangler Unlimited Willys 4X4
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There. I ABSOLUTELY maxed it out without a roller, hammer, spacers, or flares. Now everyone can stop asking... right? 馃お
No, no.....you鈥檙e absolutely incorrect.

There will always be those certain few that will be toooooo lazy to search, will ask again and again, and a huge percentage of those will require spoon feeding with a link to this thread.

Rubbers look awesome!!!!!
 
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2019 Dodge Challenger T/A 392 6 speed
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Thanks for the post. I've been thinking about doing this., but I see conflicting information out there. It's nice to see someone, who has been there, done that, write a detailed post. Your car looks great! I may go with 295s or 305s and hope it doesn't rub at all.
 

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Discussion Starter · #10 ·
Any other 315 would have cleared perfectly. I was definitely pushing the limits with this Ferrari Pzero tire. And any 305 would obviously work fine.

295s on an 11" wheel would look pretty stretched. That would be something I would put on the factory 20x9.5s then add a thin spacer to get them flush with the fenders.

In fact, that's probably what I'll end up doing for my fronts.
 

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295s on an 11" wheel would look pretty stretched. That would be something I would put on the factory 20x9.5s then add a thin spacer to get them flush with the fenders.
You don't think 295s would look too "ballooned" on the stock wheels? I thought they'd be too wide. If they will work on the factory wheels, I'll save the money on wider wheels.
 

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Discussion Starter · #12 ·
Maybe. I might settle for a 285 if I can get one without a bead protector. That way the sidewall curves nicely from the tread to the bead like my rears above.
 

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So no need for the WB to get the beefy wheels on the rear wheels at least. I bet the 1320 trim would really hook up with something like this. I'm thinking of going against most peoples advice and getting the 1320 anyway instead of the WB. I do love the look of the front end of the widebody, but the side view looks much better with the regular body IMO. I could always switch the front end out to a hellcat at some point.
 

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Opticon, great write up and thanks for the research. I've been thinking of a new set of tires and wheels for my 15 SPS and your testing has got me thinking of a direction.

From your research, can you recommendation 305/35R20 on 20x11... without any worries/fear of tire rubbing.
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Tire Wheel Car Automotive tail & brake light Vehicle

BTW... the 315/35 size is the same tire width and tire wall height on my 91 ZR1 for the rear. These are old pics and I now run Nitto 555 on those as choices are limited.
 

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Discussion Starter · #15 · (Edited)
Opticon, great write up and thanks for the research. I've been thinking of a new set of tires and wheels for my 15 SPS and your testing has got me thinking of a direction. From your research, can you recommendation 305/35R20 on 20x11... without any worries/fear of tire rubbing.
I am not aware of any 305s with the wild overall width of these oversized 315s so if you stay with my +24mm offset you are good to go.

Now if you prefer to squeeze them further under the car so you don't sandblast your rear fenders, you might try a 305 with an offset just a few mm higher than mine. You should be able to find examples of that fitment everywhere.

Also note people have put those old 315 Sumitomos up against 315 Goodyear F1s and there's a full inch difference in real width. A good example of how much the real physical dimensions can vary despite the rated size...

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Discussion Starter · #17 ·
I put those 295/40s on the front with a 7mm spacer to fill up some of the visible wheel well...

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Not thrilled that this size of Pzero had an ugly rim protector bead. But it fit very well.
 

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Have you done any 0-60 runs since you put the wider meat on it? I'm kind of curious if it makes very much of a difference compared to the stock tires.
 

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Discussion Starter · #19 ·
Huge difference in street traction. Stock 275 Pzero summers were useless by comparison. Launching well was beyond difficult (even launch control on a hot day at the lowest RPM setting would just wheelhop and give up) and a 1-2 shift would blow them right off again. These 315s are exactly what it should have had from the factory. But that's probably just as much due to the soft 160 treadwear as the width.
 

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Nice. So could a good tire place install something like this if I were to get a regular body at a reasonable cost?
 
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