does 18x10 +38 offset fit?
 

would 18x10.0 +38 with 275/35/18 or 275/40/18 fit in all four corners without modification?

I was looking at enkei rpf1. thank you.

yes, but you are placing the tire further outboard and not using all the inboard space. With wide tires you will have to flare the fender more

just as an example, 18x10.5 +43 is a good fit that uses the inboard space well

the equivalent offset in 18x10 to keep the wheel inboard would be +54

some std and custom reasonably priced options (the S197 Mustang has the same wheel pattern as the RX8): Racing Wheels - High Performance and Racing Parts - Vorshlag LLC



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The link doesn't show any 18x10.5 wheels.

The question is, is it worth giving up wheel width, weight, or availibility to get a more optimum offset.

17x10 RFP1's are lighter, cheaper, and don't have a 8 week wait like 17x10 Forgestar F14s.
18x10 RPF1's lose their cost advanatge, but gain the option of a 18x9.5 +45.

Also given that the Forgestars can be had with custom offsets, what is that best offset to stuff the biggest tire possible in the fenders? +43, 45, 50, or even more? Can you also take advantage of the wider (up to 18x12) F14 options with the right offset?

this is part of a discussion that the OP and I've been having going on at least 7+ years now

18x10.5 +43 is in reference in what has already been proven to fit and use all the space without flaring the fenders, he had PM'd me again about it just prior to making this thread, so it's a reference point I use to fitting a wheel as far inboard as possible

What he also didn't state is that he's looking at higher aspect ratio (larger OD) tires, which compounds the fitment issue substantially

RPF1 wheels have limited if not insufficient clearance for aftermarket brake packages and are also known/proven for bending easily


unfortunately the 10.5" wheel thread I started back in early 2007 no longer exists:

https://www.rx8club.com/series-i-whe...7/#post1908886


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I am running 255/35/18 on 9.5 wide +38 wheels on an aggressively lowered vehicle (spring rates 10k/7k). You likely don't need fender modification (depending on how low you are).

^^Do you have 800 HP with wide tires with extra tall sidewalls?

No, not even close ...

In all fairness he never said anything about that in the OP, so no need for all the sass. My setup is close to what he was asking so I figured I would input.

My post was was in no way out of line and my car sees enough g's to simulate heavy acceleration/deceleration.

I care more that the OP gets the correct info, not so much about your assumptions (that was your second one, fwiw). His inquiry is for fitting a 285/40-18 tire, which has 27" OD with a wide section widthy

If my Forgestars ever show up for the Mustang I can do some test fitting

19x9 +45 255/40R19
19x9.5 +52 275/40R19
19x10 +40 275/35R19
19x11 +55 295/35R19

thanks everyone. I appreciate on the mustang wheel info. tire and wheel sizing is something I just recently started learning more seriously. for straight traction, it's far easier, cheaper, and more effective to go with smaller rear wheel, higher sidewall, and lower the tire psi to achieve the largest longitudinal contact patch with respect to the car. I saw some supra guys running some crap 15" rears with 19" HRE's in the front, and now I know why! Going wider doesn't necessarily give you better straight traction. in fact, if you're going wider and sacrificing the sidewall, your straight traction will likely suffer. Going wider is good for cornering because it gives you a nice transverse tire patch which gives you cornering stability. granted, I will never drive this car that hard to know the difference, but that's another post. as an example, there is a guy running 17" oem rx7 wheel with 255/40/17 slicks putting down 600+whp. wider, especially widebody, isn't necessary to put the power to the ground. it was a revelation for me. saved me a few thousands in planned body work for a widebody and new wheels.

:Peace: OEM Fd RX-7 rims are 16"

Yeah, I wasn't sure about later JDM years though

Traction with 255/40-17 @ 600 hp = lawls, somebody needs to lay off the crack pipe

500HP with sticky 275's = spin city :)

we are going to try 335 rear and 315 front on a 4 rotor FC with about 1000HP...see how that works out :)

I can only speak from personal experience. My MT streets on 19" low profile tires with 285 width were spinning at all gears in pretty much all legal speeds. I have at least 2 credible guys on rx7 forum telling me 255/40/17 slicks holding 600+whp every gear but the first.

It's not just about the width. It's about the contact patch. Additionally, going wider on width does not always equate to a larger contact patch. It often just changes the shape of the contact patch to a transverse rectangular which gives you better cornering traction but worse straight line traction. FYI, I'm by no means an expert, and am mostly writing down what I read and made sense to me.

Check this guy out with stock 16" FD wheels. I understand he's on track with tubed tire, but you get an idea. 335 sounds great and that was the road I was also headed, but that may be little too simplistic in thinking, just imho. but dont' take it from me entirely. Read more about it and get some practical input from the drag guys we love to look down upon. :)

You cannot compare the street to a drag strip no matter what, the launch area is like fly paper.

Here check this out.

Sure, custom subframe with rear drag suspension at the track on slicks is an entirely different scenario than streetable tires on the factory suspension and an add'l 200 hp.

19x10 +40 275/35R19 look like they fit (I didn't drive the car around & check for rubbing)
19x11 +55 295/35R19 hit the inner fender in the rear at full droop

good info.

There are many decent ford racing oem wheels for roush/boss/saleen mustangs with rx8 offsets with or without a small spacer. Not a bad option.

you may have to roll the fender with 19x10+40 especially with appropriate tire width for that rim. 19x11+55 is interesting. what tire are you running with it and have you tried it with 5mm spacer? which model mustang is that from?

We've been through all that before. Sure, if you either want severe tire rub or instead decide to seriously modify the fender well to account for how tall the tires for those wheels are. Or did you forget that your original goal was to have a taller sidewall?

Not sure why you always steer away from good advice towards bad ...?

I realize 18x10.5 +43 fits well. Those are generally SSR offset, and I found that that configuration is very scarce (nonexistent so far) in the used market. Brand new, I'm looking to spend $1000/wheel at that size directly from SSR, money I rather spend on more important things. I think Mickey thompson and mustang knock-off manufacturers makes similar offset, but I heard pretty bad things about their wheels.

Having said that, I just thought it would be nice to find an OEM wheels which are generally of high quality that people let go quite cheaply as they upgrade to their aftermarket counterparts. For example, you can find BBS wheels made for BOSS Mustang used for $1000/set. They are 18x10 with 46+ offset. I found one almost 1000 miles away, and they were snatched up quickly. Maserati rear wheels are 19x10.5 with ~50 offset which would work with spacer. Finding OEM upgrade wheels made by BBS, rays, HRE, etc. that will fit our wheel wells would benefit many rather than one specific SSR configuration which would cost $2000-4000 new and rarely comes up used. I also thought about building center hub by welding and machining our bolt pattern for enkei 18x10.5 wheels, but costs add upto $2k mark with perhaps suboptimal product heavily dependent on machining and weld quality. It's just to circumvent the cost element with a viable replacement product without compromising wheel quality.

They are for a s550. And the tires are taller than the RX-8 tires.

19x11's had 295mm tires. I suspect they might fit with shorter tires and/or a spacer. I'll experiment more in the off season. The RX-8 isn't running right, so need to get that sorted first before any serious fit testing.

All that doesn't matter. There is a certain width and OD that fits without modification, which now being 11+ years since the RX8 came out, is well established. If you're willing to modify the fender and wheel well then anything can fit. The OPs issue is that with 700 whp he needs serious wheels, tires, and fender mods. Throwing on some 10.5" wide wheels with street tires won't cut it regardless ....

Well feel free to enlighten us who are new to the scene. You never actually told us what the limits are. If it's +43 10.5, what is the max tire size, who actually makes that size, and why does going 5mm to a +38 suddenly make your car explode?

P.S. my RX-8 has a LS swap, so bigger rear wheels & tires might be appropriate to help get the power down to the ground. So I might be exploring ground (max rear fittments) that wouldn't be useful for a normal rotary RX-8, and thus not so well known.

18x10.5 +43 with 285/35/18 works and generally considered the largest possible fit. that's teamrx8's point.

to answer your second question regarding +38, because 18x10.5 +43 is already pushing it.

mustang rears 18x10.5 +45 may work depending on tires (most likely not hoosier a6 305/30/18), and is the point of discussion a few posts back.

I have 275/35/18 RE-71R now on 18x9.5 and they grip after 3rd gear. so cheapest option may be stickier tires. keep the sidewall high and pressure low for acceleration/decel. maximize width for cornering. it's expensive to be able to do both with same set, so I just got 2 different sets of wheels/tires which is actually cheaper than trying to fit something that won't fit.. I probably go 15" rear just for drag if I ever get around to installing my new trans.

to my own fault, i love trying to do something different. but in the end, what's tried and true generally will save you money and time.

having said all that, 18x10.5 +43 will fit but will set you back $2000+ because that's mostly SSR fitment.

18x10.5 +45 may be an attractive alternative to fill out the wheel well for lot cheaper (popular mustang rear fitment) but that hasn't been tried and proven to our knowledge.

If you want to replicate that 18x10.5, 43mm offset SSR fitment for less, there's also this option:

FK Ethos RT-6 custom rims

A search will reveal that it's been tried on this board at least in the rear, but with an offset only 2mm different than the SSR's, it should still fit and at worst, you can add a 2mm spacer.