Confirmation on wheel backspacing and tire size before the credit card comes out. - Please don't ban me ;-)

Why 11" rims if only to fit 285 tires?

I guess I'm scared of interference running  335/30's. And they're only 25.9" OD and recommended for a 12" wheel which I'm also scared of.

Or should I run 18x10 wheels if I stick with that 285 or 295/40?

Is there any particular reason as to why you plan to go with a 17" & 18" combination rather than a 18" & 19" combination.

17" tire selection is getting less as time goes on.

Mark #5481

Hey Mark,
Unfortunately the AC-III wheels only come in 17 and 18. Those are my favorite wheels that I've found. The Forgestar F14s are my next choice but I'm not in love with them.

In back, the main interference is the edge of the rim vs the stud/washer/locking nut on the lower rear upright. Some giant Pantera-specific rear wheels are built with a second inset designed to allow that stud to ride inside the wheel's periphery. Running rear rotors on the outside of the wheel flanges shoves the wheel and tire outboard by the amount of the rotor and stub-axle flange thickness, too.  Trying to run 335-30 rear tires usually shortens the overall drive ratio enough to affect fuel mileage, attainable top end and other things. When you lower the front to visually match, it affects bump-steer unless you address that, too.

Big aftermarket wheels are HEAVY, too since they are made of denser aluminum instead of stock magnesium, so readjust your rear shocks & maybe the springs accordingly on those necessary coil-overs.  And keep in mind the requirement for both tire outside diameters to be within specs to keep from wearing those delicate limited slip clutches from differential wheel speeds. Try to choose tires with close to 26.8" OD so the speedo and odometer read correctly.

Finally, the wider the rear tires, the more critical rear wheel alignment becomes- especially camber. Ultra-wide tires need far less toe-in and camber for good handling, due to the tire rubber's compliance. And nothing detracts from the impressive look of giant rear tires quite as much as cord showing on the inside edges of those expensive meats from running excess camber. They are visible to drivers behind you- including overzealous cops looking for an excuse to "talk" to you! All this stuff is fixable but it will drain your 'discretionary income'.

Go with the Falken's.

Up front, use a 235/40-17 on a 17" x 8.0" wheel (5.375" BS, 5x114.5 PCD and 62mm CB). On the rear, use the 295/40-18" on an 18" x 11.0" wheel (6.5" BS, 5x114.3 PCD and 62mm CB). It really is OK to use a 335/30-18 but as the 295 is 12" wide, it will be fine too. You could put the 295 on a 10" wheel but the 11" gives you more flexibility with tire choices in the future (or when you go to a Pantera event, see all those 335's on 11" wheels and change your mind!). 

Two things to keep in mind: check your brake caliper clearance. The closer you can come to that spec, the thinner the center your wheel manufacturer can use, which means a deeper dish. Also, at the front, measure the distance from the wheel mounting surface to the end of the spindle. Your wheel manufacturer will want to make sure the grease cap fits under the center cap. No concerns at the rear.

You asked! 

Thanks guys. Super helpfuland much appreciated!

@jmardy posted:

I know this subject has been beat to death and I have spent days reading threads on wheel sizing and backspacing. many thanks to everyone and especially @George P for his super useful data and comments.

My car is a '73 with Ridetech coil-overs and is lowered a bit. In lowering it, I snagged the front wheel arches with my stock 15x7 and BFG TA 205/60 tires, so fender rolling is on the to-do list regardless (as is raising the car back up a little).

The wheels I'm looking at are the AC-III Cobra/Halibrand from ET:
http://www.etmags.com/ac_iii.html
For the fronts, 17x8 with 5" backspace with a 225/45ZR17 (25" OD)
https://www.tirerack.com/tires...5WR7ECS&i1_Qty=2

For the rears, 18x11 with 6.5" backspace and a 285/40ZR18 (26" OD)
https://www.tirerack.com/tires...amp;partnum=84WR7ECS

Or if I went with Falken Azenis, I could use a 295/40-18 which is a little taller at 27.2.

Thoughts on tire sizes and backspacing would be very much appreciated.

I have the AC-lll wheels on My 73. 17x8-18x11 with Continentals 245x40x17-295x35x18 I did have to roll the front a little. Can't remember the Back spacing off hand, I can look tomorrow if that helps?

Thanks @cuvee. That looks fantastic. Mine is white as well.
I took David's advice on backspacing but I did go with 225/45's instead of 235/40's because they are 25" tall. And I really hate tire rubbing.
Ordered yesterday. Will update on progress.
Going to do the Tech Bulletin fender rolling spec.

The 235/40's are only 24.4" tall. Where rubbing is a concern, height is usually a bigger issue than width.

Keep in mind, the 225/50-15 P7's we all ran decades ago, were only 23.9" tall.

Good point. I went with these:
https://www.tirerack.com/tires...tnum=245WR7RT615KPXL

https://www.tirerack.com/tires/tires.jsp?tireMake=Falken&tireModel=Azenis+RT615K%2B&partnum=94WR8RT615KPThe RT615 rear is 5 pounds lighter (!) than the RT660 and are rated better (and a little bit less expensive).

Be careful with the Tire Rack's "ratings". Things that are important to most drivers might be detrimental on a Pantera. The RT615 has more tread grooves than the RT660. As a rule, a tire with more grooves is better in the wet and more comfortable. The tire with fewer grooves would be better in the dry and be more stable under heavy braking. What's best for you depends on how you operate your vehicle.

Thanks David. My bar is set a a 5 year old set of Radial T/As so the improvement either way should be stunning.