Hello Everyone,

I am looking to purchase 2009+ Corvette wheels. A couple of options I am looking into are:

Front
18x8.5in either +40 or +56mm offset
18x9.5in +56mm offset
19x9.5in +

Rear
19x10 either +40, +56 or +79mm offset
19x11 either +63mm offset or +73mm offset
19x12 +59mm offset

I'd like to fit as wide a tire as I can, but I would like to know is any of this possible? Would I need to do any mods? Mini tubs? If possible, what tires should I use? I searched and I could not find the answers I was looking for so any insight is greatly appreciated. This would be for an '87 SS BTW.

I'm thinking about having some (Stockton) ralley wheels built for my SS 17x8 4.5 & 17x9.5 5 backspacing. Will be able to run them year-round........ Please help with feed back.

Hi Folks,

I have a small, but significant, refinement to report for calculating rim and tire widths. I was able to conform the refinement to something simpler than a quadratic fit, so it would remain easy to use on a calculator.

CASE 1: I've got a RIM of a certain width (Wr) and a certain diameter (Phir). Question: What's the best size of tire to get?

Answer: You'll need at least one additional piece of information before you can proceed.
Scenario A: I'm set on a particular tire aspect ratio (AR).

Then: Tire width = Wt = (Wr-8.4mm)/[1-0.42*((AR-5)/100)]
Tire OD = Phit = Phir + Wt*2*AR/100
Tire ID = Rim OD = Phir
Scenario B: I'm set on a particular tire OD (Phit,) probably because I want to keep speedometer calibration.

Then: AR = [100/(2*Wt)]*(Phit - Phir)
Wt = (Wr-8.4mm)/[1-0.42*((AR-5)/100)]

CASE 2: I've got a TIRE of a certain width (Wt,) a certain aspect ratio (AR,) and a certain ID (Phir.) Question: What's the best size of rim to get?

Answer: Wr = Wt*[1-0.42*((AR-5)/100)]+8.4mm
Tire OD = Phit = Phir + Wt*2*AR/100
Rim OD = Tire ID = Phir

A caution about rims: rim OD (Phir) and width (Wr) are measured at the mounting surface of the tire, and do not equate with the extreme width and diameter you would measure on the rim. A typical 17" x 8" rim would probably have an extreme OD of about 18.5" and an extreme width of about 9.2", for example. As always, use the conversion factor of 1" = 25.4mm (exactly,) since industry standards are persisting to keep units jumbled. You've got to keep units consistent within any given equation to get valid answers. And, the answers you get will rarely correspond exactly to something you can buy off the shelf. For instance, let's try a Case 2 example:

I've got a 245-45/17 tire. What's the best size of rim to get?

Plugging-in:
Wr = 245mm*[1-0.42*((40-5)/100)]+8.4mm = 217.39mm. Round to 217mm. Units conversion: 217mm*(1"/25.4mm) = 8.54"
Tire OD = 17"+(245mm*1"/25.4mm)*2*45/100 = 25.68"
Rim OD = Tire ID = 17"

Interpretation: the math tells us we need a 17" x 8.54" rim. Obviously, unless this is a custom rim, you can't get this exact width. Plus, the width equations aren't infinitely precise, but will almost certainly get you to the nearest half-inch. So what to do? 8-1/2" would probably work well. In cases of doubt, and especially when body roll plants the outer tire with positive camber, as is likely to happen mostly at the front of the car, go wider than the equation dictates. 9" at the front of the car should work quite well.

Let's try another Case 2 example, and go back several posts to the person with the 365/15/24 tire. Is his desire to run a 24" x 12" rim a good idea?

Wr = 365mm*[1-0.42((15-5)/100)]+8.4mm = 358mm = 14.1". Conclusion: a 12" rim is way, way off. Btw, even with the right rim, this is far beyond anything that mini-tubbing could afford unless you just let the wheels "hang out" and hope you never hit any big bumps.

Tire OD = 24"+(365mm*1"/25.4mm)*2*15/100 = 28.31".
Rim OD = Tire ID = 24"

Now, let's turn this into a Case 1-a question: I've got a 24" x 12" rim, and want to run a tire with a 15 aspect ratio. What tire do I buy?

Wt = (12"*25.4mm/1"-8.4mm)/[1-0.42*((15-5)/100)] = 309.39mm. Get a 305mm tire.
Tire OD = 24" + (305mm*1"/25.4mm)*2*15/100 = 27.60"
Tire ID = Rim OD = 24"

Answer: I buy a 305/15/24 tire.


Best,
MAP

PS: It would make things a whole lot easier if I could paste a spreadsheet in here. Does anyone know if this can be done, or do I need to post a link external to the forum?

Hi Folks,

In case the eye-strain factor is overwhelming in the post above, just remember this one equation:

Wr = Wt*[1-0.42*((AR-5)/100]+8.4mm

The refinement compared to the previous expression, is that we now deduct 5 points from the aspect ratio when making the sidewall convexity correction. Predicted rim widths increase modestly as a result, and more so for the lower aspect ratios.

Best,
MAP

285/40/17 the ultimate rear 17' tire for g-body. has anyone made them fit w/ stock rear springs no lip rolling ?

Running 17x9.5 5" bs, Nitto 555 Extreme in 285/40/17, with a 5/16 spacer on both sides.
A 4.75" bs would be best, as they are VERY close to the frame.
I would not recommend for everybody, rear UCA/LCA bushings need to be in good shape, otherwise you will have light contact when you drive it hard.
Front are 17x8 4.5" bs w/ Nitto 555 in 255/45/17, still running stock coils,
new coils going on this summer along w front adjustable SPC LCA.

If you run it low, you will need to roll the rear fender lips, the lines on the tire are the tire
design, not slices.

wondering if a 8.5 or 9.0 rim width would suck the sidewall in to help this or does the 285 need a 9.5 min. rim width. when I put 275/50/15 on a 8' rim it looked bubbled on sidewall and probablly lost some tire contact patch as it needed a min 9.0' rim . A fine line...... a fine line

How about 215-70R15 on the front and 255-70R15 on the back? I think they'd fit.

Fit perfect, even lowered 3", with the right backspaced wheels. Ran this setup on my old '88 SS.

Front: 15x6 with 3.5" backspace. 215/70-15
Rear: 15x8 with 4.5" backspace. 255/70-15

Eric that looks amazing...it has the perfect stance and look. I like the 3 star center caps on the Welds. That is the first I seen anything like that done. By the way love the first name.

Eric

It does look great!! Thanks for the response.

Thanks! You are welcome.


Thanks, Eric. Yeah, the 3 bar knockoffs was just something to be different. I miss that old car sometimes, but wouldn't take 100 on trade for my '86.

Here is a short video of it: http://www.youtube.com/watch?v=1mSb-coZHyQ

You can see that tire fitment a little better. You know, there was a lot of great men named Eric. Still is...... LOL! Great to meet you!

ERIC

Man Eric, your old 88 was awesome. That thing looked and sounded great. I may just need to copy that stance on it. I will send you a link to the way my Monte sounds with a 406 in it.

Thanks, bud. My '86 has the exact same stance. A 3" drop on these cars seems to be perfect in my opinion. I think I have already heard that big 406 which sounds great! But, you can send me that link anyway.

A few members have inquired so I thought I'd share some info-as seen in my sig., I run Impala SS wheels (funny story about those too) which measure out as a 17x9 wheel (5" BS) and I have 255/45/17 up front and 285/40/17 out back. Overall installed height is 28" in front and 28.1" in the rear-running Firestone Firehawk SZ50 EP series tires which have a stiff sidewall but a fairly soft tread compound-imo the best road racing style tire for the street. Full Hotchkis suspension allows me to run as tight as 1/8" at the rear frame and not have any rubbing issues. Car also sits 3" lower up front and 2.5" in rear-all custom parts-not many "catalog" parts on this car-mostly all GM components but from a variety of cars-at least 5 different cars that IO remember....lol. This car does everything extremely well-accelerates hard, stops quick and corners amazingly.

here is a 295/50/15 on an 8" rim with 4" back spacing

Would some c5 rims off a 99 vette work for a stock suspension monte? I do plan on lowering it eventually though.

The wheels are :

17x8 1/2 up front with 245/45/17 tires
and
18x9 1/2 in the back with 275/40/18 tires

I just bought an new set of 4, ZQ8 Chevrolet 16x8 with 5 x 4 3/4" bolt pattern with a 4 1/4" backspace. Looking for the widest tire I can get on the front and rear without modifying anything.

"84 ZZ4 posted pics earlier in this post of his tires: Front are 17x8 4.5" bs w/ Nitto 555 in 255/45/17 and 17x9.5 5" bs, Nitto 555 Extreme in 285/40/17, with a 5/16 spacer on both sides."

I like the height of 84 ZZ4 tires, so Im looking for a similar look of tire's for my 16's. 84 ZZ4 setup is just slightly to wide in the rear, because it would require lip rolling if I ever lowered the car 2in or 3in in the future(which I will). So, I need a tire that will not be as wide. I also want a slightly taller tire in the rear by 1 inch to 2 inches than the front. Any help or suggestions is greatly appriciated?
Thanks

So, on a 9" wheel at the rear, what will be the right offset? This is know in each wheel as the ET and on must of the brands measuere this in mm. So we know the Backspacing is 4-4.5" but what we really need to know is ths ET on the wheel for the rear and the ET for the front on 8" wide.

This is what I´m talking about

A stock 1985 SS wheel is a 15 * 7 et 10 mm

With a 18 * 9 the et -15 mm

The Inner clearence is the same and the outer Position is extended by 50mm

Check it out in this web page

http://www.1010tires.com/WheelOffsetCalculator.asp

Offset is the distance from the center of the wheel to the wheel flange (positive if the wheel flange is outboard of the centerline, negative if it is inboard.)

Backspacing is the distance from the wheel flange to the most inboard point of the rim, including the lip for the tire bead.

Width is measured from inside of the tire bead flanges, so an 8" wide rim typically measures 8.5" at it's widest point.

To convert from backspacing (BS, in inches) to offset (OS, in mm), knowing rim width (W, in inches):

OS(mm) = [(BS-0.25)-(W/2)]*25.4

conversely:

BS(in) = (OS/25.4)+(W/2)+0.25

25.4 is just the conversion from mm to in.

looking at getting some new wheels and was wondering what is the most backspacing you can run without usuing spacers.stock suspension.looking at 16x7 for the front and 16x8 on the rear.

I had posted the “chart” below in another thread but thought it might be useful here. The measurements were taken utilizing stock upper and lower controls arms with drop spindles. The spindles won’t affect the sub-frame and fender clearances, but by raising the mounting point of the wheel two inches in order to give the body a 2” drop, 17” or smaller wheels with 4.5” backspacing (or more) can or will give clearance problems at the tie rod. I know it was extremely close on my SS (less than 1/8”) when using a 17x8 SLP ZR-1 wheel with a 4.5” backspacing. However, 1/2" more radius provided by an 18” wheel (compared to the 17” wheel I used for measurements) should give ample clearance at the tie rod for more than 4.5” backspacing – I have no idea of how much more.



Basically it looks like clearance is tight, but good enough to run 245/45-17s and 245/40-18s on an 8” wheels with 4.5” backspacing. I know some have run a 255/45-17 and 255/40-18 tire on 8” wheels with 4.5” BS, but based on my measurements anything wider than a 9.8” section width is pushing things – don’t just go by the tire size since section widths vary between manufacturers and even lines of their tires. Some have reported rubbing with 245/40-18s with a 4.5” backspacing and others have not. There may be suspension differences at play, but I’d lean towards the differences in section widths and sidewall stiffness between brands of tires as the issue.

It seems from the consensus of those that participated in the original thread containing the chart, 8” wheels with the more commonly available 4.5” backspacing give the appearance the tire is sitting in a little more than “optimal”, especially when running wider tires and wheels out back. It makes sense if you think about it – If you’re taking the tire as close to the edge of the fender lip as you can in the rear, if you don’t do the same for the front, the fronts could look a little sunken. If you’re running the same size wheel/tire front and rear (or slightly larger for the rear) this probably won’t be an issue. Also, if you’re dropping the front more than a couple inches, you may need the tire to set in closer to the sub-frame than the fender anyway.

Looks aside, it appears an 8” wheel with a 4.25” backspacing will come close to centering the wheel in regard to sub-frame (under full lock) and fender lip clearance. As will an 8.5” wheel with a 4.5” BS, a 9” with a 4.75” BS and a 9.5” with a 5” BS. Technically, a 0.25” offset (bringing the center forward) is a negative 6.35mm (-6.35mm). The trend is to advertise offset and many advertise a -6mm and -7mm offset which is technically 0.236” and 0.276” respectively. I doubt that the few hundredths of an inch one way or the other will present an issue.

15x10 with 5.5 back spacing with 5/16 spacer 28x10.5 slick, notched to the seam and lip rolled. fits like a glove.

Will a 275/40/17 fit under all four corners without rubbing on a 9 inch wheel with 4.5 in backspacing and -12mm offset?

These wheels
http://www.summitracing.com/parts/brw-997793445
These tires
http://www.summitracing.com/parts/bfg-31629