Backspacing is the distance from a wheel&8217s mounting flange to the farthest point inboard on the wheel. Some manufacturers measure from the mounting flange to the bead and not to the little lip around the circumference of the rim, but Weld uses the latter method. Also, make sure to measure from the exact point where the wheel will contact the car, not from any depression that may be around the lug nuts. Deeper backspacing moves the wheel and tire inboard on the car; shallower moves them outboard. |
When measuring the width of a wheel with no tire mounted, measure only from bead to bead--not the entire width. As a rule of thumb, Weld tells us the bead is usually a half inch from the outer edge of the wheel. That’s why this wheel appears to be 61/2 inches wide overall, but from bead-to-bead it&8217s considered a 5-1/2-inch-wide wheel. |
A wheel measurement that’s become critical with today’s performance disc brakes is the mounting-pad depth, or the distance from the wheel’s mounting flange to the nearest point of contact outboard of the flange. That&8217s where the brake calipers need clearance. Old discs needed something like 5/8-inch pad depth, but Weld tells us that clearance requirements up to 15/8 inches are not uncommon these days. |
One of the more critical dimensions that affects tire clearance is the section width of the tire, or the overall width from sidewall to sidewall with the tire mounted on the rim and full of air. To check it, lay the tire on its side, place a straightedge across the tire, and measure the distance from the bottom of the straightedge to the floor. |
Here’s an unusual glitch we&8217ve run into: With some combinations of brakes and wheels, the hub may be long enough to contact the inside of the lug-nut cap on the wheel. Check it out before you buy wheels. |
To get an idea of the wheel backspacing to try, hold a straight edge against the wheel-mounting surface of the car, then use a tape measure to check clearance at all points. If you’re using 15-inch rims, hold the tape measure 71/2 inches from the center of the hub (half the rim diameter) to estimate the location of the rim. Don&8217t forget to account for sidewall bulge. |
To measure overall height, put the tire against a wall so it’s straight up and down, then place a level at the highest point and line up the bubbles. The distance from the bottom of the level to the ground is the true height. You’ll find that tires get a bit taller when mounted on rims. The BFG G-Force T/AKD is a 275/40ZR17, and it&8217s 253/8 inches tall with a section width of 111/16 on a 9-inch-wide rim. |
Both these tires are 26x11.50 M/T ET Streets. The one on the left is on a 15x10 wheel, and the one on the right is on a 16x8. Note that the right-side tire is an inch taller than the other--that’s because you can’t trust the sidewall designation to know the true height of the tire. We&8217ve yet to see a tire manufacturer print specs that are the true size of the tire. Secondly, while both these 11.50s have the same measured tread width, the tire on the 10-inch rim has a much greater section width. The wider the rim, the wider the tire will be when mounted. |
 |
This photo and the one above it show two different tires on our Duster; one is a Dunlop P235/60R15 (true tire height x width, 24-1/2x99/16) on a 15x7 with 4-inch backspacing and the other is an M/T 28x7.50-15 (really 27-1/4x7-1/6) on a 15x4 with 2-inch backspacing. Note that the closest contact point to the sheetmetal is at the front of the fender opening when the tire is steering. Both tires have about the same clearance, which tells you this: If you want taller tires, they may need to be narrower, and if you want wider tires, you usually have to go shorter to obtain the needed clearance. |
With tall tires--especially those purpose-built for drag racing--you often need greater clearance than you would with a low-profile handling tire because the sidewalls will flex more. These M/T 28x11.50-15 ET Streets (true measurements: 279/16x105/8) on 15x7s fit our Duster with about an inch of clearance to the leaf spring and the quarter-panel, but the wheel lips need to be folded to prevent rubbing during turns and hard launches. |
When measuring for tire fitment, don&8217t overlook potential contact with the tie-rod ends as shown on our 1967 Impala wearing a 17x9 Weld wheel with 5-1/2-inch backspacing. The solution is either less backspacing (5-inch would work here) or a larger rim diameter that would allow the tie rod to tuck inside the wheel. |
Many of Welds wheel fitments outlined in this story use the widest tires possible on all four corners, so the designs are often low-profile. If your car isnt lowered, tires that are too short look bad. Check out the photo of our stock-height 1967 Impala--theres way too much air around the tire. |
Lower the car 4 inches (three hefty pals on the hood) and it&8217s instant sweetness. Filling the wheel opening with rubber is key to a sharp stance. |
Weld sent us one of its new 17x9 Draglite XP wheels mounted with a BFG G-Force 275/40ZR17 (253/8x111/6) to try on our 1970 Chevelle. It fit the front perfectly, with only light contact at the rear of the upper control arm at full steering lock and full droop, a situation unlikely to occur while driving. It’s best to check-fit with the full weight of the car on the tire. |
"Wrong wheels." With those two words we’ll easily dismiss a car’s potential for a feature in the magazine. Perhaps it’s not just the look that’s wrong--could be right wheels, wrong fit. Tires hangin’ outside the fenders. Too much room between the rubber and the sheetmetal. Tread so wide you can’t steer. Meats that are just plain too dinky. Ugly, ugly, wrong, ugly.
Don’t let this happen to you. The wheel-and-tire combo is one of the biggest styling statements you can make with your car, but blundering on the fitment can wreck any combo. It’s an expensive mistake, too, since few companies will take back wheels or tires once they’ve been mounted. Tough as it seems, you have to pick the right rubber the first time. Our best advice on that score is to borrow some wheels from a friend and try before you buy. Even if the loaner rollers aren’t the right fit, you can use the photo captions in this story to help determine the perfect setup.
Here’s another plus: We found out that Weld Wheels has put a lot of effort into finding the perfect wheel sizes and backspacing to fit the biggest tires possible for a number of applications. The company test-fit real-world musclecars with rims from 15 to 20 inches in diameter with varying tires and supplied us with a sampling of the information for the cars most likely to be owned by Car Craft readers. We decided to print Weld’s findings for rims up to 18 inches in diameter. Anything bigger is pretty extreme for a street machine. Before we get into Weld’s specific recommendations, there are a few caveats. First, the backspacing information will not be accurate if you’ve either narrowed or widened your rearend, or if you’ve altered the brake system in a way that will affect the vehicle&8217s track width. Some aftermarket disc-brake hats are thicker than stock by as much as half an inch; also, swaps that involve different-than-stock spindles or control arms may move the wheel-mounting flange inboard or outboard from the factory location.
Weld tested each fitment for clearance at full jounce and rebound, so the tire/wheel combos mentioned will fit lowered cars as long as the location of the factory bumpstops has not been altered. You may run into clearance problems if your steering stops have been altered from original. Also, the older and sloppier your suspension, the more likely you&8217ll run into tire-contact problems thanks to excessive body roll.
Next, we noted that Weld seemed to be going for the widest possible tires; in our opinion, it’s sometimes better to fill the wheelwells with taller tires at the cost of slightly skinnier tread width.
Finally, know that Weld did all the fit-checking with its own wheels. Weld’s specs should work with wheels of any brand, but it&8217s possible that different manufacturers either measure or manufacture wheels just differently enough that there could be trouble. Test-fits were done with both BFG G-Force T/AKD tires and Bridgestone Pole Positions; Weld reports that, size for size, the BFGs tend to run a tad larger than the Bridgestones. So, once again, trying it out is your best bet--but this list gives you a very solid place to start.
1967-1969 Camaros and Firebirds
15-inch: 15x8 with 4-1/2-inch backspacing front and rear. With some tires the rear shocks will have to be mounted inboard; if you do that, some combinations of 9-inch rear wheels will work with 5-1/2-inch backspacing.
16-inch: 16x8 with 4-1/2-inch backspacing front and rear. The rear shocks will have to be relocated inboard. Use tires with an aspect ratio of 50 or less with section widths of 245 to 255.
17-inch: 17x9 with 5-1/2-inch backspacing front and rear. There may be lower-control-arm contact with some steering gears. Use tires with an aspect ratio of 40 or less and section widths of 245 to 255.
18-inch: 18x9 with 5-1/2-inch backspacing front and rear. Use tires with an aspect ratio of 35 or less with section widths of 245 to 255 in front and 275 in the rear.
1970-1981 Camaros and Firebirds
15-inch: 15x8 with 4-1/2-inch back-spacing up front. Camaros use 15x9 with 5-inch backspacing in the rear; Firebirds can use 15x10 with 51/8-inch backspacing in the rear. Use tires with an aspect ratio of 55 or less with widths of 255 front, 285 rear. You&8217ll need to remove the outer rear seatbelt anchor/retractor and flatten the bulge in the rear wheelwell with a hammer.
16-inch: Same as for the 15-inch recommendations but with a tire aspect ratio of 50 or less. There may be lower-control-arm contact with some steering gears.
17-inch: 17x91/2 with 6-inch back-spacing up front; you’ll need to modify the steering stops or the lower control arm to prevent contact. Camaros use 17x10 rears, Firebirds use 17x11, both with 6-inch backspacing. As mentioned in the 15-inch recommendations, you’ll need to remove the seatbelt retractor and bulge. Use tires with an aspect ratio of 40 or less with widths of 275 front, 295-315 rear. This is a really tight fit, so success will vary car-to-car.
18-inch: Use the same recommendations as for the 17-inch rims, but the tires need an aspect ratio of 30.
1982-1992 Camaros and Firebirds
15-inch: 15x8 with 4-1/2-inch back-spacing front and rear. Use tires with an aspect ratio of 55 or less with a section width of 255.
16-inch: 16x8 with 4-1/2-inch back-spacing front, 51/8 backspacing rear. Use tires with an aspect ratio of 55 or less and a section width of 255.
17-inch: 17x9 with 5-1/2-inch back-spacing front and rear. Use tires with an aspect ratio of 40 or less with section widths of 255 front, 275 rear.
18-inch: 18x9-1/2 with 5-1/2-inch back-spacing front, 18x10 with 6-inch backspacing rear. Use tires with an aspect ratio of 35 or less with section widths of 275 front, 275-295 rear.
1993-2000 Camaros and Firebirds
16-inch: 16x8 with 6-1/2-inch back-spacing front, 16x9 with 61/2-inch backspacing rear. Use tires with an aspect ratio of 50 or less with a section width of 255 front, 275 rear.
17-inch: 17x9 with 6-1/2-inch back-spacing front and rear. Use 27540R17 tires.
18-inch: 18x9 with 6-1/2-inch back-spacing front, 18x10 with 7-inch backspacing rear. Use tires with an aspect ratio of 35 or less with section widths of 275 front, 295 rear.
1978-1987 GM A- and G-bodies
15- to 18-inch: All rim diameters use 8-inch-wide wheels with 4-1/2-inch back-spacing. Use tires with an aspect ratio of 50 or less with section widths of 245 front, 255 rear. Some model/axle combinations will accept 9-inch-wide rears with 5-1/2-inch backspacing, so you need to check first.
1964-1967 GM A-bodies
15- to 18-inch: All rim diameters use 8-inch-wide wheels with 4-1/2-inch backspacing. Use tires with a 245 section width and aspect rations as follows: 15-inch, 60; 16-inch, 50; 17-inch, 40; and 18-inch, 35.
1968-1972 GM A-bodies
15-inch: 15x8 with 4-1/2-inch back-spacing front and rear. Use 255/60 tires.
16-inch: 16x8 with 4-1/2-inch back-spacing front and rear. Use 255/50 tires.
17-inch: 17x91/2-inch with 5-1/2-inch backspacing front, 17x11 with 5-1/2-inch backspacing rear. Use 275/40 front tires and 315/35 rear. This is tight in the rear.
18-inch: Same as 17-inch.
1994-2000 Mustang
16-inch: 16x8 with 5-1/2-inch backspacing front and rear. Use 245/55 tires.
17-inch: 17x9 with 6-inch backspacing front and rear. Use 255/45 tires.
18-inch: 18x9 with 6-inch backspacing front and rear. Use 255/35 tires.
1979-1993 Mustang
15- to 17-inch: All 15- to 17-inch rim diameters use 8-inch-wide rims with 5-1/2-inch backspacing and 245/55 tires.
1967-1968 Mustang and Cougar
15-inch: 15x8 with 4-1/2-inch back-spacing and 225/60 tires front and rear for 1967-1968; 1969-1970 can use 15x9 with 5-1/2-inch backspacing and 235/60 tires in the rear.
16-inch: 16x8 with 4-1/2-inch back-spacing and 225/50 tires front and rear for 1967-1968; 1969-1970 can use 16x9 with 5-1/2-inch backspacing and 245/50 tires on the rear.
17-inch: 17x8 with 4-1/2-inch back-spacing and 245/40 tires front and rear for 1967-1968; 1969-1970 can use 17x9 with 5-1/2-inch backspacing and 275/40 tires on the rear.
18-inch: 18x8 with 4-1/2-inch back-spacing and 245/40 tires front and rear for 1967-1968; 1969-1970 can use 18x9 with 5-1/2-inch backspacing and 265/35 tires on the rear.
1965-1966 Mustang
15- to 18-inch: All rim diameters use 7-inch-wide wheels with 41/4-inch backspacing and 225-section-width tires up front. Rear wheels are 8-inch with 4-1/2-inch backspacing and 235-section-width tires in the rear except for 18-inch rear wheels, which can use 245/35 tires. Tire aspect ratios for each rim diameter are as follows: 15-inch, 60; 16-inch, 50; 17-inch, 40; 18-inch, 35.