To this point, all of the suspension components have been tucked away under the car. It bugs me sometimes that we spend so much time developing these really trick suspension components, and hardly anyone ever sees them. But, the tires and wheels are right out there for everyone to see. It could be argued that the tire/wheel combo has a much larger impact on the overall look of the car than the paint. Shiny paint is great, but the stance and attitude of the car is really set by the tire/wheel combo and how it fits in the wheel wells. This is where form and function need to work hand-in-hand if you want a car that looks good and works well.
This Tech Tip is From the Full Book, HOW TO MAKE YOUR MUSCLE CAR HANDLE. For a comprehensive guide on this entire subject you can visit this link:
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Most of the earlier muscle cars came from the factory with 14- or 15-inch-diameter wheels, in 6- or 7-inch widths, wrapped in nylon cord bias-ply tires. At the time, these were considered performance tires and wheels. Goodyear brought out the belted-bias tire in 1967 and they were all the rage for five or six years. Then, the steel-belted radial tire finally began to overtake the market.
General Tire Behavior
The primary dynamic difference between bias-ply and radial tires is that the tread of the bias-ply is more flexible than the radial. During heavy cornering, this results in the tread profile bending and lifting some of the contact patch up off the ground. That’s not good for performance.
By comparison, the radial design tends to flex the sidewalls more and keep the tread surface flatter and in better contact with the road surface. This is a good thing. It can come around and bite you as you get into modern performance tires and sizes, though. These tires have shorter, stiffer sidewalls so they are less compliant. That gives you better handling and response in general, but makes the tires much less forgiving of incorrect camber. The tire carcass is stiff, and if you introduce positive camber to it in a turn, it simply lifts much of the tread off the road. In photos I’ve seen as much as half of the contact patch off the road with light under the tire! That gives you a tire contact patch about the size of a bicycle’s. This explains why I’ve had a number of inquiries from folks who’ve added modern performance wheels and tires to an otherwise bone-stock vintage muscle car. I’ve heard the same story several times: The new, modern tires felt fine at first. But, once they pushed it, the errant front end geometry did its thing and they experienced understeering out of control off a highway ramp and across a grassy embankment. That’s almost always bad. Simply put, these modern performance tires (V, Z, and Y speed-rated tires in the 17-inch or greater diameter range) are designed to work on cars with modern geometry. It’s best to correct the geometry of the car anyway, but you should at least upgrade springs, shocks, and sway bars if you plan to run tires and wheels of this type.
Can you run 15-inch-diameter wheels on a performance-handling car? Yes you can! Technically, you can also run a marathon wearing swimming fins, but I wouldn’t recommend it. There are two big problems with running 15-inch-diameter tires. The first is tire selection. There just aren’t any truly good-handling performance radials in 15-inch sizes that suit muscle cars. You’re limited to (honestly) light truck tires with white letters on them. The other problem with 15-inch (or smaller) wheels is how they seriously limit your brake choices. Remember, 13-inch-diameter front brake rotors are pretty much the standard of the industry for entry-level performance brakes today. There’s simply not enough room to fit a 13-inch rotor and caliper inside a 15-inch wheel. You are limited to either a small caliper and a 12-inch rotor, or a big caliper and an 11-inch rotor.
There’s a wide range of vintage-style wheels available today in modern sizes that let you retain the old-school look with real performance tires and serious brakes. You don’t have to run super-short-sidewall tires either; there are plenty of meaty tires available to fill out the wheel-wells in traditional hot rodding style.
Today, good performance 16-inch tires are available, but in very limited sizes; most of them are short and not larger than 255 mm in cross section. Conversely, 17-inch tires are available in a huge assortment of sizes and brands. Prices are also quite affordable. If you’re serious about performance, I suggest that your choices start with 17-inch wheels, and then, depending on your application, you may want to go larger still.
There are many manufacturers that are currently making 17-inch-plus wheels suitable for muscle-car applications. They range from factory-looking steel wheels to 22-inch-diameter chromed billet-aluminum bling monsters. Your first consideration should be the general theme of your car. If a stock-appearing Restomod look is what you have in mind, you can narrow your search to only a few manufacturers and styles. Many of these wheels are steel, but billet-aluminum clones of factory wheels are available from some sources and there’s a big selection of vintage-looking mag wheels.
A word of warning here: If you’re upgrading to bigger brakes (and you should be), check with the wheel manufacturer to be sure they clear your brake package. Wheel diameter is not your only consideration for clearance. It’s a real bummer to have new brakes, wheels, and tires and then find out you can’t bolt the wheels on the car. Some brake companies (such as Baer Brakes) have online templates available for their brake systems to assist in wheel fitment.
If an up-to-date, modern Pro Touring car is what you have in mind, you have a daunting selection of styles and manufacturers to choose from. At this point you can start narrowing your selections by style and backspacing. Many of the wheels available are intended for late-model rear-wheel-drive and front-wheel-drive cars, which tend to run a lot more backspacing than traditional muscle cars. There’s no sense agonizing over which exact style to get only to find that they don’t make it to fit your car. Sites like www.pro-touring.com and www.lateral-g.net are a big help in choosing your wheels because people often post pictures and opinions of various wheels and tires on their cars. I discuss fitment in the next section and in even more depth when I cover each model of car specifically (in Chapters 8, 9, and 10).
Tire selection is another exercise in analyzing what you need and then finding it. If your car is going to be driven regularly on the street, good tire wear and all-season capability may be requirements. You can still achieve all-around good performance with a long-wearing all-season tire, but the ultimate limits of the car are somewhat less than they would be with a no-holds-barred tire. Most performance-handling muscle cars are well served by a three-season, fair-weather Z-rated tire. There are a lot of great choices in this class. Not all of them are available in every size, so the front/rear combination you select is a big factor in your choice.
Internet Web sites like www.Tire Rack.com are invaluable when shopping for tires, sizes, reading reviews, etc. Serious cars that may see open-course road racing or track days may need to step up to Y-rated tires for their higher speed rating. If autocross or track days are in your plans, you may also want to consider a spare set of wheels and a set of race (or R-compound) tires. Check your class rules before you buy, to make sure you’re not getting something illegal for your class or selling yourself short with too conservative a choice.
Any performance car can make good use of slicks, DOT-approved street slicks, or drag radials when at the drags. High-horsepower cars (more than 600) benefit from drag radials in the rear all the time. Both B.F. Goodrich and Nitto Tire drag radials actually handle quite well with higher tire pressures in them. Yes, tire wear is poor, but it’s poor on big-horsepower cars anyway. I’ve had the opportunity to drive several cars making horsepower in the 800 to 1,000 range, and in my opinion they’re almost unsafe to drive without drag radials or other DOT-legal street slicks. At this high power threshold, tire selection is very serious business. Even with drag radials, these high-powered cars easily smoke the tires at highway speeds. Without the ultra-high-performance tires, it’s like driving on ice. All the big horsepower is going to waste if you can’t put it to the ground.
After choosing the kind of tire you need, you have to choose sizes. This is going to vary wildly for different cars, but some general rules apply to all of them. Once again, bigger isn’t always better; just right is always better.
Like many hot rodders, I spent a lot of time trying to stuff the biggest-possible tires under my cars. Then, a girl I dated pointed out that she could go faster through a particular set of tight twisties in her beat-up Ford Escort with 13-inch wheels than I could in my 1970 455-ci Firebird with the big tires. She could take it flat out and I had to lift at several places to keep the tires from rubbing on the inner fenders. It was hard on my ego, but she was right!
I was also guilty of running the largest tire I could on a given wheel size. It’s a common enough affliction, but one you should try to cure. Tires actually handle better and provide better all-around traction when mounted on wheels that are wide for the size of the tire. So you may be able to put a 275-mm cross section tire on a 7-inch-wide wheel, but a 245-mm tire actually provides better handling on the same 7-inch wheel. Put that 275-mm cross section tire on a 9-inch-wide wheel and you’ll be way ahead of the game and outperform the 245.
I know there’s nothing cool about running smaller tires, so think of this more in terms of running bigger wheels for a given-sized tire instead. That’ll make you feel better about it.
Written by Mark Savitske and Posted with Permission of CarTechBooks