What Is the Widest Rear Tire You Can Fit on Your Mustang S197?

Larger rear tires will help your Mustang put the most power to the ground and finding the largest size to maximize the tread width is important. I’ve tried a few different brands and sizes to get the most rubber back there. Here’s what I’ve learned about getting the right fitment.

What is the widest rear tire you can fit on your Mustang S197? The biggest tire that fits on the rear axle is a 305mm width on a 10-inch wide wheel. The wheel well will fit a tire with a 12-inch tread width before the tire will come into contact with the body or extend past the fender.

As with any aftermarket parts, there’s a lot of details that go along with changing parts.

 

The Easiest Way to Put a Wide Rear Tire on an S197 Mustang

Absolutely the easiest thing to do and the option that most people take is to just get a nice staggered set of wheels, usually a 9 inch in the front and a 10 inch in the back with a 255 wide tire for the front and the 305 in the rear.

One of the great things about having cars that are a little bit older is that lots of things have been tried already. Plenty of people have experimented the try to fit the biggest tire and lots of information is already known. This is why you can go to almost any wheel vendor, tell them your car make and model, and they can provide you with the exact right wheel offset, backspacing, and size for your car without having to do any guesswork.

If you want to harness the most power you can from your coyote for improved acceleration, really the back tires are where you need to look.

 

Tire Brands Make a Difference in the Actual Width

Sometimes. For example, I recently upgraded my tires from Mickey Thompson Street Comps to Michelin Pilot Sport 4Ss. I pulled all of the data posted on tire rack to compare the tires to make sure that they were going to fit properly and that I wouldn’t be losing any performance to a change in sizing since the Michelins only come in a 305/30/20 which is a bit smaller than the 305/35/20s that Mickey Thompson offers.

According to the posted information, the tread width on Mickey Thompson’s is 10.6 inches while the Michelin’s is 11.2 inches wide. While this may not sound like a big difference, since we’re trying to stuff in the absolutely largest tire we can, half an inch does make a difference.

Tire sizing also is tricky because manufacturers provide a “section width” number. This is a measurement from the very outside of the outer sidewall to the outside of the inner sidewall. So while the tread widths were different for the two tires, the section widths were both identical at 12.3 inches.

This is something you might want to consider when doing research on tire choice since the performance could arguably be greater for the Michelin’s with that extra half inch of tread actually touching the ground.

 

 Provided Courtesy of Jonathan Salmi Photography

 

The Best Wheel Size for a 305 Wide Tire

The best-sized wheel for a 305 tire on any car is a 10-12” wheel. That’s because 305mm is about 12 inches wide. It’s perfectly fine to undersize the wheel a bit when compared to the tire width, but anything less than 9.5 inches is pushing it. The tire tread will start to balloon out because it’s essentially squeezing the tire. Not to mention, it just looks weird. It looks like it’s about to burst.

Think about it for a second. If the tire is 12 inches wide and the wheel is only 9 inches wide, that’s three whole inches that aren’t supported by a sidewall that’s perpendicular to the road. Handling is going to suffer and so is traction. Not a good look.

A 10-inch wide wheel is really the largest you can fit on the back of an S197 Mustang without doing some serious modification. For daily drivers, this is really going to be your best bet. I’ve seen some 11-inch wheels fitted for racing applications, but it required modified suspension and cutting parts of the body that may come into contact in the wheel well. For daily drivers, this isn’t generally recommended.

 

How to Keep the Tire Inside of the Rear Fender

I have seen some cars with a 315 or even a 325, but those tires stuck out much farther than I would feel comfortable running, not to mention the looks. I personally don’t like when the tires stick outside of the fender. Some people may be into that, but it does cause problems when going over bumps and other suspension flex. That goes double for cars that are lowered on aftermarket suspension.

You’re also pushing the limits of the width of the wheel to hold that tire without risking deforming it when it rolls on the road. If you’re upgrading the rear of the tire to put more rubber to the road, the last thing that you want to do is ruin the shape of the contact patch, the slim, rectangular patch that actually touches the road as the car moves. It’s important that the tire can keep that shape as designed so it can bite into the road as it’s designed.

I can only imagine the amount of money that has been spent on engineering the best tread pattern. It would be a shame to ruin it by using a wheel that is too skinny or too wide.

 

A 305 Wide Tire Fit on a Lowered Mustang S197

Sure will. I personally use the Ford Racing “P” springs on my car. This is referred to as the “old man” spring because it offers a modest drop of about an inch.

The “K” springs with the aggressive drop of 1.5 inches will also work for you since the tires will tuck nicely in the fender if the axle is centered properly with an adjustable Panhard bar.

Panhard bars are often overlooked on lowered S197 Mustangs to keep costs low when modifying these cars. The factory provides a non-adjustable Panhard bar that is a bit longer than is going to work when moving the body of your car closer to the axle. Especially when it comes to going to a wider tire from the factory 235s or 255s.

It’s hard to notice an off-center axle when the tire is so far away from the fender. Once the tires start to fill up that wheel well, it will be obvious that one tire is much closer (or even sticking out) to the fender and the other is tucked inside.

Most are just interested in changing out the springs to get the drop height they’re looking for, but if you want to fit the largest tires you can, and adjustable Panhard bar will allow you to shift the axle as needed to center the axle with the body of the car. Most Panhard bars are inexpensive and well worth the small investment.

 

You May Not Want the Widest Rear Tire on Your s197 Mustang

305s will not fit on the front without some serious re-engineering. I’ve seen a few racing shops online that can do some custom work to fit wider tires on that include employing a grinder, but I wouldn’t recommend this unless you have a really good reason to do so.

That means that if you want to run a square setup, that is, a setup that has the same width for all four tires, 305s aren’t going to work for you.

The biggest “square” setup I’ve ever heard is 285 all around. Now, keep in mind, that’s just about ¾ of an inch smaller tire, so you’re not going to be losing much if you have to make the compromise. In order to get that to work, aftermarket wheels in the 10” wide variety are still going to be your main choice. Rubbing at the sides has been reported around full steering lock. Since we don’t usually encounter this type of steering maneuver at speed, it’s best to take it slower around parking lots to avoid damage.

 

What Happens If the Tire Rubs the Fender of Your S197 Mustang

S197 Mustangs aren’t generally prone to tire rub, but there’s always the chance that it could happen if you size your tires and wheels incorrectly. Most of the time, the tire will just touch the inner fender and create a noise that can be a little concerning. Depending on how the tire is contacting the body of the car, best case scenario, you’re just shortening the life of the tires since some rubber can come off of the tire.

Heat and pressure from the fender repeatedly hitting the tire will start to cut into the rubber. If it’s bad enough, it could certainly lead to a flat. Worst case scenario, you could go over a big enough pothole and the tire itself pushes on the body of the car with enough force to deform the fender, too.

Keep in mind that if the tire touches any part of the car hard enough, the tire will try to grab on to the car itself and also apply a braking force to that tire which could do anything from cause strange handling issues to locking up the tire momentarily. Overall, these are certainly things to avoid.

 

Related Questions

What is the bolt pattern for S197 Mustangs? All S197 Mustangs use a 5″x114.3mm bolt pattern. That means it’s a five lug wheel with the lugs forming a circle with a 114.3mm diameter.

Can I use 2015 mustang wheels on my s197? Yes, they will work. They’re the same bolt pattern for both model types. The offset and backspacing is also about the same.

Does increasing the width of the tire really make a difference on these cars? Yes, absolutely. The more rubber touching the ground, the easier it will be for the car to push itself forward. The 235 wide tires that came with my car were a joke. I burned them up the first year.

What tire would you recommend for a daily driver? My favorite so far has been the Michelin Pilot Sport 4S. They continue to amaze me in all sorts for conditions. However, the Continental summer tires are also extremely good value compared to the cost of the Michelins.

Do you have any recommendations for wheels? You can’t go wrong with a lightweight wheel. The lighter the wheel, the easier it will be for the car to turn them. 20″ wheels are the heaviest. I love mine, but I know they’re costing me power at the expense of looks. Most racers try to stay with an 18″ wheel that will work with their brake setup to drop as much weight as they can.

 

Featured Image Provided by Jonathan Salmi Photography