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Harley Davidson Touring: Converting to a Car Tire on the Rear

Using a car tire on the back of a motorcycle is popular among some riders, and considered stupid and unsafe by others. The increased straight line traction and longer tire life are often the reasons cited, as well as lower cost of tires. Although not illegal in the United States, there are things to consider regarding the safety of this practice.

By Bryan Wood - March 1, 2016

This article applies to the Harley Davidson Touring (2000-2015).

Motorcycle tires are expensive, there is no getting around that, especially when compared to common car tires. There is a small contingent of riders, mostly on big Touring bikes, who have begun using automotive tires on the back of their motorcycles for various reasons, but the biggest being that the tires last longer and cost less to replace.

Harley Davidson Touring Converting to a Car Tire on the Rear

Materials Needed

  • Car tire (195/60-16 is the most common size)
  • Tire mounting and balancing machine or sympathetic shop

Difference in Profile

The most obvious difference between car and bike tires are the profile of the tire. A car tire is a square shouldered block meant to have a broad flat footprint on the ground at all times. A motorcycle tire has a round profile with just a small part of the tire touching the ground at any one time. Car tires are not meant to corner on their sidewalls, which is what happens when they are used on a motorcycle or a cushy, soft riding luxury car being driven hard. Motorcycle tires have almost a gradual transition from the rounded contact area to the sidewall, and can be cornered at lean angles far beyond those available to the rider of any Harley Davidson Touring rig.

Figure 1. Here, the design differences can be easily seen.

Difference in Cornering

Running a car tire on the back of your Touring bike will change the way your bike handles, but how much really depends on what type of rider you are. Take a look at the wear of your tires. If you have huge unused "chicken strips" along the sides of both tires, chances are you aren't going to notice much difference. If you have spots on your foot boards that are ground down from throwing sparks in corners, then going to the dark side is not for you. If you swap out the stock round profile motorcycle tire for a square profile tire, you will find you have to steer through corners a lot more, and can't just lean in and have the bike steer for you due to the circumference of the tires. Lean into a corner hard with a car tire on the back and you will find the back end has a lot less traction, and feels like it wants to slide easier.

Heroic Harley corner carver throwing sparks while dragging hard parts
Figure 2. Heroic Harley corner carver throwing sparks while dragging hard parts.

Difference in Riding Styles

For Touring riders in the flatter, straighter, freeway states, how your bike corners is really not much of a concern. When the only corners you are likely to ride all day are the on and off ramps leading to the straight highway, and the state feels the need to remind you to "watch for turns" like on highway 61 in Mississippi, you hardly need to worry about cornering. If you ever want to get off the super-slab and ride the back roads though, you will be much happier with real motorcycle tires. If you are the kind of rider who steers into corners more than you lean into them, you likely aren't cornering hard enough to ever notice a difference.

Not a corner in sight
Figure 3. Not a corner in sight.

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If you do use a car tire and insist on cornering like you were still on a bike tire, this is what is looks like from under the bike. You can clearly see how little rubber you have on the ground at normal lean angles.

Common Questions

What are the advantages of using a car tire?

The reported advantages of a car tire are better traction for straight line acceleration and braking. The other reasons many people prefer a car tire is the lower cost and longer life. A rear 16" motorcycle tire will likely cost you nearly $200, while a car tire is about $100.

What are the disadvantages?

Obviously, the handling is going to be different. If you move to a car tire and continue to lean into corners, chances are you are not going to see that longer tread wear because the sidewalls are not made to be cornered on and will wear out much quicker than the flat center section. You can also expect reduced fuel economy due to the increased surface area of tire that contacts the road. You also may find in the event of an accident that your insurance company tries to blame your modification and deny the claim.

Is it safe to convert my rear tire to a car tire?

The factors that most effect safety (not addressing the handling differences) are how the tire mounts to the rim. Car rims and bike rimes, even though they are both 16" in diameter are designed slightly differently. Most car tires are not designed to fully contact a motorcycles rim shape, which can cause the tire to wiggle or "shimmy" on the rim during cornering. People do it all the time, and most of them have not had issues, but it can't possibly be as safe as using the tires the bike was designed for.

How will a car tire wear compared to a motorcycle tire?

If your riding includes turns, your car tire will wear significantly faster on the edges compared to a motorcycle tire. A car tire is not designed to withstand the force exerted on the tire when excessive camber (lean) angles take place.

How common of a modification is this?

Not very, but there are plenty of people online who have done it. Of course, there are an overwhelming majority of riders who have not done it. Perhaps the reason it is so popular with online forum member is because those people don't get out and ride much? It is most popular with large Touring rigs and highway riders. It seems owners of the Harley Davidson Touring and other larger motorcycles designed for long trek highway use, such as the Goldwing, are finding their riding style benefits from the car tire's advantages.

Common Issues

Clearance Between the Rear Wheel and Rear Fender

A car tire uses a flatter tread block compared to a motorcycle's more concave shape. When fitting your Touring with a car tire of the same size, you may notice a lack of clearance in the rear fender area. Over bumps, the clearance will become even less. Do your online research and find out what sizes and brands other owners of your bike have used without issue, and check the width and diameter of tires before buying with the manufacturer's website.

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