Riding on Air

Your tires are your friends. And bikers take care of their friends.
In the previous installment of
“Between the Lines” (Hog Tales®, July/August 2007), we looked at traction: how understanding the ways your tires interact with the road surface under varying conditions can help make you a better rider.

Since no discussion of traction is complete without a corresponding one on tires, in this article we present some basics about tires. After all, it’s your tires (and only your tires) that literally keep you in touch with the road.

In this article, we’ll take a look at some tire basics (as well as a bit of advanced information) to help you make sure everything is as it should be where the rubber meets the road.

TIRE CARE
Tire Pressure
It probably can’t be said often enough: Check your tire pressure regularly! Ideally, check it every day before you ride. Under-inflated tires can cause loss of traction, lower gas mileage, premature or uneven wear, and increased risk of blowout. Overinflated tires can increase your risk of a blowout.

Do not be confused by the air-pressure reading embossed on the tire’s sidewall. This is the maximum air pressure for that tire, not the recommended pressure. Therecommended air pressure depends on a number of factors, such as load, and whether you’re riding one- or two-up.

Consult your Owner’s Manual for the recommended pressures for the front and rear tires on your motorcycle. In fact, yourOwner’s Manual is the first place you should look for all important information about your tires.

Wear/Tread Depth
Because maintaining traction is so much more crucial on a motorcycle than a car, motorcycle tires are made of softer compounds than car tires. This helps them grip the road better, but it also makes them wear out faster. So it’s especially important to check the tread depth regularly. If you want to really do it right, you should inspect your tires (for tread depth, pressure, damage, and uneven wear) as part of your daily pre-ride inspection.

As you’re inspecting your tire, check for wear patterns. Uneven tire-wear patterns can result in deteriorated handling in wet or other less-than-ideal conditions. Excessively worn tires are more susceptible to penetrations or failure, and also don’t channel away water or road debris as effectively. It’s important to remove a tire from service when it’s worn to 1/32″ of tread remaining.

One way to easily check this is with a standard U.S. penny. Stick the top of the penny into a groove in the center tread (with Lincoln’s head pointing down). A depth of 1/32″ is right at the top of Lincoln’s head.

Some tires don’t have any tread on the centerline, in which case it becomes necessary to look at the “wear bar” to determine tread depth. The wear bars are molded into the tread at regular intervals (look for a little arrow on the sidewall to help you find one) and become visible when it’s time to replace the tire.

Tire Cleaning
When washing your motorcycle, it’s important to use only approved products to clean and protect your tire sidewalls. Using the wrong chemicals can speed breakdown of the polymers that protect your tires from damage, and cause premature wear or failure. Harley-Davidson® Wheel & Tire Cleaner can be used to safely clean wheels, tires, and whitewalls quickly and effectively. To restore pigmentation and luster to black sidewalls while maximizing UV protection, use Harley Black™ Tire Sidewall Protectant after cleaning, following label directions carefully.

TIRE CLEANING PRODUCTS AT-A-GLANCE
	Harley Black™ Tire Sidewall Protectant The black pigmented polymer formulation provides UV protection and restores the luster to black tire sidewalls.
	Harley-Davidson Wheel & Tire Cleaner The road provides plenty of nasty elements that can be potentially damaging to the finish of motorcycle wheels. Harley-Davidson Wheel & Tire Cleaner cleans wheels, tires, and whitewalls in seconds.

TIRE SELECTION
Proper Fitment
When it comes time to choose a replacement tire, keep in mind that tires for Harley-Davidson motorcycles have been validated by the Motor Company for use on that model. Though other tires may fit, if they’re not validated they have not been proven to meet the strict specifications required by Harley-Davidson, or been shown to provide adequate vehicle stability. Consult yourOwner’s Manual or an authorized Harley-Davidson dealer to find the right replacement tire for your motorcycle.

It’s also important to use the proper size tire. A larger tire may fit when it’s new, but tires change slightly in size during use. As a motorcycle accelerates, centrifugal forces cause a tire to become taller and narrower. When it slows and stops, it returns to its “original” shape.

Harley-Davidson offers a number of different tire gauges to quickly and accurately measure tire pressure. All are equipped with a built-in tread depth indicator, as well.

As a tire goes through a normal service life, and it’s subjected to a continual cycle of growing and shrinking, the tire sidewalls become more relaxed, and the effect is more pronounced. In addition, as it’s exposed to the elements, and becomes more pliable, the tire’s sidewalls become softer still.

If the motorcycle does not provide adequate clearance for the selected tire, it can result in a dangerous situation with the tire rubbing against the fender, drive belt, or other component. This is the case even if everything seems okay while the vehicle is parked.

Construction Type
There are three main types of modern motorcycle tires: bias, bias belted, and radial:

Bias (or bias-ply) tires feature plies* that run diagonally across the tire, with each successive layer slanted, or biased, in the opposite direction. You’ll generally find (unbelted) bias on the front of Harley-Davidson cruiser-style motorcycles.

Bias belted tires feature a belt around the tire for even more strength and stability. Harley-Davidson-branded front and rear touring tires and rear cruiser tires are generally belted.

Radial tires feature plies* that run radially, straight across the tire from bead to bead (90 degrees to the direction of rotation). Radial tires generate less heat at higher speeds, so they can generally be run faster. The trade-off is that radial tires need to be produced with a lower profile than bias tires. This lessens their ability to carry heavier loads.

* A ply is a layer of reinforcing fibers and rubber that gives the tire the strength to hold its space and provide deflection.

Most Harley-Davidson original equipment tires are bias or bias belted construction. Dunlop offers several basic Harley-Davidson tires: D401 or D407 (for cruiser models); D402 (for Touring models); and K591, a high performance sport bias tire that was originally developed for racing, but has been refined to meet the needs of sport and sport-touring riders.

In addition, Harley-Davidson now validates a number of Michelin tire series as replacement tires on certain models. Screamin’ Eagle® high performance tires are also available to fit certain Harley-Davidson motorcycles. As always, be sure to look for the one that fits the specific model and year of your motorcycle. Consult your Owner’s Manual for specific information.

Bias (or bias-ply) tire	Bias belted tire	Radial tire

WARNING: Use only Harley-Davidson® approved tires. See a Harley-Davidson dealer. Using non-approved tires or mixing approved tires from different manufacturers on the same motorcycle can adversely affect stability, which could result in death or serious injury.

A Word About Tubes
Most motorcycle tires these days are of the tubeless variety, but laced wheels (those with spokes) require tires with tubes – and a bit of special attention. The tubes are necessary with laced wheels because the spokes, which run through the rim, create an opportunity for air to escape. The tube, then, keeps the air inside the tire, where it belongs.

Tube tires and laced wheels are best dealt with by your Harley-Davidson dealer; balancing and spoke tensioning should be left to the professionals. And when you have a tire replaced, make sure they replace the tubes and rim bands (the rubber band-like strip that circles the wheel between the tube and the rim), as well. The tube and band both degrade with age, so it’s a relatively inexpensive safeguard to change them both along with the tire.

Sidewall Markings
To some, those mysterious markings on the sides of tires are just that: a cryptic jumble of numbers and letters. But armed with just a little bit of information, it’s easy to decode those markings and learn just about everything you need to know about that particular tire.

Example: Harley-Davidson Dunlop D401

130/90B16 M/C 73H

130:	Tire width (mm).
90:	Aspect ratio – the sidewall height as a percentage of the tire’s width. In this example, an aspect ratio of 90 on a 130 mm tire equals a sidewall height of 117 mm.
B:	Belted construction (on radial tires, you’ll typically find an “R” in this spot).
16:	Wheel diameter (inches).
M/C:	Made specifically for motorcycles.
73:	Load rating index – a rating of 73 corresponds to 805 pounds – which is not to be confused with the vehicle’s GVWR, or Gross Vehicle Weight Rating. Be sure to consult your Owner’s Manual for information on your motorcycle.
H:	Speed rating – an “H” rating on a Harley-Davidson Dunlop tire is indicative of capability based on indoor wheel testing and not valid for damaged, altered, repaired, excessively worn, underinflated, or overloaded tires.

Additional information can also be found on the tire sidewall, including:

• Manufacture date code (the week and year of manufacture)
• Wear bar indicator (location of wear bar on tread)
• Rotation indicator (shows the desired rotational direction of the tire)

WORTH THE EFFORT
In the end, most people would rather not think about their tires any more than they have to. But by making sure your tires are properly inflated and in good shape before you start your motorcycle, you can better focus on having the safest, most enjoyable ride possible.