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Common Tread

Motorcycle Tire Guide 101 and FAQ

Jul 20, 2014

Welcome to Tire School!

We're going to have a crash course (figuratively speaking!) on motorcycle tires. This is literally where the rubber meets the road.

At RevZilla, we deal with a vast spectrum of customers, from sponsored racers on rockets to green rookies on Ninja 250s, to someone pushing hundreds of miles daily on a Harley bagger — and that’s just the street riders! One thing they all have in common is that tires are critical components.

Like with most of the products we sell, making a good decision when choosing tires is a matter of understanding how you ride, being honest about your intents and abilities, and most importantly, being safe. Let’s start with a quick run-down of tire terminology.

Basic tire construction terms

  • Tread: This is the part you see that hits the road, and the part most people think about. In general, smoother tread works better on smooth, dry surfaces, and “chunkier” tires work better off-road. Some street tread patterns are designed to do better in the wet and off-road tires come in a wide variety for different surfaces, from hard-packed dirt to sand.
  • Bead: This is the part of the tire that mates to the wheel. It is typically steel wire covered heavily in rubber. The bead has a snug fit to the wheel to prevent the wheel from slipping rotationally in the tire.
  • Carcass: In simple terms, this is the “body” of the tire under the tread. Motorcycle tires are typically bias-ply or radial, which refers to how the tire is constructed. Radial tires have reinforcing belts (which are almost always steel) running from bead to bead across the tread of the tire. Bias-ply tires have belts which are typically cords made of fiber, such as polyester, aramid, or fiberglass, that run from bead to bead at an angle of 30 to 40 degrees or so. (That’s the bias!)
  • Sidewall: The area of the tire that bridges the tread and bead. A small part of the tire, it is vitally important. It gives the tire much of its handling and load transfer characteristics. This is the part of the tire we’re talking about when we reference height, profile, or aspect ratio. Typically, a shorter sidewall yields a stiffer sidewall, which tends to flex less. To a rider, this means better handling and turning, worse bump absorption, and more difficult mounting. This section greatly contributes to the tire’s role in the suspension. That’s right — the tire is a suspension component!

Cracking the code

How do you know the important stuff about a tire? Like, what’s inside it and what size it is? It's easy. By law, this information is written on the tire sidewall.

There are two ways to give tire information: alphanumeric and metric.

A quick history lesson before we start decoding: In the old days, there was only one way to size tires — alphanumeric. Radial tires didn’t exist, so there were a pretty limited number of sizes available, which made an uncomplicated system adequate. As increasingly complex tire technology became available, it was evident a new system needed to be cooked up to provide that information to consumers and sellers, so the metric system was developed. In the days of yore, tires never really got bigger than six inches across the tread (or from rim to tire edge), too, so if a tire has a size of much larger than 150, it will never be in an alphanumeric size, because they didn’t exist in the Dark Ages of motorcycling. Don’t be scared off by alphanumeric tire sizes – it’s usually easy to get a great tire that will make you happy, and in a tiny way, you’ll be using a tire that connects you to the old days of motorcycling.

There’s an older way still of sizing tires, using tire widths in inches, but bikes requiring them are antiques at this point, like 3.00x18.  If you run tires like this, give one of our Gear Geeks a call for help obtaining a set.

The image at right shows two tire sizes you might see. Let's break down the numbers.

The first, a 130/90, is a common size for Harley-Davidson tires. The 130 represents the width across the face of the tread in millimeters. This may not be exactly identical from one brand of tire to another. Each manufacturer varies slightly, and the curvature of the tire’s profile can affect the overall measurement, but the tolerances are close enough that one will fit where another goes, as long as you're sticking to stock sizes.

The second tire example, in the alphanumeric system, conveys the width with the letter “T.” Tire width charts are widely available in tire catalogs and online, so to save space, we’ll omit them here. (For those curious, the “M” indicates “Motorcycle.” Every alphanumeric tire you’ll run into will start with an “M.”)

The 90 represents the aspect ratio. The aspect ratio is the height of the sidewall expressed as a percentage of the width. Thus, this tire has a side wall height of 90 percent times 130 mm or 117 mm.

The next item you’ll see is the rim size expressed in inches. Were this tire a radial, we would see a capital letter “R” separating the aspect ratio and rim size. Since that is not the case here, you can be certain this is a bias-ply tire. Were this tire a bias-belted tire (like a bias-ply tire with additional, stiffening layers of fabric placed over the body plies), a capital letter “B” would separate the aspect ratio and rim size. It's easy to see this tire is made to be mounted on a 16-inch wheel.

Other information shown are speed ratings and load ranges. Load ranges give the maximum weight a tire can carry, and speed ratings list the maximum speed at which the maximum load can be carried. Charts to find a given load or speed for a particular letter or number again are available in a multitude of places, so we’re not including them here.  If you cannot find one, just ask us for help!

There’s one more tire “code,” called the service description, and we’ll talk about it quickly in a little bit. It’s not universal to the information given on a sidewall, so we’re not covering it here.

All these numbers and letters! How do I get the right tire?

As long as you stick to the stock size tire that your motorcycle was designed to use, you're good to go. That doesn't mean you can't experiment. Depending on your motorcycle, you may still have a choice of sport tires, designed to provide maximum grip at the expense of tread life, touring tires designed for maximum mileage, or sport-touring tires that strive to provide the best of both. For adventure bikes, you can choose between tires that are intended as 90-10 (90 percent street use, 10 percent off road) or 50-50 or some other combination.

Of course people love to experiment, and sometimes that means departing from stock tire types and sizes. Our customers have brought us some humdingers of questions, so we’re going to try to cover the ones we get most often.

The most important thing to remember when selecting a tire is something each of our Gear Geeks absorbs to the core, and we encourage our customers to take the same stance: We always will err on the side of safety. Many customers will ask, “Can I…” followed by some deviation from standard practice. Some ideas kicked off by lone amateurs have been fantastic, while others have caused injury or death. We at RevZilla respect the rights of each motorcyclist to choose what modifications to make, but because we are unable to quickly evaluate every customer’s abilities and judgment through simple phone and e-mail contacts, it is RevZilla’s stance to only recommend tires that are original size, speed rating, load rating, and construction as the original equipment manufacturer’s.

Without further ado, here’s the FAQ!

What's the widest tire I can fit on my bike?

Boy, if only it was that easy! There’s a reason that there’s not a common list of stuff that will fit on a given bike. Most people don’t sit around the shop with a stack of tires trying to fit different ones onto their wheels. A lot of things need to be taken into account when changing a tire size.

Tires need clearance in many dimensions. A tire that is too wide can rub a swingarm, chain, or other parts. A tire that is too large in circumference will change gearing ratios and speedometer readouts, and can contact fenders or swingarms. If clearance is tight when you mount the tire, keep in mind it can still cause problems. Tires “grow” at speed. Temperature and centrifugal force cause a spinning tire to be measurably larger than one at rest.

Wide tires are not necessarily better. They usually “turn in” worse than a skinnier tire of the same make and model, and usually hurt fuel mileage. The common alteration of mounting a wider rear tire may make the bike harder to steer, even unpleasantly or unsafely so.

While wider tires rarely provide performance advantages, some tire manufacturers do offer their own “plus sizing” recommendations, by listing tire sizes larger than stock that are confirmed to fit a certain size rim.

Can I mix radial and bias-ply tires? Can I switch from bias to radials?

Again, we respect a customer’s right to choose, but we only recommend sticking with a manufacturer’s recommended tire construction type.

In general, radial tires offer lower temperatures (leading to longer life), stiffer construction, and the ability to have sidewalls with a lower aspect ratio, resulting in less flex. Bias-ply tires offer a softer, more compliant ride and, typically, a little lower price. Their other main advantage is load-carrying capability. In a given size, you’ll typically see a bias handle more weight. It explains why Harley (a big player in the heavy cruiser market) and certain touring bikes use them.

Interestingly, for some manufacturers, a mix of a bias front and radial rear is the setup from the factory.

Can I put a tubeless tire on a spoked rim?

Great question. For you rookies out there: Spoked rims will leak air if the tires mounted to them do not have an inner tube installed in them to hold the air. The nipples where the spokes mate to the rim are not airtight. A notable exception to this rule is the edge-spoked rims commonly found on a few bikes, such as BMW GS-series adventure-tourers. Even some alloy rims require tube-type tires, especially older bikes.

Bottom line: If your bike came with tube-type tires with inner tubes, you're not going to be able to use a tubeless tire without some creative engineering to make the rim airtight. And even then, there's no guarantees, because the beads may not seat properly on a wheel made for tube-type tires. So this is one of those things we just can't recommend.

What if I use a tubeless tire with a tube in it?

This is generally fine to do. Note that the addition of a tube adds friction — and thus heat — into a tire. Most sources agree that if adding a tube, it's prudent to assume the tire has "stepped" down one load and speed step.

Can I reuse my old tubes when I put on a new tire?

Not a great idea. In tubeless tires, the valve stem is generally replaced at every tire swap. With an inner tube, the valve is built right into the tube itself. Rubber hardens as it heat-cycles — the process of going from cold to hot and back to cold again, every time you ride — and the tube's rubber, which should be soft and pliable, turns brittle and can be prone to cracking. Compared to tires, tubes are cheap. Bottom line: Don’t do it. Replace the tubes with the tires.

What size tube do I need?

That's easy. Here's a conversion chart!

tube size conversion chart

What size valve stem do I need for my tubeless tire?

There are two types: 8 mm and 10 mm. The larger one, which actually fits an 11.3 mm hole in the wheel, is by far the most common size. It's used by all the Japanese manufacturers and Harley-Davidson. The smaller size, actually an 8.3 mm opening, is used by some BMWs and Buells and aftermarket wheels.

Can I use tires with a different load/speed rating?

Normally, a downgrade in load/speed rating is a poor idea and we don’t recommend it at RevZilla. Maximum load and speed ratings are considered by the manufacturer and they specify tires they believe the bike needs.

Upgrading a speed or load rating won’t hurt anything, but can give a worse ride due to sidewall stiffeners being added to the tire. Factory-spec tires should be capable of handling the load the bike is approved to carry. If you're trying to exceed that, most likely the tires are not the only weak point and other parts can break, too!  A higher speed rating is rarely detrimental, though you may give up fuel mileage or tire life. We recommend sticking to the OE speed rating, but upgrading is permissible, provided you know that other riding characteristics could be affected.

When considering weights, do not forget the weight of rider, passenger, luggage, etc. Japanese bike manufacturers are notorious for expecting their customers to be featherweights.

At the time of this writing, most tire manufacturers agree that a tire that has been repaired loses any speed rating.

What do the B, C, E, etc. after the tire size mean?

If you see a letter and number combo listed after a tire size, that is a tire “service description.” Service descriptions all have a load and speed index, which are easily converted from a number of commonly available tables.

There is also additional, optional information you mayu see which can vary from manufacturer to manufacturer. It’s sometimes information that the tire producer gives to further clarify what the tire belongs on, or what job the tire was designed to do. It may indicate a slightly different version of a tire that is made specifically for a certain new model of bike, at the motorcycle manufacturer's request. Michelin Pilot Road 3 Tires are a good example of this. The “B” service description denotes a tire with extra sidewall stiffeners added. If you are unsure what a service description means, consult your friendly Gear Geek for clarification.

Can I run a Michelin in the front and a Pirelli in the back?

There are rare instances where the OEM tires are mixed brands, but other than those exceptions, RevZilla recommends replacing tires with the tire manufacturer’s recommended match front or rear. Often, a manufacturer will recommend a different model of tire for front and rear, and we will follow that recommendation. Unless a bike was equipped with two different tires from the factory, we do not recommend mixing tire brands because differences in tire handling and performance can cause an otherwise well-behaved motorcycle to act in an unpredictable, unsafe manner. Tire manufacturers engineered their tires to work with a matched partner. You paid for all that engineering, so why not use it?

How can I make sure I don't receive an old tire? Does it matter?

Yup! Tire age does matter!

Fortunately, it's easy to tell your tire's age. Molded into the sidewall of every tire is a DOT code, typically 12-16 digits or so. The code starts with the letters “DOT” and ends with a mishmash of numbers which tell many things, including the date of manufacture and plant it was produced in. We are interested in the last block of numbers. If there is a three-digit number in the final block of numbers, the tire was produced prior to 2000 and probably needs to be replaced! A four-digit number will reference the week of production in the first two digits, and the year in the last two. For example, 4209 as the final four characters in the DOT code indicates that the tire was made in the 42nd week of 2009.

If the tires on your bike are five years old, RevZilla recommends an inspection by a trained tire professional. If they're 10 years old, you should probably replace them regardless of how they look.

We do not guarantee motorcycle tires ordered from RevZilla will be of a certain age. However, be assured that our stock rolls over really frequently, and you will be getting a tire of very recent production.

How can I tell when my tire needs to be replaced?

Because it’s flat? That would be a good replacement situation…

Let’s run down a quick list of times when motorcycle tires should be replaced:

  • Sidewall puncture
  • Damage that can't be repaired
  • Tire with a puncture larger than 0.25 inches
  • Tire more than 10 years old
  • Weather-checked (cracked around the circumference), often due to UV or fluorescent exposure
  • Tire that has been run with exceedingly low pressure (damage is typically seen as a circumferential ring that looks “rubbed in”)
  • Tire with cuts or slices
  • Tire with missing tread blocks
  • Tire that is worn (less than 2/32 of an inch of tread in any area)
  • Tire displaying treadwear indicators
  • Tire that has cross section significantly altered (flatter or more pointed due to uneven wear)
  • Tire that is feathered or cupped and is making noise or exhibiting a choppy ride; some front tire cupping is normal, but a worn tire may exhibit severe feathering

If you’re asking us this question, you probably need at least one new tire, and likely two. Given that most bikes have a tire speed rating, and repaired tires lose their speed rating, many riders with any type of tire damage really need a new tire. The safest course is to consider a repair a temporary fix at best. Given how critical tires are to your safety and your motorcycle's performance, RevZilla urges customers to stay safe.

Are chatter/wobble/wear/tread issues caused by a defective tire?

Well, you could have a defective tire. Or maybe a defective install. It’s hard to say without having the situation assessed by a trained professional. As a former tire installer, I would say that perhaps two percent of all tire problems were caused by truly defective tires. Chatter from a tire typically comes from normal wear and cupping, and sometimes from incorrect inflation, or a combination of those things. Wobble is almost always caused by misaligned tires, bent axles, or, most commonly, worn bearings. Tread and wear issues are usually caused from wheels having crooked installation or improper inflation.

It’s hard to say what you may be facing without seeing the problem firsthand. If you want some suggestions from a Gear Geek on what could be going on with your particular tire, information about the bike, tire installation, circumstances surrounding the failure, and pictures are all really, really helpful. It’s the best first step in determining if you’ve got a problem, and what should be done to remedy it. We maintain great relationships with our tire manufacturers, so we often tap their experience and that can be a huge resource when we are trying to help you!

I ride aggressively on the street. Why shouldn't I get a track-day tire?

Because the street’s not the track! Track tires often have compounds requiring very hot temperatures to “stick” to the road that a rider — even an aggressive one — will not hit on the street. This means that in real use, the track-day tire may be less grippy on the street than a sporty street tire.

Track-day tires also have different cross sections, usually inviting quicker steering, but twitchier handling. They are almost never optimized for wear and they probably don't handle water or debris well, since those are usually absent on the track, though that cannot be said of city streets. Track tires also rarely take into account loaded riding that street bikes are frequently saddled with. There are a number of super-sticky street tires that really bridge the gap between track and street use and they are almost universally the best choice for the rider who asks this question.

Have a question that's not answered here? Drop us a line or give us a call. We never “tire” of talking to our customers!