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Motorcycle Tire Guide 101

Uncle Loomis - Merchandising

PUBLISHED: APR 20, 2013

Welcome to Tire School!

As you know, motorcycles are single-track vehicles, requiring a very specific set of handling characteristics to make a ride safe, enjoyable, and convenient.  We’re going to have a crash-course (figuratively speaking!) on tires - literally, on the area “where the rubber meets the road.”

Tires are an integral component in achieving the things that makes motorcycling fun and practical.  One of the things that is important to remember is that at RevZilla, we deal with a vast spectrum of customers – from sponsored racers on rockets to green rookies on Ninja 250s to folks pushing hundreds of miles daily on very large touring bikes - and that’s just the street riders!  Like most of the products we sell, choosing between them is a matter of understanding how you ride, being honest about your intents and abilities, and most importantly, being safe.  Ask a biker who does serious mileage - form almost always follows function on the stuff that really works, be it tactics, products, or the bikes themselves.  Motorcycle Tires are no exception. 

Tire Time

Let’s have a quick run-down of what’s actually in a tire. 

Basic Construction Terms

  • Tread – This is the part you see that hits the road, and the part most people think about.  For the most part, smoother tires work better on smooth, dry surfaces, and ‘chunkier’ tires work better off-road.  There are special tire designs for snow, ice, and 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 sliding rotationally in the tire.
  • Carcass – Briefly, 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 – polyester, aramid, or fiberglass, which run from bead-to-bead on an angle of thirty to forty 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 how big it is?  The tire is required by law to contain this information.  It’s found  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 was made 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.

So here’s a good breakdown of two tire sizes you might see on a tire or in a catalog:

  • 130/90 - 16 67 H
  • MT90 - 16 Load Range B

The first tire, a 130/90, is a common Harley-Davidson rear size.  130 represents the width across the face of the tread.  This is not the same from tire to tire – 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.  A caveat - if you choose to deviate from the manufacturer’s specs on tire size – then a given size in Brand A may not fit somewhere a Brand B tire  of the same size fits. 

The second tire 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 tire you’ll run into will start with an ‘M’.)

90 represents the aspect ratio.  The aspect ratio, also known as profile, is the height of the sidewall.  90 is not a linear measurement – rather, as a ratio, it is a percentage of the width.  Thus, this tire has a side wall height of 90% x 130mm or 117mm.  Thus, sidewall heights can be the same (or very close) on two tires with different aspect ratios – if their width is different.

The next item you’ll see is the rim size.  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.  The rim size is expressed in inches.  Easily enough, this has a 16-inch wheel on which the tire is mounted.

Following the tire 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.

Am I going to get the right tire? There is so much information!

We know!  That’s why we tried to create something like these crib notes - to give you some help.  We’re going to keep addressing your individual needs as they arise, but our customers have brought us some humdingers that we’ve gotten more than once, so we’re going to try and 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 of our customers will ask, “Can I…” followed by some deviation from standard practice.  Motorcyclists are a dynamic and innovative group.  Some ideas kicked off by lone amateurs have been fantastic.  Some have caused injury or death.  We at RevZilla understand that there are folks who will forge ahead with their own research and ideas, and take responsibility for their actions.  We also respect the rights of each motorcyclist to choose what modifications they are comfortable making to their respective machines. 

Unfortunately, because we are unable to quickly evaluate every customer’s abilities and judgment through simple phone and email 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.  We explain to each customer on a personal basis why we don’t suggest tire modifications from stock, and why we will not deviate from that practice.  If it helps, consider this:  the big-name manufacturers pay very educated engineers a lot of money to figure out what their machines need to handle safely and spectacularly.  The combined wisdom at RevZilla is vast and deep, but we’d never have the hubris to say that we figured something out the manufacturer missed. 

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 their 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 ‘grow’ at speed – temperature and centrifugal force cause a spinning tire to be measurably larger than one at rest. Tires need clearance in many dimensions.  Tires that are too wide can hit swingarms, chains, or driveshafts.  Tires that are too large in circumference change gearing ratios and speedometer readouts, and can contact fenders or swingarms.  They also may begin shedding water in inconvenient ways –soaking a driver or passenger.
  • Wide tires are not necessarily a better thing.  They universally ‘turn in’ worse than a skinnier tire of the same make and model, and usually hurt fuel mileage. If a rear tire is made wider and the front not adjusted for, rears have the tendency to ‘push’; effectively making the rider fight to guide the vehicle into a turn. 

The designers who engineer bikes usually are highly trained, and they apply that training to find a tire combination that accents a vehicle’s virtues, and minimizes its shortcomings.  It’s become very difficult in recent years to beat them at their own game.  With all that said, some tire manufacturers have their own ‘plus sizing’ - tire sizes larger than stock that have been a confirmed fit.  Keep in mind that a tire that fits is not necessarily a tire that handles or performs better.  In fact, it’s likely to be quite the opposite.

Can I mix radial and bias? What’s the difference? Does it matter? My bike came with bias, can I use radial or vice-versa?

Well, again – we at RevZilla respect a customer’s right to choose.  However, if asked, we only recommend sticking with a manufacturer’s recommended tire construction type. 

To be brief, radial tires offer lower temperatures (leading to longer life), stiffer construction, and the ability to make tires with lower aspect ratio sidewalls, 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 weight better.  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 bias and radial tires are factory equipment.  You’ll see the mix with radial rear and bias front tires, but we do not know of any combinations in reverse.  Anecdotally, folks have run mixed tires with success in the past.  However, most riders doing such a thing are usually aware of what they’re doing, hyper-vigilant about the fact that something negative could occur, and experimenting with a specific performance characteristic as an end goal.  With that said, RevZilla does not have a problem with a mix of radial and bias-ply tires, as long as that mix is in keeping with the OEM recommendations, and the tires are in their correct OEM positions (Bias front, radial rear).

Can I put a tubeless tire (denoted by ‘TL’ in the tire catalog) on a spoked rim or do I need to stick to a tube-type (denoted by ‘TT’ in the tire catalog)?  Can I run a TT tire without a tube?  Can I reuse my old tubes?

Great question.  For you rookies out there:  Spoked rims will leak air if the tires mounted to them do not have a 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 BMW GS-series bikes – they are the one spoked wheel we’re aware of that can run a tubeless tire.  Alloy rims typically are tubeless – but not always!  Again – check the manufacturer’s spec to see what your customer’s bike needs installed on it.  Many early 80’s Japanese bikes ran tube-type alloy rims – some bikes even specified a tube-type front setup and a tubeless rear!  Tube-type tires are not designed to be airtight, because the manufacturer knows they’ll be run with an airtight tube.

Let’s talk about each situation specifically:

Tubeless tire with tube:  The bead seat designs on the wheels are typically designed differently than tube-specific wheels.  The beads may or may not lock, especially in a low-air situation.  It’s also common to have different beads on the same motorcycle’s front and rear wheels.  The other big stinker here is that the speed rating is null and void – the extra layer of tube now allows the tire to heat to an unknown level.  Bottom-line:  Don’t do it!  If you do, tread with caution - the tire can run lots warmer.  Keep an eye on things, and take plenty of time to get familiar with how the machine handles after the change.

Tube-type tire with no tube:  Good luck getting it to seal!  It’s going to leak like crazy.  Spoked wheels are the vast majority of wheels requiring tubed tires, and with the exception of BMW’s edge-spoked wheels, it needs a tube to hold air.  The BMW bikes so equipped will typically spec a tubeless tire.  If a tubeless was installed on an alloy rim from any other bike (or a regular center-spoked BMW wheel), again, the bead may differ, depending on the wheel.  Because the tire was never designed to run without a tube, no one can guarantee how the tire will perform.  Bottom line:  Don’t do it.

Reusing old tubes:  Not a great idea.  In tubeless tires, the valve stem is replaced at every tire swap.  The brass corrodes.  Seeing as how the valve is built into the tube, that in and of itself is reason enough to replace the tube.  Tubes do not represent significant cost in regards to a tire purchase.  Rubber also hardens as it heat-cycles – the process of going from cold to hot and back to cold again.  (This process occurs every time you ride your bike.)  After so many heat cycles, what is supposed to be soft, pliable, rubber turns brittle.  Bottom line:  Don’t do it.  Replace the tubes with the tires. 

The one possible exception RevZilla takes into account is someone traveling to a super-remote area on tubeless rims.  If they had tubeless tires, and wanted to bring a set of corresponding tubes, it might get you out of a jam if a tire plug or patch proved insufficient in the event of a damaged tire.  However, their rims could be detrimental for the tubes, being radiused incorrectly.  It would work as an ‘in a pinch’ solution for someone bound for an area that had no parts readily accessible or needed to get out of a jam.

What size tube do I need?  How do I know what stem style I need?

Easy enough – here’s a conversion chart!  All tubes have a standard valve stem.

As far as fitting a valve stem to a tubeless wheel, there are two types – 8mm and 10mm.  10mm is by far the most popular size – it’s used by all the Japanese manufacturers and HD; they’re usually a simple rubber “pull-through’ automotive style.  The 8mm weirdo size is used by some BMWs and Buell – it’s a “nut-in-place” design.

My bike came with XYZ load/speed rating, but the tires I want to get are ABC load/speed, is this ok?

Well, funny question to ask.  Normally, a downgrade in load/speed rating is a poor idea – and as such, we don’t recommend it at RevZilla.  Maximum load and speed ratings are anticipated by the manufacturer, and the tires specified as OEM were chosen after plenty of research – the bike needs that equipment to perform with the loads it was designed to bear and at the speeds it is capable of running at.  Keep in mind, too, that tire cross-section varies by load rating.  Bikes requiring quicker steering have tires that have a pointed, ‘V-shaped’ cross-section, whereas bikes with less lean requirement have a gentler ‘U-shaped’ profile to maximize load carrying and tire-wear capabilities.

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.  If you’re looking to upgrade the load rating, make sure the bike is capable of bearing the load as well!  Factory-spec tires should be capable of handling the load the bike is approved to carry.  If the load weight is going beyond what the bike is designed for, most likely the tires are not the only weak point – other parts can break, too!  Choose motorcycle tires - and gear you’re bringing - wisely, and load their bike appropriately. 

When considering weights, do not forget the weight of driver, passenger, and fluids.  Japanese bike manufacturers are notorious for considering folks to be featherweights.  Driver and passenger weights that are over the manufacturer’s assumed rider/passenger weight need to be subtracted from the cargo hauling weight by equal amounts when figuring load carrying capability.

Upgrading speed ratings is one area RevZilla gives the thumbs-up to changing from OE.  A higher speed rating is rarely detrimental to a motorcycle from a safety perspective.  However, one will often 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.

Downgrading a speed rating is never a bright idea.  An item of note:   It is the "top speed" of the "slowest" tire on the vehicle which defines the maximum speed at which you should ride.  So if a customer has a ‘V’ & ‘Z’ rated tire, the bike as a whole is limited to the maximum speed of the V-rated tire.  Another item of note:  Any tire that has been repaired loses all speed rating.

What does 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’.  Like '67H', for example.  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 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..  Often, a letter will indicate a reinforced tire for greater carrying capacity, or slightly different tread designed specifically for a model of motorcycle.  Michelin Pilot Road 3s are a good current example of this – the ‘B’ service description denotes a tire with extra sidewall stiffeners added.  Because there is no current requirement for this information, 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 for the most part, this is not so.  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.  In fact, batch variations from one run of a tire to the next run of the same model tire can even have differences.  It’s best to stick with the tire maker’s recommendations - they engineered their tires to work with a partner.  You paid for all that engineering, why not use it?

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

Yup! It does!  RevZilla recommends an inspection by a trained tire professional at five years of service, and a definite replacement regardless of mileage at ten years of service.  On the sidewall of every tire there is a DOT code.  The code starts with ‘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 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 indicate that the tire was made in the forty-second week of 2009. 

We do not guarantee motorcycle tires to 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.

What are the chances of my tire being defective?  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.  On an anecdotal level – 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 from 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 relations with our tire manufacturers, so often we pick their brains.  Sometimes, they know of a particular problem, and can be a real boon to us when we’re trying to help you!

I ride really aggressively on the street; why shouldn’t I get a track-day tire for my bike?

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.  They also have different cross sections, usually inviting quicker steering, but ‘twitchier’ handling in a straight-ahead (street) situation:  the bike tends to want to “fall over” into a turn.  The tires are almost never optimized for wear, and tracks are also free of fluids and debris – unfortunately, the same 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 – one of those is almost universally the best choice for the rider who asks this question.

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 motorcycle tires should be replaced:

  • Sidewall puncture
  • Unrepairable/damaged tire
  • Tire with a puncture larger than ¼”
  • Tire over ten years of age
  • Weather-checked (cracked circumferentially) tire - often due to UV or fluorescent exposure
  • Tire that has been run with exceedingly low pressure (Typically damage is 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” tread in any area)
  • Tire displaying treadwear indicators
  • Tire that has cross section significantly altered (‘Flat’ or ‘pointed’ tires not originally designed with that cross-section.)
  • Tire that is feathered or cupped – the tire may be making noise or exhibiting a choppy ride if this condition is bad enough.  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; most people with any type of tire damage need a new tire.  They may elect to have the tire repaired, but again, RevZilla urges our customers to stay safe and keep the tires on the bike that the manufacturer planned on you using.

That’s about it - if you need help, drop us a line or give us a call; we never ‘tire’ of our customers!

-- Uncle Loomis

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