News & Events

 

Nov 12

MOTO International

Sharing Dave's ol' tech articles, episode 3

by MOTO International

 
 

Through some combination of my vague explanations and your inquiring minds, it seems that my answers sometimes only lead to more questions. Although I've touched on a few tire subjects, I've obviously left far more unanswered. So here's a much more comprehensive look at tires. Even what little I learned researching motorcycle tires amounted to enough material to fill a dozen pages.



It used to be simple: tires came in just a couple of diameters and a handful of widths. Pirelli Universals and Dunlop K70's were sold with equal enthusiasm for applications from street touring to dirt track racing. Now, just for modern street bikes we have 16, 17, 18, 19, and 21" front wheels; 15, 16, 17, and 18" rears, plus a multitude of widths, profiles, tread patterns, and rubber compounds. They're not merely round and black anymore.



It all comes down to greater choice. What I hope to provide here is a primer to help you make informed decisions on wheels and tires. I'm sure a lot of this information will be old news to many but I doubt if anyone will fail to learn something.



Tire size designations

It used to be that profile had to do with riding your bike, not choosing tires. The old 4.00 x 18 was 4" wide and also 4" tall. That is, it had a 100% aspect ratio. As horsepower increased so did the need for greater traction. The answer was wider tires, but with only 100% aspects available, each wider tire also grew in height. This raised seat heights, reduced fender clearance, and diminished tire "feedback" to the rider.



When low profile tires first came out in the early 70's they were given odd sizes such as 3.60, 4.10, and 4.60. By this we were supposed to know that they had a lower aspect ratio by some unnamed amount which I remember as 82%. I believe Dunlop was the first to produce a motorcycle tire embossed with its true aspect ratio when they introduced a K81 in 4.25/85 x 18". This meant that the tire was 4.25" wide and its height was 85% of the width at 3.6 inches. At the time, this seemed to me more difficult to understand than simply knowing it was "low profile."



As if life hadn't become complicated enough by aspect ratios, metric tire sizing was also introduced. Unlike some conversions, thinking metrically for tires is easy. In round figures, an inch equals 25mm. So the old 4.00 x 18 rear tire now becomes a 100 x 18 (The earlier dominance of the measure of King John's thumb can still be seen measuring the diameter of your bike's wheels). As with the 4.25" K81, metric sizing always includes the tire's height as a percentage of its width. A common replacement for the 4.00 x 18, for example, is a 100/90 x 18. It's 100mm wide (about 4") and 90% as tall as it is wide (about 3.6").



Making use of aspect ratios

All this talk about aspect ratios is just so much academic poo poo for the most part but it does have two very practical applications. One involves the common practice of changing to wider tires (which actually offers little advantage beyond additional weight carrying capability). What an awareness of aspect ratios can do is help you to maintain, raise, or lower overall gearing, and also vary the rate at which mileage is recorded by the odometer.



As an example, I wanted to raise the gearing of my big-bore Convert because it's capable of pulling more gearing. My standard rear tire had been a Metzeler ME88 Marathon 120/90 x 18. The nominal height of that tire is 120mm times 90% or 108mm. I found that all quality 140mm tires had an aspect ratio of 70% or lower meaning none was taller than 98mm. There are some 130/90 tires but none I wanted to use. All other 130's were 80 series - 130 times 80% equals 104mm. In other words, the tallest touring-type tire I could find was the one I already had: a 120/90!



As another example, let's say you want a wider rear tire but don't want the extra height to raise your gearing or reduce your fender clearance. A 110/90 is 99mm tall, a 120/90 is much taller @108mm, but a 120/80 is only 96mm.



The other application of aspect ratios involves steering improvement. I have found that wide and tall tires used on the front contribute to slow steering. I usually recommend a tire no wider than 90mm for 500's and 100mm for all other 18" front wheels unless it's a touring bike (requiring higher load capacity) or it's more important that the tire look big than corner quickly. When a 17" front became the hot new idea a few years ago, I installed one on my Guzzi. It dramatically improved the steering and braking of my bike. I didn't know what I was doing when I made the swap so I took a shot in the dark. Now, because I have more information at hand, I can visualize all the variables and could have made a more informed decision. Here are my choices:



Tire Size

Diameter

Diameter Reduction

Min Rim Width

Max Rim Width

Compounds Available

Weight Capacity

100/90V18

25.08

0.00

2.15

2.75

standard or race

494

110/80V17

23.94

1.14

2.15

3.00

standard or race

506

120/70V17

23.62

1.46

3.00

3.75

standard or race

520

110/70V18

24.05

1.03

2.50

3.50

race only

465

100/80V18

24.29

0.79

2.15

3.00

standard only

454

90/90V18

24.37

0.71

1.85

2.50

standard only

430



The only tire (120/70V17) offering a greater diameter reduction from my original (in bold) than the one I chose (in bold and underlined) would have required a much wider rim than I wanted to use. A similar reduction could have been had by using the 110/70VB18 but it's only available in a race compound (more on that later) and it required a wider rim than my original 2.15 x 18 so it offered no advantage over changing to a 17. Either the 100/80V18 or the 90/90V18 would have given me most of my diameter reduction without the need to change rims. The smaller tire is actually a better fit to my 18" rim than the original tire but I would have lost a lot of weight capacity. Owing more to luck than good management, I actually made the best choice considering my goal. I made a substantial reduction in tire diameter, wound up with a rim that is the best choice (rather than on the low side of the allowed range) for the tire, and gained a little in load capacity.



Cautions when considering different tires size

Many vintage (and modern) bikes are very limited in their ability to accept larger tires. Clearance for rear tires must be checked to the swingarm, the chain, the center stand, the fender, and sometimes the turn signals, wiring, and accessories such as luggage racks. For front tires check fender clearance (both in height and width). If you're considering reducing rim diameters on disc brake wheels check that it will still be possible to remove the caliper without running into the rim. Lower tires reduce ground clearance and make it harder to get the bike up onto the center stand. Taller tires may make the center stand useless unless it's lengthened.



Not everything you need to check involves measurements on your bike. Tire manufacturers' catalogs may list many tires that are not imported into the US. Make sure that want you want can actually be had.



With some shaft drive bikes, such as small Guzzis and twin-shock BMW's, there may be a more severe clearance problem getting a big tire past the rear drive than into the swingarm. If you don't mind unbolting the rear drive to swing it out of the way each time you install the rear wheel then this may still be an option for you. A slight clearance problem exists when a 120 x 18 is installed on Guzzis with a rear drum. The brake anchor gets in the way until it's repositioned to the outboard side of the attachment tab on the swingarm.



Matching tires and rims

The greatest limit on fitting larger tires is that your rim's probably not wide enough. A wide tire on the narrow rim will probably handle worse due to its pinched profile and wear more quickly because of its reduced contact patch. After running several different rear tires on my old Ducati 900, in sizes ranging from 120-130mm, I concluded that the best mileage came from the original 4.25" Michelin, the narrowest tire I used.



If you must persist, check first the tire manufacturer's recommendations for allowable rim sizes. These are becoming difficult to find, possibly due to the liability risk of letting customers choose their own combinations or the manufacturer's low opinion of the intelligence of motorcycle store employees. I keep handy a Metzeler guide that lists actual (not theoretical) tire widths plus allowable and recommended rim widths for each of their tires. Here is a sampling of tire/rim recommendations from Metzeler:



Tire Size

Minimum

Rim Width

Recommended rim

Maximum

 Rim Width

90/90V18

1.85

2.15

2.50

100/80V18

2.15

2.50

2.75

100/90V18

2.15

2.50

2.75

110/80V18

2.15

2.50

3.00

110/90V18

2.15

2.50

2.75

120/90V18

2.50

2.75

3.00

130/80V18

2.50

3.00

3.50

3.25V19

1.85

2.15

2.50

3.50V19

1.85

2.15

2.50

100/90V19

2.15

2.50

2.75

110/90V19

2.15

2.50

3.00



This information has proven invaluable. For example, a customer riding a Honda CM400T as a daily commuter wanted a premium-quality long-life touring tire. Her bike came with a 120/90 x 16 on the rear. The narrowest available tires to fit her requirements were all of 130mm width. With the Metzeler book I was able to confirm that her rim was adequate for a 130 and the mounted width of that tire would sufficiently clear her Honda's swingarm and chain.



It doesn't always work out this well. As an example, most big-twin Guzzis up until the mid 1980's came with a 2.15 x 18 rear rim. This is too small for the narrowest of the popular touring tires at 120mm. Sometimes you just gotta do what you gotta do. At least I can feel a little better about bending the rules knowing that Metzeler, in their own fitment recommendation chart, specifies a 120 for many of these bikes.



Buying tires simply by their size markings (without a spec chart) can lead to some unexpected and very disappointing results. The industry standards (set of course by the tire manufacturers) allow such a wide variance that one company's 120 can actually be wider than another's 130! The mounted width also varies with the width of rim the tire's mounted on. What this means is that if you've confirmed clearance in your swingarm for a larger tire, don't be surprised if the tire you choose doesn't fit.



Maximum speed designations

Metric tires carry speed range designations along with the measurements for width and height. The ratings are for continuous running at maximum load (weight carrying capacity). An S tire is good to 112 m.p.h., an H to 131, and a V for anything above the H maximum. These values are beyond what most of us care about but for some the information is obviously vital. It should be noted that the otherwise open-ended rating for V tires is limited to 142 m.p.h. when used with a tube.



I don't find much application for this information except on one point: most of us are buying tires of a higher speed rating than we need. Often there is no choice, but if there is, an H tire is usually less expensive than a V although not by much. I have heard it said that V's are just plain better than H's but I remain unconvinced.



My rationale is this: The biggest enemy of tires is heat. To keep a tire from overheating in high speed applications, the manufacturers make the carcass stiffer. Flexing causes friction which is heat. In other words, given otherwise identical tires, the H will be more compliant and the V stiffer. The V has been compromised to withstand the higher speed and friction. If stiffer necessarily made a better tire, there would be no great reason to make the H.



For small twins, S is sometimes the only rating available. This isn't necessarily bad. I once had a customer report a severe lack of traction after installing premium V-rated tires on his light-weight Moto Morini V-twin. Replacing those tires with a lower rated set actually provided him with far better traction.



Carcass construction

The speed code may be followed by a construction code. Typically you'll see either nothing, a B for belted, or an R for radial. A belted tire has an extra layer of a special material in the carcass that controls the outward growth of the tire at running speed. This lowers internal friction and limits the ability of centrifugal force to make the tire grow away from the rim and narrow the contact patch. Metzeler lists diameter increases @130 m.p.h. in the range of 1/2-3/4" so this is not an insignificant effect.



Metzeler's popular MBS series are all belted, but in different ways for their specific purposes. Both the belt and the carcass may use a variety of materials and the belt is applied at varying angles relative to the direction of rotation. Suffice to say that belting makes a tire better but always adds to its cost. No surprise here -- additional manufacturing steps cost more money and they wouldn't add them without good reason.



Belting has proven advantageous in sport tires by allowing manufacturers to specify less stiffness in the carcass while still meeting the V rating standards. In the case of touring tires compliance, load capacity, and long life are considered more important than razor edge handling. Rather than using a stiff carcass or a very deep tread (which causes more friction) many premium touring tires now are belted. H is commonly the highest rating available on these tires due to the demands of very high load and no great need for speed potential.



Radial tires promise still greater traction and compliance due to their softer carcass design. When first introduced, they weren't true radials because they had to be made to fit existing rims. Since radials have much less sidewall stiffness, some tires, like the Pirelli MP7R fitted to the 1987 LeMans Special Edition, had stiffening supports added to the sidewall.



The first true radial I know of to come as standard equipment on a production street bike was the Pirelli MP7S on the 1987 Ducati Paso. This tire compensated for its lack of sidewall strength by having very short sidewalls, 60% aspect ratios, and rims nearly as wide as the tread.



After a period of experimentation radials have evolved into their own range of tire and rims sizes. Fronts are typically 120mm by 17" on 3.5" rims while rears, depending on the bike's displacement, vary from 140-180mm by 17" on 5.5" rims. Aspects vary from a high of 70 down to 55.



Several manufacturers produce non-radials in radial sizes as low-cost alternatives. There's nothing wrong with that. What isn't possible, however, is to make true radials in purely non-radial sizes. So the question of whether or not to use radials is limited to the bikes that come with very wide rims, low-profile tires, and usually radial tires. For them, radials are like belted tires: you pay more and you get more.



The new load designations

Motorcycle tires are beginning to carry a load index number. Here's a sampling of this all-too-confusing designation:



Load  Index

Capacity

Load Index

Capacity

Load Index

Capacity

0

99

30

235

60

551

5

113

35

267

65

639

10

132

40

308

70

738

15

152

45

364

75

853

20

176

50

419

80

991

25

204

55

480

85

1134



Doesn't it seem that it would have been easier to just put the weight capacity on the tire, even if it was in kilograms?! Let's hope this marking gets a rethink.



Since speed causes heat it is necessary to reduce the load rating for V-rated tires above 130 m.p.h. The reduction varies by tire size and speed. Most are in the range of 5-10% for every additional 6.2 miles per hour (10 k.p.h.). Metzeler only load rates some of their tires for elevated speeds, indicating that not all V-rated tires are equally capable of withstanding high-load, high-speed applications.



There is a more positive corollary, allowing higher loads for reduced speeds, that applies equally to S, H, and V tires. By the following chart you can see that American highway speeds allows you a greater carrying capacity, although the gains are less than 10%.



Max. Speed

Allowed Load

Max. Speed

Allowed Load

Max. Speed

Allowed Load

93

100%

74

106%

56

112%

87

100%

68

108%

49

114%

80

104%

62

110%

43

116%



Tire air pressure

A popular story in the motorcycle industry a few years ago concerned the problems Dunlop was having with their Touring Elite rear tire on Honda Goldwings. There were many reports of outright failure. Dunlop sent a team to a large rally to check the condition of their tires since they were finding nothing wrong in their own testing. The team discovered that a large percentage of riders failed to maintain proper air pressure or anything close to it.



My #1 rule concerning customer's bikes in the shop is that no matter what they came in for, the tire pressure gets checked, especially if I'm going to ride it! It's amazing how often I find less than 25 lbs. in tires. For some customers I've thought about giving them 50 lbs. just so that they would be in a safe range a little longer than if I set their tires to what they should be. I guess we're all so accustomed to car tires that rarely seem to need replenishment. Motorcycle tires, especially tube-type, require constant checking. How often? I'm not going to tell you because I want you to check yours often enough to discover how much they go down so that you can establish you own safe regiment.



For the most part I would suggest that you use the pressures suggested in your owners manual. One consideration: modern tires seem to run at slightly higher pressures than tires of the early 70's. If I have no specification to go by I set big bike front tires at 33 and rears at 37. For touring bikes I would suggest even more. I've recently heard from a customer who has found after considerable experimentation that his Cal III is most stable with a combination of 32 front and 42 rear.



The old idea was that too much air would wear out the middle first. The new idea is that insufficient pressure causes more heat and more wear. Too much air will limit traction and compliance to a degree so, like everything else, there are trade-offs here.



Racing has provided a method for determining correct tire pressure that can be applied to street bikes. Check cold tire pressure, then ride long enough to fully warm the tires in your usual riding style. Check the pressure again. If the cold pressure was correct, the hot pressure should be 10% higher -- about 3-3½ pounds. If the pressure rise is greater, more initial pressure is needed. If the rise is less than 10%, the cold pressure needs to be decreased.



Relating load capacity to air pressure

The ratings for load capacity are for tires inflated to the maximum pressure allowed, as indicated on the sidewall. Reducing the pressure causes a reduction in load capacity as you can see in the following chart for H-rated tires:



Tire Size

Load  Index

27.8 lbs

32 lbs

35 lbs

39.4 lbs

42 lbs

45.2 lbs

49.6 lbs

2.75 x 18

42

182

220

257

294

330

3.00 x 18

47

213

257

299

343

385

100/80 x 16

50

264

297

341

385

418

110/80 x 16

55

308

352

396

440

479

110/80 x 17

57

319

363

418

462

506

110/90 x 17

60

345

400

453

506

550

120/90 x 18

65

396

459

519

583

638

140/90 x 15

70

457

528

598

675

737

140/90 x 16

71

470

545

616

693

759

120/90 x 18

71

396

459

519

583

638

686

759

140/90 x 15

76

457

528

598

675

737

794

880

150/90 x 15

80

517

596

675

759

825

891

990



This information answers some questions and raises others. It's not surprising to see that Metzeler makes tires of the same size (120/90 x 18) with different load ratings. The belted, high-rated (71) ME88 Marathon is designed for touring and so needs the extra weight carrying capacity. What's unexpected is that the ME88 has the same weight capacity as a tire with a 65 rating up to that tire's maximum pressure of 42 lbs. In other words, you have to run the ME88 at a pressure well beyond what's best for traction in order to make use of its load carrying advantage. If you choose to stay with a more optimal pressure then safety dictates a lighter load.



What's also apparent from the chart is that tires of the same load index don't share the same capabilities. Both the 140/90 x 16 and the 120/90 x 18 are rated 71 and so can carry the same weight. The 16-incher, though, carries it at a much lower pressure. This is disturbing in that not only do you have to know what the number 71 on the tire means, you have to know how the rating applies to the specific tire. It seems to me that if the markings can't meaningfully stand alone they serve little purpose and, in fact, can lead to dangerous misconceptions.



Matching front and rear tires

Many riders worry about matching tire brands and for good reason. Tire companies do a lot of development to make sure their tire pairs are compatible. In spite of the theoretical advantage, I've never heard of a handling problem that was solved by replacing mismatched tires with compatibles. Still, if you compose your own combination and it doesn't work, you'll probably not find a dealer or tire manufacturer that will absorb the cost.



One interesting note about mismatches came from Metzeler when the Laser front tire was introduced. They claimed that the tires in that model line were approved for use with any premium rear tire. Whether this proclamation came from the engineers or the marketing people I don't know but it's proven to be true in my experience.



When is a tire worn out?

There are a lot of factors to judge here. To a racer, if the tire was used yesterday it may be considered used up today. To some riders, the old trick of inserting a penny into the tread is still the standard. If the top of Lincoln's head isn't into the tread then the tire's worn out.



Two factors stand out to me in judging tire replacement. I change fronts sooner than rears because a worn front profile seems to have a more detrimental effect on handling. The most chilling factor, though, is realizing that the tread provides the paths through which water on the road is channeled away so the tire doesn't hydroplane. That image is usually enough to make me change now rather than try to get a few hundred additional miles out of an old skin.



Assessing your tires' capabilities

Whether you've strayed from standard recommendations or not, it's a good idea to figure out what your tires allow you to do. As an example, I've got a 110/80V17 60 front and a 120/90B18 71H rear. Because the rear tire has a lower speed rating, I'm limited to speeds of 130 m.p.h. at maximum load (I told you this rating usually meant nothing). I can carry up to 506 lbs. on the front and 759 on the rear. If my load is actually balanced to the tire capacities I can carry a total of 1265 lbs. Assuming the bike weighs about 560 with a full tank and I weigh 230 with leathers, I still have room for 475 lbs. of passenger and gear which sounds like more than enough.



Making use of that capacity, however, requires filling the front tire to 42 lbs. and the rear to 49. I like to run them at 35 and 39. My load capacity is therefore reduced to 418 and 583 respectively for a total of 1001. Now my capacity for passenger and luggage is only 211 which at best sounds marginal but probably isn't even that good due to the fact that the majority of my load will be on the rear tire. The only way to know for sure is to weigh each end of the bike with the expected size and distribution of load. My front air pressure is probably OK but the rear obviously will have to be increased for two-up touring. At least if I keep my speeds under 80 I know I have an extra 4% carrying capacity but that only amounts to 23 lbs. on the rear tire at my preferred pressure.



Tire compounds

Some tires are available in softer "racing" rubber compounds. These offer more traction at the cost of tire life but there's really more to it than that. Soft compound tires are designed to operate at the higher temperatures tires experience in racing applications. On the street you'll never reach those temperatures, or at least not consistently. For this reason you may actually have less traction on the street with soft-compound tires. There are no hard and fast rules here but at least don't assume that softer is better in all cases.



Some race-compound tires also have the undesirable trait of loosing grip after a small number of heating cycles (getting up to temperature and then cooling off). In other words, they may be good for an afternoon of racing and that's it. Others are more reusable. If soft compound tires are really what you want, gather a few opinions from various shops involved with racing and maybe go to the track to see what's hot this week.



Some race tires have additional codes indicating tread pattern, rubber compound, and carcass design. These are best confirmed with the manufacturer of the tires you plan to use.



Tube selection

There are supposedly two types of tubes although I'm not sure how to tell them apart. Cheap tubes tend to be made from a type of rubber that is subject to tearing when punctured. That mutates a slow leak-down into a blow-out -- not a happy thought on a motorcycle. Tubes that don't tear seem to be made of a rubber that doesn't hold air quite as well -- you must check pressure fairly often. My advise is to stick with name-brand tubes. I like Michelins because they're inexpensive and they work.



When to replace tubes

Some owners replace tubes with each tire change. This is cheap insurance against problems. I usually consider a tube used up if I find rust on the stem, scrubbing (wear), evidence of having been folded, or stretching (dimpling) at the spoke holes.



If a tube has been punctured, it has no place on a street motorcycle except possibly as a spare. Unlike automobiles, motorcycle tires obviously do a lot of leaning. This gives the tube more reason to rub against the inside of the tire which can encourage a patch to peel.



Storing old tubes

There's a problem if you want to use an old tube as a spare for a long trip: it has too much air in it to pack down tightly. You could suck it down with your mouth if you have no taste buds left (I know, this may be your only chance to taste the air of Mandello del Lario). The trick way of deflating an old tube is with a pressure air hose. If you blow the air almost directly across the valve stem (with the core removed) the air in the tube will be drawn out.



Valve stem caps

Of course you should always have caps in place. If not, dirt could jam the threads, foreign matter could allow air to escape, and at some speed my Guzzi has never seen the centrifugal force of the spinning wheel could overcome the spring in the tire valve allowing all the air out. One cap should be the type that doubles as a valve core remover and both should be metal, not plastic.



Why go tubeless?

The advantages of tubeless tires are many: lessened chance of rapid air loss (blow-out), easier to change, cheaper to change (no tube to buy and less time required), virtually no chance of a leak following installation, longer tire life due to less internal friction (heat directly relates to tire wear), and easier to patch on the road. Regarding the last point: a proper patch of a tubeless tire requires that the tire be removed from the wheel and a patch applied to the inside of the carcass. In an emergency, though, a decent job can be done with a plug that can be applied without even removing the wheel from the bike. This type of patch is detrimental to the tire over time and can develop a subsequent leak, but when the mosquitoes are about to make a meal of your face and arms, there is no finer fix.



Converting cast wheels from tube to tubeless

The important factor here isn't whether the wheel will hold air but instead whether the rim will hold the tire. All older cast wheels were made to the WM rim shape and are not designed to be run tubeless. Later wheels are designated MT and can be converted to tubeless. The only Guzzi models that have MT wheels that came with tubes are the Lario, T-5, and possibly the SP II. MT (which I think of as `motorcycle tubeless') rims are sized by simple inch measure: 2.15, 2.5, 2.75, 3.0, etc. WM hoops have single-digit numbers such as 2 for 1.85", 3 for 2.15, 4 for 2.5, and 5 for 3 inches. Makes a lot of sense, doesn't it?



I know there are plenty of folks running around on tubeless WM wheels. I've never heard of a problem (and problems caused by a rim loosing its grip on a tubeless tire would be remarkable to say the least) but why take the chance? If WM rims were adequate for tubeless, I don't think the MT standard ever would have been developed.



A caution on using tubes in cast wheels

Whether it be a tubeless MT wheel or an old WM design, there is a special circumstance to avoid when running a tube. It's very possible to trap air between the rim and the tube. Having 36 or 40 spoke holes used to take care of that problem. Metzeler claims that trapped air can damage the tube due to chafing. They recommend that you never tighten the stem nut in these cases.



Replacement rim designations

Some rims are actually made to the MT tubeless standard. There is a good reason to use these rims (if you can find them) as replacements even though you obviously can't run tubeless (believe me, I've tried) because there is no practical and positive way to seal centrally-located spoke holes.



My preference is based on the fact that modern tires are primarily designed for MT rims and adaptable to WM designs. What this means is that most tires fit more positively onto MT rims. The practical significance is that it's much easier to mount tires on MT rims. The worst tire mounting combination in the world must be a Metzeler tire and an old Borrani rim. Even with a lot of tire mounting lube and a high-volume hose, it can take 100 pounds of air to get the tire completely beaded up. I have fateful visions of older Guzzi wheels exploding in my face just before the light go out. Tire companies tell us not to use that much pressure but they don't tell us how else to bead up their tires.



Another consideration when replacing a rim is width. Even if you don't plan to use wider tires, it's worth knowing that any given width modern tire is probably designed to run best on a wider rim than in the past. Again, try to find the manufacturer's recommendations.



The realities of replacing rims

There are many sad truths about reworking a wheel. Attempting to take apart the old wheel will reveal that the factory probably didn't use any sort of lubrication on the spoke threads. This means your old spokes and nipples will probably be difficult to reuse because of corrosion having made it impossible to get them all apart without rounding nipples and breaking spokes. More problems come with your shiny new rim. If you buy a rim off the rack, unless it's made specifically for your bike, the spoke holes will not be drilled on the correct angles. There are, also, different numbers of spoke holes, usually 36 or 40. Some aftermarket rims have different depths to their nipple holes requiring different length spokes. All this makes a home job close to impossible. There are, however, some good options available.



Many local shops farm out wheel repairs to companies such as The Wheel Works and Buchanon's Frame Shop. These shops buy their rims undrilled and then drill them to the application. Why start with something that's wrong? They also make custom spokes and nipples of various materials and in different finishes. I find it's easiest to just send them the hub and tell them what it's supposed to be when done.



Mounting a new tire

There's not a lot of reason to mount your own tires since you probably have to take the wheel to a shop for balancing anyway. Furthermore, tubeless tires can't be blown up without an air compressor capable of both ample pressure and volume. Sometimes an inflatable bead expander is used to sufficiently seal the tire to the rim in order to start inflation and sometimes we use a couple of tie-down straps and a big crowbar.



The minimum tools required to do the job are good quality tire irons and some sort of rim protectors. The key to success is to realize that you haven't a chance of "stretching" the tire over the rim. The tire's rim cord has way too much tensile strength to allow that. What you do instead is to try to keep the portion of the tire you have mounted contained within the drop center area (where the spoke holes usually are) between the rim beads (the portion of the rim onto which the tire mounts when aired up). This is more difficult on narrow rims and some of the very wide rims that have a shallow drop center.



The usual point at which tire mounting gets difficult is when the first side is done and the second is a little over half way. The key here is to push the mounted portion of the tire off the bead and into the drop center, both on the side you're mounting and the side that's already completely mounted. This frees up more of the available tire bead for use at the point you're rolling the tire over the edge of the rim.



As I've mentioned before it can be quite a task to bead up the tire once mounted. It helps to have used some form of lubricant when mounting the tire to the rim. I have heard people use everything from talcum powder to WD-40. I refrain from using products not specified for the purpose. I don't want to find out the hard way (and neither does my insurance company) which products rot the tire and which ones let the tire spin on the rim and decapitate the tube stem.



Many tires have lines embossed along the bead so you can visually confirm that the tire is fully beaded up. Metzeler recommends nothing above 150% of running pressure be used to bead up a tire. We commonly use much more knowing that the consequences can be disastrous but that we have no options.



Direction arrows

This part is simple: mount the tire in accordance with the direction arrow on the sidewall. Most modern tires are only for use in either front or rear applications. Those approved for use on either end have two direction arrows. In some specialized applications, such as small-bore racing, I've seen tires used on the wrong end. In that case the tire is mounted in reverse rotation. The drawback is that the tread pattern will prove useless in wet conditions.



Date of manufacture markings

Sometimes it's nice to know the age of a tire. Maybe some shop's stock looks like it's been there forever or you've just purchased a used bike. Embossed on the sidewall next to the letters DOT (for the US Department of Transportation) you will usually find a 3-digit number that indicates when the tire was made. The first two digits tell the week of manufacture and the last indicates the last digit of the year. By this a #067 was made during the 6th week (mid February) of a year ending in 6 (could be 1986, 1976, ?).



Balancing wheels

This is a job that almost assuredly requires taking the wheel to a shop. It really isn't possible to properly balance a wheel on its axle, adding weight to light spots until its stopping point becomes random. Wheel bearings have too much friction for accuracy. This method can only be trusted if the axle is set on special low-friction bearings designed for the purpose. This is still a legitimate method. In fact, I saw Ken Roberts's wheels balanced this way at Laguna Seca back in the 70's. If it works for him at 160 m.p.h. it's good enough for me.



The more common balancing methods are the so-called bubble balancer (where the wheel is checked statically) and the dynamic (spin) balancer. There are supposedly advantages to the latter but I haven't had any complaints using the bubble balancer. I think shops use the "computerized" spin balancer in part as a sales aid. I have found that our spin balancer is more convenient and I have more faith in the results.



Don't be surprised if your wheel comes back from balancing with a lot of weight on it. Do be surprised if the amount varies greatly from tire to tire (assuming you always use quality rubber) on the same wheel. This is because good tires are really well balanced but wheels (especially some by Guzzi) are often a long way out. After all, the wheel outweighs the tire by far. If you suspect this, have a shop check your bare wheels for balance so as to establish a baseline.



We used to believe that some mark on the tire indicated the point at which the valve stem was to be located for best balancing (using the least additional weight). It seems that this is no longer the case and maybe it never was. I found no reference to balance installation markings in the Metzeler tech book.



Cautions on using a new tire

Tires have a coating to preserve the rubber that is not conducive to traction. Manufacturers recommend caution for the first 200 miles while it wears off. The same period of time should be allowed for the new tire to truly settle into the rim before full speed or maximum load is applied.





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