Motorcycle tyre

A rear motorcycle tire for street use

Motorcycle tires (tyres in British English) are the outer part of motorcycle wheels, attached to the rims, providing traction, resisting wear, absorbing surface irregularities, and allowing the motorcycle to turn via countersteering. The two tires' contact patches are the motorcycle's connection to the ground, and so are fundamental to the motorcycle's suspension behaviour, and critically affect safety, braking, fuel economy in automobiles fuel economy, noise, and rider comfort.

History

The history of motorcycle tires is a clear progression of steady improvement in grip, allowing better acceleration, braking, and turning, along with improved comfort, safety, durability, and reliability. This progression has generally meant a steady increase in tire width, so much so that Kevin Cameron noted the assumption among riders that "bigger must be better in every way", leading to, "the temptation to overwhelm motorcycles with the biggest tires the owner can find." While many advances in tire materials and construction have yielded unalloyed benefits, at a given level of technological sophistication, every design choice, such as tire width, diameter, cross-section curvature, and the geometry of the motorcycle the tires are intended for is a trade-off and a compromise.

Pneumatic tires were invented by John Boyd Dunlop in 1888, and were in widespread use on bicycles and some early motorcycle prototypes by 1895. They were used on the first production motorcycle, the 1894–1897 Hildebrand & Wolfmüller, and have been on nearly all production and special motorcycles ever since. During this period tire sizes were usually 22 to 28 inches (560 to 710 mm) diameter and 1+1⁄2 to 2 in (38 to 51 mm) wide.

A: Typical outer casing of a tire.
B: Continuous, one-piece, or open-end inner tube assembly, where first a joint is made where one end slips into the other, with the collar member forced out tightly against the inner face of the retaining member.
C: A butt-end tube, where the tapered, closed end fits into the open end, expanding to seal when inflated.

The early wheels were spoked, made of all metal, or wood and metal, and used inner tubes to hold air. Flat tire Flats were a constant problem; largely the fault of poor roads and not necessarily tires. For easier repair, butt-ended or open ended inner tubes were used on some models, and some brands made rear wheels easier to detach. Spoked wheels with tubes remained standard until the 1970s, when solid, usually alloy, wheels began to appear and eventually dominate street motorcycles, making lighter tubeless tires practical.

As the early motorcycle industry progressed, larger tire sizes accompanied larger engine displacements, so that by 1909–1914, 2+1⁄4 in (57 mm) section, 26 in (660 mm) diameter tires were used on 250 to 350 cc (15 to 21 cu in) motorcycles, and 2+3⁄8 to 2+1⁄2 in (60 to 64 mm) section tires appeared on motorcycles with displacements over 350 cc. Indian tires reached 3.0 in × 28 in (76 mm × 711 mm), giving even greater rider comfort but with a taller seat height.

From 1915 to 1929, tire quality continued to increase, and beaded edge tires began to be replaced by wired-on beads, which used steel loops embedded in the tire's edge to prevent it from expanding under pressure, so the bead no longer needed a grooved rim to hold it in place. Banded-edge tire were obsolete and replaced entirely by the wired-on type by 1930. In the period 1956–1964, typical tire grip increased by 40%, resulting in better cornering, shorter stopping distance and overall improved safety. This was the result of a greater range of tire sizes appearing on the market, from small 3.5 in × 8 in (89 mm × 203 mm) scooter tires through 4.5 in × 19 in (110 mm × 480 mm) heavyweight motorcycle tires. A variety of rubber compounds and tread patterns further expanded the options, specialized for wet roads, smooth dry roads, racing, off-road use, and sidecars. Both natural and synthetic rubber were used, and tires included fibers of cotton, nylon, and rayon for various structural benefits.

Elena Myers knee dragging while hanging off her Suzuki GSX-R1000 AMA Superbike at Road America.

During the 1970s, the increasing widths of tires led to major changes in road racing cornering technique, leading to riders hanging off or knee dragging, in which the rider moves their body far off center for the purpose of changing the combined center of gravity of the rider plus bike, in order to turn at a given radius and speed at less of a lean angle. Racer John Surtees had been hanging off his MV Agusta as far back as the 1950s, in spite of resistance to the practice at that time from other riders, saying, "The idea is to keep the machine as upright as possible for maximum traction." Tires of the 1960s and early 1970s had a rounder profile, but as they grew in width from the mid-1970s, the cross section became more oval, and the greater width of the tire meant the contact patch was further off center, increasing either steering effort or turn radius, at a given lean angle and speed, than it would have been with a rounder profile. To compensate, riders leaned out, moving their body's center of gravity away from the motorcycle, eventually leaning out so far that their knee would skid along the pavement. Ablative knee pucks or knee sliders were then added to the riders' racing leathers to allow their knees to scrape smoothly along the tarmac through turns.

The first radial tires for cars appeared in 1943, but motorcyclists waited forty more years for this technology to come to motorcycles. These were the 1983 Pirelli MP7 radials, introduced on the European version of the 1984 Honda VF1000R, a limited edition exotic motorcycle that showcased a number of new technologies including carbon fiber reinforced bodywork and air-adjustable anti-dive front forks. The new radial tires had to provide race-replica handling for the very heavy 238 kg (524 lb) dry weight chassis, up to a top speed of 240 km/h (150 mph), making it the fastest production motorcycle of its day. The MP7 radials came to the US market in 1985. Radial construction uses textile or steel belts arranged at 90 degrees to the direction of travel, along with a layer of belts running around the tire's circumference, with motorcycle radials deviating from the true radial design by adding belts running at angles to the radial belts, in the manner of bias-ply tires, allowing the grip, durability, feel, and other characteristics to be adjusted to suit the tire's design. The benefit of radial tires is that the tires run cooler yet maintain great flexibility, allowing engineers to coax significant increases in both grip and tread life, without compromise, under a broader range of conditions than bias-ply tires.

Marc Márquez, elbow down at the 2013 British Grand Prix

Changing tire technology continued to influence riding style in 2013 in MotoGP, when rider Marc Márquez adjusted the knee-down cornering style begun by Mike Hailwood to a more extreme knee-and-elbow down turning, with much of his upper body off center. Márquez was working to use to best advantage the characteristics of the spec Bridgestone tyres all teams had been assigned since 2011, moving off center to keep the bike as upright as possible in the corner apex, and off the relatively flexible edge of tread area. To keep pace, other riders had to learn this physically demanding maneuver, requiring practice to change body position smoothly without upsetting the bike, a properly set up suspension keyed for this style of riding, and targeted muscle development to hold body position.

Types

Motorcycle tires are available for many different applications, including: Sport, Sport Touring, Touring, Cruiser, Scooter, On/Off Road, Dual-Sport, Enduro, Motocross and Racing. There are tires designed for dirt bikes, touring, sport and cruiser bikes. | Sport/performance tires provide excellent grip but may last 1,000 miles (1,609 km) or less. Cruiser and "sport touring" tires try to find the best compromise between grip and durability. There is also a type of tire developed specifically for racing. These tires offer the highest of levels of grip for cornering. Because of the high temperatures at which these tires typically operate, use on the street is unsafe as the tires will typically not reach optimum temperature before a rider arrives at the destination, thus providing almost no grip en route. In racing situations, racing tires would normally be brought up to temperature in advance by the use of tire warmers.

Sport Touring tires are generally not used for high cornering loads, but for long straights, good for riding across the country.

Sport Street tires are for aggressive street riders that spend most of their time carving corners on public roadways. These tires do not have a long life, but in turn have better traction in high speed cornering. Street and sport street tires have good traction even when cold, but when warmed too much, can actually lose traction as their internal temperature increases.

Pirelli Diablo Superbike slick tires (left) and rain tires (right)

Track or Slick tires are for track days or races. They may have more of a triangular profile, which in turn gives a larger contact patch while leaned over. These tires are not recommended for the street by manufactures, and are known to have a shorter life on the street. Due to the triangulation of the tire, there will be less contact patch in the center, causing the tire to develop a flat spot quicker when used to ride on straightaways for long periods of time and have no tread so they lose almost all grip in the wet. Racing slicks are always made of a softer rubber compound and do not provide as much traction as street tires until warmed to a higher internal temperature than street tires normally operate at. Most street riding will not put a sufficient amount of friction on the tire to maintain the slick's optimal tire temperature, especially in colder climates and in spring and fall.

Studded front tire with spikes used on Ice speedway

Cruiser tires are relatively new. Until recently other tires would be used for cruisers, resulting in a tire that wasn't quite right for cruising. Sport tires for example, were often used to enhance the appearance of the bike, even if the bike doesn't have the power to use the tires to their full extent. Cruiser tires are often thinner and fatter than sports tires, meant for a good grip and smooth ride. They are often decorated with custom rims, whitewalls, or tire stickers.

Off road tires have knobby, deep treads for maximum grip on loose dirt, mud, sand, or gravel; such tires tend to be less stable on paved surfaces.

Touring tires are usually made of harder rubber for greater durability. They may last longer, but they tend to provide less outright grip than sports tires at optimal operating temperatures. The tradeoff is that touring tires typically offer more grip at lower temperatures, meaning they can be more suitable for riding in cold or winter conditions whereas a sport tire may never reach the optimal operating temperature.

Properties

There are several properties of motorcycle tires that influence the performance, handling, and stability of a motorcycle.

• Rolling resistance is the resistance that occurs when a tire rolls on a flat surface. The rolling resistance coefficients of motorcycle tires are about 0.02. It tends to increase with forward speed and decrease as inflation pressures increase.
• Cornering force is the lateral (i.e. parallel to the road surface) force produced by a vehicle tire during cornering. Cornering force coefficients of motorcycle tires tends to decrease with increased vertical load, increased inflation pressure, and increased temperature.
• Camber thrust is the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch.
• Pneumatic trail is a trail-like effect generated by compliant tires rolling on a hard surface and subject to side loads, as in a turn. It is the distance that the resultant cornering force of side-slip occurs behind the geometric center of the contact patch.
• Relaxation length describes the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value.

Dual-compound tires

Since about 2005 many manufacturers are producing rear tires with the center made of harder, long lasting "rubber" and the edges made from softer material, often high in silica. Most road bike manufacturers now specify these dual compound tires as standard equipment due to their proven performance advantage. Single-compound tires tend to wear down the center strip well before the sides are worn out. The superior grip of the softer side material allows better grip at more extreme angles in dual compound construction.

Speed and construction

As with four-wheeled vehicles, tires for motorcycle have a tire code, which describes a tire's width, height/width aspect ratio, wheel diameter, load index and speed rating. The most common are:

• 3 digit number: The "nominal section width" of the tire in inches; the widest point from both outer edges.
• /: Slash character for character separation.
• 2 or 3 digit number: The "aspect ratio" of the sidewall height to the total width of the tire, as a percentage.
• An optional letter indicating construction of the fabric carcass of the tire:
  • B: bias belt (where the sidewalls are the same material as the tread, leading to a rigid ride)
  • D: diagonal
  • R: radial
    • if omitted, then it is a cross ply tire
• 2 digit number: Diameter in inches of the wheel that the tire is designed to fit.
• 2 or 3 digit number: Load index; see table below
• 1 or 2 digit/letter combo: Speed rating; see table below

Load index

LI	kg	LI	kg	LI	kg	LI	kg	LI	kg
19	77,5	36	125,0	53	206	70	335,0	87	545,0
20	80,0	37	128,0	54	212,0	71	345,0	88	560,0
21	82,5	38	132,0	55	218,0	72	355,0	89	580,0
22	85,0	39	136,0	56	224,0	73	365,0	90	600,0
23	87,5	40	140,0	57	230,0	74	375,0	91	615,0
24	90,0	41	145,0	58	236,0	75	387,0	92	630,0
25	92,0	42	150,0	59	243,0	76	400,0	93	650,0
26	95,0	43	155,0	60	250,0	77	412,0	94	670,0
27	97,5	44	160,0	61	257,0	78	425,0	95	690,0
28	100,0	45	165,0	62	265,0	79	437,0	96	710,0
29	103,0	46	170,0	63	272,0	80	450,0	97	730,0
30	106,0	47	175,0	64	280,0	81	462,0	98	750,0
31	109,0	48	180,0	65	290,0	82	475,0	99	775,0
32	112,0	49	185,0	66	300,0	83	487,0	100	800,0
33	115,0	50	190,0	67	307,0	84	500,0	-	-
34	118,0	51	195,0	68	315,0	85	510	-	-
35	121,0	52	200,0	69	325	86	530,0	-	-

Speed rating

Rating	Speed (km/h)	Speed (mph)
Moped	50	30
J	100	62
K	110	69
L	120	75
M	130	81
P (or-)	150	95
Q	160	100
R	170	105
S	180	113
T	190	118
U	200	125
H	210	130
V	240	150
W	270	168
Z	over 240	over 150

See also

• Bicycle tire
• Inner tube
• Outline of motorcycles and motorcycling
• Outline of tires
• Tire manufacturing

External links

• Motorcycle tire measurement