How To Repair Flat Tire On Riding Mower

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• Dishonest Sizing
• Fractional vs. Decimal Sizing
• Measuring Rims
• The ISO/East.T.R.T.O. System
• Tubulars ("Sew-ups")
• Traditional Sizing Systems
• Width Compatibility
• WTB'due south Global Measuring System
• A Bit of History

This article is also bachelor in British English!

For more than general tire data, see my Tires article.

Which Size Tire Fits Which Size Rim?

Wheel tires come up in a bewildering variety of sizes. To make matters worse, in the early days of cycling, every country that manufactured bicycles adult its own arrangement of marking the sizes. The same size tire would be known by unlike numbers in dissimilar countries. Even worse, dissimilar-sized tires that were not interchangeable with one another were often marked with the same numbers!

This page covers sizes in common use as of its writing, and a number of older sizes. Sutherland'due south Handbook for Wheel Mechanics, third through 6th edition, covers dozens of boosted, antique sizes. The 6th edition is available on CD ROM from Sutherland's. Better bike shops have a copy.

Which Size Tire Fits Which Bike?

To make up one's mind which tire size will fit, perform measurements on the bicycle's fork and frame.

If the wheel has rim brakes, the rim must line upward with the brake shoes then but one rim size or a modest range of sizes will work. So, first measure the distance from where the center of the hub axle would be in a dropout to the center of a brake shoe. Then look upward the rim radius in the ISO table on this page. A unlike rim size may be possible with unlike brakes, though longer restriction accomplish more often than not results in poorer brake performance.

The front tire must not attain the fork crown; the rear tire must not achieve the seatstay span or chainstay bridge. Take measurements from the axle position to the fork crown, chainstay bridge and seatstay bridge. Tire outside radius is nominally the rim radius plus the tire width, and as much as 1 cm greater for a tire with a deep tread. A tire must have typically 1 cm clearance, two cm if a fender will exist installed, but do not use a wheel that is much smaller, or a pedal is too probable to strike the basis in cornering. On a bicycle with horizontal dropouts, additional clearance to the chainstay bridge is desirable so the cycle tin can be removed without deflating the tire.

The infinite between the fork blades or stays must be wide enough to clear the tire, with a few mm extra on each side in instance the bike goes slightly out of true. Measure out at the radius of the widest part of the tire, unremarkably the rim radius plus half the tire width --except that the widest part may exist at the tread of an off-route tire. Nominal tire width is marked on the tire; bodily width can exist measured if the tire is installed on a rim.

If the bicycle has hub brakes (drum, disk, coaster), dissimilar rim sizes are possible equally long as the tire is fits the frame. A larger rim goes with a skinnier tire, and vice versa..

Traditional Sizing Systems

The traditional sizing systems are based on a measurement of the exterior diameter of a tire. This would usually be measured in inches (26", 27", etc.) or millimeters (650, 700, etc.).

Unfortunately, evolution of tires and rims has made these measurements lose contact with reality. Hither'south how it works: Let'due south start with the 26 x ii.125 size that became popular on heavyweight "balloon tire" bikes in the belatedly '30'south and withal remains mutual on "beach cruiser" bikes. This size tire is very shut to 26 inches in actual diameter. Some riders, still, were dissatisfied with these tires, and wanted something a flake lighter and faster. The industry responded by making "middleweight" tires marked 26 x 1.75 to fit the same rims. Although they are still called "26 inch", these tires are actually 25 5/viii", non 26". This same rim size was adopted past the early pioneers of west-coast "klunkers", and became the standard for mountain bikes. Due to the ambition of the market, you tin can get tires equally narrow as 25 mm to fit these rims, and then you wind up with a "26 inch" tire that is more than similar 24 7/viii" in actual diameter!

A second number or letter of the alphabet code would indicate the width of the tire. (26 10 1.75, 27 x one ane/four...650B, 700C...)

Does Point Seven Five Equal Iii Quarters?

Inch-based designations sometimes limited the width in a decimal (26 ten i.75) and sometimes as a common fraction (26 ten 1 three/4). This is the most common cause of mismatches. Although these size designations are mathematically equal, they refer to different size tires, which are Not interchangeable. It is dangerous to generalize when talking about tire sizing, only I would confidently state the following:

Brownish'due south Law Of Tire Sizing:

If two tires are marked with sizes that are mathematically equal,
just ane is expressed every bit a decimal and the other every bit a fraction,
these two tires volition non be interchangeable. (well, there are 3 exceptions, noted in the tables below...)

Dishonesty in Sizing

Competitive pressures accept often led to inaccuracy in width measurement. Here's how it works: Suppose you are in the market for a high-operation 700 x 25 tire; you might reasonably investigate catalogues and advertisements to endeavour to notice the lightest 700-25 bachelor. If the Pepsi Tire Company and the Coke Tire Company had tires of equal quality and technology, but the Pepsi 700-25 was actually a 700-24 marked equally a 25, the Pepsi tire would be lighter than the accurately-marked Coke 700-25. This would put Pepsi at a competitive reward. In self defense, Coke would retaliate by marketing an even lighter 700-23 labeled as a 700-25.

This scenario prevailed throughout the '70'due south and '80'south. The state of affairs got then out-of-paw that cooler heads have prevailed, and there is a strong (but not universal) trend toward authentic width measurements.

Some road bicycles take extremely tight clearances and will not fit an honest 28mm tire. Encounter comments in our article on fenders.

B.S.D.

ISO, the International System for Standardization, has developed a universal tire and rim sizing arrangement that eliminates confusion. (This organisation was formerly known as the "E.T.R.T.O." arrangement, developed by the Eastwarduropean Tyre and Rim Technical Organisation.)

The ISO system uses 2 numbers. The first is width in millimeters. For the rim, this is the inner width between the flanges, as shown in the diagram; for the tire, it is the inflated width. This volition vary a bit depending on the width of the rim.

The second ISO number is the disquisitional i: it is the diameter of the bead seat of the rim, in mm ("B.Due south.D."). More often than not, if this number matches, the tire involved will fit onto the rim; if it doesn't match, the tire won't fit.

For case, a 700 x xx C road tire would be a 20-622; a 700 ten 38 hybrid tire would be a 38-622. The width difference between these sizes would make them less-than platonic replacements for one some other, but any rim that could fit one of them would work after a fashion with the other.

A general guideline is that the tire width should be between 1.45/2.0 x the inner rim width.

If you pull the chaplet apart and mensurate the total width from dewdrop to bead, it should exist approximately 2.5 x the ISO width.

If your tire is likewise narrow for the rim, there'south an increased adventure of tire/rim damage from road hazards.

If its too wide for the rim, there'southward an increase risk of sidewall wear from brake shoes, and a greater risk of loss of control in the result of a sudden apartment.

The tables below give a partial list of traditional tire sizes, with their ISO bead-seat equivalents. The ISO comparison listing at the bottom of this page covers all sizes which we know to be in product as of 2022. The fractional, decimal and French lists cover mutual sizes.

Fractional sizes:

Fractional	ISO	Applications
36 inch	787 mm	Unicycles, some novelty bicycles
32 inch	686 mm	Unicycles, some novelty bicycles
29 inch	622 mm	This is a marketing term for wide 622 mm ("700C") tires.
28 x i 1/2	635 mm	English, Dutch, Chinese, Indian Rod-brake roadsters (Also marked F10, F25, 700 B)
	622 mm	(F.13) Rare Canadian designation
28 x 1 5/eight x 1 1/2		Northern European designation for the 622 mm (700 C) size
	635 mm	Old Swedish designation
27 x anything except "27 v" and 609 mm Danish	630 mm	Older road bikes.
27 x i ane/2	609 mm	Rare Danish size
26 10 one (650 C)	571 mm	Triathlon, time trial, minor road bikes. Old Schwinn Due south-four
26 10 1 1/4	597 mm	Older British sport & club bikes
26 x 1 3/8 (S-6)		Schwinn "lightweights"
26 10 1 3/eight (E.A.iii)	590 mm	Virtually English language 3-speeds, section-store or juvenile 10 speeds
26 x ane 1/two (650B)	584 mm	French utility, tandem and loaded-touring bikes, a very few Raleigh (U.S.) & Schwinn mount bikes.
26 ten 1 3/four (S-7)	571 mm	Schwinn "middleweight" cruisers
26 10 1, ane 1/eight		High operation wheels for smaller riders, common on Cannondale bicycles
24 ten i	520 mm	High operation wheels for smaller riders; Terry front end
24 x i 1/viii	520 mm or 540 mm!	Caveat emptor. 540mm is common on wheelchairs.
24 10 one 1/4	547 mm	British or Schwinn Juvenile
24 x ane 3/8 (Southward-five)		Schwinn Juvenile lightweights
24 x 1 3/4 (S7)	520 mm	Schwinn "Middleweights"
24 x 1 3/8 (Eastward-v)	540 mm	British Juvenile, well-nigh wheelchairs; common on women's utility bicycles in Japan.
22 ten i 3/viii NL	489 mm	Dutch juvenile
20 x 1 1/viii 20 x 1 ane/4 20 x 1 3/8	451 mm	Juvenile lightweights, BMX for light riders, some recumbents, some folding bicycles
20 x ane 3/four	419 mm	Schwinn juvenile
20 x 2	438 mm	Swedish
18 x 1 iii/8	400 mm	British juvenile
17 x 1 1/4	369 mm	Alex Moulton AM serial
16 ten 1 3/eight	349 mm	Older Moulton; Brompton & other folders, recumbent forepart, juvenile
16 x i 3/eight	337 mm	Mystery tire
16 x 1 iii/8	335 mm	Polish juvenile
16 x 1 iii/4	317 mm	Schwinn Juvenile
fourteen x 1 3/eight	298 mm	Moulton mini, etc.
12 1/2 x anything	203 mm	Juvenile, scooters
10 x 2	152 mm	Wheelchair pulley
8 ten i 1/4	137 mm	Wheelchair caster

Traditionally, fractional sizes are made for straight-sided rims. Loftier-performance sizes (520 mm, 571, 622 mm etc.) are preferably used with hook-edge rims, which can hold higher pressure and eye the tires more reliably. Tubeless tires may use special hook-border rims that form an airtight seal.

Decimal sizes:

Decimal	ISO	Applications
29 inch	622 mm	This is a marketing term for wide 622 mm ("700C") tires.
28 x decimal		Some German tire companies use this non-standard designation for 622 mm ("700C") tires -- violates Brown'southward police force!
"27 v" (meaning 27.5)	584 mm	Marketing term for wide, knobby 584 mm tires. Some Mount bikes
26 x 1.00 through v.0	559 mm	Almost Mount bikes, cruisers, fatbikes etc. Erstwhile Schwinn designation was S-ii
26 x 1.25 (rare)	599 mm	Very old U.S. lightweights
26 10 1.375 (rare)		Very old U.S. lightweights
24 x i.5-24 ten ii.125	507 mm	Juvenile mountain bikes, cruisers
22 10 i.75, 22 ten ii.125	457 mm	Juvenile
20 ten one.5-20 x 2.125	406 mm	Nigh BMX, juvenile, folders, trailers, some recumbents
18 10 ane.5	355 mm	Birdy folding bikes
18 ten 1.75-18 ten 2.125		Juvenile
16 ten 1.75-sixteen ten two.125	305 mm	Juvenile, folders, trailers, Strida, early on DaHon, some recumbents
14 x i.75-14 x 2.125	254 mm	Juvenile
12 1/2 x anything	203 mm	Juvenile, scooters

French sizes:

In the French system, the first number is the nominal outside diameter in mm, followed past a letter code for the width: "A" is narrow, "D" is wide. The letter codes no longer represent to the tire width, since narrow tires are oftentimes made for rim sizes that originally took wide tires; for instance, 700 C was originally a wide size, merely at present is available in very narrow widths, with actual outside diameters as small as 660 mm.

French Size	ISO	Applications
700 A	642 mm	Obsolete
700 B	635 mm	Rod-brake roadsters.
700 C	622 mm	Road bikes, hybrids, "29 inch" MTBs. (28 x one 1/2 F.13 Canada)
650 A	590 mm	French version of 26 ten one iii/8; Italian high-functioning bikes for smaller riders
650 B	584 mm	French utility bikes, tandems, and loaded-touring bikes; some older Raleigh and Schwinn mountain bikes. Also called 27 5. See We have a page about this size.
700 D	583 mm	Oddball size formerly used on some GT models. 650B tire (584 mm) is shut plenty, peradventure with wide rim tape.
650 C	571 mm	Triathlon, time trial, loftier performance road bikes for smaller riders
600 A	540 mm	European Juvenile route bikes, about wheelchairs
550 A	490 mm	European Juvenile road bikes
500 A	440 mm	European Juvenile, folding
450 A	390 mm	European Juvenile
400 A	340 mm	European Juvenile
350 A	288 mm	European juvenile

ISO Cross Reference:

Dewdrop Seat Bore, mm	Dewdrop Seat Radius, mm	Traditional Designations
787	393.five	36 inch
686	343	32 inch
635	317.five	28 x 1 1/2, 700 B, 28 x 1 5/viii x 1 1/2 (old, Sweden)
630	315	27 ten anything except "27  five" and 609 mm
622	311	700 C, 28 x 1 5/viii ten one ane/two and other pairs of numbers, (but besides see 635), 29 inch, 28 x 1 1/ii F.xiii Canada
609	304.v	Rare Danish size, 27 x 1 one/two
599	299.5	26 x 1.25, x 1.375 -- one-time US size
597	298.5	26 10 1 1/4, 26 10 one iii/8 (Southward-vi)
590	295	26 x ane iii/eight (E.A.three), 650 A
584	292	650B, 26 10 1 i/2, "27 five"
583	291.5	700 D -- oddball size made by GT
571	285.5	26 10 i, 26 x 1 3/4, 650 C
559	279.5	26 10 1.00- ten 2.125, besides fatbike tires upward to 5 inches wide
547	273.5	24 ten 1 1/4, 24 x i 3/8 (Southward-5)
541	270.5	600 A
540	270	24 x ane 1/8, 24 10 1 3/eight (E.5),
520	260	24 x 1, 24 x ane 1/8, 24 ten one iii/four
507	253.5	24 x 1.v- x 2.125
501	250.5	British, 22 x 1 3/8, 22 x 1.00
490	245	550 A
489	244.v	Dutch juvenile 22 x 1 1/viii NL, 22 10 ane 3/viii NL
484	242	550 B
457	228.5	22 x 1.75; ten 2.125
451	225.5	20 x ane 1/8; ten ane i/four; x 1 3/8
440	220	500 A
438	219	Dutch juvenile, 20 ten 1 iii/viii NL
428	214	Swedish, 20 x ii
419	209.5	20 x 1 3/four
406	203	20 x 1.5- x 2.125
390	195	450 A
369	184.5	17 x 1 one/4
355	177.5	18 x 1.five- ten 2.125
349	174.5	xvi x 1 3/8
340	170	400 A
337	168.5	16 x 1 3/8
317	158.5	xvi x i 3/4
305	152.5	16 ten i.75- x 2.125
298	149	14 x ane iii/viii, Moulton Mini
288	144	350 A
254	127	14 10 1.75
203	101.five	12 1/2 X anything.
152	76	10 ten 2
137	68.five	8 x ane 1/4

Nigh of this information was compiled by John Allen for Sutherland's Handbook For Bike Mechanics, the bible of bicycle technology. Sutherland'southward, sixth edition has a more detailed, more thorough version of this chart.

Got an unmarked rim but no tire? Click Here for how to measure Rim Size.

Width Considerations

Although you can use practically any tire/rim combination that shares the same bead-seat diameter, as already noted, information technology is unwise to use widely disparate sizes.

If you use a very narrow tire on a broad rim, you take chances pinch flats and rim damage from road hazards.

If yous employ a very broad tire on a narrow rim, y'all adventure sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, electric current mountain-bike fashion pushes the edge of this. In the involvement of weight saving, virtually current mount bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of broad tires, and puts undue stress on the rim sidewalls.

The "fatbike" phenomenon has led to the availability of very wide tires and rims. These should only be used together.

Georg Boeger has kindly provided a chart showing recommended width combinations:

Which tire fits safely on which rim? [all dimensions in millimeters]
	Tire width
Rim width (interior)	18	twenty	23	25	28	32	35	37	xl	44	47	50	54	57
13	X	Ten	X	10
15			X	X	10	X
17				X	Ten	X	Ten	Ten
xix					X	X	X	X	X	X
21							X	X	X	X	10	X
23									X	Ten	Ten	10
25										X	10	X	10	X

Note: This nautical chart may err a bit on the side of caution. Many cyclists utilise slightly wider tires with no problem.

A Bit of History and Math

The cross-department of a tire's fabric is an arc of a circle -- merely a total circle with tubulars. The rim takes upwardly the part of the circle that is not represented by the tire.

The rim is typically 0.7 times every bit broad as the tire, and a scrap of trigonometry volition go you that the rim occupies about 90 degrees of what would be the circumference of the circle.  The tire occupies the other 270 degrees (iii/4 of the circle) and so the width when mounted on the rim is 4/(3  * pi), virtually 0.4, times the width when laid out flat.

Rim and tire widths of form vary, and so this result is not verbal.

A proffer to measure tire width with the tire laid out apartment offset appeared in the third edition of Sutherland's Handbook for Bicycle Mechanics (1980), and I was the author of that proposition.

That edition also included the first published tire-size chart using the ETRTO marking standard, other than in the original ETRTO technical certificate. I performed the calculations for the chart on a Hewlett-Packard Model 27 pocket computer.

--John Allen

Wilderness Trail Bikes' Global Measuring System

From the WTB Website:

GMS Global Measuring System The current industry standard for specifying the actual inflated size of a bicycle tire does non business relationship for subtle variation in tread and casing size. To address this problem and provide you with more than information for comparing tires, WTB has introduced the Global Measuring Organization (GMS) for tire measurement.

The GMS uses a ii-number arrangement: the start number is the width of the casing, and the second number is the width of the tread, both in millimeters. These measurements are taken on a rim which is 20 mm wide at the bead-capturing signal, with a tire inflated to 60psi and maintained for 24 hours.

In addition to existence able accurately to size a tire, knowing the actual casing size and tread width provides an indication of air volume, tread characteristics and tread contact expanse; all of which provide you with a more concise idea of what ride characteristics to wait from each of WTB'south tires.

Tubular Tires ("Stitch-ups")

Tubular tires are mainly used for racing. A tubular tire has no beads; instead, the 2 edges of the carcass are sewn together (hence the term "stitch-upwardly") with the inner tube inside. Tubulars fit only on special rims, where they are held on by cement.

Unless special cement which does non allow on-road replacement of a tire is used, tubulars "squirm" against the rims and are slower than the best wired-on tires, fifty-fifty though lighter -- run into details from Jobst Brandt.

Tubulars existed in several unlike sizes, but merely 700c and 26-inch tubulars are readily available these days. Beware: sizes of 26" and 24" tubulars are not well-standardized. Take the rim with y'all when buying a tire, and vice versa. Size variations of tubulars are covered in Sutherland'south Handbook for Bicycle Mechanics, 7th Edition, bachelor from Sutherland's, and on the mechanic's bookshelf at improve bike shops.

• Full-sized tubulars fit rims of the same diameter as 622 mm (700c) clinchers. This size is sometimes referred to as "28 inch" or "700". It is likewise, confusingly, sometimes referred to as "27 inch." The "27 inch" designation is inaccurate and obsolete, but y'all'll sometimes meet it in older printed material.

  In clincher tires, there is a real difference between "700c" and "27 inch" sizes, but for tubulars this is a false stardom. Whenever you see mention of "27 inch tubulars" the writer is actually referring to standard full-sized tubulars, every bit used on most racing bikes.

• "26 inch" or "650" tubulars are smaller, mainly used on time-trial or motorpacing track bikes. In that location are 2 common "26 inch" sizes, corresponding to the 584 mm and 571 mm ISO sizes. There are a couple of oddball sizes as well.
• "24 inch" (2 slightly dissimilar sizes), "22 inch" "xx inch" and "18 inch" tubulars were formerly used for children'due south racing bikes, but are pretty much extinct these days. The "18 inch" size corresponds to the "17 inch" (369 mm) size used on Moulton bicycles.

Tubulars are as well sometimes called "sew-ups" or "tubs" (British usage.)

If you want to sound like an ignorant yahoo, phone call them "tubies" or "tubeless tires." Tubeless tires for bicycles have bead wires, and are special only in beingness designed to hold air without an inner tube.

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Terminal Updated: by John Allen

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