How To Measure Wheel Size On A Bike

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• Diameter
• Circumference
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Bore

The rim's diameter will generally be about ten mm larger than the ISO/E.T.R.T.O. bead-seat bore, depending on how high the rim flanges stick up higher up the bottom of the rim channel.

Lay your measuring record or ruler across the rim from one side to the other. Go the largest measurement, between two points directly opposite one some other. Slide one end of the tape dorsum and along along the rim until the measurement is largest. Measure beyond a few different diameters and take the boilerplate, in example the rim isn't quite circular. (If it's way out of round, don't employ it. If it'due south a millimeter or 2 out of round, the spokes volition pull a shallow-section aluminum or steel rim into shape -- not so much for a deep-section carbon-fiber rim..)

Side by side you lot go out your pocket figurer or smartphone app, or old-school paper and pencil. Equally an example, the measured diameter of the rim shown in the photo is twenty seven/8 inches, or 20.875 inches. Multiplying past 25.4 gives the diameter in millimeters, 530 mm.

The table beneath gives common (and uncommon) rim sizes with the respective bead seat circumference dimensions. 530 mm is the exterior diameter, and the ISO/East.T.R.T.O. diameter is a few millimeters smaller, so this is a 520 mm rim.

If you are working with an empty rim, it is easiest to measure out the diameter, but if you have a built-upwards wheel, the hub will get in the fashion of the tape measure, making it hard to get an accurate measurement. For a built-upwardly wheel, it is easier to measure the rim'southward circumference. It may likewise be helpful to take a circumference measurement to confirm that the bore measurement was correct.

Instructions on measuring using the circumference are below the tabular array.

Traditional Designation	Applications/Notes	ISO Bead Seat Diameter	Dewdrop Seat Circumference (Rim measurement)
36 inch	Mostly unicycles	787 mm	2472 mm	97.3 inches
32 inch	Mostly unicycles	686 mm	2155 mm	84.eight inches
28 x 1 1/ii, 700 B	English, Dutch, Chinese, Indian Rod-brake roadsters (As well marked F10, F25, 700 B)	635 mm	1995 mm	78.v inches
27 x anything except "27 v" and rare Danish 27 x 1 i/2	Older road bikes, went out of fashion in the early on 1980s	630 mm	1979 mm	77.nine inches
700 C, 28 10 one v/8, 29 inch (28 x one 1/ii F.xiii Canada)	Near newer adult bikes for route use use this size, including near road bikes and hybrids. 29 inch are fat tires, same rim diameter. Besides 700C tubular.	622 mm	1954 mm	76.9 inches
27 x 1 1/2	Rare Danish size	609 mm	1913 mm	75.3 inches
26 x 1.25, 10 1.375	Very Rare U.South. size, 1940s and older. Non available.	599 mm	1881 mm	74.1 inches
26 x 1 i/four EA.1, 26 x ane 3/8 (Due south-6), 650	Schwinn "lightweights", older English "club" bikes	597 mm	1875 mm	73.viii inches
26 x 1 3/eight (East.A.3), 650 A	Most 3-speeds except Schwinn; department-store or juvenile 10 speeds	590 mm	1853 mm	73.0 inches
Mavic 26" tubular	Older Mavic 26" tubulars	587 mm	1844 mm	72.6 inches
650B, 26 ten 1 1/2, 26" tubular, "27 five"	French utility bikes, tandems, and loaded-touring bikes; some mountain bikes.This size is currently undergoing something of a renaissance. "27 five" are fat MTB tires. Some 26" tubulars.	584 mm	1834 mm	72.ii inches
700 D	Oddball size formerly used on some GT models. Not available. 584 mm tires may work. Note: 700D is often incorrectly identified as 587mm dewdrop seat.	583mm	1832 mm	72.1 inches
26 x ane, 650 C, 26" tubular	Triathlon, time-trial, high-operation road bikes for smaller riders. Some 26" tubulars.	571 mm	1793 mm	70.6 inches
26 10 1 3/iv	Schwinn cruisers
26 x 1.00- x 2.125, and wider on fatbikes	Most mount bikes, cruisers, fatbikes	559 mm	1756 mm	69.1 inches
24 x 1 1/4, 24 x ane iii/8 (South-5)	Rare British or Schwinn juvenile	547 mm	1718 mm	67.7 inches
600A	French juvenile, very shut to the nearest British size.	541 mm	1699 mm	66.nine inches
24 x 1 ane/8, 24 x 1 iii/8 (E.5)	British juvenile, most wheelchairs. French 600A is 541 mm, close plenty. Saavedra 25" tubular	540 mm	1696 mm	66.8 inches
24 x 1, 24 10 1 1/eight, 24" tubular	Loftier-performance wheels for smaller riders; Terry front, well-nigh 24" tubulars.	520 mm	1633 mm	64.3 inches
24 x i.5- 10 2.125	Juvenile mountain bikes, BMX cruisers	507 mm	1593 mm	62.7 inches
22 x 1 three/8	Wheelchair	501 mm	1573 mm	62.0 inches
550 A, 22 x 1 3/8	European juvenile, folding bicycles	490 mm	1539 mm	60.six inches
550C, 22 ten one one/iv", 22" tubular	European juvenile and racing bicycles (rare); 22" tubular	470 mm	1477 mm	58.ane inches
22 ten 1.75; x ii.125	Rare juvenile size...Schwinn	457 mm	1436 mm	56.5 inches
xx ten 1 1/viii; x 1 ane/four; x 1 3/viii	Juvenile lightweights, BMX for light riders, some recumbents, Bike Friday Pocket Rocket	451 mm	1417 mm	55.viii inches
500 A	European juvenile, folding	440 mm	1382 mm	54.iv inches
20 10 ane iii/4, xx" tubular	Rare Schwinn juvenile, specialty racing bicycles, older Easy Racers recumbents	419 mm	1316 mm	51.8 inches
twenty x 1.5- x two.125	Nigh BMX, juvenile, folders, trailers, some recumbents	406 mm	1275 mm	50.2 inches
18 x 1, 18 x i three/viii	Wheelchair	400 mm	1257 mm	49.5 inches
450 A	European juvenile	390 mm	1225 mm	48.2 inches
17 x 1 1/4, 18" tubular	Alex Moulton AM series, 18" tubular for specialty racing bicycles.	369 mm	1159 mm	45.half-dozen inches
eighteen ten 1.5- x ii.125	Birdy folding bikes	355 mm	1115 mm	43.9 inches
16 x 1 3/viii	Older Moulton, Brompton & other folders, recumbent front, Greenspeed trikes, juvenile	349 mm	1096 mm	43.2 inches
400 A	European juvenile	340 mm	1068 mm	42.i inches
16 x ane 3/eight	Very rare mystery tire	337 mm	1059 mm	41.7 inches
16 x one 3/viii	Very rare Polish juvenile	335 mm	1052 mm	41.4 inches
16 x one iii/4	Rare Schwinn juvenile. Probably the same rim bore as 16" tubulars.	317 mm	996 mm	39.2 inches
xvi ten 1.75- ten 2.125	Juvenile, folders, trailers, some recumbents	305 mm	958 mm	37.vii inches
12 1/2 X anything, deicmal or fraction.	Juvenile, scooters, trailers.	203 mm	638 mm	25.1 inches
x x ii	Wheelchair casters	152 mm	478 mm	xviii.eight inches
8 x 1 one/4	Wheelchair casters	137 mm	431 mm	16.9 inches

Circumference

You lot may measure the circumference of a rim past wrapping a measuring tape all the way around the rim. Y'all derive the diameter from the circumference.

A narrow, metal tape mensurate -- 1/4 inch or 6 mm wide -- volition fit into the well of the rim. (A wide metal tape measure won't fit into the well of the rim and and won't curve smoothly around the rim.)

Don't trust a fabric measuring tape as used in fitting clothing. This kind is unremarkably inaccurate, because the fabric stretches.

Utilise the metal tape mensurate as shown in the epitome below.

Hither are the steps to measure out using the circumference:

1. The tape has a tab at the end. Hook the tab into the valve hole and wrap the tape all the style around the rim, measuring the total circumference at the bottom of the well.
2. Carve up the circumference past pi (3.142) to get the diameter of the well.
   
3. If the tape measure is divided in inches, also multiply by 25.four to get the diameter of the well in millimeters.
4. Add twice the height from the well to the dewdrop seats (run across instructions beneath).

If you don't accept a narrow tape measure, you could wrap a length of thin, flexible electrical wire or bicycle cable inner wire around the rim, marker 2 places on the wire which line up with one another, lay the piece out flat and measure the distance betwixt the two marks.

Our example rim is a hook-edge rim without clearly-divers bead seats, so we'll measure from the well (but not the lesser of the recessed spoke holes) to the exterior of the rim and then subtract twice the typical flange height. Our highly-sophisticated tool for this chore is a cycle spoke. We are too using a small ruler as a bridge across the rim flanges. Property the spoke with a thumbnail against the ruler gives usa a practiced enough measurement for our purposes.

The measurement can exist transferred to the ruler:

At present, calculating, the circumference of the well measured as 64 1/8 inches, (64.125 inches). Multiplying past 25.4 gives 1629 mm; then dividing past pi (3.142) the diameter is 518.5mm. 16mm boosted (twice the depth of the well) gives 534 mm, but the bead seat diameter is exist nearly 10 mm smaller, and this is a 520 mm rim.

More sophisticated tools

This commodity has featured mutual, inexpensive and improvised tools. More sophisticated tools such as a caliper with a depth estimate can brand the work go faster.

About mathematics

Measuring rims involves some elementary-school or pocket-calculator math. Sheldon quoted Robert Heinlein at the end of the commodity:

Anyone who cannot cope with mathematics is not fully human being. At all-time he is a tolerable subhuman who has learned to wear shoes, breast-stroke, and non make messes in the business firm.

--Robert A. Heinlein

More than nearly that quote. OK, so Heinlein (actually, a character in i of his books) said that, and Sheldon quoted that, simply anyone who cannot accept that other people have different abilities and educational opportunities shows an unfortunate lack of pity! -- John Allen, whose wife teaches immigrants who never got to nourish school in their countries of origin.

But also at that place'due south this:

"Practise not worry about your difficulties in Mathematics. I tin clinch you lot mine are still greater."

--Albert Einstein

I'm hoping that this article provides an like shooting fish in a barrel guide to some practical math, and helps to dispel math feet. Also, a longer discussion of the Einstein quote is online, in case yous're interested...

Sutherland's Rim Measuring Organization

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How To Measure Wheel Size On A Bike,

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