Want to Know What Bicycle Tire Size, Type, PSI or TPI?
All about bicycle tires... And warding off The Puncture Fairy!

Want to Know What Bicycle Tire Size, Type, PSI or TPI?

Hello and welcome, Dear Reader, it’s good to have you along for this trip into the mysteries of bicycle tires and possibly puncture fairies 😀 There’s much to do so let’s fit those rubber boots and find exactly where the rubber meets the road! So with puncture resistance, tire weight, comfort and speed seemingly all competing against each other in just the one set of tires, it can be difficult to find the most appropriate tire for your riding. For me, finding the right tire for my own riding style has been a continually evolving process of empirical trial and error. What I’ve picked up, I’d like to share, and at the very least I’d you’d gain familiarisation with some of the terms we encounter talking about bicycle tires if you’re not already so.

There’ll be some degree of duplication between this and the my “Parts of a Bicycle Wheel” Article but there might be further information there to expand your understanding too 🙂 For now, since the title asks, ‘Want to Know What Bicycle Tire Size, Type, PSI or TPI?’ I’d like to answer those using as plain language as I can while covering all the bases. Sound okay? Let’s go…

Q: How is a bicycle tire measured?

A:  Do you have a tire already on your wheel? In which case, the question could be, “What do the numbers on my tire mean?” Yes, check around the sidewall of the tire for embossed figures which will indeed contain the tire’s measurement. As though to make things complicated, that measurement can be in one or more of several different measurement forms, for example, the same tire can be variously marked thus:

  • 37-622
    • this is the ETRTO technical standard in mm. It’s the tire width figure, here 37mm, and the tire’s inner bead diameter, here 622mm
  • 700 x 37c
    • this is the older French designation of which the 700c / 650B sizings are the most prominent remaining. Again 37C refers to the width in mm, the C for Crotchet rim / Clincher.
road-tyre-showing-size-and-pressure
Good clear markings showing sizes in standard ETRTO tire width (23mm) and bead seat diameter (622mm) and the French system
  • 28 x 1.5″ (or 29 x 1.5″)
    • The imperial system where the 28 inch or 29 inch refers  very approximately to the full outer diameter of the inflated tire. It’s not always entirely accurate, however it’s still widely used.
tires-continental-mtb-in-inches
My ol Continental 29er MTB tires, with width measurement in inches (2.4″)
  • Older Imperial styles such as 26 x 1 3/8 are more rare. Still found on some vintage bicycles and utility roadster type bicycles.
vintage-tire-imperial-measurement
A decrepit old vintage tire showing the imperial 26 inches diameter x 1 3/8 inches wide through the cracks!

So now we can read the figures off the tire sidewall, all we have to do is to replace like for like and we’re golden! However, maybe you’re wondering what happens if there’s no tire on my wheel? How do I know what size tire is needed then?

Q: What size bicycle tire do I need for my wheel if I have no tire for comparison?

A: Does your rim have any detail on it? Most bicycle rims have a logo and size either etched on or as a sticky label. Locate that on your rim and get a suitable tire to match the sizing.

If, there appears to be no information at all on your rim – this happened to me with some vintage Westwood rims designed for use with rod brakes (before I had any clue what they were!) – or, if you simply want to know how to measure a rim, just go grab a tape measure and we’ll just measure it ourselves. We need two measurements from the tireless wheel: its diameter and the width. Okay, so what we want to know now is, “How do I measure a bicycle wheel size for a tire?” Place the wheel on its side, take the tape measure, place its zero millimetres/centimeters digit on the outermost edge of the wheel rim, stretch the tape measure past the hub axle in the center of the wheel and right across to the opposite outermost edge of the wheel rim on the other side. Make sense? The tape measure should be as straight as possible.

This measurement won’t be exact because we haven’t gone through the exact center of the axle, but around its outer edge, but it’ll be a good enough measurement for what we need. What is the diameter measurement in millimeters? Check what you’ve got against the table below, this gives us our tire height designation from the previous question above. If necessary repeat so you’re satisfied you have the right measurement.

Wheel NameDiameter in mmTypical Bicycle Types Using this Sizing
27 inch630 / 635Vintage / Indian 3-speed roadsters
700c622Most modern road / pavement bicycle wheels
29er622 (same as 700c just using fatter tires on wider rim)29er Mountain Bike
26 x 1 3/8 inch590Vintage English 3-speed roadsters / older dept store road bikes
650B584Either older style road bicycles, or some newer road bicycles which take 700c wheels use these smaller diameter wheels because they allow the use of fatter tires
27.5 inch584 (same diameter as 650B)Medium sized MTB wheels, a standard halfway between 26 inch and 29er
26 inch559Standard MTB size
20 inch406 Standard BMX size, also found on folding bicycles and shopper-style bicycles

Okay, done? So once we’ve got our wheel’s Bead Seat Diameter, remember, BSD? then what we need now is to measure how WIDE the rim is. We can take this measurement with the rim still on its side for convenience. We want the measurement across the rim left inner side of the rim to right inner side where the tyre will sit against the rim. This measurement won’t necessarily need to be super accurate, as ever, good enough is usually good enough. Margins of error are generally inbuilt for this reason. But take the measurement as accurately as possible. From 13mm to around 35mm covers most applications. Specialist applications for bicycles that take much fatter tires, 650B+, 29er+ and Fatbikes will have rims that are 40mm – 80mm wide.

Your bicycle tire size must be directly compatible with your bicycle wheel size. When we say size we mean the diameter and the width. Firstly, the diameter will be the measurement of the wheel itself, not the tire, from one inner edge where the spokes through the centre (where the hub axle is) to the opposite inner edge. What’s the measurement in millimeters?

  1. If your bicycle wheel diameter measures 630mm or 635mm, is it from an older vintage bicycle? It needs a 27 inch tire (which can require a little more searching than others to find. But at the very least you can now search for a 630 or 635mm tire).
  2. If your bicycle wheel diameter measures 622mm, if it’s for a standard road/pavement type bicycle then it needs a 700c tire. If your bicycle is a large wheeled mountain bike, you’ll want a 29er tire.
  3. If your bicycle wheel diameter measures 590mm, is it an older vintage roadster bicycle? If so, you’ll be wanting a 26 by 1 and 3/8 inch tire
  4. If your bicycle wheel diameter measures 584mm, is it an older vintage road bicycle? In which case it might need a 650B tire. If your bicycle is a modern mountain bike, it’ll take a 27.5 inch tire.
  5. If your bicycle wheel diameter measures 559mm, and your bicycle is a mountain bike / MTB, it’s a standard 26 inch tire it’ll take.
  6. If your bicycle wheel diameter measures 406mm, and your bicycle is a BMX, folding bike, or city shopper type bicycle, it uses a 20 inch tire.

How clear is all that? I hope you’re following ok. If not, or you got a measurement not listed – and don’t worry, there are others out there! – let me know!

So if we’ve established the diameter – the height so to speak – of our wheel and tire, next thing we want to know is what width do I need. Well, this can be dependent on several factors. What your style of riding is, and where or on what surfaces you’re riding, for example. Given a certain rim diameter, two tire sizes of different widths, say 700 x 23C and 700 x 28C will behave differently on your bicycle. The wider 28C tire might feel more comfortable, it may even roll faster depending on where you’re riding. However, certain rim and tire width compatibility exists, see table below:

Tire Width
(mm)
13C
Rim
15C
Rim
17C
Rim
19C
Rim
21C
Rim
23C
Rim
25C
Rim
27C
Rim
29C
Rim
20ok
23okok
25okokok
28okokok
32okokok
35okokok
37 (1.5")okokokok
40 (1.6")okokokok
42 (1.65")okokokokok
44 (1.7")okokokokok
50 (1.95)okokokokokok
52 (2.0")okokokokokokok

Many other sizes exist on the larger side of this table, particularly with Fatbike tires running up to 4.8 inch width (at time of writing). Here this table covers the major 700C sized tires just for illustration purposes. I’ve ran 2.4″ 29er tires on a 17C rim before so other combinations beyond these kinds of tables can work out fine – even though that tire came up very tall on the rim I never had any real issues. But as ever it’s a case of “entirely at operator’s risk” etc 😮

Q: What is the ‘C’ for in bicycle wheel and tire sizes?

A: Well spotted! Again, it depends on which “C” we’re thinking of! Firstly we have the 700C sizing, and secondly we have a 23C tire for example.

  1. So 700C, what does that even mean? Well, really nothing much of relevance. It’s a signifier from a while back from a standard that originated in France. There were 700a, 700b, 700c designations, and each meant that the diameter of the wheel plus tire was approximately 700mm. What these variants meant was that a fatter/taller tire mounted on a slightly less tall rim maybe a “700c” would be about the same height as a thinner/less-tall tire mounted on a slightly taller rim, maybe a 700b or 700a. Not sure which way round it was, maybe you know? But it was the 700c we were left with after the survival-of-the fittest process deemed it would be so. The 700c rim standard is, as listed above 622mm. I checked wheels that I have currently, and on mine with a 25mm or 28mm wide tire respectively the diameter is 677mm and 682mm, so not quite the 700 (and a fairly poor mathematical approximation too!) The same logic applies to the 650b naming convention.
  2. And then, for example, a 23C or a 28C tire refers to the Crotchet or clincher type of rim into which the tire’s bead will seat.
    road-tire-c-designator
    Road tire 28C designator, where C indicates meant for crotchet rim

    This is distinct from either a tubular rim or a flat-walled rim, both without a crotchet lip or hook.

bicycle-tire-for-hooked-rim
Instructions on this road tire to mount on “hooked” rim – this refers to the hook of the Crotchet that clinches the tire bead

I have some further information in the “Clinchers, Tubulars & UST”section of my Parts of a Bicycle Wheel article

Q: What creates the pressure inside a bicycle tire?

A: In physics terms, we’d use Boyle’s Law which itself is derived from the Ideal Gas Law. We attach a pump hose onto the valve of our inner-tube or tire itself if it’s tubular or UST. As we pump air through the valve we are forcing a higher and higher volume of air into roughly the same volume of tire/tube. The increased number of gas molecules inside the same fixed volume of tire/tube causes a tighter packing and more molecular collisions against their butyl or latex container, ie. greater pressure.

Little FYIs…

… Just because every article deserves a sprinkling of Physics!

  • Tire pressure and ambient air temperatures are related (Ideal Gas Law). You can probably notice this relationship between temperature and pressure when you hand pump a tire at the roadside for example – the increases in pressure at the pump can cause it to feel hot, right? What that means is that as the ambient air temperature drops so too does your tire pressure and as the ambient air temperature rises so too does your tire pressure. These aren’t likely to be troubling changes though, pressure rises about 1psi for every 10 degree Fahrenheit change (approx 5.5 degree Celsius)
  • While the standard unit of pressure measurement is the Pascal Pa, or Kilopascal kPa, in tire terms, we usually use PSI (pounds per square inch) or Bar. The Bar is 100 kilopascals. One bar is about the same as one atm or one atmospheric pressure which is pressure of the atmosphere that daily pushes on us.

Q: What pressure should I inflate my bicycle tire to?

A: There’s a simple answer to this. And then there’s a more complicated answer too. The simple answer is to inflate your tire to somewhere within the pressure range indicated on the sidewall of the tire itself. The more complicated answer is that it depends again on your weight (and any load on the bicycle), your wheel diameter, your style of riding and your riding goals and personal preferences.

pressure-reading-on-wider-bicycle-tire
Clear (maximum!) pressure reading in bar and psi. This being a wider tire 2.0″ the pressure can go lower
  • A lower bodyweight is generally matched to a tire pressure that is lower on the tire’s indicated pressure range whereas a higher bodyweight (or a greater luggage load say on the bicycle) is generally matched to a pressure nearer the top end of the tire’s range. I’ve added approximate inflation pressures for a few different rider weights in the table below to give you a starting point that you can adjust to suit your own riding.
Tire Width
(mm)
130lbs (60Kg) Rider190lbs (86Kg) Rider240lbs (110Kg) Rider
23100psi (7Bar)110psi (7.5Bar)125psi (8.5Bar)
2590psi (6Bar)100psi (7Bar)115psi (8Bar)
2880psi (5.5Bar)96psi (6.5Bar)110psi (7.5Bar)
3265psi (4.5Bar)80psi (5.5Bar)96psi (6.5Bar)
3760psi (4Bar)70psi (5Bar)90psi (6Bar)
4050psi (3.5Bar)65psi (4.5Bar)90psi (6Bar)
4740psi (3Bar)60psi (4Bar)70psi (5Bar)
5035psi (2.5Bar)60psi (4Bar)70psi (5Bar)
5530psi (2Bar)40psi (3Bar)60psi (4Bar)
6030psi (2Bar)40psi (3Bar)60psi (4Bar)
  • In general, the higher up the pressure range, the lower the rolling resistance and puncture resistance. However, there’s also evidence to suggest that a slightly lower tire pressure can – perhaps somewhat counter-intuitively – decrease rolling resistance, specifically on rougher asphalt. For many like myself, this would be categorized “normal” asphalt!
  • These higher pressures can also lead to rider fatigue on tarmac over distance, so there’s a balance that’s unique to each rider.
  • Small wheels such as those on folding bikes generally also utilize higher pressures.
  • For off-road riding, lower pressures can often encourage the tread to hold the surface better. Too low though and the tire may not hold corners as well.

Q: What’s the meaning of a bicycle tire TPI?

A: TPI is the abbreviation for Threads Per Inch. It refers to how tightly woven the fibres of the tire carcass are. Generally speaking, the higher the TPI figure the better quality the tire is. There’s also a correlation between greater thread counts and higher puncture resistance but it’s not always the case because very high thread counts 120TPI and above say, the threads themselves are understandably thinner. So there’s a balance in this as in all things 🙂 Manufacturers will normally include one or several breaker layers underneath the outer rubber if puncture resistance is an important aspect of the tire type.

Q: What is the difference between a wire bead bicycle tire and a folding bicycle tire?

A: Tires with wire beads can’t be folded without bending the wire core of the bead irreparably. If you buy them mail order they’ll come in a wheel-sized box. Folding tires can be packaged much smaller. Folding tires have not a wire bead, but a kevlar-stranded bead. This, though it can appear creased when unfolded from its packaging, re-shapes once on the rim and inflated. If a particular tire comes in both variants what you’ll normally notice is:

  1. The wire bead tire is heavier in weight, usually by around 40-100 grammes – and heavier tires require more of your pedalling energy to rotate them so they’re less efficient which is a concern of many riders.
  2. The wire bead tire will normally be cheaper to purchase which may offset its weight penalty for you as an individual consumer.

Q: What are Presta and Schrader valve types? And which valve do I have on my bicycle?

A: The Presta or Sclaverand valve is the narrower of the two. It’s 6mm whereas the Schrader or auto valve is 8mm in diameter. The Presta valve usually has a knurled rim nut which can assist in attaching a pump against a deflated inner tube but isn’t strictly necessary (pros generally do without!) The Schrader valve, if full thread like the one pictured can have a rim nut too. Sometimes the tube rubber half covers these valves leaving only threads at the end exposed for the valve cap, see pic below…

cycling-questions-presta-schrader-valve-differences
Presta valve left and Schrader valve right

Though you may not be familiar, the most common bicycle inner tube valve type is the older Dunlop valve. I see these mostly on vintage bicycles with original tires and tubes. Bear in mind though, highest bicycle usage worldwide is in Asia, not the west, Dunlop Valve, see pic below…

cycling-questions-dunlop-valve-inner-tube
Dunlop valve inner tube. They’re harder to get here, you’ll mostly get valve adapters for presta/schrader pumps

Q: Which way should a bicycle tire tread face?

A: If the tire has a unidirectional tread pattern then embossed somewhere on the sidewall of the tire should be an indication of rotation direction – it’s usually an arrow with the words “rotation” or on older tires it can say “drive” or similar.

bicycle-tire-rotation-direction
Sometimes the instruction is clear when mounting your tire on your rim…

You may need to shine a light or the torch on your phone at a shallow angle across the surface of your tire’s sidewall to highlight the label though as they’re often small.

bicycle-tire-difficult-to-find-rotation-direction
… Other times the tire rotation direction is almost impossible to find without forensic examination! This was only on one side of the tire too #moneysaving

For road tires, the tread pattern is usually cosmetic as even on wet roads, a slick tire is preferable for grip and adhesion. Narrow road tires mean aquaplaning that can happen on motor vehicles can’t feasibly happen on the bike. Offroad tires require different tread patterns depending upon the hardness or softness of the ground they’re designed for riding on, from hardpack or gravel to plain ol mud-plugging.

Q: How do I avoid the constant bike punctures?

A: I totally feel your pain! I know those rides where you get the impression the Puncture Fairy has taken a shine to you, your tires somehow magnetically attract goatheads, or where there seems to be traversing the endless Fields of Broken Glass on your way to Mordor lol. I think often it’s just one of those things you have to be philosophical about. I rode all last year through the worst of the wet winter on smooth asphalt to thorn-strewn cycle paths on a set of Continental Gatorskin Hardshell tires without a single puncture. How come some reviews claim they’re useless? “Three punctures in a week” they say? Maybe it’s just manifesting bad luck. I don’t know for sure.

Tire pressure is a factor, specially on the road. Number of punctures rise dramatically on a pressure that’s too low so be sure you’re in the ballpark tire pressure for your weight table

Besides the obvious solutions of changing tires either for more puncture-resistant ones, or for a complete UST tubeless setup with sealant, there’s also the check, which I’ve forgotten to do myself and which resulted in multiple punctures – feel carefully around the inside of the tire carcass after a puncture in case the offending object is still lodged there!

Snakebite punctures where the inner tube is nipped between the tire bead and rim seemed to happen to me on hurried roadside repairs, particularly when the tire and rim weren’t great matches and the tire was a faff to get re-installed without hacking away with a couple of levers. I now carry some washing liquid in a little vial to ease a tight tire over a larger diameter rim outer for installation, see my pocket pouch article.

Q: What about solid or airless bicycle tires? Those would be puncture-proof, right?

A: Yes, they surely would. And in fact, having sought out information, there’s a feasible option from a company called Tannus. The solid tire is comparable in weight to a regular tire plus inner tube. I ain’t no salesman so you can check it out if you’re interested. I haven’t looked into the off-road tire versions. Fitting seems a bit of a faff (and an even bigger one to remove the tire) but still do-able. But for the road tires, my only concern would be the level of road adhesion. The few reviews I’ve seen appear inconclusive. Maybe I should give them a try!

So that’s us drawing to a conclusion. Thank you for reading!

I haven’t mentioned much about tubulars or tubeless (Universal Standard Tubeless or UST) tires just because I don’t have any personal experience of those at the moment. I don’t like pretending I’m some kind of expert lol 😮

What’s your experience of UST so far? It’s a consideration of mine, but on the long finger at the moment as we say here. From what anecdotal evidence I have, both the USTs and tubs when used with sealant definitely look hard to beat for puncture-proofing and low rolling resistance. Most tire manufacturers seem to be putting their money behind UST at the time of writing. From what I’ve seen, the difficulties arise in getting good tire and rim compatibility therefore a good seal on the USTs? For me personally, while I’d be keen to give them a try out on my road bike, it would mean upgrading to a new set of wheels and tires which isn’t on my radar just at the moment. Either that or trying the rim conversion tape. To me, while that process looks easy on film, I imagine it would be a complete faff to get right? Also, how difficult or messy are UST tires to change out? I’m keen to hear some first hand experience, though I guess, one man’s meat is another’s poison and all that! 😀

But in the meantime, thank you for reading. I’m always looking forward to your comments, thoughts, suggestions for the article or for others if you feel minded to. Keep that rubber spinning, ride safe and have fun, David.

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