What Does 700x38c Mean?
700x38c is a 38mm-wide tyre for a 700c (622mm) rim — written 38-622 in ISO. Here's every part decoded, the widths chart, and whether it fits your bike.
By the Bikefinest Editorial Team
The short answer
700x38c is a tyre size. It's a 38mm-wide tyre built for a 700c wheel — the 622mm rim standard that road, gravel, touring and hybrid bikes almost all share.
The 'c' is the part that throws people. It's an old French rim-diameter code, and it has nothing to do with inner tubes, valves or tube type. Write the exact same tyre in modern ISO/ETRTO shorthand and it becomes 38-622: width first, rim diameter second.
700x38c, part by part
Three chunks, three jobs. Here's what each one is actually telling you.
Part What it means The detail that matters 700 Nominal outer diameter class, in mm A rough size class inherited from the old French system, not a precise measurement of anything on your bike. It's the family the tyre belongs to, not a figure you measure with calipers. 38 Tyre width, in mm Measured inflated, casing edge to casing edge, on a suitable rim. Mount it on a wider rim and it'll measure a millimetre or two more. c Rim / bead-seat size code From the French a/b/c/d classes. 'c' pins the bead seat to 622mm — that's the number that decides whether the tyre physically seats on your rim. Not tube type. Not valve type. Not tyre width. Just the diameter class. = 38-622 The ISO/ETRTO version Same tyre, no guesswork. 38 = width, 622 = bead-seat diameter in mm. This is the pair of numbers that actually guarantees a fit. Decoding 700x38c into its parts Why the 'c' trips everyone up
France used to size tyres by their outer diameter and gave each rim a letter — 700a, 700b, 700c, 700d. All four were meant to finish up around 700mm across the outside. The skinnier the tyre, the bigger the rim you needed to hit that number; the fatter the tyre, the smaller the rim. The letter told you which rim.
700c is the one that survived. Its 622mm bead seat became the global standard, and 700a, 700b and 700d are effectively museum pieces now. So when you see that 'c', read it as '622mm rim'. It says nothing about Presta versus Schrader, tubes versus tubeless, or anything else — it's a diameter code, full stop.
Common 700c widths, and where each one lands
The 700 and the c stay put across all of these — only the middle number changes. That middle number is what decides how the bike rides.
Size ISO What it's for 700x23c 23-622 Old-school road racing width. Fast, harsh, mostly retired now. 700x25c 25-622 The modern road default. Quick, and comfier than a 23. 700x28c 28-622 Endurance and all-road. What most new road bikes ship on. 700x32c 32-622 Commuting, light touring, smooth gravel. Grippy and tough. 700x38c 38-622 Gravel, touring, hybrids. Your size — a proper do-anything width. 700x47c 47-622 Adventure and chunky gravel. Same 622mm rim a 29er MTB uses. Common 700c tyre widths Will a 700x38c fit your bike?
The wheel isn't the question. Any 700c/622mm rim will take a 38mm tyre. Clearance is the question, and 38mm is wide.
Most road frames top out around 28 to 32mm — go wider and the tyre fouls the frame, fork or brakes before you've ridden a metre. Gravel bikes, hybrids, touring frames and cyclocross bikes swallow 38mm with room to spare. Rule of thumb: you want roughly 3-4mm of gap each side of the inflated tyre for mud and a bit of wheel wobble. Pump one up and eyeball it, or check the manufacturer's stated max tyre width before you buy.
On the rim itself, a 38mm tyre is happiest on an internal rim width of about 18 to 24mm. Too narrow and it balloons into a lightbulb shape; too wide and the casing gets stretched flat and squared-off.
700c, 29er and 622mm — one rim, three names
This is the bit that stops you overpaying at the counter. A 700c road/gravel rim, a 29-inch mountain bike rim, and anything marked 622 are all the identical bead-seat diameter. A 700x38c tyre and a 29 x 1.50 tyre mount on the same wheel — 1.50 inches is roughly 38mm, so they're near enough the same tyre in two dialects.
The naming split is just history — road bikes kept the French '700c', mountain bikes went with inches. So if the shop only has '29er' tubes and you ride 700x38c, they'll fit fine. You match the width, not the wheel-size name.
Tubes and pressure, quickly
Two things people get wrong once they've decoded the size.
- Tubes: one labelled 700 x 35-43c covers a 38mm tyre. You don't need an exact 38 — tubes stretch across a width range, so anything spanning 38 works.
- Valve: Presta or Schrader is down to you and your rim's drilling. It's completely independent of the 700x38c number — that size code doesn't specify a valve.
- Pressure: a 38mm tyre runs low. With tubes, somewhere around 45-60 psi for a ~75kg rider on mixed surfaces is a sane starting point. Tubeless and off-road, you can drop into the 30s. Lighter rider, go lower; rougher ground, go lower.
- Always check the tyre sidewall for its own printed min/max pressure and stay inside it.
Bottom line
700x38c is a 38mm-wide tyre on a 622mm (700c) rim — written 38-622 in ISO. The 'c' is a rim code, not a tube spec.
If your frame clears 38mm — and gravel, touring and hybrid frames do — you're good to go. Match the width, and grab a tube in the 35-43 range.