700c Tires Explained: What I Wish Someone Had Told Me Years Ago

When I bought my first road bike back in 2012, the guy at the shop kept throwing around “700c” like I was supposed to know what that meant. I just nodded along pretending I understood. Took me embarrassingly long to actually learn what it means, so let me save you that confusion.

The Short Version

700c is basically the standard wheel size for road bikes. The “700” supposedly refers to the outer diameter in millimeters, and the “c” is… well, it’s kind of a historical leftover that doesn’t mean much anymore. It comes from an old French sizing system where they had 700a, 700b, 700c, etc. for different widths. Only the “c” version survived.

Here’s the thing that confused me forever: the actual rim diameter is 622mm, not 700mm. The 700 is approximately the outer diameter when you include the tire. So yeah, bike sizing is weird and inconsistent. Welcome to cycling.

Why This Size Won

I asked a bike historian about this once (yes, those exist) and he said 700c basically won through a combination of standardization and the fact that it works pretty well for most adult riders. It’s big enough to roll smoothly over road imperfections but not so big that it makes bikes unwieldy.

There used to be more variety – 27-inch wheels were common on older road bikes, 26-inch is still around on some mountain bikes – but 700c became the standard that everyone agreed on. Makes life easier when you can walk into any bike shop in the world and find tubes and tires that fit.

700c vs Other Sizes (Based on Bikes I’ve Actually Owned)

I’ve ridden a few different wheel sizes over the years, so here’s my take:

650b: I put these on my gravel bike last year. Smaller diameter (584mm) but you can run much wider tires. They feel a bit more nimble, accelerate a touch quicker, and I personally think they handle rough stuff better. The trade-off is they don’t roll quite as fast on smooth pavement. For mixed terrain riding, I’m actually a big fan.

29-inch (mountain bikes): These are technically the same diameter as 700c but with much wider tires. When I switched from a 26-inch mountain bike to a 29er, the difference was noticeable immediately – rolled over roots and rocks way easier. Felt a bit like cheating at first.

26-inch: These are mostly fading out except on some kids bikes and older mountain bikes. I still have an old 26er in my garage that I refuse to get rid of. It’s more maneuverable and the lower standover height works well for some people, but the industry has largely moved on.

The Tire Width Thing

This is where it gets interesting. Within 700c, you have a huge range of tire widths, and this affects your ride more than most people realize.

When I started road cycling, everyone was on 23mm tires and the attitude was basically “narrower equals faster.” We now know that’s not entirely true. Modern testing shows that slightly wider tires – like 28mm – can actually be faster because they deform less and roll more efficiently. Who knew.

Here’s roughly how I think about widths:

• 23-25mm: This is still common for racing but I find them harsh on anything but perfect pavement. I flatted constantly when I used to run 23s.
• 28-32mm: This is my sweet spot for road riding. Currently running 28mm on my road bike and it’s way more comfortable than when I was on 25s, without feeling sluggish.
• 35-40mm: Gravel territory. Wide enough to handle unpaved roads and light trails. My gravel bike has 40mm tires and I’ve taken it on some gnarly stuff.
• 42mm and up: This is getting into adventure bike territory. You can run these on 700c if your frame has clearance, but at some point 650b starts making more sense.

One thing I learned the hard way: check your frame clearance before buying wider tires. I once ordered 32mm tires only to find they rubbed on my fork. Returned those real quick.

Tubeless vs Tubes

I resisted tubeless for years because it seemed complicated. Finally made the switch about two years ago and honestly wish I’d done it sooner.

The main benefits: you can run lower pressures without risking pinch flats, and small punctures seal themselves (usually). I’ve had thorns go through my tire and just keep riding because the sealant plugged the hole. That never happened with tubes.

The downsides: setup can be messy, you need to add sealant every few months, and if you do get a flat that won’t seal, it’s a bigger hassle than just swapping a tube. I carry a tube anyway as backup.

If you’re running 28mm or wider, I’d say tubeless is worth considering. For narrower race tires, the benefits are less clear and some people still prefer the simplicity of tubes.

What I’m Currently Running

On my road bike: Continental GP5000 in 28mm, tubeless. They’re not cheap but the grip and durability are excellent. Been riding the same set for about 4,000 miles with just normal wear.

On my gravel bike: WTB Riddler 45mm on 650b wheels. Great for the mixed terrain around here – can handle fire roads and singletrack but still reasonable on pavement.

Quick Buying Tips

When shopping for tires, pay attention to:

Compound: Softer compounds grip better but wear faster. Dual-compound tires (harder center, softer edges) are a decent middle ground.

Puncture protection: More protection usually means more weight. I go for moderate protection on training tires, less on race tires.

TPI (threads per inch): Higher TPI generally means a suppler, faster-rolling tire but less durability. Budget tires are often 60 TPI, nice ones are 120+ TPI.

Don’t overthink it too much though. Any decent quality tire from a reputable brand will serve most riders fine. The differences matter more at the margins – competitive racing, extreme conditions, that kind of thing.

And hey, now you know what 700c means. Only took me like five years to really get it. Hopefully this saves you some of that confusion.