Tire size notation - how to read what's on the sidewall

Two numbering systems, one tire. How to decode metric (80/90-14) and inch (3.50-17) tire sizes, load ratings, profile shapes, and know what actually fits your EUC.

Every EUC tire has numbers molded into its sidewall. Those numbers tell you the tire’s width, how tall the sidewall is, and what rim it fits - but only if you know which system you’re reading. There are two: metric and inch. Both are common in EUC. Neither is hard once you see the pattern.

The two systems

Metric notation: 80/90-14

This is the standard used in motorcycle and scooter tires. Three numbers, two separators:

80 / 90 - 14

• 80 = tire width in millimeters, measured at the widest point of the mounted, inflated tire
• 90 = aspect ratio - the sidewall height as a percentage of the width
• 14 = rim diameter in inches

So on an 80/90-14 tire: the tire is 80 mm wide. The sidewall height is 90% of 80 mm = 72 mm. The rim it fits is 14 inches in diameter.

The aspect ratio is the part most people miss. It’s not a size - it’s a proportion. An 80/90 tire has taller sidewalls relative to its width than an 80/60 tire. Higher aspect ratio = taller sidewall = more cushion = more flex. Lower aspect ratio = shorter sidewall = stiffer = more precise.

Inch notation: 3.50-17

The older system. Two numbers, one separator:

3.50 - 17

• 3.50 = tire width in inches
• 17 = rim diameter in inches

That’s it. No aspect ratio. The inch system doesn’t tell you sidewall height directly - you need to check the manufacturer’s specs or measure the tire. This makes inch-notation tires harder to compare on paper, but the system is simpler to read.

How they relate

You can roughly convert width between systems: 1 inch = 25.4 mm.

• 2.50” wide ≈ 64 mm
• 2.75” wide ≈ 70 mm
• 3.00” wide ≈ 76 mm
• 3.50” wide ≈ 89 mm
• 4.00” wide ≈ 102 mm

These are approximate. Actual mounted width varies by rim width and tire construction. But it’s close enough to compare tires across systems.

Calculating the overall diameter

This is what actually determines how big the tire is on your wheel - and whether the marketing “inch” label matches reality.

Metric formula:

Overall diameter = (rim diameter in mm) + (2 × sidewall height in mm)

For an 80/90-14:

• Rim: 14” × 25.4 = 355.6 mm
• Sidewall: 80 × 0.90 = 72 mm
• Overall: 355.6 + (2 × 72) = 499.6 mm ≈ 19.7 inches

So an 80/90-14 tire on a 14” rim gives you roughly a 20-inch wheel. That’s why many “20-inch” EUCs run this size.

Inch notation doesn’t give you this calculation directly. A 3.50-17 tells you the rim is 17” and the tire is 3.5” wide, but you need the manufacturer’s data for overall diameter.

Common EUC tire sizes decoded

Here’s what you’ll actually see on EUC tires and what the numbers mean:

2.125-16 - a narrow tire on a 16” rim. Common on older or lighter 16-inch EUCs. Width: ~54 mm. Think city commuter tires.

2.50-14 - moderate width on a 14” rim. Width: ~64 mm. Used on some compact wheels.

2.75-14 - slightly wider on a 14” rim. Width: ~70 mm. Better grip and cushion than 2.50, same rim. Common on mid-range wheels like the Inmotion V11Y.

3.00-14 - a wider option for 14” rims. Width: ~76 mm. More contact patch, more stability, slightly more rotating mass.

80/90-14 - the metric equivalent neighborhood of the 3.00-14. Width: 80 mm, sidewall: 72 mm, overall ~20” diameter. Widely used in the 20-inch EUC class. You’ll see this on Sherman variants and similar wheels.

100/65-14 - wider tire (100 mm), shorter sidewall (65% aspect ratio = 65 mm). Overall diameter is smaller than 80/90-14 despite being wider. This is what aspect ratio does - a wider tire isn’t automatically a bigger tire.

100/90-14 - a very wide tire on a 14” rim. Width: 100 mm, sidewall: 90 mm, large air volume, and tall overall diameter. In EUC this is a rare factory size - currently associated mainly with the Extreme Bull Commander GT Pro+ and its stock Maxxis S98, which gives excellent predictability and confidence on asphalt. You can also look for scooter equivalents, for example 100/90-14 57P TL. Historically, the Ninebot Z10 also showed how strongly a very wide tire can define a wheel’s character.

3.00-16 - 76 mm wide on a 16” rim. Gives a larger overall diameter than the same width on a 14” rim. Used on larger-class EUCs.

3.50-17 - wide (89 mm), big rim. This is deep into motorcycle territory. Large overall diameter, significant rotating mass. Veteran Oryx and other wheels in that class.

Load index and speed rating

After the size, you’ll often see two more characters - a number and a letter. Take this real tire marking:

Michelin City Extra 80/90-14 50S

The 50 is the load index - how much weight the tire can carry. The S is the speed rating - the maximum speed the tire is certified for.

Load index table

The load index is not kilograms directly - it’s a code. Here are the values you’ll encounter on EUC-size tires:

What it means in practice

This matters for EUC riders more than most people realize. A single tire carries the entire load - rider, gear, and the wheel itself. There’s no second tire sharing the weight.

Real example: you weigh 100 kg (220 lbs), your Begode Master Pro V3 weighs ~60 kg (132 lbs). Total load on that one tire: ~160 kg (353 lbs). A tire with load index 44 (160 kg) gives you virtually no margin. A tire with load index 50 (190 kg) gives you 30 kg (66 lbs) of margin. More margin is better - dynamic forces during acceleration, braking, and bumps temporarily push the effective load well above static weight.

If you’re a heavier rider (100+ kg / 220+ lbs), pay attention to the load index. A tire rated for 140 kg (309 lbs) with a 100 kg (220 lbs) rider on a 60 kg (132 lbs) wheel is already over its limit statically. Going a few load index steps higher costs nothing in ride quality and buys real safety margin.

Speed rating

The letter after the load index indicates the maximum certified speed:

For years, speed rating was almost never the limiting factor in EUC. For wheels that realistically ride at 40-70 km/h (25-43 mph), even a J rating (100 km/h / 62 mph) had plenty of margin. That is still true for most riders and most wheels.

But with the 2025/2026 top-performance generation, you need to pay closer attention. Inmotion officially lists the P6 with a 150 km/h (93 mph) top speed, Begode Race has a reinforced tubeless rim and 200 km/h no-load speed, and the X-Max pushes even further into extreme high-voltage territory. That does not mean you choose a tire by the letter alone. It means that on the most powerful wheels, in high ambient heat, during long fast riding, with a hot motor, speed rating stops being pure paperwork.

Practical rule: on a normal EUC, you still choose size, load index, compound, and profile first. On top performance wheels, also check whether the speed rating has real margin against your actual riding speed, not just against the marketing “top speed”.

Other markings on the sidewall

Beyond size, load, and speed, you’ll see abbreviations stamped on the tire. Here’s what they mean:

TL = Tubeless. The tire is designed to hold air without an inner tube, using a sealed bead against the rim. Can also be run with a tube inside.

TT = Tube Type. The tire requires an inner tube. Do not run this tubeless without proper conversion.

M/C = Motorcycle. Indicates the tire is built to motorcycle standards. This is common on EUC tires since most come from the motorcycle/scooter supply chain.

RF or Reinf = Reinforced. The tire has a stronger carcass than the standard version - thicker plies, stiffer sidewalls, higher load capacity. Reinforced tires are heavier but more resistant to punctures and sidewall damage. A good pick for heavier riders or rough roads.

F = Front. R = Rear. On motorcycles, front and rear tires have different profiles. On an EUC this distinction doesn’t apply since the wheel doesn’t lean into corners the same way. Most EUC riders ignore F/R markings and choose based on profile shape and compound.

DOT followed by a 4-digit code = manufacturing date. The last four digits indicate the week and year. “2524” means week 25 of 2024. Relevant if you’re buying tires that have been sitting in storage - rubber compounds degrade over time. Avoid tires older than 5 years.

Tube vs tubeless when choosing a tire

The full tube vs tubeless decision is covered in Tube vs tubeless tires in EUCs. Here you only need the marking-level version.

TT (Tube Type) means the tire expects an inner tube. It is simple to service, but tube punctures can lose air quickly.

TL (Tubeless) means the tire is designed to seal against the rim without a tube. It can also be run with a tube, but a real tubeless setup depends on rim shape, valve fit, pressure, and bead seating. Sealant is optional, and rim tape is not a universal EUC step.

Do not choose TL just because the letters look more modern. If the rim is not tubeless-ready, the conversion quality matters more than the sidewall marking. Read the full tube vs tubeless guide before treating TL as a safety upgrade.

Scooter tires vs motorcycle tires

EUC tires come from the motorcycle and scooter supply chain. The two types are built differently, and the difference matters.

Scooter tires (like the Michelin City Extra, CST C6017, or many stock EUC tires) use a rubber compound designed to work at ambient temperature. You get on, you ride, the tire grips from the first meter. The compound doesn’t need thermal cycling to reach optimal performance. This is what you want on an EUC - you’re not doing warm-up laps before your commute.

Motorcycle sport tires use compounds engineered for higher temperatures. They reach peak grip after the rubber heats up through aggressive cornering and braking - typically after several kilometers of spirited riding. Until they’re warm, grip is noticeably lower than their rated performance. On an EUC, these tires often do not reach operating temperature because there is not the same sustained load, lean angle, and braking energy as on a sport motorcycle. You end up riding on a compound that works below its designed range.

That does not mean a tire in the “motorcycle” category is automatically wrong. Urban, commuter, adventure, or small-displacement motorcycle tires can work very well if size, profile, construction, load rating, and pressure all fit. The problem is usually track tires, overly sporty compounds, tires that are too heavy, too wide, or shaped wrong for the EUC rim.

The practical rule: start with scooter-class or urban tires. They are closer to the loads, speeds, and thermal conditions an EUC actually produces. Motorcycle sport compounds are optimized for a use case that usually does not exist on a single-wheeled vehicle doing 40-60 km/h (25-37 mph).

At the same time, an EUC is not a cold system. The tire heats from carcass flex, friction, braking, acceleration, carving, bumps, and ambient temperature. On powerful wheels, motor heat also travels through the rim arms into the rim and tire. So the precise version is this: an EUC usually does not bring sport/track motorcycle tires into the range where they show their full potential. But a fast wheel, hot day, heavy rider, and long ride can raise tire temperature for real.

There’s another difference: scooter tires tend to have flatter profiles and harder-wearing compounds. Motorcycle tires tend to have rounder profiles and softer compounds for lean-angle grip. This leads directly to the next point.

Tire profile shape: V vs D

If you look at a tire head-on (from the contact patch direction), you’ll see its cross-section profile. This shape changes how the tire handles. Two basic types:

V-profile (round) - the tire’s cross-section is more rounded, almost pointed at the center. The contact patch is narrow when upright and gets wider as you lean. This is the classic motorcycle sport tire shape. On an EUC, a V-profile makes the wheel more responsive to lean input - it “tips in” more eagerly. The downside: smaller contact patch when riding straight, which means less straight-line stability and less braking grip when upright.

D-profile (flat) - the tire’s cross-section is flatter across the top, with a wider contact patch when upright. Think of the letter D laid on its flat side. This is the typical scooter tire shape. On an EUC, a D-profile gives more stability in a straight line, more predictable behavior, and a larger braking contact patch. The trade-off: it resists lean changes more - the wheel feels “heavier” when initiating turns.

For most EUC riding, a neutral or slightly D-shaped profile is a better match than a very pointy V. EUCs usually do not lean into corners like motorcycles at the same turn radius - you steer primarily through weight shift, and the wheel stays closer to upright through most everyday riding. A flatter profile gives you more rubber on the ground in the orientation you actually use most.

Some riders ride differently: they lay the wheel over, carve deeply, and want instant response to lean input. For them, a V-profile can make sense. But for commuting, cruising, and general riding, the stability and larger contact patch of a neutral/D profile usually serve you better.

Just watch the extremes. A tire that is too flat can tramline, amplify the gyroscopic feel, and resist transition into a turn. A tire that is too triangular can feel nervous. You are looking for a profile that fits the rim width and your riding style, not a magic letter.

Rim diameter vs. overall diameter

This is where confusion lives. EUC manufacturers label wheels by approximate overall tire diameter, not rim diameter. The handling physics are covered in Wheel diameter - what it actually changes; here the key is fitment. So:

• A “16-inch” EUC might have a 14” rim with a tire that brings the overall to ~16” OD
• A “20-inch” EUC often has a 14” rim with an 80/90-14 or similar tire giving ~20” OD
• A “22-inch” EUC may use a 16” or 17” rim depending on the model. Inmotion V13 is a 3.00-16 example; Begode Master Pro V3 is a 17” rim example
• The old 24-inch Begode Monster Pro is the rare 18” rim case. This is where sizes like 90/90-18, for example Michelin City Extra 90/90-18 57S, enter the conversation

The rim is always smaller than the marketed wheel size. The tire makes up the difference. This is why tire choice changes your effective wheel diameter - swap to a tire with a different aspect ratio or profile, and your “20-inch” wheel isn’t exactly 20 inches anymore.

What the numbers mean for choosing a tire

When shopping for a replacement tire, three things must match your rim:

1. Rim diameter - non-negotiable. A 14” tire goes on a 14” rim. Period
2. Width - must be compatible with your rim width. Too narrow on a wide rim and the tire profile distorts. Too wide and it may not seat properly or rub against the shell
3. Overall diameter - determines clearance inside the EUC shell. A tire that’s taller than stock might physically not fit

Rim width changes the mounted shape a lot. On wide Begode rims in the EX30/Master Pro V3 family, a Michelin City Extra 90/80-17 can mount flatter than people expect and still ride light. A Michelin Anakee Street 90/90-17 on the same class of wheel changes the machine much more - more GT monster, more willingness to lay into carving, but much more resistance to initial turning.

Some riders experimented with 3D-printed bead spacers/rings on wide Begode rims to make the tire sit narrower at the bead and change the profile. Some liked the feel. 555 take: I would not treat that as a normal tire fitment method. The bead seat is where big forces, side loads, impacts, heat, and pressure all meet. If a tire only feels right because a printed spacer is changing how it sits on the rim, I would rather choose a tire that fits the rim correctly in the first place.

Beyond fit, the numbers tell you about ride characteristics:

• Wider tire (higher first number) = more contact patch, more grip, more air volume for comfort, more rotating mass
• Higher aspect ratio (metric second number) = taller sidewall, more flex, more cushion, but also more squirm under hard cornering
• Lower aspect ratio = shorter sidewall, stiffer, more direct steering feel, less bump absorption from the tire itself

After the tire fits, pressure becomes the next tuning variable. The short version lives in the tire pressure dictionary entry, and the range impact is covered in EUC range.

Quick reference cheat sheet

Reading a tire marked 80/90-14 50S TL M/C RF:

• 80 mm wide
• Sidewall is 90% of 80 = 72 mm tall
• Fits a 14-inch rim
• Overall diameter ≈ 500 mm (19.7”)
• Load index 50 = rated for 190 kg (419 lbs)
• Speed rating S = certified to 180 km/h (112 mph)
• TL = tubeless-ready
• M/C = motorcycle standard
• RF = reinforced carcass

Reading a tire marked 3.00-14:

• ~76 mm wide (3.00 × 25.4)
• Fits a 14-inch rim
• Sidewall height: check manufacturer specs

Reading a tire marked 2.75-14:

• ~70 mm wide (2.75 × 25.4)
• Fits a 14-inch rim
• Sidewall height: check manufacturer specs

The rule: the last number is always the rim diameter in inches. Everything before it describes the tire itself.

555 take

Tire notation looks cryptic until you see it once. Then it’s just width, shape, and rim size. The metric system gives you more information (aspect ratio tells you sidewall height). The inch system is simpler but less complete. Both work. Learn to read both because you’ll encounter both when shopping for EUC tires.

The one thing to internalize: the number your EUC manufacturer puts on the box is the overall diameter with the tire mounted - not the rim size. Your “20-inch wheel” has a 14-inch rim. Knowing this saves you from ordering the wrong tire.

Don’t overlook load index - especially if you’re a heavier rider. One tire, one contact patch, full load. Make sure the tire is rated for what you’re actually putting on it, at the pressure you actually ride.

Default to scooter, urban, or commuter tires. Your EUC usually does not bring track/sport motorcycle compounds into the range where they make sense, though powerful wheels can heat the tire through the motor and rim too. A good scooter or urban tire with a fitting profile, the right load index, and correct size will be a better choice for most riders than an exotic motorcycle tire chosen only because it looks more serious.