How do I convert metric tire sizes to inches?

A metric tire like 285/70R17 means: 285mm width, 70% aspect ratio, 17" rim. The sidewall height is 285 × 0.70 = 199.5mm (7.85"). Total diameter = 17 + (2 × 7.85) = 32.7 inches. This calculator does all the math instantly.

What's the difference between metric and standard tire sizing?

Metric sizes (e.g., 285/70R17) list width in mm, aspect ratio as a percentage, and rim size in inches. Standard sizes (e.g., 35x12.50R17) list overall diameter and width in inches. Both describe the same tire, just different notation systems.

How much bigger is a 35 tire vs a 33?

A 35" tire has 2" more overall diameter than a 33", which translates to 1" more ground clearance. It also increases circumference by about 6%, which affects speedometer accuracy, gear ratio effectiveness, and fuel economy.

Will bigger tires affect my speedometer?

Yes. Larger tires cover more ground per revolution, so your speedometer will read lower than your actual speed. For example, 35" tires on a vehicle calibrated for 31" tires will create about a 13% speedometer error.

What tire size fits my truck without a lift?

Most half-ton trucks fit 33" tires on stock suspension with minor trimming. Wranglers and Broncos can often fit 33s stock. Going to 35" almost always requires at least a 2.5" lift and potential fender modifications.

Interactive Tool

Tire Size Calculator

Convert between metric and standard tire sizes, calculate diameter, and compare sizes to see the real-world differences.

Quick Answer: A 285/70R17 tire is 32.7″ tall and 11.2″ wide. To convert metric to inches: multiply width (mm) by aspect ratio, divide by 25.4, double it, and add rim diameter. Use this calculator for instant conversions and side-by-side comparisons.

HOW IT WORKS

Enter Your Tire Size

Type any metric (285/70R17) or standard (35x12.50R17) tire size

Convert or Compare

Instantly see diameter, width, sidewall, and revs per mile

Share & Save

Copy a shareable link or save comparisons for later

Metric → Standard

Convert metric sizing (e.g., 285/70R17) to inches

Enter Metric Tire Size

Format: Width/Aspect Ratio + R + Rim Size

Standard Equivalent

32.7x11.22R17

Diameter

32.7"

Width

11.2"

Sidewall

7.9"

Circumference

102.8"

Revolutions per Mile

617

Standard → Metric

Convert standard sizing (e.g., 35x12.50R17) to metric

Enter Standard Tire Size

Format: Diameter x Width + R + Rim Size

Metric Equivalent

318/72R17

Diameter

35.0"

Width

12.5"

Sidewall

9.0"

Circumference

110.0"

Revolutions per Mile

576

Understanding Tire Sizes

Metric Sizing (e.g., 285/70R17)

285 = Tire width in millimeters | 70 = Aspect ratio (sidewall height as % of width) | R = Radial construction | 17 = Rim diameter in inches

Standard Sizing (e.g., 35x12.50R17)

35 = Overall tire diameter in inches | 12.50 = Tire width in inches | R = Radial construction | 17 = Rim diameter in inches

WHAT CHANGES WHEN YOU GO BIGGER

A tire size change isn't just about looks. Every inch of diameter you add triggers a chain reaction across speedometer accuracy, gearing, fuel economy, and clearance.

Speedometer Error

Your speedometer is calibrated to a specific number of wheel revolutions per mile. Larger tires cover more ground per revolution, so your speedo reads slower than you're actually going. Smaller tires do the opposite.

Stock → 33"

~3-4%

Minor

Stock → 35"

~10-13%

Noticeable

Stock → 37"

~16-19%

Must fix

At 70 mph indicated with 35" tires on a 31" stock vehicle, your actual speed is closer to 79 mph. That's ticket territory.

Fix options: performance tuner, inline calibrator, or dealer reflash.

Gearing Impact

Bigger tires effectively make your gearing taller, your engine works harder to turn those larger, heavier wheels. The result: sluggish acceleration, transmission gear-hunting, and higher RPMs on the highway.

Tire Increase	Effective Gear Change	How It Feels	Regear?
31" → 33"	3.73 → ~3.50 effective	Slightly lazy off the line	Optional
31" → 35"	3.73 → ~3.30 effective	Noticeably sluggish, hunts gears	Recommended
31" → 37"	3.73 → ~3.12 effective	Painful. Transmission overheats.	Required

Use our Gear Ratio Calculator to find the right regear ratio for your setup.

Rubbing & Clearance Risk

Every tire size has three clearance checkpoints: fender well (at full lock), upper control arm (at full compression), and frame/body mounts. Rubbing usually starts at full steering lock on bumps.

NO-LIFT ZONE

Up to 33"

Most trucks and Wranglers. May need minor fender trimming or a leveling kit. Check tire-to-lift guide.

MODERATE LIFT

34"–35"

2.5"–3.5" lift typically required. Fender flares or trimming common. Wheel offset matters, aggressive offset pushes tires outward.

SERIOUS BUILD

37"+

4"+ lift, fender mods, and likely a regear. Check wheel fitment before buying.

Ground Clearance Math

Every 2 inches of tire diameter adds roughly 1 inch of ground clearance, half above, half below the axle centerline. But don't confuse tire size with approach/departure angles, which depend on bumper design.

Ground Clearance Gain

(New Diameter − Stock Diameter) ÷ 2 = inches gained

31" → 33"

+1.0"

31" → 35"

+2.0"

31" → 37"

+3.0"

31" → 40"

+4.5"

Fuel Economy Impact

Bigger, heavier tires increase rolling resistance and rotational mass. Expect 1–3 MPG loss depending on tire weight, tread pattern, and driving conditions. Mud-terrains hit harder than all-terrains.

Run the numbers: MPG Impact Calculator →