Tire Size Calculator
Compare any two tire sizes: height, width, speedometer error, and what it does to your gearing.
Because apparently millimeters × a percentage + wheel inches was the clearest way to label a tire. Compare any two sizes and get the numbers that actually matter.
The short version
Enter what you have and what you want. We'll turn the sidewall hieroglyphics into actual diameter, clearance, speedometer error, and gearing impact—then show the axle ratio that gets your stock performance back.
The de-confuser
Put two tires head-to-head
265/70R17 · ≈ 31.6x10.4R17 flotation
285/75R17 · ≈ 33.8x11.2R17 flotation
Same ground. Different consequences.
Diameter
+2.2"
31.6" → 33.8" (+7.0%)
Width
+0.8"
10.4" → 11.2"
Ride height
+1.1"
at the axle (half the diameter change)
Sidewall
+1.1"
7.3" → 8.4"
Speedometer reality check
69.6 mph actual
Bigger tires: you travel faster than the speedometer shows · 596 vs 638 revs/mile
Gearing gut-check
3.48 effective
Re-gear to ≈3.99 to restore stock performance
Computed from nominal sizes. Mounted dimensions vary by brand, load range, and rim width — check the manufacturer's spec sheet before buying.
How to use the tire size calculator
- Enter your current sizefrom the sidewall, in metric (265/70R17) or flotation (35x12.50R17). LT and P prefixes are fine. Works for any tire, or tyre, if you're reading this from across the pond.
- Enter the size you're thinking about. You get a side-by-side tire height comparison, width and sidewall difference, and how much the truck sits up at the axle.
- Check the speedometer and gearing numbers before you buy. Set your usual cruising speed and axle ratio to see your real speed and the re-gear that gets the factory feel back.
Popular tire size comparisons
The upgrades truck owners run the numbers on most. Click a comparison to load it in the calculator, or a size for its full breakdown and what's in stock.
| From | To | Taller by | At 65 mph indicated | Upgrade |
|---|---|---|---|---|
| 265/70R17 | 285/70R17 | 1.1" (3.5%) | 67.3 mph actual | Stock F-150, 4Runner, Ram to a 33 |
| 265/70R17 | 285/75R17 | 2.2" (7.0%) | 69.6 mph actual | Stock to a tall 33 |
| 285/70R17 | 315/70R17 | 1.7" (5.1%) | 68.3 mph actual | 33 to 34.4" on 17s |
| 265/70R17 | 35x12.50R17 | 3.4" (10.7%) | 72.0 mph actual | Stock to 35s |
| 275/60R20 | 35x12.50R20 | 2.0" (6.1%) | 69.0 mph actual | Stock 20s to 35s |
| 275/65R18 | 295/70R18 | 2.2" (6.8%) | 69.4 mph actual | Stock 18s to 34s |
| 245/75R16 | 265/75R16 | 1.2" (3.9%) | 67.5 mph actual | Older half-ton and Tacoma bump |
| 285/75R17 | 35x12.50R17 | 1.2" (3.5%) | 67.2 mph actual | Tall 33 to 35 |
What the numbers mean
The four things your sidewall refuses to explain
Diameter is the number that matters most. It sets your ground clearance at the axles, how the truck gears feel, and how far off the speedometer reads. Sizes within about 3% of stock behave like stock; beyond 8–10% most owners budget for a re-gear.
Width decides flotation in sand and snow — and whether the tire rubs. A taller narrowtire often clears where an equally tall wide one won't, and does better in ruts and on fuel economy.
Speedometer error compounds quietly: GPS apps, tolls, and your odometer (hence resale mileage and maintenance intervals) all drift with tire diameter. Recalibration is cheap on most platforms.
New to the notation itself? Start with our guide to how to read a tire size, then use the calculator to compare candidates for your build. Or skip the math entirely: the truck tire size chart lists every common truck and SUV size from 28 to 37 inches with its real height and width, and each size has its own page with the tires in stock in it.
Frequently Asked Questions
How do I compare two tire sizes?+
Enter your current size and the size you want in the calculator above, in metric (265/70R17) or flotation (35x12.50R17) format. It shows the difference in overall height, width, sidewall, and ride height, your real speed when the speedometer reads a given number, and the gear ratio that restores factory performance.
How tall is my tire in inches?+
For a metric size, multiply the width by the aspect ratio, convert to inches, double it, and add the wheel diameter: 285/70R17 works out to 32.7 inches. The calculator does it for you, and the truck tire size chart lists the height of every common size.
What is the difference between metric and flotation tire sizes?+
Metric sizes like 285/75R17 give the section width in millimeters (285), the sidewall as a percentage of that width (75), and the wheel diameter in inches (17). Flotation sizes like 35x12.50R17 state the overall diameter (35") and width (12.5") directly in inches. Neither is "bigger" by definition — a 285/75R17 and a 33.8x11.2R17 are the same tire described two ways.
Do bigger tires make my speedometer wrong?+
Yes. Your speedometer counts wheel revolutions calibrated to the factory tire diameter. A larger tire covers more ground per revolution, so the speedometer reads lower than your true speed — roughly 3% low for a 3% larger tire. Many trucks can be recalibrated with a handheld tuner or by the dealer.
When do I need to re-gear after a tire upgrade?+
Larger tires reduce your effective axle ratio, which costs acceleration and can push highway cruising out of the engine’s happy RPM range. As a rule of thumb: up to ~3% diameter increase is rarely noticeable, 3–8% is a judgment call (towing and automatics feel it more), and beyond ~8–10% most owners re-gear to a ratio that restores the factory effective gearing.
Will a bigger tire size fit my truck?+
Diameter is only part of fitment — width, offset, backspacing, and suspension travel decide whether a tire rubs at full lock or full compression. Check a vehicle-specific fitment guide for your platform; small lifts, wheel spacers, or minor trimming are often part of the recipe for popular sizes.
How accurate are these numbers?+
The math is exact for the nominal size, but real mounted tires vary slightly from nominal — typically within a few tenths of an inch of diameter — depending on brand, load range, rim width, and inflation. Use the manufacturer’s spec sheet for the final check.