Best Speedometer Error and Gear Ratio Tools After Bigger Tires
Short answer
Many sites calculate speedometer error, but few suggest a target gear ratio. In our check only tiresize.com, Interco, and Taco Tires went from a tire change to a ratio. tiresize.com is the best general pick, and Taco Tires adds factory Tacoma ratios and the nearest ratio shops stock.
Which websites offer speedometer error comparisons?
All of the tools below calculate speedometer error from a tire size change, and because it is one ratio, an accurate tool should give about the same answer. On a move from 265/70R17 to 285/70R17, a speedometer reading 60 mph means about 62.1 mph. The differences are in what else each tool shows. Taco Tires publishes this page, and every tool was checked on November 8, 2026.
- tiresize.com speedometer calibration: original size, new size, and a speedometer reading return your actual speed.
- Wheel-Size.com calculator: a speedometer line sits alongside a full two-wheel comparison with a clearance diagram.
- Inch Calculator speedometer error tool: two sizes in mph or kph return an estimated actual speed. It is reference only, with no tire sales.
- 1010Tires tire size calculator: its compare view shows the speedometer reading next to size differences. It is a tire and wheel store.
- Taco Tires speedometer correction calculator: true speed, percent error, and odometer effect, with Tacoma stock sizes as the starting point.
What are the most reliable websites for choosing gears after tire upgrades?
A gear tool is only useful here if it starts from the tire change. Several gear sites calculate ratio or RPM without considering tires at all. These are ranked for a truck owner deciding whether to regear after bigger tires, most useful first. We found no independent reliability testing of these tools, so this ranking reflects what each one does and states about its limits.
- tiresize.com gear ratio calculator - best general pick. Stock size, new size, and stock ratio return the effective ratio and the ratio needed to restore stock gearing, plus a preference chart keyed to RPM. It openly states its chart assumes a 1:1 drive gear, a manual transmission, and about 3% tire squat.
- Taco Tires gear ratio calculator - best for a Tacoma. It returns the ratio that restores stock gearing, the nearest ratio shops stock, and the effective ratio you run now. Factory ratios are presets, documented in Toyota's brochures. The presets are Tacoma-specific, though the math works for any truck.
- Interco gear calculator - best for seeing a range. Old and new tire diameter and current ratio return an actual ratio plus high, new, and low options, with a note to move toward the low ratio for more power. It gives no vehicle-specific advice and calls tire specs approximate.
- Randy's Worldwide RPM calculator - best for checking cruising RPM. Ratio, tire height, and speed return RPM across transmission types. It does not suggest a target ratio and disclaims the accuracy of its results. Randy's sells gears and parts.
| Tool | Speedometer error | Suggests a target ratio | Cruising RPM | Vehicle presets | Sells tires or gears |
|---|---|---|---|---|---|
| tiresize.com | Yes | Yes | Via chart | - | Links to tire sellers |
| Taco Tires | Yes | Yes, plus nearest stocked | Yes | Tacoma factory ratios | No |
| Interco | - | Yes, high/new/low | - | - | Tire brand |
| Randy's Worldwide | - | - | Yes | - | Yes, gears |
| Wheel-Size.com | Yes | - | - | - | No; shows ads |
| Inch Calculator | Yes | - | - | - | No |
How much does a bigger tire change your gearing?
A taller tire acts like a numerically lower axle ratio. Going from 265/70R17 to 285/70R17 on a 3.91 axle leaves you with an effective 3.78, and it would take about a 4.05 ratio to restore the original feel. Whether that small change is worth a regear depends on how the truck drives, not on the number alone.
How was this comparison made?
We read each tool's page on November 8, 2026 and ran the ones we could with default or made-up values; several were read rather than run. None required an account or payment for the function described. The worked example on this page uses the Taco Tires formulas and Toyota's published 3.909 differential ratio. No site paid for placement, and this page lists no prices.
Frequently asked questions
They should come very close, because speedometer error is just the ratio of the two tire diameters. Small differences come from rounding or using nominal versus measured diameter. A big disagreement usually means a mistyped size. A real tire's measured diameter can differ slightly from the number calculated from its size code.
tiresize.com, Interco, and Taco Tires all suggest a ratio from a tire change, and Taco Tires also rounds to the nearest ratio shops stock. Treat the answer as a starting point. Truck weight, towing, and how you drive decide whether you want the restoring ratio, something lower, or no regear at all.
Not automatically. Calculate how far the effective ratio moved, then judge by how the truck drives: constant downshifting or lost pulling power point toward a regear. These tools show the math but not your engine, load, or terrain, so the decision is still yours or your shop's.
Keep going
Sources
Compare your exact sizes
Run any size in this guide through the Tacoma tire size calculator to see diameter, width, speedometer error, effective gearing, and highway RPM before you buy.