Why we built this
Garage math shouldn't take a notebook, a phone calculator, and three browser tabs. AxleTally puts the everyday automotive numbers — tire dimensions, towing limits, running costs, and engine output — in one place, in the US units you actually use, with the real formulas instead of vague rules of thumb.
How we calculate
Every tool uses an established, published formula. The table below documents the exact math and the key assumptions behind each calculator so you can see precisely what each result represents.
| Calculator | Core formula | Key assumptions |
|---|---|---|
| Tire Size | Ø = rim + 2×(W×(AR/100)/25.4); revs/mi = 63,360/(π×Ø) | Standard P-metric size; exact 25.4 mm/in. |
| Tire Size Comparison | %Δ = (Ø_new − Ø_old)/Ø_old × 100 | Keep within ±3% of stock diameter. |
| Speedometer Error | true speed = indicated × Ø_new/Ø_old | Linear with diameter; ignores tire growth at speed. |
| Plus Sizing | target AR = ((Ø_old − rim)/2)×25.4/W × 100 | Rounds to nearest standard aspect ratio. |
| Gear Ratio / RPM | RPM = MPH × 336 × axle × trans ÷ Ø | 336 = 63,360/(π×60); trans = 1.0 direct, ~0.70 overdrive. |
| Towing Capacity | payload = GVWR − curb; max trailer = GCWR − curb − (pax+cargo) | Never exceed the door-jamb / manual ratings. |
| Tongue Weight | target = 10–15% of gross trailer weight (12% default) | Conventional ball hitch. |
| GCWR | max trailer = GCWR − loaded vehicle weight | Weigh the loaded truck at a certified scale. |
| Car Wrap Cost | vinyl = size×coverage%; DIY = vinyl×rate; pro ≈ vinyl×$9–13 | Typical 2025–26 US ranges; varies by installer/finish. |
| EV Charging Cost | kWh = batt×Δ%/eff; cost = kWh × rate | ~90% charging efficiency; your utility's $/kWh. |
| Cost Per Mile | fuel/MPG + maint/mi + fixed/annual miles | Fixed = insurance + registration + depreciation. |
| Horsepower | HP = Torque × RPM ÷ 5,252 | 5,252 = 33,000/2π; crank figures unless noted. |
The calculators run entirely in your browser in plain JavaScript. Nothing you type is sent to a server or stored — your numbers stay on your device.
Sources & how we keep this accurate
Formulas and constants come from published standards and reference data: the industry P-metric tire-size system (Tire Rack), the SAE J2807 tow-rating standard, the physics constant 5,252 for horsepower, U.S. EIA electricity prices, and the IRS standard mileage rate as a cost benchmark. Each calculator carries its own cited source and a review date. We review the formulas periodically and welcome corrections via the contact page.
Methodology last reviewed June 2026
What this is not
AxleTally gives educational estimates to help you plan and shop. It is not engineering, safety certification, or professional advice. Towing, wheel/tire fitment, and electrical decisions carry real risk — always verify against the manufacturer's ratings and a qualified professional before relying on a result.
Get in touch
Want a calculator we don't have yet, or spot a number that looks off? Tell us on the contact page.