Advanced Wheel & Rim Size Calculator
Compare two wheel-and-tire setups — overall diameter, sidewall, revs/mile, speedometer error, offset, backspacing, track change and poke/tuck.
How to Use
- Enter your current (stock) tire + wheel in Setup A — or paste a code like "225/45R17" into the Tire Code field to auto-fill.
- Enter the new setup in Setup B — offset and rim width change the fender clearance and track width.
- All outputs (overall diameter, speedometer error, revs/mile, track change, poke/tuck) calculate live.
- Check the two visualizers — the <em>Side view</em> overlays both tires so diameter differences are immediately visible; the <em>Top view</em> shows wheel position relative to the fender.
| Measurement | Setup A | Setup B | Δ | Δ % |
|---|
| Speedometer reads | Actual speed | Error |
|---|
Show Work
Formulas
Tire code reference
225 — Section width in mm.
45 — Aspect ratio (sidewall height as % of width).
R — Radial construction (D = diagonal/bias, B = bias-belted).
17 — Rim diameter in inches.
91 — Load index (91 = 615 kg per tire). See table below.
W — Speed rating (W = 270 km/h / 168 mph). See table below.
M+S — Mud & Snow rating (three-peak snowflake = severe snow cert).
Speed rating chart
Load index (selected — see tire for full range 0-150)
| LI | kg | lb | LI | kg | lb |
|---|---|---|---|---|---|
| 75 | 387 | 853 | 95 | 690 | 1521 |
| 80 | 450 | 992 | 100 | 800 | 1764 |
| 85 | 515 | 1135 | 105 | 925 | 2039 |
| 87 | 545 | 1202 | 110 | 1060 | 2337 |
| 89 | 580 | 1279 | 115 | 1215 | 2679 |
| 91 | 615 | 1356 | 120 | 1400 | 3086 |
| 93 | 650 | 1433 | 125 | 1650 | 3638 |
| 94 | 670 | 1477 | 130 | 1900 | 4189 |
Rim-width ↔ tire-width fitment
Every tire has a recommended, minimum, and maximum rim width. Running too narrow pinches the bead and rounds the contact patch; too wide stretches the sidewall and makes the tire profile pointy (sometimes called "stretch").
Rule of thumb: minimum ≈ section × 0.0224, ideal ≈ × 0.0236, max ≈ × 0.0276 (convert mm to inches via /25.4). The calculator above shows if your current rim is in range.
About this calculator
Modelled after the classic wheel-size.com comparison tool but with added outputs for track-width change, poke / tuck (how much the wheel sits outside the fender relative to stock), backspacing auto-conversion, effective gearing impact, and speedometer error at three reference speeds. The side-view visualizer overlays the two tire outlines so you can see at a glance how much ride height changes; the top-view visualizer shows the rim relative to a reference fender line so you can check poke before ordering wheels.
All calculations are client-side — the tool doesn't send your build data anywhere, doesn't store cookies, and works offline once the page is cached. Input values are locale-independent (the Units toggle only changes the display, not the internal math).
About the Advanced Wheel & Rim Size Calculator
Use the Advanced Wheel & Rim Size Calculator — a free, easy tool for automotive and vehicle projects. Nothing is uploaded, and you do not need an account. Compare two wheel-and-tire setups — overall diameter, sidewall, revs/mile, speedometer error, offset, backspacing, track change and poke/tuck.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
How much diameter change is safe?
Stay within ±3% overall diameter to avoid significant speedometer / ABS / stability-control error. Beyond 3% you should recalibrate the speedometer (OBD tuner or instrument-cluster service) or adjust final drive. Anti-lock braking uses wheel-speed sensors that reference ABS stored calibrations — large mismatch can trigger traction-control intervention at inappropriate times.
What is offset, really?
Offset (mm) is the distance from the wheel's mounting hub-face to its centerline. <strong>Positive offset</strong> = hub face is OUTBOARD of centerline → wheel tucks into the fender. <strong>Negative offset</strong> = hub face is INBOARD → wheel pokes out. Stock passenger cars usually have +35 to +55 mm. Trucks and off-road rigs go to 0 and beyond negative (−12 to −44) for a stanced/deep-dish look. Drifting/track wheels often run +15 to +25 to get them closer to fender.
Offset vs backspacing?
They describe the same geometry two ways. <strong>Backspacing</strong> = distance from mounting face to the <em>inboard</em> lip of the rim. Formula: backspacing (in) = (rim_width/2) + (offset/25.4). A 9-inch wheel with +20 mm offset has backspacing = 4.5 + 0.787 = 5.29 in. Offset is international / metric; backspacing is the older US/truck convention.
Rim width limits for a given tire width?
Each tire has a recommended rim-width range. Rule of thumb: min rim width = section width × 0.0224, ideal = × 0.0236, max = × 0.0276 (convert mm to in via /25.4). A 245-wide tire fits rims roughly 8.0 - 9.5 inch, ideal 8.5. Running narrower pinches the contact patch; running wider stretches the sidewall and changes handling.
Will bigger wheels hurt acceleration?
Slightly. Overall tire diameter changes final-drive effective ratio proportionally: new_ratio = old_ratio × (new_Ø / old_Ø). Going 3% larger = 3% taller gearing = slower 0-60 but higher top speed. Rotational mass increase also hurts — a 28-lb 20-inch wheel vs a 22-lb 17-inch wheel costs measurable 0-60 time from unsprung rotational inertia.
What does plus-sizing mean?
Going to a larger-diameter rim while keeping the overall tire diameter constant so speedometer and gearing stay correct. Plus-1 = one inch larger rim + shorter sidewall (lower aspect ratio). Example: 225/60R16 → 225/55R17 → 235/45R18. Handling sharpens (shorter sidewall flex) but ride gets harsher (less sidewall air).
How do I use the Advanced Wheel & Rim Size Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Plus-size wheels
Upsize rim and compensate with a thinner sidewall to keep overall diameter within 3% of stock — sharper turn-in without speedometer error.
Off-road oversize
Step up from 31" to 33" tires on a 4x4 — this tool shows you the new circumference, speedo error, and gearing penalty.
Stance / fitment
Calculate poke or tuck for a new offset / wider rim before buying. See exactly how far outboard the new wheel sits relative to the fender.
Performance swap
Compare 225/45R17 vs 245/40R18 — track width change, contact-patch increase, rotational mass change.
Speedometer calibration
After a tire size change, use the Speedometer error table to see how much off your indicated speed is at 30/60/90 mph.
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