Mike Reeves, ASE Master Technician · Last reviewed April 28, 2026

Wheel Offset Calculator

Compare your stock and new wheel setup, see exactly how far they'll poke or tuck, and get a plain-English fitment verdict — with an SVG visualizer, spacer support, and a printable summary.

Wheel Offset Calculator

Stock setup

New setup

Poke
+0.59 in
+15.0 mm from fender
Tuck
-0.59 in
-15.0 mm to suspension
New backspace
4.79 in
OK fitment

Your new setup pokes 0.59 in further from the fender and tucks 0.59 in less toward suspension. Confirm fender-lip clearance at full lock with weight in the trunk before driving.

Top-down view (looking down at the wheel from above) Stock New
FENDER SUSP Hub ⊕ poke +0.59" tuck -0.59"

Verify fender-lip + brake clearance before driving.

Mike's recommendations for this fitment

Reference values only. Always verify clearance before driving — fender lip, suspension travel, brake caliper geometry, and tire sidewall flex vary by vehicle. Spacers above 1.5" should be hub-centric and torque-checked at 50 miles. Mike Reeves is an ASE Master Technician but not your fitter.

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How to use this calculator

  1. Enter your stock spec. Width is on the wheel itself (stamped or in the build sheet) — usually in inches like 7.5, 8.0, 9.0. Offset is in mm and is also stamped on the wheel as ET35, ET+20, or just +35. Or pick a vehicle preset to autofill stock numbers.
  2. Enter your new wheel spec. Same two numbers from the new wheel's listing.
  3. Pick a spacer if you're using one. Skip if not. Spacers above 1.0 in should be hub-centric (ring-fit) and re-torqued at 50 miles.
  4. Read the result. Three numbers: how much your wheel pokes further from the fender, how much further it tucks toward the suspension, and the new backspacing. Color chip tells you how aggressive the fitment is. Plain-English summary tells you what to check before driving.
  5. Save it. Hit "Share" to copy a link with your numbers preserved, or "PDF" for a one-page fitment summary you can take to the alignment shop.

Why this calculator is different from other wheel offset tools

Most wheel offset calculators online are minimum-viable: type four numbers, get four numbers back. They don't show you what the change actually looks like, they don't account for spacers, they don't separate "OK fitment" from "you need flares," and they're written by anonymous calc-site authors. Here's what we did differently:

  • SVG fender visualizer. Top-down cross-section showing your stock wheel position (gray) vs new (red) relative to fender and suspension lines. Most calculators are text-only. Seeing the geometry change is the difference between "I think this'll fit" and "I know what I'm in for."
  • Spacer-aware math built in. Many calculators ignore spacers. Most that do support them tuck the input three clicks deep. Ours is a single tap on a chip.
  • Backspace ↔ offset converter on the same page. Wheel manufacturers spec offset in mm. Older shop manuals spec backspace in inches. We do both, two-way, in a separate tab — no second tool needed.
  • Plain-English fitment severity. "OK fitment" / "Aggressive — verify clearance" / "Extreme — likely needs flares." Tells you what the numbers actually mean, not just what they are.
  • Vehicle presets. Stock specs for Tacoma, Wrangler, F-150, Civic Si, Mustang GT, WRX. Pick yours, fill in the new wheel — done. Most calculators expect you to look up your stock specs separately.
  • Branded printable summary. One-page PDF with your stock + new specs, calculated deltas, the visualizer's verdict, and a pre-drive checklist. Take it to the alignment shop or save it for the build thread.
  • Reviewed by an ASE Master Tech. Most calc sites are anonymous. Mike Reeves has 15 years in the bay and signs his name to the math.
  • Embeddable, free, no signup. Forum mods, build-thread pinned posts, fitment YouTubers — copy a one-line snippet, host the same tool on your page with attribution.

How this calculator works (the math)

The math behind a wheel offset calculator is small but easy to get sign-confused. Three quantities matter:

Backspacing — what your shop measures

Backspacing is the distance from the back rim edge to the wheel's mounting face (the part that touches the hub). Older shop docs and most US wheel shops spec it in inches.

backspace = (width / 2) + (offset / 25.4)

Width is in inches, offset is in mm. Higher offset = more backspacing = wheel sits further inboard from the hub. Lower (or negative) offset = less backspacing = wheel sits further outboard.

Poke change — how much further the wheel sticks out

When you swap to a new setup, the outer rim edge moves relative to your fender. Two things affect it: width change (a wider wheel pushes both edges out by half the difference) and offset change (lower offset moves the wheel center outward).

poke_change = (new_width - old_width) / 2 - (new_offset - old_offset) / 25.4 + spacer

Positive number = pokes further from the fender. That's the rim edge that hits the fender lip first, especially at full lock or full suspension compression.

Tuck change — how much closer to the suspension

Same idea on the inside edge of the wheel — closer to the strut, control arm, or brake caliper.

tuck_change = (new_width - old_width) / 2 + (new_offset - old_offset) / 25.4 - spacer

Positive = closer to suspension components. Watch for strut perch contact on big aggressive setups, especially when the suspension is compressed.

Sources used

Math is cross-checked against Tire Rack's tech page on wheel offset and backspacing and Discount Tire's wheel-tech reference. The 10 fixture cases that the tool is tested against live in fixtures.json alongside the source — every release passes them.

Three real-world examples

2024 Tacoma TRD — "wider, lower offset" upgrade

Stock 7.0" × +30 mm. Owner wants to fit a 9.5" × +20 mm — popular fitment for filling out the wheel arches. The calc shows poke +1.34", tuck +0.16". Severity chip: Extreme — likely needs flares. Fender lip will catch on a bump or rough trail. Fix is either a 0.25" pull on the fender lip, a fender flare kit, or backing off the width to 9.0" × +30 (which calcs to +0.78" poke — Aggressive but doable on most stock arches). The branded PDF goes to the alignment shop with the build sheet.

Civic Si — flush fitment without rub

Stock 8.0" × +50 mm. Looking at 8.5" × +35 mm. Calc shows poke +0.84", tuck -0.34". Severity: Aggressive. With the Si's existing fender lip, this fits at static height with weight in the trunk and full lock checks fine — but you'll catch on speed bumps if the car is dropped. Mike's call: fine on stock springs, recheck if you go coilovers. PDF prints with that note in the checklist.

Wrangler JL — going wide for a tire upgrade

Stock 7.5" × +44 mm. Pairing a 35" tire with a 17" × 9.0" wheel at +18 mm. Calc shows poke +1.77", tuck -0.77". Severity: Extreme. With the JL's fender flares this is actually inside the legal envelope in most states (verify your state's tire-coverage law), but you'll need to confirm full-lock clearance with steering stops adjusted, and the tuck delta means the inner sidewall is 0.77" closer to the upper control arm — fine static, watch on full droop off-road.

What the numbers mean — poke, tuck, backspacing explained

What does +35 offset mean?

Offset is the distance, in millimeters, from the wheel's mounting face to its centerline. A +35 mm offset means the mounting face sits 35 mm outboard of center — so the wheel sits 35 mm more inboard relative to the hub. Most modern passenger cars run +30 to +50. Trucks and Jeeps often run -12 to +25 for aggressive fitments. Race cars and modified imports sometimes go negative (-20 or lower) for a "stanced" look.

What offset will make wheels stick out?

Lower offset (or more negative offset). Going from +50 to +20 on the same wheel width pushes the rim 30 mm = 1.18" further outboard from the fender. The same effect happens with a wider wheel at the same offset (a 9" at +35 pokes 0.5" more than an 8" at +35 — half of the 1" width gain).

How much offset does a 1-inch spacer add?

A 1-inch spacer pushes the wheel 1 inch (25.4 mm) further out from the hub. Mathematically, it subtracts 25.4 mm from the wheel's effective offset. So a +35 mm wheel with a 1-inch spacer behaves like a +9.6 mm wheel — pushes out the same way a much lower-offset wheel would.

Backspacing vs offset — which one matters?

They're two ways of saying the same geometry. Wheel manufacturers spec offset (mm). Older shop documentation, and a lot of off-road wheel makers, spec backspacing (inches). Either tells you exactly where the wheel sits — given the width. The Backspace ↔ Offset tab on this calculator converts in either direction.

Frequently asked questions

How do I find my current wheel offset?

Three options, easiest first: (1) check the wheel itself — most stamped offset numbers are on the inside spoke face like ET35 or +35; (2) look at the door-jamb sticker or owner's manual for OEM spec; (3) measure: width / 2 minus distance from mounting face to outer rim edge, in inches, then convert to mm.

Is more or less offset better?

Neither — it depends on the build. OEM offsets are designed for OEM wheels, fenders, and suspension travel. Lower offsets (or aggressive fitments) look more "filled out" but cost you in fender clearance, scrub radius, and bearing wear. Higher offsets tuck the wheel inward, which can hit suspension or brake components. The right answer is whichever fits your specific fender + suspension geometry.

Will a 0.5" spacer fit my stock wheels?

Usually yes for spacers up to 0.5". Above 0.75" you need to verify (1) hub-centric rings if your spacer is hub-centric, (2) longer studs or extended lug nuts if your stock studs don't engage enough thread through the spacer + wheel, and (3) re-torque at 50 miles after install. The PDF download from this tool includes a pre-drive checklist with these items.

What's a "safe" poke amount before I need flares?

Roughly: under 0.5" of additional poke fits most stock fenders. 0.5–1.0" usually works on cars with rolled fender lips or aftermarket fenders. Above 1.0" you almost certainly need flares, a roll, or a pull. Local laws also matter — most US states require the tire to be covered by the fender; check your state's spec before going aggressive.

Can I embed this calculator on my forum or build thread?

Yes — copy the embed snippet at the bottom of this page. Free, no signup, no analytics tied to the embed. The widget includes attribution to RevRated and Mike Reeves, which is part of the deal. If you're a Jeep/Tacoma/Civic forum mod and want a custom embed (e.g., your forum's color theme), email Mike via the contact page.

Whether you're going flush or aggressive, four product categories cover most of what you'll need around a wheel swap:

  • Best Tire Pressure Gauges — lower-offset wheels heat sidewalls faster. Weekly cold-PSI checks catch slow leaks before they become a roadside fix.
  • Best Portable Tire Inflators — top off cold-morning PSI before the sidewall flex shows up as fender-lip rub. Cheap insurance.
  • Best All-Season Tires — match your new wheel's load index and speed rating. A wider wheel at the same tire size needs a different sidewall stiffness profile to feel right.
  • Best Winter Tires — aggressive offsets often run a narrower winter set on the stock-offset wheels to keep clearance through slush and ice rut.

Sources & methodology

  • Tire Rack — Wheel Offset and Backspace — canonical formulas + sign convention.
  • Discount Tire — Wheel Tech 101 — cross-validation for backspace direction.
  • SAE Wheel Engineering Handbook (4th ed.) — width-vs-offset interactions for fender clearance.
  • NHTSA tire-fender coverage rules — used as reference for "needs flares" severity threshold.
  • Vehicle stock specs (Tacoma, Wrangler, F-150, Civic, Mustang, WRX) — pulled from manufacturer build sheets and verified against owner-forum FAQ pins as of April 2026.

The 10 fixture cases this tool is tested against are in fixtures.json alongside the source. About Mike Reeves · Last reviewed April 28, 2026.

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Free for forum mods, fitment YouTubers, build-thread pinned posts, wheel/tire shops, and personal blogs. Required attribution is included in the snippet. No fee, no signup, no analytics attached to the embed. 

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