{"id":374,"date":"2026-10-14T13:06:32","date_gmt":"2026-10-14T13:06:32","guid":{"rendered":"https:\/\/millimeters.to\/?page_id=374"},"modified":"2026-10-14T13:06:32","modified_gmt":"2026-10-14T13:06:32","slug":"wheel-offset-calculator","status":"publish","type":"page","link":"https:\/\/millimeters.to\/es\/wheel-offset-calculator\/","title":{"rendered":"Wheel Offset Calculator"},"content":{"rendered":"    <div class=\"mmc-wo-page\">\n\n      <h1>Wheel Offset <span class=\"mmc-wo-accent\">(ET)<\/span> Calculator<\/h1>\n      <p class=\"mmc-wo-lede\">Compare two wheels to see how far the inner and outer edges move, include a spacer, or convert between offset in millimetres and backspacing in inches.<\/p>\n\n      <div class=\"mmc-wo-tabs\" role=\"tablist\" aria-label=\"Mode\">\n        <button type=\"button\" class=\"mmc-wo-tab mmc-wo-tab-active\" data-mode=\"compare\" role=\"tab\" aria-selected=\"true\">Compare two wheels<\/button>\n        <button type=\"button\" class=\"mmc-wo-tab\" data-mode=\"convert\" role=\"tab\" aria-selected=\"false\">Offset \u2194 backspacing<\/button>\n      <\/div>\n\n      <div class=\"mmc-wo-card\">\n\n        <div id=\"mmc-wo-compare\">\n          <div class=\"mmc-wo-panels\">\n                <fieldset class=\"mmc-wo-panel\">\n      <legend>Current wheel<\/legend>\n      <div class=\"mmc-wo-two\">\n        <div class=\"mmc-wo-field\"><label for=\"mmc-wo-a-w\">Width (in)<\/label><input id=\"mmc-wo-a-w\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"7\"><\/div>\n        <div class=\"mmc-wo-field\"><label for=\"mmc-wo-a-et\">Offset ET (mm)<\/label><input id=\"mmc-wo-a-et\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"40\"><\/div>\n      <\/div>\n          <\/fieldset>\n                    <fieldset class=\"mmc-wo-panel\">\n      <legend>New wheel<\/legend>\n      <div class=\"mmc-wo-two\">\n        <div class=\"mmc-wo-field\"><label for=\"mmc-wo-b-w\">Width (in)<\/label><input id=\"mmc-wo-b-w\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"8\"><\/div>\n        <div class=\"mmc-wo-field\"><label for=\"mmc-wo-b-et\">Offset ET (mm)<\/label><input id=\"mmc-wo-b-et\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"35\"><\/div>\n      <\/div>\n              <div class=\"mmc-wo-field\"><label for=\"mmc-wo-b-sp\">Spacer (mm, optional)<\/label><input id=\"mmc-wo-b-sp\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"0\"><\/div>\n          <\/fieldset>\n              <\/div>\n          <div class=\"mmc-wo-result\" id=\"mmc-wo-cresult\" aria-live=\"polite\"><\/div>\n          <div class=\"mmc-wo-tip\" id=\"mmc-wo-ctip\"><\/div>\n        <\/div>\n\n        <div id=\"mmc-wo-convert\" hidden>\n          <div class=\"mmc-wo-two mmc-wo-three\">\n            <div class=\"mmc-wo-field\"><label for=\"mmc-wo-dir\">Convert<\/label>\n              <select id=\"mmc-wo-dir\" class=\"mmc-wo-input\"><option value=\"o2b\">Offset \u2192 backspacing<\/option><option value=\"b2o\">Backspacing \u2192 offset<\/option><\/select>\n            <\/div>\n            <div class=\"mmc-wo-field\"><label for=\"mmc-wo-cw\">Wheel width (in)<\/label><input id=\"mmc-wo-cw\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"8\"><\/div>\n            <div class=\"mmc-wo-field\"><label for=\"mmc-wo-cv\" id=\"mmc-wo-cv-label\">Offset ET (mm)<\/label><input id=\"mmc-wo-cv\" class=\"mmc-wo-input\" type=\"text\" inputmode=\"decimal\" value=\"25\"><\/div>\n          <\/div>\n          <div class=\"mmc-wo-field mmc-wo-bsunit\" id=\"mmc-wo-bsunit\" hidden>\n            <label for=\"mmc-wo-unit\">Backspacing unit<\/label>\n            <select id=\"mmc-wo-unit\" class=\"mmc-wo-input\"><option value=\"in\">Inches<\/option><option value=\"mm\">Millimetres<\/option><\/select>\n          <\/div>\n          <div class=\"mmc-wo-result\" id=\"mmc-wo-vresult\" aria-live=\"polite\"><\/div>\n        <\/div>\n\n      <\/div>\n\n      <h2>Backspacing to offset chart<\/h2>\n      <p class=\"mmc-wo-section-intro\">Offset in mm for common wheel widths. Positive = wheel sits further inside the arch.<\/p>\n      <div class=\"mmc-wo-table-wrap\">\n        <table class=\"mmc-wo-table\">\n          <thead><tr><th>Backspacing<\/th><th>7 in wide<\/th><th>8 in wide<\/th><th>9 in wide<\/th><th>10 in wide<\/th><th>12 in wide<\/th><\/tr><\/thead>\n          <tbody>\n                      <tr><td>3.5 in<\/td>\n                              <td>-13 mm<\/td>\n                              <td>-25 mm<\/td>\n                              <td>-38 mm<\/td>\n                              <td>-51 mm<\/td>\n                              <td>-76 mm<\/td>\n                          <\/tr>\n                      <tr><td>3.75 in<\/td>\n                              <td>-6 mm<\/td>\n                              <td>-19 mm<\/td>\n                              <td>-32 mm<\/td>\n                              <td>-44 mm<\/td>\n                              <td>-70 mm<\/td>\n                          <\/tr>\n                      <tr><td>4 in<\/td>\n                              <td>0 mm<\/td>\n                              <td>-13 mm<\/td>\n                              <td>-25 mm<\/td>\n                              <td>-38 mm<\/td>\n                              <td>-64 mm<\/td>\n                          <\/tr>\n                      <tr><td>4.25 in<\/td>\n                              <td>+6 mm<\/td>\n                              <td>-6 mm<\/td>\n                              <td>-19 mm<\/td>\n                              <td>-32 mm<\/td>\n                              <td>-57 mm<\/td>\n                          <\/tr>\n                      <tr><td>4.5 in<\/td>\n                              <td>+13 mm<\/td>\n                              <td>0 mm<\/td>\n                              <td>-13 mm<\/td>\n                              <td>-25 mm<\/td>\n                              <td>-51 mm<\/td>\n                          <\/tr>\n                      <tr><td>4.75 in<\/td>\n                              <td>+19 mm<\/td>\n                              <td>+6 mm<\/td>\n                              <td>-6 mm<\/td>\n                              <td>-19 mm<\/td>\n                              <td>-44 mm<\/td>\n                          <\/tr>\n                      <tr><td>5 in<\/td>\n                              <td>+25 mm<\/td>\n                              <td>+13 mm<\/td>\n                              <td>0 mm<\/td>\n                              <td>-13 mm<\/td>\n                              <td>-38 mm<\/td>\n                          <\/tr>\n                      <tr><td>5.25 in<\/td>\n                              <td>+32 mm<\/td>\n                              <td>+19 mm<\/td>\n                              <td>+6 mm<\/td>\n                              <td>-6 mm<\/td>\n                              <td>-32 mm<\/td>\n                          <\/tr>\n                      <tr><td>5.5 in<\/td>\n                              <td>+38 mm<\/td>\n                              <td>+25 mm<\/td>\n                              <td>+13 mm<\/td>\n                              <td>0 mm<\/td>\n                              <td>-25 mm<\/td>\n                          <\/tr>\n                      <tr><td>5.75 in<\/td>\n                              <td>+44 mm<\/td>\n                              <td>+32 mm<\/td>\n                              <td>+19 mm<\/td>\n                              <td>+6 mm<\/td>\n                              <td>-19 mm<\/td>\n                          <\/tr>\n                      <tr><td>6 in<\/td>\n                              <td>+51 mm<\/td>\n                              <td>+38 mm<\/td>\n                              <td>+25 mm<\/td>\n                              <td>+13 mm<\/td>\n                              <td>-13 mm<\/td>\n                          <\/tr>\n                      <tr><td>6.5 in<\/td>\n                              <td>+64 mm<\/td>\n                              <td>+51 mm<\/td>\n                              <td>+38 mm<\/td>\n                              <td>+25 mm<\/td>\n                              <td>0 mm<\/td>\n                          <\/tr>\n                      <tr><td>7 in<\/td>\n                              <td>+76 mm<\/td>\n                              <td>+64 mm<\/td>\n                              <td>+51 mm<\/td>\n                              <td>+38 mm<\/td>\n                              <td>+13 mm<\/td>\n                          <\/tr>\n                    <\/tbody>\n        <\/table>\n      <\/div>\n\n      <h2>Offset to backspacing chart<\/h2>\n      <p class=\"mmc-wo-section-intro\">Backspacing in inches for common offsets (ET) and wheel widths.<\/p>\n      <div class=\"mmc-wo-table-wrap\">\n        <table class=\"mmc-wo-table\">\n          <thead><tr><th>Offset (ET)<\/th><th>6.5 in wide<\/th><th>7 in wide<\/th><th>7.5 in wide<\/th><th>8 in wide<\/th><th>8.5 in wide<\/th><th>9 in wide<\/th><th>10 in wide<\/th><\/tr><\/thead>\n          <tbody>\n                      <tr><td>ET-25<\/td>\n                              <td>2.77 in<\/td>\n                              <td>3.02 in<\/td>\n                              <td>3.27 in<\/td>\n                              <td>3.52 in<\/td>\n                              <td>3.77 in<\/td>\n                              <td>4.02 in<\/td>\n                              <td>4.52 in<\/td>\n                          <\/tr>\n                      <tr><td>ET-12<\/td>\n                              <td>3.28 in<\/td>\n                              <td>3.53 in<\/td>\n                              <td>3.78 in<\/td>\n                              <td>4.03 in<\/td>\n                              <td>4.28 in<\/td>\n                              <td>4.53 in<\/td>\n                              <td>5.03 in<\/td>\n                          <\/tr>\n                      <tr><td>ET0<\/td>\n                              <td>3.75 in<\/td>\n                              <td>4.00 in<\/td>\n                              <td>4.25 in<\/td>\n                              <td>4.50 in<\/td>\n                              <td>4.75 in<\/td>\n                              <td>5.00 in<\/td>\n                              <td>5.50 in<\/td>\n                          <\/tr>\n                      <tr><td>ET10<\/td>\n                              <td>4.14 in<\/td>\n                              <td>4.39 in<\/td>\n                              <td>4.64 in<\/td>\n                              <td>4.89 in<\/td>\n                              <td>5.14 in<\/td>\n                              <td>5.39 in<\/td>\n                              <td>5.89 in<\/td>\n                          <\/tr>\n                      <tr><td>ET15<\/td>\n                              <td>4.34 in<\/td>\n                              <td>4.59 in<\/td>\n                              <td>4.84 in<\/td>\n                              <td>5.09 in<\/td>\n                              <td>5.34 in<\/td>\n                              <td>5.59 in<\/td>\n                              <td>6.09 in<\/td>\n                          <\/tr>\n                      <tr><td>ET20<\/td>\n                              <td>4.54 in<\/td>\n                              <td>4.79 in<\/td>\n                              <td>5.04 in<\/td>\n                              <td>5.29 in<\/td>\n                              <td>5.54 in<\/td>\n                              <td>5.79 in<\/td>\n                              <td>6.29 in<\/td>\n                          <\/tr>\n                      <tr><td>ET25<\/td>\n                              <td>4.73 in<\/td>\n                              <td>4.98 in<\/td>\n                              <td>5.23 in<\/td>\n                              <td>5.48 in<\/td>\n                              <td>5.73 in<\/td>\n                              <td>5.98 in<\/td>\n                              <td>6.48 in<\/td>\n                          <\/tr>\n                      <tr><td>ET30<\/td>\n                              <td>4.93 in<\/td>\n                              <td>5.18 in<\/td>\n                              <td>5.43 in<\/td>\n                              <td>5.68 in<\/td>\n                              <td>5.93 in<\/td>\n                              <td>6.18 in<\/td>\n                              <td>6.68 in<\/td>\n                          <\/tr>\n                      <tr><td>ET35<\/td>\n                              <td>5.13 in<\/td>\n                              <td>5.38 in<\/td>\n                              <td>5.63 in<\/td>\n                              <td>5.88 in<\/td>\n                              <td>6.13 in<\/td>\n                              <td>6.38 in<\/td>\n                              <td>6.88 in<\/td>\n                          <\/tr>\n                      <tr><td>ET40<\/td>\n                              <td>5.32 in<\/td>\n                              <td>5.57 in<\/td>\n                              <td>5.82 in<\/td>\n                              <td>6.07 in<\/td>\n                              <td>6.32 in<\/td>\n                              <td>6.57 in<\/td>\n                              <td>7.07 in<\/td>\n                          <\/tr>\n                      <tr><td>ET45<\/td>\n                              <td>5.52 in<\/td>\n                              <td>5.77 in<\/td>\n                              <td>6.02 in<\/td>\n                              <td>6.27 in<\/td>\n                              <td>6.52 in<\/td>\n                              <td>6.77 in<\/td>\n                              <td>7.27 in<\/td>\n                          <\/tr>\n                      <tr><td>ET50<\/td>\n                              <td>5.72 in<\/td>\n                              <td>5.97 in<\/td>\n                              <td>6.22 in<\/td>\n                              <td>6.47 in<\/td>\n                              <td>6.72 in<\/td>\n                              <td>6.97 in<\/td>\n                              <td>7.47 in<\/td>\n                          <\/tr>\n                    <\/tbody>\n        <\/table>\n      <\/div>\n\n      <h2>Offset, ET, inset and backspacing explained<\/h2>\n      <div class=\"mmc-wo-def\">\n        <div><b>Offset \/ ET<\/b><span>Distance in mm from the wheel centreline to the mounting face. The number after \"ET\" on a wheel.<\/span><\/div>\n        <div><b>Positive<\/b><span>Mounting face towards the outside, so the wheel sits further <em>in<\/em>. Most modern cars use +30 to +50.<\/span><\/div>\n        <div><b>Negative<\/b><span>Mounting face towards the inside, so the wheel sits further <em>out<\/em> (\"deep dish\").<\/span><\/div>\n        <div><b>Backspacing<\/b><span>Distance from the mounting face to the rear edge of the wheel, usually in inches.<\/span><\/div>\n      <\/div>\n\n      <h2>How to measure wheel offset<\/h2>\n      <p>Lay the wheel face-down and place a straight bar across the back edge. Measure from the bar down to the mounting surface: that is the backspacing. Measure the overall width of the wheel from lip to lip and use half of it as the centreline. Offset is the backspacing minus that half-width, converted to millimetres. If the wheel carries an ET number stamped on the back, use that rather than measuring.<\/p>\n\n      <h2>How the calculation works<\/h2>\n      <p>The inner edge of a wheel sits at half the width plus the offset from the mounting face, and the outer edge sits at half the width minus the offset. Comparing two wheels, the change in the inner edge is (new width \u00f7 2 + new ET) \u2212 (old width \u00f7 2 + old ET), and the change in the outer edge is the same calculation with the sign of the offset reversed. A spacer lowers the effective offset by its thickness. For wheel width, the page uses the nominal size in inches (for example 8 for an 8J wheel) and converts it to millimetres.<\/p>\n      <p>This tool shows how a wheel change moves the wheel relative to your current setup. It cannot tell you whether a wheel will fit your particular car: that depends on the suspension, brakes and arches, so check with the wheel supplier.<\/p>\n\n              <style>\n          .mmc-dp h3 { font-size: 17px; font-weight: 700; letter-spacing: -.01em; margin: 24px 0 6px; color: #0a0e1f; }\n          .mmc-dp ul, .mmc-dp ol { max-width: 65ch; color: #3a4056; line-height: 1.65; padding-left: 22px; margin: 0 0 14px; }\n          .mmc-dp li { margin-bottom: 6px; }\n          .mmc-dp-ex { background: #f7f8ff; border: 1px solid #e4e8ff; border-left: 4px solid #2b3dff; border-radius: 12px; padding: 14px 18px 4px; margin: 0 0 18px; max-width: 70ch; }\n          .mmc-dp-why { background: #fff8e6; border: 1px solid #ffe2a3; border-left: 4px solid #e8a400; border-radius: 12px; padding: 14px 18px 4px; margin: 0 0 18px; max-width: 70ch; }\n          .mmc-dp-tag { display: block; font-family: ui-monospace, \"JetBrains Mono\", monospace; font-size: 11px; font-weight: 600; text-transform: uppercase; letter-spacing: .08em; color: #2b3dff; margin-bottom: 6px; }\n          .mmc-dp-why .mmc-dp-tag { color: #9a6a00; }\n          .mmc-dp-table-wrap { overflow-x: auto; border: 1px solid #ddE1ee; border-radius: 14px; background: #fff; margin: 0 0 18px; }\n          .mmc-dp-table { width: 100%; border-collapse: collapse; font-size: 14px; }\n          .mmc-dp-table th { text-align: left; padding: 10px 12px; background: #eef0fb; color: #5a6178; font-family: ui-monospace, monospace; font-size: 11px; text-transform: uppercase; letter-spacing: .06em; white-space: nowrap; }\n          .mmc-dp-table td { padding: 9px 12px; border-bottom: 1px solid #eef0fb; }\n          .mmc-dp-table td:first-child { font-weight: 600; }\n          .mmc-dp-rel { display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 10px; margin-bottom: 18px; }\n          .mmc-dp-rel a { display: block; padding: 13px 15px; border: 1px solid #ddE1ee; border-radius: 12px; background: #fff; text-decoration: none; color: #0a0e1f; }\n          .mmc-dp-rel a:hover { border-color: #2b3dff; box-shadow: 0 0 0 3px #e4e8ff; }\n          .mmc-dp-rel b { display: block; color: #1b2bd6; margin-bottom: 2px; }\n          .mmc-dp-rel span { font-size: 13px; color: #5a6178; }\n        <\/style>\n            <div class=\"mmc-dp\">\n\n      <h2>Worked examples<\/h2>\n\n      <div class=\"mmc-dp-ex\">\n        <span class=\"mmc-dp-tag\">1 \u00b7 Fitting a wider wheel: 7J ET40 to 8J ET35<\/span>\n        <p>The wheel is an inch wider (25.4 mm) and the offset is 5 mm lower. Half the extra width goes to each side, so each edge moves 12.7 mm, and the lower offset pushes the whole wheel 5 mm further out.<\/p>\n        <p>The <strong>outer edge<\/strong> moves 12.7 + 5 = <strong>17.7 mm outward<\/strong>. The <strong>inner edge<\/strong> moves 12.7 \u2212 5 = <strong>7.7 mm inward<\/strong>, towards the suspension. The track is 10 mm wider overall.<\/p>\n      <\/div>\n\n      <div class=\"mmc-dp-ex\">\n        <span class=\"mmc-dp-tag\">2 \u00b7 Adding a spacer: 8J ET35 with a 15 mm spacer<\/span>\n        <p>A spacer behaves like a lower offset. A 15 mm spacer on an ET35 wheel gives an effective offset of ET20. Compared with the same wheel without a spacer, the whole wheel sits 15 mm further out, and both edges move with it. Against the original 7J ET40 wheel, the outer edge is now 32.7 mm further out and the inner edge has moved 7.3 mm outward, away from the suspension.<\/p>\n      <\/div>\n\n      <div class=\"mmc-dp-ex\">\n        <span class=\"mmc-dp-tag\">3 \u00b7 Don't forget the tire<\/span>\n        <p>A wider tire changes things too. Going from a 205 to a 225 tire adds 20 mm of width, so each sidewall sits roughly 10 mm further out and 10 mm further in than before (real tires vary a bit with the rim width). Add that to the wheel change above and you have the full picture of where the rubber ends up.<\/p>\n      <\/div>\n\n      <h2>Reading the numbers stamped on a wheel<\/h2>\n      <p>Most wheels have their specs on the back of a spoke or inside the barrel. Here's how to read a typical one: <strong>8Jx17 ET35 5x112 CB66.6<\/strong>.<\/p>\n      <div class=\"mmc-dp-table-wrap\">\n        <table class=\"mmc-dp-table\">\n          <thead><tr><th>Code<\/th><th>Means<\/th><\/tr><\/thead>\n          <tbody>\n            <tr><td>8J<\/td><td>The rim is 8 inches wide. The J is a code for the shape of the rim flange.<\/td><\/tr>\n            <tr><td>x17<\/td><td>The rim diameter is 17 inches.<\/td><\/tr>\n            <tr><td>ET35<\/td><td>The offset is +35 mm.<\/td><\/tr>\n            <tr><td>5x112<\/td><td>5 bolts on a circle 112 mm across (the PCD, or pitch circle diameter).<\/td><\/tr>\n            <tr><td>CB66.6<\/td><td>The centre bore, the hole in the middle, is 66.6 mm.<\/td><\/tr>\n          <\/tbody>\n        <\/table>\n      <\/div>\n      <p>The offset can't make up for a wrong bolt pattern or centre bore. The PCD must match your hub exactly. If the wheel's centre bore is bigger than your hub, a hub-centric ring fills the gap so the wheel sits centred on the hub, not hanging from the bolts.<\/p>\n\n      <h2>How much change is okay?<\/h2>\n      <p>There's no number that suits every car. As a starting point, staying within about 5 mm of the original keeps things close to what the engineers designed. Beyond that, it's worth checking clearance at full steering lock and over bumps, brake callipers, and any rules about wheels sticking out beyond the arch where you live. The best test is a supplier who knows your car, or a careful test fit.<\/p>\n\n      <h2>Mistakes to avoid<\/h2>\n      <ol>\n        <li><strong>Comparing the offset on its own.<\/strong> The same offset on a wider wheel puts the edges in different places. Always compare the width and the offset together.<\/li>\n        <li><strong>Mixing up the sign.<\/strong> A higher positive offset pulls the wheel in. A lower or negative offset pushes it out. If your edges are moving the wrong way, check the sign.<\/li>\n        <li><strong>Forgetting the tire.<\/strong> A wheel might clear, but a wider tire on it might not.<\/li>\n        <li><strong>Treating spacers as risk-free.<\/strong> Use hub-centric spacers of good quality, make sure the wheel studs or bolts are long enough, and re-check the torque after a short drive.<\/li>\n        <li><strong>Trusting a rough conversion.<\/strong> Backspacing and offset conversions assume a typical rim flange. Real wheels vary a little, so for a tight fit, measure the wheel itself.<\/li>\n      <\/ol>\n\n      <div class=\"mmc-dp-why\">\n        <span class=\"mmc-dp-tag\">Why this matters<\/span>\n        <p>A wheel that sits a few millimetres too far in or out can rub the suspension, catch the arch or change how the car steers. Those few millimetres are easy to measure before you buy and expensive to fix afterwards.<\/p>\n      <\/div>\n\n      <h2>Related tools<\/h2><div class=\"mmc-dp-rel\"><a href=\"https:\/\/millimeters.to\/tire-size-calculator\/\"><b>Tire size calculator<\/b><span>Compare two tire sizes and see the speedometer error<\/span><\/a><\/div>\n    <\/div>\n          <h2>Frequently asked questions<\/h2>\n              <details open>\n          <summary>What is wheel offset (ET)?<\/summary>\n          <p>Wheel offset, written ET in Europe and South Africa (from the German Einpresstiefe), is the distance in millimetres from the centreline of the wheel to the face that bolts to the hub. A positive offset means the mounting face sits towards the outside of the wheel, which tucks the wheel further in. Zero offset means the mounting face is on the centreline, and a negative offset pushes the wheel further out.<\/p>\n        <\/details>\n              <details>\n          <summary>What is the difference between offset and backspacing?<\/summary>\n          <p>Offset is measured from the centreline of the wheel and is quoted in millimetres. Backspacing is the distance from the mounting face to the rear edge of the wheel, usually quoted in inches. They describe the same thing: for a given wheel width, one can be converted to the other. This calculator uses the common convention that the overall width is the nominal width plus about 1 inch, so an 8-inch wheel with 0 offset has 4.5 inch backspacing.<\/p>\n        <\/details>\n              <details>\n          <summary>How do I convert backspacing to offset?<\/summary>\n          <p>Subtract half of the overall wheel width from the backspacing, then multiply by 25.4 to get millimetres. For an 8-inch wheel with 4.5 inch backspacing: overall width = 8 + 1 = 9 in, half = 4.5 in, 4.5 \u2212 4.5 = 0, so the offset is 0 mm. With 5.5 inch backspacing it is (5.5 \u2212 4.5) \u00d7 25.4 = +25.4 mm.<\/p>\n        <\/details>\n              <details>\n          <summary>What is the difference between inset and offset?<\/summary>\n          <p>Inset is another word for positive offset: how far the mounting face is moved towards the outside of the wheel and so the wheel is pulled in towards the car. Some wheel brands quote &quot;inset&quot; for the same measurement as offset or ET. A larger positive number always means the wheel sits further inside the arch.<\/p>\n        <\/details>\n              <details>\n          <summary>What does ET35 or ET40 mean on a wheel?<\/summary>\n          <p>It is the offset in millimetres. A wheel marked ET35 has its mounting face 35 mm outboard of the wheel centreline. The same number on different wheel widths puts the wheel in different positions, so always compare the width and the offset together.<\/p>\n        <\/details>\n              <details>\n          <summary>How do wheel spacers change offset?<\/summary>\n          <p>A spacer pushes the wheel outwards by its thickness, so it lowers the effective offset by that many millimetres. A 10 mm spacer on an ET40 wheel gives an effective offset of ET30. Enter the spacer thickness in the compare tool to include it.<\/p>\n        <\/details>\n      \n    <\/div>\n\n    <script>\n    (function () {\n      var $ = function (id) { return document.getElementById(id); };\n      function num(v) { var n = parseFloat(String(v).replace(',', '.').replace('\u2212', '-')); return isNaN(n) ? null : n; }\n      function fmt(n, d) { return n.toLocaleString('en-US', { maximumFractionDigits: d, minimumFractionDigits: 0 }); }\n      function signed(n, d) { return (n > 0.0001 ? '+' : n < -0.0001 ? 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' outward' : ' inward');\n        var tr = 2 * shift, trTxt = near(tr) ? 'No change' : signed(tr, 1) + ' mm <small>(' + signed(tr \/ IN, 2) + ' in)<\/small>';\n        out.innerHTML = '<div class=\"mmc-wo-result-head\">What changes<\/div><div class=\"mmc-wo-tiles\">' +\n          tile('Inner edge', inTxt, dIn > 0.05 ? 'towards the suspension and brakes' : dIn < -0.05 ? 'away from the suspension' : '', true) +\n          tile('Outer edge', outTxt, dOut > 0.05 ? 'towards the arch \/ fender' : dOut < -0.05 ? 'away from the arch' : '', true) +\n          tile('Wheel centre', shTxt, '') +\n          tile('Track width', trTxt, 'both sides together') +\n          tile('Backspacing now', fmt(A.bs, 2) + ' in', fmt(A.bs * IN, 0) + ' mm') +\n          tile('Backspacing new', fmt(B.bs, 2) + ' in', fmt(B.bs * IN, 0) + ' mm' + (B.sp ? ' \u00b7 with ' + fmt(B.sp, 1) + ' mm spacer' : '')) +\n          '<\/div>';\n        var msgs = [];\n        if (dIn > 5) msgs.push('The inner edge moves ' + fmt(dIn, 1) + ' mm towards the suspension, so check clearance to the struts, springs and brake calipers.');\n        if (dOut > 10) msgs.push('The outer edge moves ' + fmt(dOut, 1) + ' mm outward, so the wheel will sit further out. Check it against the arch or fender, and the local rules on wheel protrusion.');\n        else if (dOut > 5) msgs.push('The outer edge moves ' + fmt(dOut, 1) + ' mm outward. Check the arch clearance, especially at full steering lock and on suspension compression.');\n        if (!msgs.length) msgs.push(near(dIn) && near(dOut) ? '<strong>The wheel sits in the same place.<\/strong>' : '<strong>A small change.<\/strong> Both edges move by 5 mm or less, which is usually fine, but always confirm with the wheel supplier.');\n        tip.innerHTML = msgs.join(' ');\n      }\n\n      function convert() {\n        var dir = $('mmc-wo-dir').value, w = num($('mmc-wo-cw').value), v = num($('mmc-wo-cv').value), out = $('mmc-wo-vresult'), unit = $('mmc-wo-unit').value;\n        $('mmc-wo-bsunit').hidden = dir !== 'b2o';\n        $('mmc-wo-cv-label').textContent = dir === 'o2b' ? 'Offset ET (mm)' : 'Backspacing (' + (unit === 'in' ? 'in' : 'mm') + ')';\n        if (!(w > 0) || v === null) { out.innerHTML = '<div class=\"mmc-wo-result-head\">Enter the wheel width and a value<\/div>'; return; }\n        var et, bsIn;\n        if (dir === 'o2b') { et = v; bsIn = (w + 1) \/ 2 + et \/ IN; }\n        else { bsIn = unit === 'in' ? v : v \/ IN; et = (bsIn - (w + 1) \/ 2) * IN; }\n        var front = (w + 1) \/ 2 * IN - et;    \/\/ outer spacing in mm\n        out.innerHTML = '<div class=\"mmc-wo-result-head\">Result<\/div><div class=\"mmc-wo-tiles\">' +\n          tile('Offset ET', signed(et, 1) + ' <small>mm<\/small>', fmt(et \/ IN * 1, 2) + ' in', dir === 'b2o') +\n          tile('Backspacing', fmt(bsIn, 2) + ' <small>in<\/small>', fmt(bsIn * IN, 0) + ' mm', dir === 'o2b') +\n          tile('Mounting face to outer lip', fmt(front \/ IN, 2) + ' <small>in<\/small>', fmt(front, 0) + ' mm') +\n          '<\/div><div class=\"mmc-wo-tip\">' + (et > 0.5 ? 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