Wheel | Tire Fitment Calculator

How to Use the Wheel & Tire Fitment Calculator

Three steps. Takes less than 60 seconds.

1

Enter Your Current Setup

Fill in your existing tire width (mm), aspect ratio, and rim diameter (inches), plus your current wheel width and ET offset. Find these on your tire sidewall and wheel spec sheet.

2

Enter the New Setup You're Considering

Enter the specs for the wheel and tire package you're looking at buying. Not sure about ET offset? It's listed on every wheel product page on DragRacingWheels.com.

3

Review Your Results Instantly

Results update live as you type. Check the suspension diagram to see poke and inset visually, switch to height view to compare tire diameters, and review the full measurements table for every spec you need to make a confident buying decision.

Pro tip: Not sure which wheel size is right for your vehicle? Call our team at 1-(833)-287-6088. We've confirmed hundreds of fitments for late-model American Muscle vehicles including the Challenger, Charger, Camaro, Mustang, and Corvette. Our team can help get you set up with a new set of drag racing wheels today!

Upgrading your drag racing wheels or tires? Before you buy, make sure your new setup fits perfectly. Our free wheel and tire fitment calculator lets you compare your existing wheel and tire combination against any new setup. This will show you the exact measurements for poke, inset, overall diameter, sidewall height, circumference, and ride height change all in real time, right in your browser.

Whether you're running a Dodge Challenger Hellcat widebody, a Chevy Camaro SS, a Ford Mustang Shelby GT500, a Corvette C7 or C8, or building a dedicated Pro-Mod race car, getting your wheel fitment right the first time saves you money, prevents clearance issues, and keeps you on the track instead of the garage.

Wheel & Tire Fitment Calculator | DragRacingWheels.com
Wheel & Tire Fitment Calculator
Compare your existing setup to a new wheel & tire combination — see poke, inset, diameter & height differences
Current setup
Tire
Existing tire width in millimeters, between 100 and 400
Existing tire aspect ratio percentage, between 20 and 90
Existing rim diameter in inches, between 10 and 30
Wheel
Existing wheel width in inches, between 3 and 20
Existing wheel offset ET in millimeters, between negative 150 and positive 150
New setup
Tire
New tire width in millimeters, between 100 and 400
New tire aspect ratio percentage, between 20 and 90
New rim diameter in inches, between 10 and 30
Wheel
New wheel width in inches, between 3 and 20
New wheel offset ET in millimeters, between negative 150 and positive 150
Overall Diameter
— —
Circumference
— —
Sidewall Height
— —
Top-down suspension view — poke & inset profile
Existing
New
⬅ Inboard (vehicle body)  ·  Hub face = zero reference  ·  Lower ET = more poke outboard  ·  Higher ET = more inset  ·  ➡ Outboard
Formulas: Sidewall = width(mm) × (aspect ÷ 100) ÷ 25.4  ·  Diameter = rim(in) + 2 × sidewall(in)  ·  Poke = wheelWidth(in) ÷ 2 − ET(mm) ÷ 25.4  ·  Inset = wheelWidth(in) ÷ 2 + ET(mm) ÷ 25.4  ·  Rev/mile = 63,360 ÷ circ(in)  ·  Speedo error = (newCirc − oldCirc) ÷ oldCirc × 100
Detailed fitment comparison between existing and new wheel and tire setup
Measurement Existing New Difference
DragRacingWheels.com  ·  Need help? Call 1-(833)-287-6088  ·  Results are estimates. Always verify fitment before purchase.
The Wheel & Tire Fitment Calculator is provided for informational purposes only. The calculations and results generated by this tool are based on the input parameters provided by the user and are not guaranteed to be accurate or suitable for every application. By using this calculator, users acknowledge and agree to the terms of this disclaimer and understand that it is their responsibility to independently verify and validate the results obtained from the tool. Users are solely responsible for their decisions and actions based on the calculated results, and they should consider seeking professional advice when in doubt.

Wheel & Tire Fitment — Frequently Asked Questions

Common questions about wheel fitment, ET offset, poke, inset, and tire sizing for drag racing and performance builds.

What is ET offset and how does it affect wheel fitment?

ET offset — short for Einpresstiefe, German for "insertion depth" — measures the distance in millimeters between a wheel's hub mounting face and its centerline. A lower or negative ET pushes the wheel further outboard, creating more poke. A higher positive ET pulls the wheel inward, creating more inset. For example, an ET0 wheel positions the hub face exactly at the wheel centerline, while an ET30 wheel sits 30mm inboard of center. Our calculator uses the verified formula: Poke = (wheel width ÷ 2) − ET offset. This is why a widebody Challenger typically runs ET0 while a narrowbody runs ET30 to achieve a similar flush stance.

What is the difference between poke and inset?

Poke refers to how far the outer edge of your tire sits outboard of the hub face, towards the fender. A positive poke value means the tire face protrudes past the hub mounting surface. Inset refers to how far the inner edge of your tire sits inboard of the hub face, towards the brake caliper, rotor, and suspension components. Both measurements are critical: poke determines fender clearance and visual stance, while inset determines whether your tire will contact calipers, control arms, or inner wheel well surfaces.

How do I read my tire size?

Tire sizes follow the format Width / Aspect Ratio R Rim Diameter. For example, 315/50R17 means: 315mm wide tread, a sidewall height equal to 50% of the tread width (315 × 0.50 = 157.5mm), mounted on a 17-inch diameter rim. Enter these three numbers into the calculator, width in mm, aspect ratio as a whole number percentage (50, not 0.50), and rim diameter in inches. The calculator converts everything to inches internally for all displayed results.

Why does changing tire diameter affect my speedometer?

Your vehicle's speedometer calculates speed based on how many times your tires rotate per mile, which is determined by the tire's circumference. A larger diameter tire travels further per revolution, so it completes fewer rotations per mile. This causes the speedometer to read lower than your actual speed. A smaller diameter tire causes the opposite, the speedometer reads higher than your actual speed. Our calculator displays the exact speedometer error percentage and your true speed at both 60 mph and 100 mph, so you can factor this into your build decisions and safety planning.

What ET offset should I run on a widebody vs narrowbody Challenger or Charger?

As a general rule, ET0 is the standard rear offset for widebody Challenger and Charger Hellcat, Redeye, and Jailbreak models running a 10" or 10.5" wide wheel. ET30 is typically correct for narrowbody models to achieve a comparable flush or slight poke stance. However, fitment varies depending on wheel width, tire size, suspension modifications, and whether you're running a spacer. Use the calculator to confirm your specific combination, or call our fitment team at 1-(833)-287-6088. Our team can help get you set up with a new set of drag racing wheels today!

Can I use this calculator for front drag wheels and skinnies?

Yes, the calculator works for any wheel and tire combination, including narrow front drag wheel setups like 15×3.5, 15×4, or 17×4.5 paired with 26×4.5 or 27×4.5 drag tires. Enter your current front setup in the Existing column and the new skinny setup in the New column to see how the overall diameter, ride height, and circumference change affects your front end geometry and traction bar setup. This is particularly useful when switching between front tire sizes for different track conditions or weight transfer setups.

What does revolutions per mile mean for drag racing?

Revolutions per mile (rev/mile) is the number of complete tire rotations needed to travel one mile. It is calculated as 63,360 ÷ tire circumference in inches. For drag racers, rev/mile directly impacts gear ratio calculations, trap speed accuracy, and launch RPM tuning. When you change tire size, your effective gear ratio changes. A tire with fewer revolutions per mile effectively acts like a numerically lower gear ratio, reducing acceleration but increasing top speed potential. Knowing the rev/mile difference between your current and new tires lets you compensate with transmission or differential tuning.

How accurate is this fitment calculator for race applications?

The calculator uses industry-standard formulas verified to three decimal places: Sidewall = width(mm) × (aspect ÷ 100) ÷ 25.4  ·  Diameter = rim(in) + 2 × sidewall(in)  ·  Circumference = π × diameter. These are the same formulas used by wheel and tire manufacturers. Results are theoretical dimensions based on published tire specifications, actual mounted measurements may vary slightly between brands, compounds, and inflation pressures. Always physically verify critical clearances on your vehicle before competition use, and treat all results as estimates to be confirmed with a tape measure on the actual parts.

Does this tool work for all vehicles including the Corvette C7, C8, and Stingray fitments?

Yes. The calculator handles any staggered or square fitment, including the staggered front/rear setups common on Corvette C6 Z06, C7 Z51/Z06/ZR1, and C8 Stingray/Z06/E-Ray. Enter your current front setup versus a new front size, or your current rear versus a new rear size, to see diameter differences, speedometer impact, and ride height changes. For Corvette-specific fitment guidance including WELD Racing and Forgestar wheel recommendations, call our team at 1-(833)-287-6088.

Is my data saved or tracked when I use this calculator?

No. All calculations run entirely within your browser, no data is transmitted to any server, stored in a database, or associated with your account. Your wheel specs, tire sizes, and build details remain completely private. No login, email, or registration is required to use the tool. The calculator uses no cookies and makes no external data requests. Your build information stays yours.

Still have questions about fitment for your specific build?

📞 Call Our Fitment Experts — 1-(833)-287-6088