6 tools · free, no sign-in

Plan before you spend

Calculators, planners and printable checklists for the decisions before you buy parts, book a shop or buy a car. The calculators run in the browser; the checklist, flowchart and score sheet are built to print.

Each tool pairs with the guide that frames its decision

Live tool · Tire size

Will the new size throw your speedometer?

Type the size on your sidewall and the one you are considering. Diameter, sidewall and the speedometer error update as you type.

Current

Reads 225/45 R17

New

Reads 235/40 R18

Overall diameter25.4 in645 mm, was 25.0 in
Change+1.7%within 3% of the current size; still check the door placard
Sidewall94 mmwas 101 mm, less sidewall
Est. speed at 6061.0 mphestimated road speed when the dial reads 60; 794 revs/mile, was 808
Open the full calculator

The two sizes carry over to the full calculator.

Check the numbers before you order the parts.

The tire-size instrument is a compact version of the Tire Size Calculator. The other tools are below.

  1. Tire Size Calculator Calculator
  2. Window Tint Cost Estimator Estimator
  3. Beginner Mod Budget Planner Planner
  4. Tire Pressure Troubleshooting Flowchart Flowchart
  5. Used Car Inspection Checklist Checklist
  6. Car Show Judging Score Sheet Score sheet

All 6 tools With the guide each one pairs with

CalculatorTire Size CalculatorCompare tire diameter, sidewall height and estimated speedometer changes before discussing fitment with your installer.Pairs with Staggered Setup vs. Square by Danny KowalskiEstimatorWindow Tint Cost EstimatorBuild a planning estimate by vehicle, film material and window coverage, then compare written installer quotes.Pairs with 20% vs 35% Window Tint: Visibility, Heat and Cost by Sarah ChenPlannerBeginner Mod Budget PlannerPlan your modification budget before buying parts.Pairs with Customizing a Car on a Budget Without Wasting Money by Marcus ReidFlowchartTire Pressure Troubleshooting FlowchartWork through low-pressure symptoms and decide what to check next.Pairs with Cold-Weather MPG: Warm-Up and Tire Pressure Myths by Sarah ChenChecklistUsed Car Inspection ChecklistTake a structured checklist to your next used-car viewing.Pairs with What a Clean Carfax Actually Hides by Sarah ChenScore sheetCar Show Judging Score SheetUse a printable score sheet to organize judging at a car show.Pairs with Car Show Judging Systems and Score Sheets by Josh Hartley

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