Quick Answer
- Toyota's 2024 Camry manual lists T155/70D17 (25.54 in) as the spare for 235/40R19 tires (26.40 in), a difference of -3.3%.
- Owner's manuals publish limits, not a safe percentage: Toyota, Lexus, Mazda, Jeep, RAM and Audi say not to exceed 50 mph (80 km/h) with a compact spare.
- A spare does not fit any car. Use the spare size in your own owner's manual or on the spare tire label.
Enter your primary and spare tire dimensions below. The calculator shows the diameter difference and what owner's manuals say about spare tires; it does not use a made-up "safe percentage", because manufacturers publish speed limits and drive-mode restrictions rather than diameter tolerances.
Primary Tire (currently fitted)
Spare Tire
Donut Spare Tire Size Chart: Spare Listed for Each Tire Size
Each row pairs a tire size with the spare that the same owner's manual lists for it. Overall diameters and differences are calculated.
| Vehicle (manual) | Regular tire | Spare listed | Regular diameter | Spare diameter | Difference |
|---|---|---|---|---|---|
| Toyota Camry 2024 | 205/65R16 | T155/70D17 | 26.49" | 25.54" | -3.6% |
| Toyota Camry 2024 | 235/45R18 | T155/70D17 | 26.33" | 25.54" | -3.0% |
| Toyota Camry 2024 | 235/40R19 | T155/70D17 | 26.40" | 25.54" | -3.3% |
| Toyota Corolla 2025 | 195/65R15 | T125/70D17 | 24.98" | 23.89" | -4.4% |
| Toyota Corolla 2025 | 205/55R16 | T125/70D17 | 24.88" | 23.89" | -4.0% |
| Toyota Corolla 2025 | 225/40R18 | T125/70D17 | 25.09" | 23.89" | -4.8% |
| Toyota RAV4 2025 | 225/65R17 | T165/80R17 | 28.52" | 27.39" | -3.9% |
| Toyota RAV4 2025 | 225/60R18 | T165/80D17 | 28.63" | 27.39" | -4.3% |
| Toyota RAV4 2025 | 235/55R19 | T165/90D18 | 29.18" | 29.69" | +1.8% |
| Toyota Tacoma 2025 | 245/70R17 | T175/90D18 | 30.50" | 30.40" | -0.3% |
| Toyota Tacoma 2025 | 265/70R17 | 245/75R17 (full-size spare) | 31.61" | 31.47" | -0.4% |
| Toyota 4Runner 2025 | 245/70R17 | T175/90D18 | 30.50" | 30.40" | -0.3% |
| Lexus IS 350 2024 | 235/40R19 | T155/70D17 | 26.40" | 25.54" | -3.3% |
| Lexus RX 350 2024 | 235/60R19 | T165/90D18 | 30.10" | 29.69" | -1.4% |
| Lexus RX 350 2024 | 235/60R19 | T165/70D20 | 30.10" | 29.09" | -3.3% |
| Mazda CX-30 2024 | 215/65R16 | T135/80D17 | 27.00" | 25.50" | -5.6% |
| Mazda CX-30 2024 | 215/55R18 | T135/80D17 | 27.31" | 25.50" | -6.6% |
Spare availability and size vary by trim and market. Check the spare tire label and your owner's manual. For the difference between any two sizes use the tire size difference calculator.
What Owner's Manuals Say About Spare Tires
| Manual | Statement (paraphrased) |
|---|---|
| Toyota and Lexus (Camry, Corolla, RAV4, Tacoma, 4Runner, IS, NX, RX) | Do not drive faster than 50 mph (80 km/h) with a compact or temporary spare. With it installed, systems such as ABS, VSC and TRAC may not operate correctly, and the AWD or 4WD system cannot be fully used and may negatively affect drive-train components. |
| Mazda (CX-5, CX-30, Mazda3, MX-5) | Do not exceed 80 km/h (50 mph) with the temporary spare. The CX-5 manual says not to fit it on the front driving wheels (move a regular tire to the front and fit the spare at the rear). Ground clearance is reduced, do not use chains on it, and its tread life is under 5,000 km (3,000 miles). |
| Jeep and RAM (Wrangler, Grand Cherokee, Cherokee, 1500, 2500) | Compact and collapsible spares are for temporary emergency use only: do not drive more than 50 mph (80 km/h). They have limited tread life. The 2025 Grand Cherokee manual adds: do not drive with the spare installed for more than 50 miles (80 km), at a maximum of 50 mph. |
| Audi (A4, Q5, Q8) | Do not drive faster than 50 mph (80 km/h) with a compact or collapsible spare. All four wheels must have the same brand, construction and tread pattern so the drive system is not damaged by different tire speeds, so use a different spare only temporarily and in an emergency. |
| Ford F-150 (2025) | With a full-size dissimilar spare (different brand, size or appearance): do not exceed 70 mph (113 km/h), do not use snow chains on that end of the vehicle, and do not engage any four-wheel drive mode. The manual says a significant size difference can limit four-wheel drive functionality and cause extra noise from the transfer case. |
| GMC Sierra 1500 (2025) | If the vehicle has four-wheel drive and a different size spare is installed, do not drive in four-wheel drive until the flat tire is repaired or replaced. The vehicle could be damaged and the repairs would not be covered by the warranty. |
These come from the specific 2023 to 2025 manuals we read and may not apply to every model or year. Your own owner's manual is the authority for your vehicle. A spare ages even if it is never used, so you can read the age of your spare from its DOT code, and the AWD tire size guide covers mixing sizes.
How to Read a Spare Tire Size Like T125/70D17
| Part | Meaning |
|---|---|
| T | Temporary. Bridgestone says T stands for temporary and is for your spare tire. |
| 125 | Section width in millimetres. |
| 70 | Aspect ratio: the sidewall height as a percentage of the width (Michelin and Bridgestone). |
| D | Diagonal (bias ply) construction. Bridgestone lists D as diagonal or bias ply, against R for radial. Some spares are marked R instead. |
| 17 | Wheel diameter in inches. A compact spare usually has a different wheel diameter from your regular wheels, so use the spare wheel itself, not your wheel size. |
Sources: Bridgestone, How to Read Tire Size; Michelin USA, How to Read Tire Markings.
How to Use the Spare Tire Calculator
- 1Enter your regular tire size (the ones fitted to the vehicle), for example 235/40R19.
- 2Enter your spare size, for example T155/70D17, and choose whether it is a compact or a full-size spare.
- 3Pick your drivetrain and click Compare Spare.
- 4Read the calculated diameter and percentage difference and the manual statements, then read the spare tire section of your own owner's manual, because limits differ by vehicle.
Overall diameter
Rim + 2 x width x aspect / 100 / 25.4. For 235/40R19: 19 + 2 x 94 / 25.4 = 26.40 in. For T155/70D17: 17 + 2 x 108.5 / 25.4 = 25.54 in.
Difference
Spare diameter / regular diameter - 1, times 100. For this pair: 25.54 / 26.40 - 1 = -3.3%.
What the manuals publish
Speed limits (50 mph for compact spares in the Toyota, Lexus, Mazda, Jeep, RAM and Audi manuals, 70 mph for the Ford F-150 dissimilar full-size spare), drive-mode limits and sometimes a distance (Grand Cherokee 2025: 50 miles) or tread life (Mazda: 3,000 miles).
Frequently Asked Questions
This calculator uses standard tire geometry to estimate diameter differences and quotes statements from the owner's manuals we hold. Actual limits depend on your vehicle, year and spare. Always follow your vehicle manufacturer's instructions for spare tire use, especially on AWD and 4WD vehicles.