**Tire Size Code Breakdown (2025 Standard)**:.

**Example: P215/65R15 95H**.

**Each Component Explained**:.

**1. "P" - Tire Type Prefix**: - **P (Passenger)**: Car, minivan, small SUV (most common). - Load rating: Up to 1,500 lbs per tire. - Speed rating: Up to 149 mph (H-rated). - **LT (Light Truck)**: Pickup truck, large SUV, commercial van. - Load rating: Up to 3,000 lbs per tire (stronger construction). - Speed rating: Lower (usually S or T, 112-118 mph). - **No Prefix (Euro-Metric)**: European passenger cars. - Example: 225/45R17 (no P or LT). - Similar to P-metric but slightly different load standards. - **T (Temporary)**: Space-saver spare tire. - Use < 50 mph, < 50 miles. - **ST (Special Trailer)**: Trailer-only tires (never use on cars).

**2. "215" - Section Width (millimeters)**: - **Definition**: Width of tire tread from sidewall to sidewall (measured in mm). - **215mm = 8.46 inches** (215 ÷ 25.4 mm/inch). - **Range**: 125mm (narrow compact car) to 355mm (performance/truck). - **Impact**: - **Wider** (235, 245): Better grip, higher fuel consumption, more road noise. - **Narrower** (195, 205): Better snow/rain traction, lower cost, quieter.

**3. "65" - Aspect Ratio (percentage)**: - **Definition**: Sidewall height as % of section width. - **Calculation**: 215mm × 0.65 = **139.75mm sidewall height** (5.5 inches). - **Range**: 25 (ultra-low-profile sports) to 85 (truck/off-road). - **Impact**: - **Lower Ratio** (45, 50, 55): Sportier handling, harsher ride, easier wheel damage. - **Higher Ratio** (70, 75, 80): Smoother ride, better off-road, taller overall diameter.

**4. "R" - Construction Type**: - **R (Radial)**: 99% of modern tires (layers run radially from bead). - Better fuel economy, longer tread life, smoother ride vs bias-ply. - **D (Diagonal/Bias)**: Rare, only on trailers/classic cars. - **B (Belted Bias)**: Obsolete (1970s technology).

**5. "15" - Rim Diameter (inches)**: - **Definition**: Diameter of wheel that tire mounts on. - **Range**: 13" (compact cars) to 24" (trucks/luxury SUVs). - **Common Sizes**: - 15-16": Economy cars, older vehicles. - 17-18": Mid-size sedans, crossovers (most common in 2025). - 19-20": Sports cars, luxury sedans. - 20-24": Trucks, performance SUVs. - **Note**: You **cannot** change rim diameter without buying new wheels.

**6. "95" - Load Index (optional but important)**: - **Definition**: Maximum weight each tire can carry at max pressure. - **95 = 1,521 lbs per tire** (× 4 tires = 6,084 lbs total vehicle capacity). - **Common Load Indexes**: - 80-90: Compact/mid-size cars (990-1,323 lbs/tire). - 95-105: Full-size sedans, crossovers (1,521-2,039 lbs/tire). - 110-120: SUVs, light trucks (2,337-3,086 lbs/tire). - 121+: Heavy-duty trucks (3,197+ lbs/tire). - **Critical**: Never install tires with **lower** load index than OEM spec (unsafe).

**7. "H" - Speed Rating (optional but important)**: - **Definition**: Maximum safe speed tire can sustain. - **H = 130 mph** (210 km/h). - **Common Speed Ratings** (2025): - **S (112 mph)**: Economy cars, winter tires. - **T (118 mph)**: Standard all-season tires. - **H (130 mph)**: Performance all-season (most common). - **V (149 mph)**: Sports sedans, performance crossovers. - **W (168 mph)**: High-performance cars. - **Y (186 mph)**: Exotic sports cars, supercars. - **ZR (>149 mph)**: Includes (Y) or (W) after size. - **Rule**: You can upgrade to higher speed rating, but **never downgrade** (safety risk).

**Real-World Example Decoding**:.

**LT245/75R16 120/116Q E**: - **LT**: Light truck tire (pickup, heavy SUV). - **245mm**: 9.65" section width. - **75**: Sidewall is 75% of 245mm = 183.75mm (7.2"). - **R**: Radial construction. - **16"**: Rim diameter. - **120/116**: Dual load rating (single 3,086 lbs / dual 2,756 lbs per tire). - **Q**: Speed rating 99 mph (lower than passenger tires). - **E**: Load range E (10-ply rated, 80 PSI max pressure for heavy hauling).

**Alternative Tire Sizes (Safe Substitutions)**:.

**General Rules for Safe Tire Swaps**: 1. **Overall Diameter**: Stay within **±3%** of OEM tire diameter. - **±3% = ±1 inch** for typical 28-30" diameter tires. - **Why**: Larger = speedometer reads slow, smaller = reads fast; affects ABS/traction control calibration. 2. **Load Index**: Equal or greater than OEM (never lower). 3. **Speed Rating**: Equal or greater than OEM (never lower). 4. **Rim Diameter**: Must match your wheel size (can't change without new wheels).

**How to Calculate Overall Diameter**:.

**Formula**: Diameter = (2 × Sidewall Height) + Rim Diameter.

**Example (P215/65R15)**: - Sidewall Height: 215mm × 0.65 = 139.75mm = 5.5". - Overall Diameter: (2 × 5.5") + 15" = **26.0 inches**.

**Safe Alternative Sizes for P215/65R15** (26.0" OEM diameter):.

**3% Rule**: 26.0" × 0.03 = 0.78" → Safe range is **25.2" to 26.8" diameter**.

**Compatible Sizes**: 1. **P205/70R15** = 26.3" (larger, +1.2% diameter): - Narrower tread (205mm vs 215mm) = better snow traction. - Taller sidewall (70 vs 65) = smoother ride. - **Use Case**: Winter tires, comfort upgrade.

**Popular Plus-Sizing Examples** (2025 Vehicles):.

**Original: 225/65R17** (29.5" diameter) → **Upgrade Options**:.

**+1 Sizing** (18" wheels): - **235/60R18** = 29.1" (-1.4%, safe). - **225/55R18** = 27.7" (-6.1%, **too small**, causes rubbing/speedometer error). - **Correct +1**: **235/55R18** = 28.2" (-4.4%, borderline). - **Best +1**: **245/55R18** = 28.6" (-3.1%, ideal).

**+2 Sizing** (19" wheels): - **245/50R19** = 28.6" (-3.1%, safe). - **235/50R19** = 28.3" (-4.1%, acceptable).

**+3 Sizing** (20" wheels): - **255/45R20** = 29.0" (-1.7%, safe). - **245/45R20** = 28.7" (-2.7%, safe).

**Tire Size Comparison Table** (Common Swaps):.

| **Original Size** | **Overall Diameter** | **Safe Alternatives** | **Diameter Change** | **Notes** | |-------------------|----------------------|----------------------|---------------------|-----------| | **P195/65R15** | 25.0" | P205/60R15 | +0.8% | Wider, lower profile | | **P215/60R16** | 26.2" | P225/55R16 | +0.4% | Wider, sportier | | **P225/65R17** | 28.5" | P235/60R17 | -0.7% | Wider, common swap | | **P235/65R17** | 29.0" | P245/60R17 | -1.0% | Wider, better grip | | **LT265/70R17** | 31.6" | LT285/70R17 | +2.4% | Truck lift, off-road | | **P275/55R20** | 31.0" | P285/50R20 | -2.3% | Performance SUV |.

**Speedometer Error Calculation**:.

**Formula**: Error % = (New Diameter - OEM Diameter) ÷ OEM Diameter × 100.

**Example**: OEM 26.0" → New 26.8" tire: - Error: (26.8" - 26.0") ÷ 26.0" × 100 = **+3.1%**. - **Impact**: Speedometer shows 60 mph, actual speed is 61.9 mph. - **Within Safe Range** (±3%).

**When Error Is Too Large** (+5% example): - OEM 26.0" → 27.3" tire (oversized). - Error: +5%. - Speedometer shows 60 mph, actual speed is **63 mph** (dangerous, inaccurate odometer, ABS issues).

**Common Tire Sizing Scenarios (2025)**:.

**Scenario 1: Winter Tires (Go Narrower)**: - **Summer Tire**: P245/45R18 (26.7" diameter). - **Winter Tire**: P225/50R18 (26.9" diameter, +0.7%). - **Why Narrower**: 225mm width cuts through snow better than 245mm (less "floating").

**Scenario 2: Truck Lift Kit (Go Taller)**: - **Stock Tire**: LT265/70R17 (31.6" diameter). - **After 3" Lift**: LT285/75R17 (33.8" diameter, +7% acceptable with lift). - **Benefit**: Aggressive look, better off-road clearance. - **Drawback**: -7% speedometer error (need recalibration), lower MPG.

**Scenario 3: Performance Upgrade (Go Wider + Lower Profile)**: - **Stock**: P205/55R16 (24.9" diameter). - **Performance**: P225/50R16 (24.9" diameter, 0% change, wider tread). - **Benefit**: Better cornering grip, no speedometer error.

**Scenario 4: Plus-Sizing for Aesthetics (Bigger Wheels)**: - **Stock**: P215/65R16 (27.0" diameter, 16" wheel). - **Upgrade to 18" Wheels**: P225/50R18 (26.9" diameter, -0.4%). - **Result**: Bigger wheel, lower profile, same overall diameter (no speedometer error).

**Tire Size Restrictions & Warnings**:.

**1.

TPMS (Tire Pressure Monitoring System)**: - **2008+ Vehicles**: Federal law requires TPMS sensors. - **Changing Tire Size**: TPMS still works, but pressure recommendations change. - **Example**: OEM 215/65R15 requires 32 PSI; upgrade to 225/60R15 may need 35 PSI (check door jamb sticker).

**2.

Rubbing Issues** (Tire Contacts Fender/Suspension): - **Caused By**: Too wide (rubs fender), too tall (rubs suspension when turning). - **Test**: Full lock steering at low speed, listen for rubbing noise. - **Solution**: Smaller tire, wheel spacers, fender rolling, suspension lift.

**3.

Warranty Concerns**: - **Dealership**: May void warranty if tire size change causes damage (rubbing wears suspension). - **Safe Harbor**: Stay within ±3% diameter, OEM load/speed ratings → No warranty issue.

**4.

Fuel Economy Impact**: - **Wider Tires** (215 → 245mm): -2 to -5% MPG (more rolling resistance). - **Taller Tires** (26" → 28" diameter): -1 to -3% MPG (heavier, more rotational mass). - **Lower Profile** (65 → 50 aspect ratio): +1% MPG (less sidewall flexing).

**Quick Reference: Find Alternative Sizes**:.

**Online Tire Size Calculators** (2025 Tools): - **TireSize.com/calculator**: Compare sizes, see diameter/speedometer error. - **WillTheyFit.com**: Visual overlay of old vs new tire. - **Tire Rack Tire Decision Guide**: Recommends compatible sizes for your vehicle.

**Key Takeaway**: Tire size code P215/65R15 95H means: Passenger tire, 215mm wide, 65% aspect ratio (sidewall height), Radial construction, 15" rim, 1,521 lb load capacity, 130 mph speed rating.

Safely swap to alternative sizes by keeping overall diameter within ±3% (±0.8" for typical 26" tire), maintaining or exceeding load/speed ratings, and matching rim diameter.

Best swaps for 215/65R15: P205/70R15 (winter, narrower), P225/60R15 (summer, wider), P215/60R16 (plus-size, requires 16" wheels).

Always calculate new diameter using: (2 × sidewall height) + rim diameter, then compare to OEM to ensure <3% change.

**Consequences of Wrong Tire Size (2025)**:.

**1.

Speedometer & Odometer Inaccuracy**:.

**How It Works**: - Your car's computer calculates speed based on **tire revolutions per mile** (OEM tire spec). - **Larger Diameter Tire**: Fewer revolutions per mile → Speedometer reads **SLOW** (shows 60 mph, actually going 63 mph). - **Smaller Diameter Tire**: More revolutions per mile → Speedometer reads **FAST** (shows 60 mph, actually going 57 mph).

**Real-World Example**:.

**Original Tire: P225/65R17** (28.5" diameter, 727 revolutions/mile): - Speedometer calibrated for 727 rev/mile.

**Scenario 1: Oversized Tire (P245/70R17, 30.5" diameter, 679 rev/mile)**: - **Diameter Change**: +7.0% (30.5" vs 28.5"). - **Speedometer Error**: +7.0%. - **Impact**: - Speedometer shows **60 mph** → Actual speed **64.2 mph**. - Odometer shows **10,000 miles** → Actual driven **10,700 miles**. - **Consequences**: - **Speeding Tickets**: Think you're going 65 mph in 70 mph zone, actually doing 69.6 mph (7% over limit). - **Warranty/Resale**: Odometer understates mileage by 7% (10k showing, 10.7k actual wear on engine). - **Oil Change Intervals**: Car says change at 5,000 miles, actually drove 5,350 miles (premature wear).

**Scenario 2: Undersized Tire (P215/60R17, 27.2" diameter, 762 rev/mile)**: - **Diameter Change**: -4.6% (27.2" vs 28.5"). - **Speedometer Error**: -4.6%. - **Impact**: - Speedometer shows **60 mph** → Actual speed **57.2 mph**. - Odometer shows **10,000 miles** → Actual driven **9,540 miles**. - **Consequences**: - **Slower Than Traffic**: Think you're doing 70 mph on highway, actually 66.8 mph (causing traffic flow disruption). - **Longer Trips**: GPS says 100 miles, odometer will show 105 miles. - **Premature Maintenance**: Car says change oil at 5,000 miles, actually only driven 4,770 miles (wasting money).

**Safe Speedometer Error Range** (Industry Standard): - **±3% Diameter Change**: Acceptable (±1 mph error at 60 mph). - **±5% Diameter Change**: Borderline (±3 mph error at 60 mph). - **>±5% Diameter Change**: Dangerous (ABS/traction control issues, speeding tickets).

**Solution (If You Install Wrong Size)**: - **ECU Recalibration**: Dealer or tuner can reprogram car's computer for new tire size ($100-300). - **Speedometer Corrector Module**: Aftermarket device adjusts signal ($150-400). - **GPS Speedometer App**: Use phone app to verify actual speed (free temporary fix).

**2.

Fuel Economy Impact**:.

**Factors Affecting MPG**:.

**A.

Tire Width** (Section Width in mm): - **Wider Tire**: More rolling resistance, lower MPG. - **Example**: 215mm → 245mm (+30mm width) = **-3 to -5% MPG**. - 30 MPG highway → 28.5-29.1 MPG. - **Cost**: Extra $150-250/year in fuel (at $3.50/gallon, 12,000 miles/year).

**B.

Tire Weight** (Overall Diameter & Construction): - **Heavier Tire**: More rotational mass, engine works harder. - **Example**: 26" OEM tire (22 lbs) → 28" oversized tire (28 lbs) = **+27% weight**. - **Impact**: -2 to -4% MPG. - LT tires (10-ply) weigh 30-50% more than P-metric (4-ply) → -5 to -8% MPG.

**C.

Rolling Resistance** (Tire Compound): - **Performance Tires** (soft compound, wide tread): -5 to -10% MPG vs all-season. - **Eco Tires** (low rolling resistance, harder compound): +3 to +8% MPG vs standard. - **Example**: Michelin Energy Saver vs Bridgestone Potenza: - Same size (P225/50R17), but Energy Saver gets **+6% MPG** (1.8 MPG improvement).

**D.

Aspect Ratio** (Sidewall Stiffness): - **Lower Profile** (50 vs 65 aspect ratio): Stiffer sidewall, less flexing = **+1 to +2% MPG**. - **Higher Profile** (75 vs 65): More sidewall flex, slightly lower efficiency.

**Real-World MPG Examples**:.

**Scenario 1: Truck with Oversized Off-Road Tires**: - **Stock**: LT265/70R17 (31.6" diameter, 55 lbs, all-terrain tire). - **MPG**: 18 highway, 14 city. - **Upgrade**: LT285/75R17 (33.8" diameter, 65 lbs, aggressive mud tire). - **Changes**: +7% diameter, +18% weight, +50% rolling resistance. - **New MPG**: **15 highway (-17%), 12 city (-14%)**. - **Annual Cost**: Extra $800-1,000/year in fuel (12,000 miles, $3.50/gal).

**Scenario 2: Sedan with Plus-Sized Performance Tires**: - **Stock**: P215/60R16 (26.2" diameter, 20 lbs, eco all-season). - **MPG**: 32 highway, 25 city. - **Upgrade**: P225/50R17 (25.9" diameter, 22 lbs, performance summer). - **Changes**: -1% diameter, +10% weight, -8% MPG (soft compound). - **New MPG**: **29 highway (-9%), 23 city (-8%)**. - **Annual Cost**: Extra $200-300/year.

**Scenario 3: Hybrid with Low Rolling Resistance Tires**: - **Stock**: P195/65R15 (25.0" diameter, eco tire). - **MPG**: 52 combined. - **Downgrade to Cheap Tire**: P195/65R15 (same size, but non-eco compound). - **MPG Impact**: **-6% = 49 MPG** (waste hybrid efficiency advantage).

**3.

Vehicle Safety Consequences**:.

**A.

ABS (Anti-Lock Braking System) Malfunction**: - **How It Works**: ABS monitors wheel speed to prevent lockup during hard braking. - **Problem with Wrong Tire Size**: If four tires have different diameters (mixing sizes), ABS sees "different wheel speeds" and may activate incorrectly or fail. - **Example**: - Front: P215/65R16 (27.0" diameter). - Rear: P225/60R16 (26.6" diameter, -1.5% smaller). - **Result**: ABS thinks rear wheels are slipping (they spin faster), activates unnecessarily → **Longer braking distances**. - **Solution**: All four tires must be within **±0.2" diameter** (ideally identical size).

**B.

Traction Control & Stability Control Issues**: - **Same Problem as ABS**: System sees mismatched wheel speeds, intervenes incorrectly. - **Example**: Truck with LT265/70R17 on front, LT245/75R17 on rear (different diameters): - Stability control constantly activates, thinking rear is losing traction. - **Consequence**: Reduced power output, rough acceleration, "Service Traction Control" warning light.

**C.

All-Wheel Drive (AWD) / 4WD Damage**: - **Critical Issue**: AWD/4WD systems split power between axles based on wheel speed. - **Mismatched Tire Diameters**: Front axle has 28" tires, rear has 27" tires → Front spins slower than rear → Transfer case thinks front is slipping → Constantly engages clutches. - **Result**: **Transfer case overheats and fails** ($2,000-5,000 repair). - **Industry Rule**: AWD/4WD vehicles must have all four tires **within ±2/32" tread depth** and **identical size**. - **Example Failure**: - 2018 Subaru Outback: Owner replaces one damaged tire with slightly different size. - After 5,000 miles: Transfer case failure ($3,500 repair, not covered by warranty due to tire mismatch).

**D.

Rubbing & Suspension Damage**: - **Too Wide Tire**: Rubs against fender during turns or when suspension compresses (hitting bumps). - **Example**: Install P245/65R17 (9.65" width) on vehicle designed for P225/65R17 (8.86" width) → +0.79" wider. - **Result**: Tire rubs fender liner at full steering lock, wears through plastic, eventually damages fender metal. - **Too Tall Tire**: Hits suspension components (upper control arm, strut tower) when turning. - **Example**: Install 33" off-road tire on stock truck suspension designed for 31" tire → Tire contacts upper control arm → Tears sidewall, causes blowout. - **Repair Cost**: Damaged suspension ($500-1,500), torn fender ($300-800), new tire ($150-400).

**E.

Brake Clearance Issues**: - **Larger Wheels with Wrong Offset**: Wheel spokes contact brake calipers. - **Example**: Install 18" aftermarket wheel on car designed for 17" OEM → Inner spoke hits Brembo brake caliper → Wheel cannot rotate, locked up. - **Solution**: Use wheel spacers (5-10mm) to push wheel outward ($100-200), but reduces load capacity.

**F.

Load Capacity Reduction (Wrong Load Index)**: - **Dangerous Mistake**: Install tires with **lower** load index than OEM. - **Example**: - OEM Spec: P235/65R17 **104H** (1,984 lbs per tire × 4 = 7,936 lbs total capacity). - Installed: P235/65R17 **100H** (1,764 lbs per tire × 4 = 7,056 lbs total capacity). - **Vehicle Weight**: 4,500 lbs + 1,200 lbs passengers/cargo = **5,700 lbs** (within capacity). - **Problem**: Load index 100 tires operate at **81% of max capacity** (5,700 ÷ 7,056) → Excessive heat buildup, premature wear, increased blowout risk. - **If Overloaded to 7,500 lbs**: Tires operate at **106% capacity** → **Blowout risk on highway** (catastrophic failure at 70 mph).

**G.

Speed Rating Downgrade (Safety Risk)**: - **Example**: - OEM Spec: P225/50R17 **94V** (V = 149 mph speed rating). - Installed: P225/50R17 **94T** (T = 118 mph speed rating). - **Problem**: Car is capable of 135 mph (sports sedan), but tires rated for only 118 mph. - **Risk**: Driving 120+ mph → Tire overheats, tread separates, blowout. - **Even if You Don't Speed**: Speed rating also indicates overall tire quality (high-speed tires have better heat dissipation, stronger construction).

**4.

Warranty & Insurance Consequences**:.

**A.

Manufacturer Warranty Void**: - **Scenario**: Install oversized tires (33" on stock truck), causes rubbing that damages CV axle. - **Dealer's Response**: "Aftermarket tire modification caused failure, not covered by warranty." - **Out-of-Pocket**: $1,200 CV axle repair.

**B.

Insurance Claim Denial**: - **Scenario**: Accident caused by ABS malfunction due to mismatched tire sizes. - **Insurance Adjuster**: Finds different tire sizes on front vs rear → Determines you modified vehicle unsafely. - **Result**: **Claim denied**, you pay $15,000 damage out-of-pocket.

**C.

Resale Value Impact**: - **Trade-In**: Dealer sees oversized tires with rubbing damage on fenders. - **Offer**: $2,000 below market value to account for fender repair and suspension wear.

**5.

Tire Wear Patterns (Wrong Size)**:.

**A.

Cupping/Scalloping** (Mismatched Diameters): - **Cause**: AWD system constantly engaging due to front/rear tire size mismatch. - **Result**: Tires wear unevenly in wavy pattern, noisy at highway speeds, need replacement at 20,000 miles (vs 50,000 OEM lifespan).

**B.

Center Wear** (Overinflated to Compensate for Wrong Size): - **Cause**: Install wider tire (245mm on 7" rim designed for 225mm), overinflate to 40 PSI (vs 32 OEM) to prevent squirming. - **Result**: Center of tread wears 2x faster than edges, need replacement at 25,000 miles.

**C.

Edge Wear** (Underinflated Due to Wrong Load Index): - **Cause**: Install light-duty P-metric tire on heavy truck (should use LT-metric), sidewalls flex excessively. - **Result**: Outer edges wear 2x faster, tire fails at 15,000 miles.

**6.

Legal Consequences** (State Inspections):.

**States with Vehicle Inspections** (2025): - **Strict States**: MA, NY, PA, VA, TX, CA (SMOG), etc. - **Tire Size Rule**: Some states fail inspection if tire size differs from door jamb placard by >5%. - **Example**: Massachusetts rejects inspection if oversized tires cause speedometer error >10% (safety hazard).

**7.

How to Avoid Wrong Tire Size Issues**:.

**Step 1: Check Door Jamb Placard**: - **Location**: Driver's door jamb (silver sticker). - **Info**: OEM tire size, load index, speed rating, inflation pressure. - **Example**: "P225/65R17 102H, Cold Pressure: 32 PSI Front, 30 PSI Rear.".

**Step 2: Use Tire Size Calculator** (Online Tools): - **Input**: OEM size (P225/65R17) + Alternative size (P235/60R17). - **Output**: Diameter difference (+0.3%), speedometer error (+0.3%), width difference (+10mm). - **Verdict**: Safe swap (within 3% diameter).

**Step 3: Consult Tire Dealer** (Tire Rack, Discount Tire): - Provide vehicle VIN → They lookup OEM size → Recommend compatible alternatives. - **Free Service**: Most dealers won't sell incompatible sizes (liability risk).

**Step 4: Test Fit Before Buying**: - **Ask Dealer**: "Can I test-fit one tire to check for rubbing?" - **Full Lock Test**: Turn steering wheel full left/right while parked, listen for contact noise. - **Bump Test**: Drive over speed bump at slow speed, ensure no rubbing on suspension.

**Quick Reference: Tire Size Change Consequences**:.

| **Change** | **Impact** | **Severity** | **Fix Cost** | |------------|-----------|--------------|--------------| | **+7% Diameter** | Speedometer -7%, odometer understates | Moderate | ECU recalibration $200 | | **Mismatched Front/Rear (AWD)** | Transfer case failure | **SEVERE** | $2,000-5,000 repair | | **Lower Load Index** | Blowout risk when loaded | **SEVERE** | Replace all tires $800+ | | **Lower Speed Rating** | Blowout at high speed | **SEVERE** | Replace all tires $800+ | | **Too Wide (+30mm)** | Rubbing, -3-5% MPG | Moderate | Fender rolling $300 | | **Too Tall (+2 inches)** | Suspension contact, rubbing | High | Lift kit $1,500 or smaller tires |.

**Key Takeaway**: Installing wrong tire size causes speedometer inaccuracy (±7% diameter = ±4 mph error at 60 mph), fuel economy loss (wider/heavier tires = -3 to -10% MPG), and serious safety risks (ABS/traction control malfunction, AWD damage $2,000-5,000, blowout from low load rating).

Stay within ±3% diameter change, never downgrade load index or speed rating, ensure all four tires match on AWD vehicles (within 2/32" tread depth), and check for rubbing before installing wider/taller tires.

Use online tire size calculators to verify compatibility and consult OEM door jamb placard for correct specifications.