How much speedometer error do bigger tires cause?

Every 1" increase in tire diameter creates roughly 3% speedometer error. Stock 31" tires to 35" tires = 12.9% error. That means at a GPS-verified 79 mph, your speedometer only shows 70.

Can I get a speeding ticket for speedometer error?

Yes. Law enforcement uses radar/laser, not your speedometer. If you're actually going 79 in a 70 zone, the ticket stands regardless of what your dash says. Calibrating after a tire change is the responsible move.

What's the best way to fix speedometer error?

For most trucks and Jeeps, a performance tuner like the Superchips Dashpaq+ or HP Tuners is the easiest fix at $300–$600. It reprograms your PCM and also corrects shift points and ABS calibration. Dealer reflash is another option at $100–$200.

Does speedometer error affect my odometer?

Yes. If your speedo reads 12.9% low, your odometer under-reports mileage by the same percentage. Over 15,000 miles per year, that's nearly 2,000 miles of phantom 'free' mileage, which also affects resale value and maintenance intervals.

Interactive Tool

Speedometer Calibrator

See exactly how far off your speedometer is after bigger tires, and get the right fix.

Quick Answer: Going from 31-inch to 35-inch tires creates a 12.9% speedometer error: your speedo reads 70 mph when you are actually doing 79. It also throws off the odometer, shift points and ABS. Enter your sizes below to see your exact numbers and the fix options.

HOW IT WORKS

Enter Tire Sizes

Input your stock and new tire diameters using sliders or exact sizes

See the Error

View speedometer error, actual speed at 70 mph, and annual odometer drift

Get the Fix

Compare tuner, calibrator, and dealer reflash options for your vehicle

Enter Your Tire Sizes

Stock Tire Diameter

32"

New Tire Diameter

35"

Speedometer Error

+9.4%

Your speedometer reads slow, you're going faster than indicated

Speedo says 30 mph

32.8 mph actual

Speedo says 70 mph

76.6 mph actual

Odometer error/year

1286 miles lost

Indicated vs actual speed

Indicated (mph)	Actual (mph)
30	32.8
40	43.8
50	54.7
60	65.6
70	76.6
80	87.5

Correction Values for Your Device

Correction ratio:1.0938

Percentage:109.4%

Increase:+9.4%

Need a diameter from a size like 285/70R17? Use the tire size calculator.

How to Fix It

Three ways to correct a 9.4% speedometer error

Performance Tuner

$300–$600

Pros

Corrects ALL systems (ABS, TC, trans)
Performance gains included
Adjustable for future tire changes

Cons

Higher cost
Potential warranty concerns
Vehicle-specific

Best for: Modern trucks (2015+) wanting performance + correction

Inline Calibrator

$100–$200

Pros

Low cost
No ECU modification
Transferable between vehicles

Cons

Only fixes speedo/odo
May not correct ABS/TC
Wiring splice required

Best for: Older vehicles or budget-focused builds

Dealer Reflash

$50–$200

Pros

100% warranty-safe
Corrects all systems
No hardware needed

Cons

Not all dealers offer it
Limited tire size options
May refuse modified vehicles

Best for: Warranty-critical or factory-option tire sizes

Read Full Calibration Guide

At 9.4% error, these systems are affected:

• Transmission shift points• ABS activation thresholds• Traction control intervention• Stability control calculations• Cruise control accuracy• Fuel economy display• Tire pressure monitoring• Odometer accuracy

Interactive Tool

MPG Impact Calculator

Estimate fuel economy loss from bigger tires, lifts, and roof racks with annual cost projections

Calculate MPG Impact

Speedometer Calibrator

HOW IT WORKS

Enter Tire Sizes

See the Error

Get the Fix

Enter Your Tire Sizes

Indicated vs actual speed

How to Fix It

Performance Tuner

Inline Calibrator

Dealer Reflash

MPG Impact Calculator

RELATED CONTENT

Speedometer Calibration Guide

Re-Gearing 101

Tire Size & MPG Impact

33s, 35s, or 37s, Everything Changes

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