# Tire Size Comparison Calculator

> Compare two tire sizes side by side, including diameter change, revs per mile, and speedometer error.

**Category:** Math
**Keywords:** tire, wheel, diameter, circumference, comparison, automotive, speedometer
**URL:** https://complete.tools/tire-size-comparison

## How it calculates

The calculations in this tool are based on the following formulas: 
1. Diameter = (Tire Width × Aspect Ratio × 2) ÷ 100 + Wheel Diameter. 
2. Revs per mile = 63360 ÷ (Diameter × π). 
3. Speedometer Error (%) = ((New Revs per Mile - Original Revs per Mile) ÷ Original Revs per Mile) × 100. 
In these formulas: 
- Tire Width is the width of the tire in millimeters. 
- Aspect Ratio is the ratio of the tire's height to its width, expressed as a percentage. 
- Wheel Diameter is the diameter of the wheel in inches. 
- π is approximately 3.14159, a constant used in circular calculations. 
These relationships help users understand how changes in tire size influence vehicle performance and speedometer accuracy.

## Who should use this

1. Automotive technicians assessing the impact of tire size changes on vehicle performance. 
2. Racing engineers optimizing tire specifications for competitive vehicles. 
3. Fleet managers determining appropriate tire sizes for different vehicle usages. 
4. Off-road vehicle enthusiasts selecting tires for varying terrain. 
5. Mechanics performing vehicle modifications needing precise tire data.

## Worked examples

Example 1: A user wants to compare a tire size of 225/65R17 with 245/70R17. 
- For the first tire, Diameter = (225 × 65 × 2) ÷ 100 + 17 = 28.5 inches. 
- For the second tire, Diameter = (245 × 70 × 2) ÷ 100 + 17 = 29.5 inches. 
- The diameter change is 29.5 - 28.5 = 1 inch. 

Example 2: A user has a vehicle with original tires of 215/60R16. 
- Revs per mile = 63360 ÷ (Diameter × π) = 63360 ÷ (27.2 × 3.14159) ≈ 736. 
Now, they change to 225/65R17. 
- New Diameter = 28.5 inches. Revs per mile = 63360 ÷ (28.5 × 3.14159) ≈ 703. 
- Speedometer Error = ((703 - 736) ÷ 736) × 100 ≈ -4.49%. This indicates the speedometer will read approximately 4.49% lower than actual speed.

## Limitations

This tool assumes that the tire width, aspect ratio, and wheel diameter are input correctly, as any inaccuracies in these values lead to incorrect calculations. It does not account for variations in tire manufacturing, such as actual tire height differences due to load or wear. The calculator also assumes a uniform tire profile, which may not apply to all tire designs. Additionally, it does not consider the effects of tire pressure, which can affect the actual diameter and ride height. Lastly, the tool does not factor in the real-world performance impacts of different tread patterns or materials.

## FAQs

**Q:** How does tire aspect ratio affect vehicle handling?


**A:** The aspect ratio influences the sidewall height, which can affect ride comfort and handling. A lower aspect ratio typically provides better handling but a harsher ride.


**Q:** Why is it important to know revs per mile?


**A:** Revs per mile helps in calibrating speedometers and odometers, ensuring accurate speed readings and mileage tracking, which is critical for maintenance and performance assessments.


**Q:** What could lead to inaccuracies in speedometer error calculations?


**A:** Inaccuracies can arise from incorrect tire specifications, variations in tire profile due to manufacturing differences, or changes in tire pressure affecting the diameter.


**Q:** How do tire diameter changes impact fuel efficiency?


**A:** Larger tires can lead to a higher rolling resistance, potentially reducing fuel efficiency, while smaller tires may improve it due to lower resistance but can affect handling and stability.

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*Generated from [complete.tools/tire-size-comparison](https://complete.tools/tire-size-comparison)*