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Loan Calculator
Works out the monthly payment, total interest and full repayment schedule for any loan from…
Tire Size Calculator
Compares two tyre sizes for overall diameter, sidewall height, ground clearance and speedometer error.
Calculators
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No sign-up
Free, unlimited
Enter your figures and press Calculate.
In short
Tire Size Calculator is a free online tool on inputtesthub.com that compares two tyre sizes for overall diameter, sidewall height, ground clearance and speedometer error. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Tire Size Calculator
- Enter your figures in the input fields.
- The result updates as you type, together with the full working.
- Check the breakdown table to see exactly how the number was reached.
About the Tire Size Calculator
The Tire Size Calculator compares two tyre sizes for overall diameter, sidewall height, ground clearance and speedometer error. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Checking a plus-size wheel and tyre change.
- Working out how far the speedometer will read out.
- Comparing ground clearance between two sizes.
Details
| Usual tolerance | ±3% diameter |
|---|---|
| 205/55 R16 | 632.7 mm diameter |
| Beyond 3% | Speedometer, ABS and ESC affected |
| Load and speed rating | On the door placard |
The maths behind it
This tool uses Overall diameter = rim in mm + 2 × (width × aspect ÷ 100). Speedometer error is the ratio of new to original diameter. Every intermediate value is shown on screen, so the result can be checked by hand.
Three per cent is the usual tolerance because the speedometer, odometer, ABS and stability control are all calibrated to the original rolling circumference. Check clearance at full lock and full suspension travel, and match at least the original load and speed ratings.
Frequently asked questions
Can I put a different size tyre on my car?
Within about 3% of the original overall diameter, usually yes — beyond that the speedometer, odometer and stability systems read wrong. Also check clearance at full steering lock and that the load and speed ratings match the door placard.
How much does tyre size affect the speedometer?
Directly. A tyre 2% larger makes the speedometer read 2% low, so an indicated 100 km/h is really 102. The calculator shows the true speed at an indicated 100 for any pair of sizes.
Does the Tire Size Calculator cost anything?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the utility.
Is what I paste into the Tire Size Calculator stored?
No. The Tire Size Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses Overall diameter = rim in mm + 2 × (width × aspect ÷ 100). Speedometer error is the ratio of new to original diameter. The full working is printed under the result, so you can follow every step rather than trusting a black box.
When would I actually need the Tire Size Calculator?
In practice it gets used for three things: checking a plus-size wheel and tyre change. Working out how far the speedometer will read out. Comparing ground clearance between two sizes. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there a catch?
Three per cent is the usual tolerance because the speedometer, odometer, ABS and stability control are all calibrated to the original rolling circumference. Check clearance at full lock and full suspension travel, and match at least the original load and speed ratings.
What figures does the Tire Size Calculator work from?
Usual tolerance is ±3% diameter. 205/55 R16 is 632.7 mm diameter. Beyond 3% is Speedometer, ABS and ESC affected. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.
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