Tyre Size Calculator - A Handy Tool Perhaps?

[Imbiber]

In light of recent tyre discussions and the ongoing supply problems for certain size tyres I looked into the possibility of changing the tyre size for our motorhome.

Conscious that I needed to match the overall diameters to ensure the ride height and gearing / speedo don't change I located the following useful Calculator.

+ / - 2.5% is considered the maximum difference in diameters and this calculator offers suggestions well within those tolerances.

NB: It appears to be an American website but the calculations are transferable.

Thought it might be a useful starting point for those struggling to find replacement tyres in a sufficient timescale.

Tyre Size Calculator

 

[funflair]

But it would most likely require different rims as well as for example any change in aspect ratio will require a different width to give the same rolling circumference, then of course you need to check for clearance on suspension components.

Not straightforward.

Martin

 

[Imbiber]

But the calculator factors all that in?

It provides the alternate tyre sizes you can switch to from your present tyre and offers a visual tyre size comparison alongside speedo errors.

I appreciate height may be an issue but at least its a starting point for considering alternate options.

 

[tacr2man]

Rims might not need changing , as there is usually a range of rim width allowable for a particular tyre width . You can usually find on tyre manufacturer websites.
eg

 

[pappajohn]

The only one I can calculate is 225 75/15 to 205 75/16 which give a Speedo error of around 1 mile per hour slower than shown against the first size at all speeds.

It is not a simple calculator.
A simple calculator would show all equivilent sizes for a given (original) size.

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[tonyidle]

It's also worth knowing your actual speedo error before you start. Mine was a full 10% on my last van. Even going from 15" to 16" wheels and using a greater width at the same aspect ratio would have been fine.