Visual Tyre Size Calculator

If you are thinking of changing your car tyre size or are planning on buying a new wheel/tyre combination then you can use the flash tool below for a visual tyre size comparison of your stock wheel and tyre size versus your new wheel and tyre combination.





Got a comment or question regarding the current version of the tyre size calculator? Click here to leave a comment or ask a question.

Vesion 2 of the tyre size calculator is in development, if there’s anything you’d like to see in version 2 then please feel free to leave a comment here: Tyre Size Calculator V2: Wishlist.

Why is this important?

Matching the combined wheel and tyre diameter is important as it will ensure your ride height and speedometer readings don’t change drastically. An example of this would be fitting 17″ wheels to a car that has 14″ wheels as standard, there are three main consequences:

  1. the ride height will change, the car body will be further from the ground.
  2. the top speed will increase slightly and the speedometer will under read.
  3. the car will accelerate slower.

Read on to see the reason for this in detail.

Tyre Size Guide

Ride Height

Take the default example in the flash tyre size calculator above, here we have a stock tyre size of 165/55R14 and a new tyre size of 215/45R17. There is a total difference of 8.82cm in the two wheel and tyre diameters, if we divide this by two we get a difference in radius of 4.41cm. If we ignore tyre pressures and the effects of adding larger, wider wheels to suspension geometry; then this is roughly how much higher the car will be from the ground.

Speedometer

Then there’s the speedometer, a cars speed reading is usually taken from the transmission and is set based on a number of predefined constants. When you change your wheel and tyre combination you are taking one of these constants and making it variable. The speedometer does not know the new value and so continues to read based on the original wheel & tyre size. If you look at the above default example again you will see that with a 215/45R17 wheel and tyre combination there is a difference of 16.4% in the speedometer reading over the stock setup. As you can see, at 60mph your speedometer should actually be reading 69.9mph!

Acceleration

If we fall back to the default example again, the 215/45R17 wheel and tyre combination has a larger overall diameter by 8.82cm. A larger diameter has a greater rotational inertia which requires more energy to accelerate. Or in other words: the bigger the wheel, the slower the acceleration.

It should be noted that putting a bigger wheel and tyre combination on your car does not reduce your cars power. Your cars power remains the same; however it takes more force to turn your car’s wheels resulting in slower acceleration.

Tyre Width Equivalency Table

You may also find the following table of recommended tyre widths for given rim widths useful when changing your tyre width.

Rim width
Min tyre width
Ideal tyre width
Max tyre width
5 .0 inches
155 mm
165 ou 175 mm
185 mm
5.5 inches
165 mm
175 ou 185 mm
195 mm
6.0 inches
175 mm
185 ou 195 mm
205 mm
6.5 inches
185 mm
195 ou 205 mm
215 mm
7.0 inches
195 mm
205 ou 215 mm
225 mm
7.5 inches
205 mm
215 ou 225 mm
235 mm
8.0 inches
215 mm
225 ou 235 mm
245 mm
8.5 inches
225 mm
235 ou 245 mm
255 mm
9,0 inches
235 mm
245 ou 255 mm
265 mm
9.5 inches
245 mm
255 ou 265 mm
275 mm
10.0 inches
255 mm
265 or 275 mm
285 mm
10.5 inches
265 mm
275 or 285 mm
295 mm
11.0 inches
275 mm
285 or 295 mm
305 mm
11.5 inches
285 mm
295 or 305 mm
315 mm
12.0 inches
295 mm
305 or 315 mm
325 mm
12.5 inches
305 mm
315 or 325 mm
335 mm

via pneus-online.co.uk

356 thoughts on “Visual Tyre Size Calculator”

  1. I am planning to change my stock tyres 275/45R19 to 255/55R19. some people recommend not to change sizes more than 3%. I am safe to change to 255/55R19

    1. Hi Garry, 3% usually relates to one width up or down e.g. 285 or 265 for your 275 width tyre. However I have heard a few tyre fitters say that if the new tyre width is 0 to 1 inch wider or narrower than your rim width then you should be safe, 1 inch to 2 inches and your pushing it, and if the difference is over 2 inches you’re unsafe.

      Assuming your rim is 10 inches wide I would expect a width of 255 would be fine but I would say a 255/50R19 would be better as it minimises any speedo error. If your rim is any wider then I would say 255 tyres aren’t worth the risk and always check with your tyre fitter before purchasing… don’t rely on my work as I’m far from perfect 😉

      You may also find the following table of recommended tyre widths for given rim widths useful when changing your tyre width.

      Rim width
      Min tyre width
      Ideal tyre width
      Max tyre width
      5 .0 inches
      155 mm
      165 ou 175 mm
      185 mm
      5.5 inches
      165 mm
      175 ou 185 mm
      195 mm
      6.0 inches
      175 mm
      185 ou 195 mm
      205 mm
      6.5 inches
      185 mm
      195 ou 205 mm
      215 mm
      7.0 inches
      195 mm
      205 ou 215 mm
      225 mm
      7.5 inches
      205 mm
      215 ou 225 mm
      235 mm
      8.0 inches
      215 mm
      225 ou 235 mm
      245 mm
      8.5 inches
      225 mm
      235 ou 245 mm
      255 mm
      9,0 inches
      235 mm
      245 ou 255 mm
      265 mm
      9.5 inches
      245 mm
      255 ou 265 mm
      275 mm
      10.0 inches
      255 mm
      265 or 275 mm
      285 mm
      10.5 inches
      265 mm
      275 or 285 mm
      295 mm
      11.0 inches
      275 mm
      285 or 295 mm
      305 mm
      11.5 inches
      285 mm
      295 or 305 mm
      315 mm
      12.0 inches
      295 mm
      305 or 315 mm
      325 mm
      12.5 inches
      305 mm
      315 or 325 mm
      335 mm

      via pneus-online.co.uk

  2. My Corsa had a bad wobble between 20-30mph and I noticed one wheel never ran true (had a slight flat spot on rotation).
    I got a new tyre and during rebalancing found the wheel was 20g out. Also during the re-fit I noticed a 4″ flat spot on the alloy rim itself which the tyre shop said wouldn’t cause the wobble because it wasn’t bad enough. Re-fitted the new tyre and balanced perfectly the wobble has reduced a lot but is still there, only now it is between 35-40mph.

    Anyway….I’m convinced the flat spot on the alloy is the problem, so have found a new one with a 195/50/R15 tyre fitted.

    My originals are 185/55/R15 and the difference would be 8mm lower.

    Assuming the new alloy is perfectly round, will this cure the wobble regardless of the new or old tyre fitted?

    Currently got 185/55/R15 on a Corsa but got a flat spot on the alloy which I think is causing a wobble around 40-45mph. (wheel balanced perfectly)
    I have found a new alloy with a 195/50/R15 tyre and worked out it is only 8mm lower. If the alloy is perfectly round will that cure the wobble, even if I keep / change the tyre?

    1. Hi Eddie,

      Whatever caused the flat spot may have affected your tracking so you should probably have that checked too. The new alloy should have the odd size tyre removed and a 185/55R15 fitted before you put it on the car, especially if its a drive wheel.

      Of course it may not be limited to just that, have a look at this good Popular Mechanics article which might help:
      Diagnosing And Repairing Wheel Vibration

    1. Hi, I expect your plus will have 15 inch wheels, I know that the Ford Fusion can have up to 17 inch wheels as standard (or factory fit options) on the higher specced models. If the car is still in warranty then I wouldn’t advise going any larger than that and to try and keep the wheel width and offset the same as the standard 17″ ford options. This should stop you voiding your warranty as some dealerships can be very picky about non standard parts.

  3. Hi, how is this tyre size calculator help if i want to change just the rim size? I want to change the alloy rim of my corolla seg from 14 to 15 or 16. Will it affect the speedometer and accelaration too?

    1. Not necessarily Eric, as you increase the size of the rim you would usually decrease the profile of the tyre that you fit. For example a 14 inch wheel with 165/55R14 tryres fitted would have the exact same rolling radius as a 15 inch wheel with 195/40R15 tyres.

      Of course, the tyre size 195/40R15 may not exist, go to an online tyre company like blackcircles.com and you can search to see if that size exists, if that size isn’t available you can fiddle with the calculator till you find a size that is and doesn’t affect the speedo too much.

      Hope that helps.

  4. I have changed cars and where I currently live we must by law to put on winter tyres on the our car between end of October to End of April, my old winter car tyres are 205 55 R16 (from a Jag x-type) my new car tyres are 225 55 R16 (Audi A4 Avant), my question is can I use my old cars winter tyres on the new car if they are still in good condition?

    1. Your old tyres might be stretched a fair bit depending on the Avant’s wheel width. Its a difficult one to answer with out knowing the widths of the wheels.

    1. You should be fine at that, although it does depend on the width of your wheels. If you know the width of your wheel then you can scroll down this page a bit to find a Wheel Width/Tyre Size table to help you make a descision.

      Unless your certain I would advise consulting your local tyre fitter before buying new tyres.

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