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.


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!


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


356 thoughts on “Visual Tyre Size Calculator”

  1. i have a golf 4 motion with 8j on the fron and 10.5 on the rear.. i have 255/35/19 on the rear but need an a tyre for the front with the same raduis so not to wind my diff up and break it… cant get very big tyre on the front due to catchin…. can you please help

  2. Can I replace 195/65/15 stock tires on my new honda civic with 205/65/15. What difference will it make on the fuel economy, suspension, height & acceleration??

    1. Kamran & Haider,

      You should be fine running 205’s instead of 195’s. The tyre wall will be a little taller giving you a slightly more comfortable ride but you’ll get more sidewall flex meaning handling during cornering is affected.

      Although we’re talking 6.5mm difference in the sidewall height here so I doubt you’ll even notice the theoretical differences I have mentioned above.

    1. Hi Neeraj, the rolling radius label should actually read “circumference”. It was an oversight when I built this version of the calculator. I should probably just change it and make an incremental release rather than waiting till I finish the new version…

  3. I have a mitsubishi galant 2.0liter GLS 1999 with alloy wheeels size:195 65 R14.
    I have just bought similar car 2001 with a converted alloy wheels size :215 45 R17.
    I have checked this and ended up with small difference from the original size, something like 2cm.
    Should this be ok or not??. please advise me as matter of urgency, as i am trying this car on the motorway, and seems to loose power after a speed of 70m/hr. Not sure if the wheel conversion has any thing to do with it??
    Please reply to my private email listed above

    1. Your new tire is 2.7% bigger than the stock, and the limit is 3. For fuel consumption, generally speaking, the % of the new wheel total weight must be divided in 2 to get the effect on the fuel consumption.

      So, if your new wheel is 20% heavier, you’ll need 10% more fuel for the same distance than the stock wheel.

  4. Please advise me on the following query.
    I have a car with a converted wheel size from 195 65 R14 to 215 45 R17
    Should this have any detrimental effect on the car?
    Please write back direct on my email address above.

    1. Hi Muhanned, the wheels will not be causing the power loss. While it is true that larger wheels have a greater rotational inertia and this affects acceleration… but it is still slight.

      I would suggest the problem is more likely to be the engine, possibly fueling related as you could be running lean. Maybe the fuel pressure regulator, blocked fuel filter, knackered fuel pump or lambda sensor. If its air/fuel related then also check your MAF or MAP sensor.

  5. I want to know if i can switch from 245/70R/16 to a 265/70R/16 on my jeep grand cherokee or if this will cause a drastic difference.

    1. Sidewall height will increase, more sidewall flex and the tyres themselves will look a little more rounded on the rim due to the increased width but I don’t imagine it would be a huge problem. Unless you do offroading in which case it could make the tyres more susceptible to popping off the rims? I’m not a jeep/offroader person so as I’ve said before always consult you local tyre specialist before parting with your hard earned cash 😉

  6. Will a change from 205/50/R15 to 195/55/R16 be OK.

    I realise that the car will be a little higher off the ground which is fine, but will I have any problems due the the overall diameter being larger?

    1. The obvious things to check would be for clearance in the wheel wells. You’ll have less of a ground contanct patch with those wheels tho so you may find the handling is compromised slightly.

  7. Hi, I am going to change my rims and tyre siza and want to know if it is ok with the sizes. I have a Rover 400 and present size is 185/60/14. I got rims R15 7J and think of adding 195/55/15 tyres. I saw on calculator that difference is 3,1%. I want to know if this combination is ok to follow as I am trying to escape from too low profile tyre as my suspension will broke faster. Also sppedometer is not a problem as now is showing 7km mor then real speed on 100km/h. Thank you in advance.

    1. The new tyre profile will result in a greater overall diameter of wheel & tyre but you’ll have a shorter sidewall. It’ll look better but there will be less sidewall flex, so if you felt the ride was harsh before it is likely to be moreso with the new tyre profile that you are looking at.

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