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:
 the ride height will change, the car body will be further from the ground.
 the top speed will increase slightly and the speedometer will under read.
 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

hi, can you tell me what the difference in mm’s would be from a trye with a profile of 50 to one with a 60 profile please, assuming that they are 15″ rims and 195 in width.
Easy, 195mm width, 50% of the width gives the wall, 15” rim diameter. In a wheel total diameter you have walls and 1rim:
195mm 2×50% 15inches
195mm 100% 15”
195mm 195mm 15”
New tire:
195mm 2×60% 15inches
195mm 120% 15”
195mm 235mm 15”
235195=40, so your new tire is 40mm bigger than the stock one.
But, the rule for bigger tires is max 3% bigger in total diameter, and your new tire is almost 7% bigger so I really don’t recommend it.
Hope it helps
How much effect on riding quality does tyre size have (particularly wall thickness)? Say 245/45 R17 against 255/50 R127 tyres, which would give the softer ride on the same suspension?
@Barry: As a rule of thumb a bigger sidewall will often have a softer ride. In your example, if you were comparing a 245/45R17 Toyo Proxes to 255/50R17 Toyo Proxes the 50 profile tyre sidewall will be 17mm deeper, and assuming all tyres were made equal they would offer the more comfortable ride while sacrificing a tiny amount of handling due to the increased sidewall flex. However all tyres aren’t equal and there are variances in rubber compound and construction that could make a difference.
Hope that helps 🙂
I have a 2005 BMW 7 Series and the Tyre Size is 275 34 R20. I also have a set of Tyres from my old 1997 BMS 7 Series which I have now sold. Would I be able to use my old wheels and tyres on my new car. They are 235 60 R16
@Malcolm: There actually isn’t a whole lot of difference between the two sets of wheels & tyres in terms of overall rolling radius; your old 16″ wheels being a little under 4cm shorter with those tyres. What you would need to watch is the PCD, Center bore and offsets of the two sets of wheels. I believe that BMW are pretty consistent with their PCD/Center bores which are usually 5×120 and around 72mm for the C/Bore I think, although you should check because I’ve been wrong before. The offset will almost certainly be different as there is a 40mm difference in width between the two sets of tyres.
I’ve a visual offset calculator that would help if I ever got round to finishing it, but off the top of my head (and without checking offsets) I expect your old wheels and tyres would fit but sit fairly deep inside the arches.
I hope thats of some help.