The tyrestore Upsize calculator for your tyres

Well if all that maths seems a little beyond you, and judging by the volume of e-mails we get on this subject, we've made a little Javascript application below to help you out. Select the tyre size you currently have, and then the size you're interested in. Calculate each tyre size and then click on the Click to calculate the difference button. It will show you all the rolling radii, circumferences, percentage differences and even speedometer error. Happy Upsizing!.

Current wheel/tyre	New wheel/tyre
145 155 165 175 185 190 195 205 215 225 230 235 245 255 265 275 285 295 305 315 325 335 / 30 35 40 45 50 55 60 65 70 75 80 82 85 100 R 12 13 14 15 15.5 16 16.5 17 18 19 19.5 20 21 22 23	145 155 165 175 185 190 195 205 215 225 235 245 255 265 275 285 295 305 315 325 335 / 30 35 40 45 50 55 60 65 70 75 80 82 85 100 R 12 13 14 15 16 16.5 17 18 19 19.5 20 21 22 23
Current RR:mm	New RR:mm
Current circumference:mm	New circumference:mm
Difference in circumference:mm or %
Tyrestore recommends an Upsizing only if the difference if less than 2%
So when your speedo reads 70mph, you're actually travelling at mph

A Speedometer error means an odometer error too.

It stands to reason that if you change the rolling radius of your wheels and tyres, and the speedometer no longer reads correctly, that your odometer will also gradually become inaccurate. Assume for example that you bought a car brand new and changed the wheels and tyres on day one from 195/65R14 to 205/50R15 - not an uncommon change. By the calculator above, that makes your speedometer over read by 1.7%. Consequently, the registered odometer reading will also be out by the same value. So for example, when you get to 10,000km of driving (in the real world), your odometer will actually read 10,170km. OK so that's not a huge difference but it is one of the reasons why most car dealers have a disclaimer on their secondhand vehicles telling you that they won't guarantee the displayed mileage. ("Clocking" the odometer is the other reason). Odometer errors due to mis-matched tyres and wheels will happen on regular odometers as well as the newer digital ones.

Introducing the new Rim Upsize calaulator!

The correct tyre upsize has to be complimented with the correct Rim Upsize for optimal performance. For more details walk into Siremull Hirachand's Tyrestore, Greams Road, (Behind TVS Kohinoor 2 wheeler showroom) Chennai, India Ph: +91 9840920870 / 044-28294589 Email:tyrestore@vsnl.net