Mod Description
Whether you want to use wider tyres on your standard alloys or match the original rolling radius with your new alloys, the data is here.Mod Details
PremiumNo Difficulty
Mod ID780
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Linkhttps://www.evilution.co.uk/mod/tyre-dimension-information.htm Copy to ClipboardTyre Calculator
There are very good online tyre calculators already so I don’t think I need my own. Click here
Tyre Width Information
Depending on the width of the alloy, you have a range of tyre widths you can choose.
It is important not to exceed the minimum or maximum widths.
| Rim width | Minimum tyre width | Ideal tyre width | Maximum tyre width |
| 3.5 inches | 125 mm | 135 or 145 mm | 155 mm |
| 4.0 inches | 135 mm | 145 or 155 mm | 165 mm |
| 4.5 inches | 145 mm | 155 or 165 mm | 175 mm |
| 5.0 inches | 155 mm | 165 or 175 mm | 185 mm |
| 5.5 inches | 165 mm | 175 or 185 mm | 195 mm |
| 6.0 inches | 175 mm | 185 or 195 mm | 205 mm |
| 6.5 inches | 185 mm | 195 or 205 mm | 215 mm |
| 7.0 inches | 195 mm | 205 or 215 mm | 225 mm |
| 7.5 inches | 205 mm | 215 or 225 mm | 235 mm |
| 8.0 inches | 215 mm | 225 or 235 mm | 245 mm |
| 8.5 inches | 225 mm | 235 or 245 mm | 255 mm |
| 9.0 inches | 235 mm | 245 or 255 mm | 265 mm |
Adapted from Pneus-Online
It is also very important that if you increase the width of the tyre, you decrease the profile.
The profile number (width/profile/diameter) is a percentage of the width. That means if you go wider with the same profile, the tyre will be taller. A good rule of thumb is for every 10mm you increase the width of the tread, decrease the profile by 5. For example, if you start with 175/55/15 on a 5″ wheel, the maximum width according to the table above is 185 so you should go for 185/50/15.
This is because the traction control unit expects the wheels to rotate at approximately the same speed. If a pair of tyres are much larger or smaller in diameter than the other 2, the car thinks it’s skidding. You will then get the traction control light on and the car will be down on power and may not accelerate.
Tyre Profile (Side Wall)
Because of the horrendous suspension on the smart, some people increase the height of the tyre side wall to give a bit more deflection. The extra height of the tyre allows a bit of extra movement before it goes into the suspension.
Obviously, increasing the tyre side wall size will increase the over all diameter of the tyre. You can’t go too mad with the over-size or the tyre will start touching the wheel arch during suspension travel and other steering components during steering.
Tyre side walls are listed as a percentage of the tread width so a 205/45/15 will have a tread width of 205mm and the side wall will be 45% of that. In this case, 92.25mm.
The side wall number increases in 5’s. 45, 50, 55, 60 etc. You will be safe just increasing your current side wall size by 5. You might just about get away with increasing it by 10…..MIGHT!
The important part of changing the side wall size is that the circumference of the front and rear tyres are similar. The car measures the rotational speed of all 4 wheels. If it sees the wheels not all rotating about the same speed, it thinks the car is skidding and will activate the ESP/ABS. If you stick massive tyres on the back and leave the normal tyres on the front, the rear tyres will rotate slower than the front.
Try to match the front and rear tyre circumference so the difference is less than 2.5%. The easiest way to know if to use a tyre comparison calculator like this. Click here.
Putting on larger tyres will also affect the speedo reading. It’s recommended that you double check your actual speed with GPS against the speed shown on the speedo once you’ve fitted larger tyres as you could be going faster than indicated.
Tread Depth
Taken and adapted from Nick’s Tyres Essex.
The legal minimum tread depth for car tyres in European is 1.6mm throughout a continuous band comprising of the central three quarters of the breadth of tread and round the entire outer circumference of the tyre. Most car tyres have tread wear indicators, usually at least six small ribs across the bottom of the main tread grooves, and when the tread surface becomes level with these ribs the tyre is at the legal limit and must be replaced.
Simple and cheap gauges are widely available to give an acceptable guide to tread depth.
One of the features of tyre tread pattern design is to give good grip in wet conditions. Generally speaking, available grip reduces as the tyre wears or as the road surface water depth increases. You should reduce speed in such conditions.
Nicks Tyres is in Brentwood and Chelmsford and is my local tyre shop. They are very helpful so if you live in the area, check them out for their services.
Tread Wear Indicators
Here is a nearly new tyre. Inside the tread, across the middle 75%, dotted around the circumference of the tyre are raised indicators.
And this is an old tyre. You can see that the tread wear indicators are flush with the rest of the tyre face meaning that the tyre is too worn and is illegal.
Tyre Calculator
There are very good online tyre calculators online so I don’t think I need my own.