What is a tire calculator for? How to read the results?

Tire calculator - in what situation it will be useful Useful when you do not know what alternative size of wheels and tires to put on your car. Based on the results, you will know whether the option you have planned can be installed and how it will affect the driving performance of the car. 

The replacement has nothing to do with a lower quality product. We are talking about a departure from the model proposed by the manufacturer in favor of another product. In some cases, of course, such a change may be associated with additional inconvenience. A size converter will come in handy to help troubleshoot any issues.

What does the tire selection calculator look like?

You can find various interchangeable calculators on the Internet. The most important fields to pay attention to are:

• tire width;
• tire diameter;
• tire profile.

After filling in these values, the program will show you the proposed models. On what basis are substitutes chosen?

What does the tire size calculator take into account?

When choosing a specific tire or rim diameter, the choice of substitutes will certainly be limited. The program takes into account the tire selection criteria and shows you several options from which you can choose. It works on the basis of basic principles known to every vulcanizer. One is to account for the change in percentage range of tire and rim size.

This range is small, from -2% to +1,5% tire size difference. What does it mean? This is best illustrated with an example. Let's say your car has 175/55 R15 tires and you're looking for a slightly lower profile but the same rim size. What options can you consider? The program will offer you the following options:

• 195/50 P15;
• 215/45R15.

In both cases, the percentage difference in size is within the expected range of 0,4% and 0,2%, respectively. Basically, nothing will change when it comes to tire sizes. Why does the tire size calculator take into account precisely such ranges of change and does not offer other options?

Tire replacement should be chosen wisely

Driving safety is influenced not only by the selection of tires of the right quality, but also the right size. Suppose that the manufacturer has provided wheels with 205/50 R17 tires in your car. It's pretty big for a car. The dimensions of the brakes, specifically the discs, are also one step behind. Can you put the R20 rim option on your car without any problems? Of course, if the suspension components allow it. However, in this case, expect the replacement to be sized, for example, 215/30.

Every tire size change, with or without a calculator, has consequences. Here, in addition to a very attractive appearance and good driving performance, one has to take into account the greater appetite of the engine for fuel, increased noise and the high price of tires.

Tire height calculator and safety

Why doesn't the tire calculator include tires outside the -2% to +1,5% range? In older types of cars without security systems, this decision is dictated by the convenience and the ability to install this type of wheel on the hub. In newer models, the correct operation of ESP and ASR is also important. The program allows you to find models that will not have a serious impact on the operation of these systems.

The popular ESP system, i.e. track stabilization when cornering, depends largely on the quality and size of the tires. Its task is to slow down one or more wheels when a skid is detected, which allows you to get out of it safe and sound. It is easy to guess that after installing wheels that differ significantly in type and size from those provided by the manufacturer, the car may behave uncontrollably. This is because tires of different widths also have different traction. Loss of traction can make driving difficult. For this reason, it is worth following the indications regarding the diameter of the wheel.

Tire calculator and speed question

The tire option you choose, based on the tire size calculator, will affect your driving experience and comfort on the road. You may be surprised, for example, when the speedometer shows different readings than before while driving. What is the reason? The outer diameter of the wheel differs from the original version set by the manufacturer.

It's better to use another example. If your vehicle was previously fitted with homologated 205/55 R16 rims and tires, the outer diameter was 63,19 centimeters. The program will indicate a replacement that will not exceed a percentage range of -2% to +1,5%. The minimum diameter that will not affect the speed change is 61,93 cm and the maximum diameter is 64,14 cm.

When you exceed the upper limit set for tires, you will notice that the speedometer reading is higher than usual. When changing to smaller rims and lower tires, the speed will be reduced. This is important when driving at the maximum permissible speed, for example, in built-up areas.

Tire replacement calculator - what else is worth paying attention to?

There are several other parameters to consider when choosing replacement tires. One of them is their load capacity, which is denoted by the symbol LI. This is the maximum weight that falls on one tire. This value should not be exceeded as it has a significant impact on safety while traveling. Even if you find a replacement tire that suits you in terms of size and price, pay attention to their load capacity.

What else should you consider? The speed index is important, with a one- or two-letter symbol, which is always followed by the load index. The letters indicating the maximum allowable speed on the bus are not in alphabetical order, so you need to decipher their meaning. 

On city cars, you will most often see the symbol T, which means that the tires can reach a maximum speed of 190 km / h. Incorrect selection of the speed index carries the risk of damaging the tire during fast driving, shortening the service life and increasing the braking distance.

The diameter of the circle, or how to decipher the symbols?

To work with such a program, you need to know the basic nomenclature associated with meaningful values. Of course, anyone with even the slightest interest in the automotive industry knows that rim diameter is given in inches, tread width in millimeters, and tire profile (height from rim to tread) as a percentage. Each of these values ​​are in different units, so you need to standardize them to find the result.

1 inch equals 2,54 centimeters. Therefore, it is easy to calculate that the popular R16 wheels have a diameter of 40,64 cm. If the tread width is 205 mm, it is very easy to convert it to centimeters - this is exactly 20,5 cm. 

What's with the profile? The program will cope when you enter a percentage value into it, but this may not be enough when calculating on your own “on foot”. Let's say your tires have a profile of 55. This means that the profile height is 55% of the tread width, in this case 11,28 cm. The outer diameter of the wheel takes into account the rim size (40,64 cm) and twice the profile height (22,56 cm ). These values ​​give a diameter of 63,2 cm.

Tire change table - needed when you don't want to count

If you don't want to count on foot, the tire change table comes to the rescue. Below we have analyzed the most popular tire size for city cars (195/55 R15) and suggested alternatives in accordance with the regulations. You don't need to thank.

Tire conversion factor for variant 195/55 R15

What is the outside diameter of this wheel? This is 38,1 + 21,45 = 59,55 cm. Translated into millimeters - 595,5 mm. What is the maximum size range within +1,5%? 604,43 mm. The minimum, however, is 583,59 mm. Here is a tire change for size R15:

• 135/80 (+0,2%);
• 165/65 (0%);
• 175/60 ​​(-0,8%);
• 185/55 ​​(-1,9%);
• 185/60 (+1,2%);
• 205/50 ​​(-1,6%);
• 215/50 (+0,1%).

However, that's not all, because there are not only instances with the same rim diameter. Now some examples for size R14:

• 145/80 ​​(-1,3%);
• 155/80 (+1,3%);
• 165/70 ​​(-1,5%);
• 165/75 (+1,3%);
• 175/70 (+0,8%);
• 185/65 (+0,1%);
•  195/60 ​​(-1%);
• 205/60 (+1%).

And what results will you get if you enter larger options into the tire calculator? Here are examples for R16 rim:

• 175/55 (0,6%);
• 185/50 ​​(-0,7%);
• 195/50 (+1%);
• 205/45 ​​(-0,8%);
• 215/45 (+0,7%);
• 225/40 (-1,6%)

But that's not all, because if the design of the car allows, then even R17 wheels can be put on the car:

• 195/40 ​​(-1,3%);
• 205/40 (0%);
• 215/40 (+1,4%);
• 225/35 ​​(-1%);
• 245/35 (+1,3%).

An interesting fact is that the percentage difference rule applies to 205/35 R18 tires in this case.

Changing tires - why is it a safe form of tire selection?

As you can see, the choice is really great. It may happen that among the proposed models there will not be your choice, although you have seen car designs on the Internet that successfully drive, for example, on such a rim size and with such a tire profile. So who to believe? The fact that such tires are placed in the wheel arch does not automatically mean that driving such a vehicle is convenient and safe. Tuners often focus primarily on the appearance of the car, and not on the safety of driving, so keep this in mind. If you really want to deviate from the standard option, use only the substitutes indicated by the program.