Tire Dimensions

• What is the exact circumference of my tire?
• Why is it that tires are often actually narrower than the ETRTO tire section width?
• Will the tire fit my frame?
• Which tire fits which rim?
• Can I use a narrower rim?

What is the exact circumference of my tire?

In order to accurately program a bicycle computer it is generally necessary to enter the exact tire circumference.

The tire circumference varies depending on the rim, the tire pressure and the load on the tire. For these reasons, it is not possible to list exact tire circumferences. In order to accurately program a bicycle computer, we recommend a simple rolling test with the rider on the bicycle.

The approximate tire circumferences for the most common sizes are listed in the table below.

Why is it that tires are often actually narrower than the ETRTO tire section width?

Standard tire widths are calculated using fairly wide, standard rims. Yet in practice, narrower rims are used more often, which in turn leads to tires becoming slightly narrower as well.

In order to ensure that tires have sufficient frame clearance, tire
manufacturers generally prefer to keep production closer to the lower end of the permitted tolerance (+/- 3 mm).

Carcass casing materials have become more and more sophisticated over time, that reduces the tire widening after the fitting. In order to correct this tire widening, over the past few years slightly wider carcasses have been used, so that the actual widths are now much closer to the standard widths.

Will the tire fit my frame?

The question whether tires will fit into a particular frame is often asked in relation to our ultra-wide tires.

It is easy to appreciate that with the large number of different bicycle models it is impossible to check the compatibility of all framesand tires.

The following list shows the exact diameters and widths of our ultrawide tires. This should allow you to identify if there is sufficient frame clearance for the selected tire.

Image
A = max. width
B = max. diameter
C = diameter at max. width

Which tire fits which rim?

The inner diameter of the tire must match the rim bead seat diameter. For instance, a tire size 37-622 fits on a 622 x 19C rim. The inner diameter of the tire corresponds to the rim bead seat diameter of 622 mm.

Furthermore, the tire width must match the rim width. The following table shows possible combinations of tire widths and rim widths according to ETRTO.

Since 2006, the combination of extra wide tires and narrow 17C and 19C rims is officially approved by ETRTO. This just caught up with reality, because this combination has already been an every day occurance in MTBs and Balloonbikes for many years and has not caused any problems.

Often the use of a wider rim is useful because it brings additional stability to the tire. The tire pressure can be reduced slightly before the stability becomes “spongy”.


European Tire and Rim Technical Organization Standards Manual - 2007

Can I use a narrower rim?

Wide tires are often fitted on narrower rims, as with Mountain Bikes, and also our BIG-APPLE tire. This saves weight, but it is also because very few wide rims are actually available in the market.

The rim manufacturer should be consulted before such fitment and only if they judge it safe. In order to prevent excessive stress on the rim, we advise not to inflate the tire to maximum pressure.

As a general guide, MTB tires of say 54 mm width fitted on standard 17C and 19C rims should not be inflated to more than 55 psi. Very wide tires of ca. 60mm fitted on narrow rims should not be inflated to more than 45 psi. Under no circumstances should rims of less than 17 mm be used.