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2.8″ tires are a bit too wide for rims with 30mm internal width. That said, the combination could still work to a satisfactory level.

If maximum performance is needed, going for a narrower tire or a wider rim will be necessary so that the shape of the tire remains as intended by the manufacturer.

Understanding Rim Width

A rim has two widths – internal and external. The external width represents the total width of the rim while the internal is the distance between the bead hooks of the rim. (The bead hooks are the element to which clincher tires attach.)

In most cases, the indicated rim width in product descriptions is the internal one as it has a direct effect on the type of tires that the unit can accept.

Sometimes, people add the letter “i” before the width to indicate that the mentioned width is the internal one. (e.g., an i30).

There’s a direct correlation between internal rim width and the supported tire width. (The wider the tire, the wider the rim is expected to be.)

A Formula For Determining Rim and Tire Compatibility Based On Width

The general rule is to multiply the inner rim width by 2 to 2.3.

If the inner rim width is 30mm, this formula gives us a range between 60 and 69mm or 2.35 to 2.72 inches.

A tire in that range will be ideal for a rim of such inner width. That said, some deviations are allowed without facing degraded performance.

It’s also worth noting that tire sizes aren’t incredibly accurate. For example, a 2.8″ model from one brand could be narrower or wider than that of another.

Based on the formula above, we get the following table for rim and tire compatibility:

FAQs: What are the downsides of combining a 2.8″ tire with a i30mm rim?

30mm rims are slightly too narrow for a 2.8″ tire. When a rim is too narrow, the tire tends to “sit high” because the rim isn’t wide enough to stretch the tire.

The downside of a rim that sits high is the possibility of it rolling to one side when cornering.

Think of the tire as a lever acting against the rim. A tire that sits high is a longer lever. When the rider corners, his weight and that of the bike exert force on the tire (lever). If the tire rolls, traction is lost and a fall may occur.

To prevent this outcome, it’s necessary to pump the tires to higher air pressure. The narrower a rim is, the greater the air pressure has to be to prevent the tire from “folding” when cornering.

In the case of a 2.8″ tire and an i30 rim, excessive tire folding isn’t expected, especially when the air pressure is adequate.