Bead diameter & Rim diameter

[Kasrawy]

Hi all, sorry if this has been asked before but if it was I couldn't find it anywhere here. I just wanted to know the difference between the specified bead diameter on say... Hoosier's tires and the rim diameter of the same tires, I'm not talking recommended values here, I'm talking pure semantics.

[Zac]

Both will be controlled by Tire and Rim Association standards.

[Kasrawy]

could you elaborate please?

[Zac]

The geometry of both the rim flange and the tire's bead area is dictated by TR&A (or ETRTO in Europe), a trade association that sets some standards on tire size, wheel geometry, and loading (for a given size and pressure).

The tire will be undersized compared to the rim though.

[Kasrawy]

Please excuse my repeatedly asking questions like this, but after I researched the matter I understand that the rim diameter and bead diameter are very similar, but despite that fact Hoosier states on their 20.5x7.0-13 tires that the rim diameter is 8". How could this be when the bead diameter is stated as 13"?
Thank you for your time Zac, I appreciate it http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Zac]

you're confusing rim diameter and rim width.

[Kasrawy]

I see that now, thanks for your trouble.