Sidewall indentation is a cosmetic problem in monoply tires. To improve the indentation, we modeled two simple indentation phenomena. We also evaluated an actual indentation depth in inflated tires using several textile cords of different moduli.
We used two models of sidewall indentation. One was that the indentation occurs in tires having the same cords applied to the carcass. In this case the indentation depth had a strong relationship with cord modulus. Another is the case where a higher elongation cord than that of a nonsplice region was used at a localized splice region. In this case the depth was expressed by an equation including the moduli and a number of cords.
The indentation depth could vanish theoretically at the modulus ratio of 0.5 between splice and nonsplice regions (Es/Ens = 0.5).
The above prediction is verified by experiments on the actual sidewall indentation for given tires having a specific construction. The indentation depth minimized at the ratio of elongation at specified load (EASL) of splice and nonsplice region of 2.0 or the modulus ratio of 0.5 (EASLs/EASLns = 2.0 or Es/Ens = 0.5).