Iowa Code Title VIII. Transportation [Chs. 306-330B] § 321.440. Restrictions as to tire equipment

a. Any part of the ply or cord exposed.

b. Any bump, bulge or separation.

c. A tread design depth of less than one-sixteenth of an inch measured in any two or more adjacent tread grooves, exclusive of tie bars or, for those tires with tread wear indicators, worn to the level of the tread wear indicators in any two tread grooves.

d. A marking “not for highway use”, “for racing purposes only”, “unsafe for highway use”.

e. Tread or sidewall cracks, cuts or snags deep enough to expose the body cord.

f. Such other conditions as may be reasonably demonstrated to render it unsafe.

g. Been regrooved or recut below the original tread design depth, excepting special tires which have extra under tread rubber and are identified as such, or if a pneumatic tire was originally designed without grooves or tread.