People with cluttering (PWC) often receive feedback, such as "Slow down!", even so, this fluency disorder cannot be cured by only slowing down the speakers' speech rate. When PWC accelerate their speech rate, language planning difficulties and word structure errors might occur, which might result in breakdowns in fluency and/or intelligibility. In the present paper characteristics of the frequency of disfluencies were examined in four different speech tasks from deliberately slow to maximum speech rate, whether speech rate changes have effects on cluttered speech. Twenty participants of this investigation were individuals suspected of cluttering with ages between 20 and 50 years of both genders. The results show that PWC are able to change, not only their speech rate but articulatory rate as well. Moreover, disfluencies were produced the most frequently in the speech task of maximum speech rate, where PWC do not have enough time for speech planning. The research provides empirical, measured data for a better insight into the nature of cluttering. Understanding the correlation between speech rate and disfluencies in cluttered speech is fundamental to improve the diagnosis of cluttering.