Negatives:

• It only shows up to 10 terms for any search term and does not give any sort of search volume estimate.
• Only shows terms that specifically start with the letter sequence you type it. This will not help you find related searches that have modifiers before the core term. On a positive note this does make it easy to see what are the most common ending modifiers for plural and singular versions of search terms.
• Like most Google products they are not particularly clear how this data is organized.

ABC Tires:
For my ABC Tires example Google Suggest recommended 10 different terms, (and a few more for A B C tires) and about 75% of their suggestions led to conversions.
Google Keyword Sandbox:
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