The combobox displays a blank field by default even though the combobox is populated with a number of values
ColumnSpeed.DataSource = speedList;
ColumnSpeed.ValueType = typeof(string);
I also tried the following, but it still displays the blank text.
foreach (DataGridViewRow row in myDataGridView.Rows)
{
    DataGridViewComboBoxCell cell = row.Cells[ColumnSpeed.Index] as DataGridViewComboBoxCell;
    if (cell != null)
    {
        cell.DataSource = speedList;
        cell.Value = cell.Items[0].ToString();
    }   
}