combobox width problem

this is my code :

Code:

 xtype: 'combobox',                                    editable: false,
                                    fieldLabel: 'Fatura Saati',
                                    emptyText: '0',
                                    store: Ext.create('Ext.data.Store', {
                                        fields: ['FTR', 'TIM'],
                                        data: [
                                            { 'FTR': '', 'TIM': '0' },
                                            { 'FTR': '', 'TIM': '1' },
                                            { 'FTR': '', 'TIM': '2' }
                                        ]
                                    }),
                                    displayField: 'TIM',
                                    valueField: 'FTR',
                                    margin: '10 7 0 0 ',
                                }

if i added this code line "width : 70(or higher , or lower than)" combobox is too little, look like this pic :

i am waiting answer for this problem ty

combobox width problem