On this page, the following information is given.


  Use a roll out method ie measure circumference with a mark on the tyre
  and roll forward one exact revolution measure with a tape measure the
  distance covered preferably sat on bike, then put dimension into the
  custom setting for wheel size, youtube shows a good example.


According to the manual linked to by @Batman, it looks like you can enter a custom wheel size after you have clicked through all the predefined wheel sizes. Based on the fact that it's 4 digits, the custom wheel size is most likely in mm. 

Another way of calculating the circumference, is to take wheel diameter (total distance across, and multiply by pi (3.14).  If you don't have any measuring device and want something reasonably close, take the bead seat diameter, for 650B, this is 584mm, add in 2 times the tire size. Assuming you have 2 inch tires, that's 50.8 mm. So we end up with 584 + 2 * 50.8 = 685.6 mm diameter, and when multiplying by pi gives us a circumference of 2152.8 mm.

Bike computer wheel size setup
I have created a module and EAV tables for that. Module's tables are very similar to customer_Address entity and i have defined Attribute AttrA, AttrB and AttrC for this table. 

So table structure is very similar to as follows:

+------------------+----------------------+------+-----+---------------------+----------------+
| Field            | Type                 | Null | Key | Default             | Extra          |
+------------------+----------------------+------+-----+---------------------+----------------+
| entity_id        | int(10) unsigned     | NO   | PRI | NULL                | auto_increment |
| entity_type_id   | smallint(5) unsigned | NO   |     | 0                   |                |
| attribute_set_id | smallint(5) unsigned | NO   |     | 0                   |                |
| increment_id     | varchar(50)          | YES  |     | NULL                |                |
| parent_id        | int(10) unsigned     | YES  | MUL | NULL                |                |
| created_at       | timestamp            | NO   |     | 0000-00-00 00:00:00 |                |
| updated_at       | timestamp            | NO   |     | 0000-00-00 00:00:00 |                |
| is_active        | smallint(5) unsigned | NO   |     | 1                   |                |
+------------------+----------------------+------+-----+---------------------+----------------+


and AttrA, AttrB and AttrC values are stored in tables with respective data type.

Now using the basic syntax, I am able to add value of attributes AttrA, AttrB and AttrC. Which is:

$model = Mage::getModel('customer/address');
$model-&gt;setAttrA('ValA')-&gt;setAttrB('ValB')-&gt;setAttrC('ValC');


doing this correctly sets the values of AttrA, AttrB and AttrC but value of parent_id in customer_entity sets to NULL by default.

Here I want to be able to set the parent_id to some other value. 

For this i tried suggestion given in different post using setParentId(&lt;parent-id-value&gt;). Which is not working in my case. Any idea how i can do this?
