Re-developed site, need to keep previous rankings

Our client has an established presence on search engines (outside of pay per click marketing) for some of their outer product pages (static). As we are completely redeveloping their web site to include a new database driven shopping system, all these pages are disappearing. So: will they immediately lose all their current ranking or perhaps no longer be ranked at all?

Has anyone had experience with this? What is the best course of action to keep their current ranking in the search engines?

Regards
David

The chance of losing rankings is very high.

The best solution is to rewrite your dynamic urls so that they match the previous static urls.

If you cannot do this redirect the static URLs using server side 301 redirects to the new dynamic URLs.

I was afraid of this. It is going to mean a lot more work...

What about a general redirect? Eg. all Levi's pages and subpages redirected to the new Levi's brand page.

it won't maintain your subpage listings, but it would help the homepage.

Thanks Chris