There are several things that "everybody knows" about changing website addresses (URLs). For two months, I tracked the changeover of a large and complex site to a new URL. This gave me an opportunity to verify, without bias or guesswork, exactly how the process occurred.
Each day I tracked:
Number of pages indexed by Google under the old URL
Number of pages indexed by Google under the new URL
Page Rank (PR) of the new URL
Organic search visits from Google (and any change in this on same-day-previous-
week and month-to-date comparisons.
I also periodically reran (every 1-2 weeks) Google rankings for over 200 search terms under the old and the new URLs.
Conclusion? These rules hold up very well:
1. Use 301 redirects and Page Rank will transfer.
2. Rankings are likely to dip somewhat, for a period of time during the transition but should recover rather quickly.
3. The whole changeover can take a few weeks.
4. Overall site traffic should not suffer.
We actually found it took nearly two months for the process to complete. By that time, the new URL was being fully indexed, and had the rankings for all but two of the search terms.
One reason for the lengthy changeover was we didn?t initially catch all the places where the old URL was referenced in internal links! We also initiated changing of external links to show the new URL.
The overall effect of the changeover on traffic to the site was minor. On a same-day-last week comparison, over the course of the two months, the site lost only 15 visits from Google.
One interesting phenomena was the number of pages re-indexed by Google. It spiked way up after we made the change, but it has continued to run way above the previous norm for a long time afterwards.
It became clear that Google visits, revisits, and re-re-visits pages several times before fully effecting this kind of change.
For example, it was 11 days after we initiated the changeover that Google showed the site?s home page under the new URL. At this point, however, it still had over twice as many pages indexed under the old as the new URL. It was a full month before the index showed more pages under the new URL. It was another three weeks before the number of pages indexed under the new URL stabilized.