Surprising discovery

[wie]

Recently I noticed how fast I am with one arm crawl.
One arm crawl I mean one arm constantly in front, the other crawling.

So, today I looked at the clock and found this:
50 m normal crawl, all out: ca. 40 s (kick off from the edge)
50 m one arm crawl: ca. 50 s (changing sides ca. every 8th pull)

Question: Is this normal?
I suspect that this is because I am swimming more on the side in one arm crawl and therefore am better streamlined.