Let me start off by saying that all I am trying to do is help you (the original poster) out. This isn't the 41, I'm not going to tell you to HTFU and deal with it. I'm trying to analyze the perceived problem and help you come to a proper solution. That said, here we go:I just input your gearing and tire size into an on-line calculator. If you were pedaling with a cadence of 120 in 2/5 (38/18) you should be seeing a speed of 20.5mph. You say that you're doing around 12.5mph, which would actually put you around 70-75 for cadence.2/6 for you is 38/15. At a cadence of 60, you'd be doing around 12.3mph, which isn't too far off from your average speed.I don't think that you need another gear. I believe you think that you need another gear because you are uncomfortable riding at higher cadences. If you want to see 15mph at 60RPM, use 48/15 (3/6). If you want to see 15mph at 90RPM, use 38/18 (2/5).
After running the numbers, I stand by what I said earlier: you're cadence is much lower than you think it is. My suggestion would be to ride more and become more comfortable riding at a higher cadence. Installing a new cassette will, in my opinion, be a waste of money and time because your current goals are completely attainable with your current setup.
In the attached link, please find the spreadsheet data with regard to your current setup:
http://www.machars.net/bikecalcs.php...s=mph&call=xls
Please see my response to the original poster above. The numbers do not lie.
For the record, I did read the original poster's post (I read all of yours too, even though your posts are somewhat hard to read). I suggest that you read mine and learn something about gearing instead of suggesting that someone waste money on unnecessary gearing changes. I'm not trying to sound harsh, but suggesting that myself and the others didn't read the original post is rather rude, and I take offense to it.