Speedometer way off... :S

[AlmightyHeretic]

So I ordered a mini speedometer from JP Cycles a few weeks ago and finally got it all set up today. I did a little test run in the driveway and it was putting me at 25 just after I hit second gear. I took it out on the highway and sure enough, it's way off. It was showing 110mph while cars were pulling away from me in a 55mph zone. I'm using the stock cable and though it's not tight, it's not loose. I ran it the cleanest path I could straight to the speedo. Is the speedo bad or should I have looked for a specific spec when I was ordering? I don't think there's anything wrong with the cable since it was hooked up to the stock speedo a couple weeks ago and running accurately.