freeway

Hello all, first-time poster. I'm a fairly casual rider, my stock '09 DRZ400SM is the first bike I've owned and it's a ton of fun so far. I live in the city riding every day to work, and love it. One of my few gripes with it is how much the engine screams on the freeway. From what I read, plenty...

so i was ridin on the freeway the other day and i was pinned in 5th and my speedo read 81 mph. i am running 21 18" rim sizes yet i still have the speedo chuck that is meant for the 17" front rim. so basically i am goin faster than what it reads. how fast do you guys think i was goin