Want to go faster? Its you not the bike. By the sound of it your always going at the same pace effort. You need to increase cadence and effort over short periods to improve.
INTERVALS at 90-100% MHR:
1 to 2 minutes. Recovery 1 to 5 minutes. Repeat from 3 up to 10 times. Depending on fitness and period. High cadence 100 – 105 rpm.
INTERVALS at 90 – 95% MHR:
3 to 5 minutes. Recovery 5 to 10 minutes. Repeat from 3 up to 10 times. Depending on fitness and period. Heavy gear, up hill at cadence of 80 to 90 rpm.
Note the effort and cadence required
If you want to go faster then train harder and measure what your doing HRM, power meter etc. I find turbo is the best for this sort of training. You can go hard and not worry about the road. Join a road club. 180 miles couple weekends ago club run average 18 mph. Lots of fast sections and hills in Wales.