Originally Posted by cyclezen

a heart rate of the mid to upper 170s, for almost all riders, would mean they're getting into an anerobic state. It's not a on/off switch, so some can motor on for quite some time, others (like me) have to back off after some time. Pros can stay at that rate while in a peloton at 30+ mph. Riding alone they'll likely be able to keep up at 26-28 mph (road not TT equipped). Everyone else less so.
Francesco Moser maintained an avg 174 for his hour record (30 yrs ago...), velodrome, TT position, 51.15 kph for the hour.

If you are 'maxed' when you ride at that heart rate, then that's prolly right...
If you're not feeling 'maxed', then I would check your Heart Monitor, because the reading is likely very much off...

Whatever speed you can maintain, on a roadie, flat with no preceivable headwind (other than apparent wind) is a factor of your fitness. To ride faster, you need to train (ride more often) at faster paces, and spend more time 'near' that AT/LT.

You can use zones, or use a determined 'LT/AT' and ride near that.

Weight only means something relative to overall structure/mass (and climbing). I know a few guys who can motor well on flats, and are 20-25 lbs heavy for their frame... but bog down on the uphill.

18-19 is a really solid, good 'average' for a ride, but if that's just a velocity number that you see when you're HR is in the 170s, then not so great.

heart rate zones - meh... they can be guidelines for training, but you can do the same even if you don't put numbers in 'zones.

if I'm riding 130s-140's HR, I'm likely out for a steady, longish ride and not lookin to stress myself, enjoying the bike time. If I'm staying 150 to 165, I'm mostly hammering when I can and humpin up every uphill I can find...

for comparison - if I'm on mostly level terrain, small ring (39), riding a mid to upper 70 inch gear, at 19.5/20 mph, my heart rate is gonna be 145 ish - I'm 65, 165 lbs, 5' 10.5" and currently lacking much in the way of miles or riding time (currently about 100-120/wk...) If I was riding more and harder, the heart rate at that pace would be 140 ish...
My Last tested AT/LT (last year, with a bunch of strong miles in the legs) was at HR 163/164..., now more likely to be at 160 ish...

need to ride harder/stronger/faster to be faster. ride in a fast experienced group, do intervals, spend one day a week attacking longer, harder climbs, at your strongest effort, get rid of the extra lbs. These all have worked for me.

Don;t get me wrong about zones and Heart rates. I believe strongly in heart rate based training. I just don't do the II, III, IV thing...

EDIT... FYI, I have Afib , so I don't do much time at 178 or above - at 180ish+ my Afib often kicks in... Once I hit the mid 170s, its just a matter of minutes before I back off - per my doc' recommendations), but doin the weekly hammerfest is still in the cards - I just suck more wheel than I used to...