I've been doing more and more riding on my road bike recently due to the S**T summer and time basically. Now I get that a higher cadence is better for using less energy but what would a good average cadence be for longer rides (30+ miles)

Higher cadence doesn't mean less energy.

It's about keeping your body working at it's most comfortable rate. Some people are happier pushing hard on the pedals and turning the crank relatively slowly. Others prefer less effort but at a higher rate of turn. Both may be expending similar energy.

On a road bike I prefer a cadence around 90rpm and will do my best to maintain this (unless I run out of gears) no matter what the terrain does – uphill or downhill. I find the higher cadence is better for my knees 😀

Mark Beaumont (round the world cyclist) has an astonishingly high cadence. Lance Armstrong pedals quite quickly too.

But I think it's all down to individuals, and how your muscles work best.

lala lovers would tell you 90rpm. Which is probably what I seem to do.

TBH, do whatever feels comfortable, rather than what you think you should be doing – the old boys who turned massive gears slowly were still jolly quick.

30 miles isn't a "longer" ride! That's barely a warm up..!

Don't worry about comparing yourself to anybody else, just try and stay smooth. If you are pushing on just give yourself an easier gear as soon as you feel the resistance building, especially on inclines. In my mind the main benefit of a higher cadence is that it keeps you below your lactate threshold for longer and keeps you smooth which avoids wasted energy – this may be nonsense.

For me anywhere between 95 – 105rpm is comfortable for road riding. If going flat out I often get above 110rpm which I can keep up for extended periods upwards of 30 mins. Don't know if this is either "good" or "bad", it's just what I do.

The flipside of prefering a high cadence is that I tend to suffer when the revs drop below 70rpm and I'm trying to deliver power, i.e. uphill on a road bike! I'm starting to cure this but building leg strength (a combo of spinning at the gym and hilly climbs) and have found new speed on and off-road as a result. 😀

Towards the end of winter I tend to work on quite a lot of high cadence road work (>100rpm) as well as overgeared work (often SS MTB climbs sat down)

The net result of both types of session is pretty positive, as your body essentially becomes accustomed to spinning bigger gears really.

I had a mate that I used to ride with, I am basically chunky in build he (literally) a marathon runner.

Oddly I preferred c.90 rpm, he was much slower & grinding a lower gear. Generally similar result but if I had been asked to guess it would have been the other way around.

Whatever you are comfortable with

lala lovers would tell you 90rpm. Which is probably what I seem to do.

Though to be fair 90rpm has been the figure mentioned for as long as I can remember, and probably for as long as the people before me.
Incidentally why do people call Lance lala? What's the reference to?
Interestingly it's also the recommended figure for running. My hunch is that is where it came from. Presumably it's based on some combination of natural pendulum frequencies and spring stiffness in running, and as it would then seem to be the a speed our legs are optimised to move at, it transposes well onto cycling.
I find changing cadence can be quite a handy way of transferring loads to different bits of the body, so I find that a high cadence is easy on the legs but hard on the heart and lungs, but dropping the cadence seems to put more load on the legs but less on the lungs for a given speed. Not sure that there's any proper evidence to support that though.

Whatever you're happiest with.
Loads of people will quote 90rpm at you with no real idea of where this figure came from or how it was worked out, it's acquired similar status to the "220-age" bollocks that people spout for calculating max HR.

Personally I find a lower cadence more comfortable which is why I use standard (39/53) gearing on my road bike, I'll happily sit there at 75rpm for hours and will get up hills no worries on 50rpm a lot quicker than the poor souls sat there spinning away at 90rpm in silly low gears.

Just ride the bike and find out what you're comfy with.

I've just checked my Garmin Connect account and my Average Cadence for the past 365 days is 66RPM

Count:
126 Activities
Distance:
2,332.28 mi
Time:
225:42:06 h:m:s
Elevation Gain:
229,634 ft
Avg Speed:
10.3 mph
Avg HR:
135 bpm
Avg Run Cadence:
—
Avg Bike Cadence:
66 rpm
Calories:
170,323 C
Max HR:
201 bpm
Avg Elevation Gain:
1,822 ft
Max Speed:
53.3 mph
Avg Distance:
18.51 mi
Avg Time:
01:47:28 h:m:s

60 is generaly considdered too low, 120 is too high, between those two just find whats comfortable, generaly going slightly faster than you'd imagine seems to be considdered best as it pumps the blood out of your vains quicker, thus removing lactic acid quicker.

Find a long, straight and completely flat stretch of road (or a constant climb). Ride allong it at a given heart rate, say 155bpm, and find a comfortable cadence, shift up a gear, alter your cadence to keep the heart rate constant, does your speed rise or drop. Shift up/down untill you get the highest speed and you'll find your most efficient cadence.

One tip is to imagine that there is an egg (hen's) between your foot and the pedal. For spinny cadences, you should not be pushing down on the pedals hard enough to break the egg. The exact cadence doesn't matter.
The result of spinning is that you shift the workload from your legs onto your heart and lungs, which are better able to cope with the strain for long periods.

The thing I don't quite get about the high cadence though is this:

If I was on an exercise bike with no load and did 3 hours turning my legs at 90rpm I'd be a lot more tired than if I'd sat there turning them at 50rpm.

why do people call Lance lala

I guess it's that his initials are L A, but if you called him "La" you'd sound like a scouser.