Geoff reminds us that Chuck has bashed out a pretty awesome century a few years ago, which I had forgotten about. He did a geared 36" road century in 6h57m - 7h02m (he didn’t time the non-riding time, so it is an estimate, but still plenty faster than anyone else I know about).
My best one was 8h05m on moderately hilly roads, with ungeared 36/102mm. I did the first 100 miles of my 24 hour track record in 7h05m (ungeared, 36/90mm) but that doesn’t really compare well against rides on real roads with hills etc. - I am more interested by real ‘going for a ride’ centuries… but official records for IUF or Guinness have to be on measured tracks for good reasons.
I am mulling over having a crack at the official (IUF + Guinness) 100 mile record next year. It’ll be on a geared 36 and a nice large track. I have no idea what time to aim at yet.
Sam
I’d aim at 6:40 and work my way down from there. 
Some of you might find this amusing, but when I ordered my 45" big wheel in 1981, I had thoughts of tackling the 100 mile record that existed at that time. It was 10:37 and was set by Cathy Fox (yes, a woman!) in 1980 on a 40" Tom Miller big wheel. So I ordered a 45" wheel.
But it took Tom a whole year to complete the order, by which time the record had dropped to a much faster 9:20 and I was discouraged. Plus you have to remember we’re talking Schwinn seats, no handlebar technology, nobody was wearing bike shorts yet, etc. 
So it only took me another 30 years to get to my first century ride…
I’m still trying to find a nice track before I decide to go all out and train a bunch. I have yet to find anything nice in the area. I’ve been interested in trying to set the record for a while…
I’m making my unicycle century attempt this Sunday (finally!) morning on the Chief Ladiga - Silver Comet paved rail-trail (bike path). Going to ride from Piedmont, AL to just past Hiram Rd trail head and back to Cedartown, GA. I will be riding my KH24 GUni as that is what I’ve been training with and riding many long rides in over the past several months. I really like the setup. My only goal is to finish, but I do think I should be able to go under 10 hours based on a recent 50 mile road ride that was on a much hotter day and on much hillier terrain. I’ll be sure to post my result after the fact. The mileages on the trail are well measured but I’ll be using a combination of GPS and other tracking software to make sure I get my 100 miles in! I’ll have my wife and some friends running some crew support as well.
That’s the killer for record setting. I have spent countless hours of my life on Google Maps looking at aerial photos of places wondering where I could find a good big track. A 400m sports track loop is OK, and I used one last time, but it does kill your speed on every turn as it is so tight at speed.
My eye is currently on a horse-racing track in my home town (a massive factor is being able to practice on the actual track to establish that it will really work), which has an access road loop inside the grass circuit, It is similar shape to a running track oval but with 2km per lap. So it has long, long straights and very gentle corner curvature. If you could get access to an airfield runway that would be awesome for it.
Good luck finding your perfect track. There are plenty of records out there which are due being bettered!
Sam
It was mentioned in a thread from a couple years back, and you commented on it with some info on his epic ride across the US on his 24" Schwinn, with those strange handlebars. And he did it in 1981! Tumbles had posted the thread with a link about it, but the link didn’t work for me.
Have fun!
May the wind be at your back and the rubber down. ‘getrdid’
JM
Fastest Average Cadence?
This thread, and my own pending 100 mile attempt (don’t worry, the record is safe! 
), got me thinking that it might be useful to track what everybody’s average cadence was for their 100 miler. This is an attempt to somewhat equalize comparisons to different attempts using different sized wheels, crank lengths and geared or ungeared. Just a thought.