Currently I can’t go faster than 27 km/h (16.7 mph). It is my brain that stops me at the same speed on my geared 29" (137mm cranks) as well as on the geared 36" (150mm cranks), without looking on the speedo 
realized my records aren’t in the running list so i’ve added them. Both verified by my cycle computer(or by computers of cyclists following me in the downhill case)
Speed (mph), Name, Location, Unicycle, Crank size
29-ish, Christian Hoverath, ungeared Coker, 125mm
28.0 mph, Madison Johnston, Portland Oregon, Ungeared Nimbus 36 114mm cranks(downhill)
26.8 mph, Jan Logemann, Remscheid, Germany, Geard KH36, 125mm
26.7 mph Sam Wakeling, Wales, UK, Ungeared 36, 114mm
26.1 mph, Corbin Dunn, Los Gatos CA USA, Geared KH36, 150mm
25.9 mph, (41.7 kph), turtle on “turtle’s V”, Gearded 29", 125mm
24.2 mph, Lars Lottrup, Nivå Denmark, Nimbus 36, 114mm
24.2 mph, John Moriarty, Sarasota FL, 24" Schlumpf muni, 125mm
24.1 mph, Roland Kays, Albany NY, Geared KH36, 165mm
23.5 mph, David Stone, Lobster, 29" Schlumpf, 125mm
22.5 mph Madison Johnston, Portland Oregon, ungeared Nimbus 36 125mm cranks(flat ground)
22.9 mph, Scott Wilton, Madison WI USA, Nimbus 36, 114mm
22.74 mph(36.6kph) Jacob Flansberry Gatineau, Quebec, Canada. KH26 Schlumpf, 137mm
22.6 mph, Spencer Owen, Nottingham UK, Schlumpf 29, 127mm
22.1 mph Tyler Nail, California, ungeared UDC 36er, 125mm
22-ish, John Foss, 45" Unicycle Factory Big Wheel (28 pounds), 6.5" cranks
21.75 mph (35.0 kph) Geoff Houghton, Ashland, Oregon, USA Florian Green
36" with Schlumpf, 165mm
21.43 mph (34.5 kph) Jacob Flansberry, Gatineau, Quebec, Canada. Nimbus Night Rider 36", 137mm.
21.43 mph (34.5 kph) Nathan Hoover, Kenya, Schlumpf KH 36, 150mm
21.1 mph, Øivind Stuan, Trondheim Norway, Nimbus 36, 125mm
20.8 mph, Steve Relles, Delmar NY US, KH36/Schumpf, 165mm
20.8 mph, Nathan Hoover, Norway, Hunter 36, 125mm
20.2 mph, Samuel Farmer, West Sussex England, Qu-ax 36, 114mm
19.9 mph, Peripatet, Jacksonville FL USA, KH36, 125mm
19.0 mph, Joe Sowul, Anaheim CA USA, Nimbus Nightrider 36, 125mm
17.5 mph, John Foss, Max. indicated speed on 24" with 125mm (multiple repeats)
17.0 mph, Rob Northcott, Somewhere on Dartmoor, Mongrel 36er, 145mm
15.5mph, Bob Griffiths, Shrewsbury Cycle Track,UK, Coker 36, 150s
12.8 mph BrianP, Ocala FL US, KH24 w 150s
[/QUOTE]
40 mph
On a 29er flat road, cops even gave me a ticket
You’re sure you got 40mph? Maybe 40kph, but it’s stills incredibly fast for a 29er, or just any unicycle! I hope you have a geared hub on that thing!
That fish must have been 6 feet long!
OK, call me a curmudgeon–a slow curmudgeon.
My fastest time on a 36" is about 16.7 mph according to my cycling computer. I am sure I could go a bit faster. Since most unicycles are fixed gears, we can convert the speed into rpm using only a few simple assumptions:
Many of these speeds are on 36" unicycles. A typical measured diameter of a 36" unicycle under load is just under 280 cm. I will use this value.
At 1.000 MPH, the number of cm traveled in one hour is 1.609 X 10^5. Dividing by the wheel diameter in cm gives me the number of rotations in one hour: 574.6 rotations per hour. Dividing by 60 minutes in an hour give the rotations per minute = 9.58 rpm.
On a fixed gear 36", each one mile per hour corresponds to 9.58 rpm. To get the total rpm, just multiply this constant (9.58) by the mph.
As an example, let’s take the value of 22.9 MPH reported by Scott Wilton, who is one of the fastest unicyclist around (he won the criterium in this years Nationals). His 22.9 RPM would correspond to 219 rpm. This value is far above the cadence cyclist usually ride. However, the speed sound credible.
As a second example, let’s try some old codger like myself. 
My 16.7 rpm would correspond to 160 rpm. Not very impressive, but certainly doable.
We can also examine some of the Schlumpf hub records. In this case we need to divide by about 1.5 ( I am unsure of the precise gear ratio.) If we take Corbin as an example, his 26.1 MPH would be reduced to 17.4 mph with the Schlumpf correction, and the cadence would be 167 RPM–that is almost an old man’s cadence! Admittedly, 26.1 mph would scare the crap out of me, but I do not have a Schlumpf hub.
Now let’s examine two of the most recent claims (but there are many others I could pick on.) Madison Johnston reports 28.0 MPH, which coverts to 268 rpm. That is a crazy high number, but he does report it going downhill.
Still, for many of these claims I would like to see the speed independently clocked by some more reliable method than our cycling computer. Alternatively, why don’t we report what circumference we are using in our cycling computers. If I put in 380 cm my speeds are MUCH higher.
Finally, we have a report of 40 mph on a (fixed?) 29". Using the same method, with a circumference of 231 cm, I find an cadence of 464 rpm.
Hmmm.
Orange County Skeptic
I don’t think the 28 mph speed, or “29-ish” for Hoverath, are plausible. Neither includes a speed reading from the cycle involved, and given that they’re significant outliers in this list, I’m prone to discount them.
The 40mph claim is just silly, unless he’s talking about a 29er bike. (Even then it’s quite impressive).
I have gotten a ticket on a BIKE before for speeding. It was through a town on a hill I was doing 45-ish when the speed limit was 30.
The high gear in a Schlumpf hub is indeed 1:1.5. Keep in mind that in high gear the reduced cadence is paid for by significantly increased pedalling effort. This also goes for all braking/steering corrections with the legs. If you are weak and tired then riding fast in high gear is not that much easier than doing it in low gear.
40mph on a unicycle? coughbollockscough
The speeds in the mid-20s are pretty amazing, but I know they’re possible by some people with twiddly legs and no fear. But 40, no way (and on a 29er!)
If it’s true then I take that back - you’ve got the fastest legs on the planet (by a huge, and extremely implausible, margin)!
Rob
Speed (mph), Name, Location, Unicycle, Crank size
29-ish, Christian Hoverath, ungeared Coker, 125mm
28.0 mph, Madison Johnston, Portland Oregon, Ungeared Nimbus 36 114mm cranks(downhill)
26.8 mph, Jan Logemann, Remscheid, Germany, Geard KH36, 125mm
26.7 mph Sam Wakeling, Wales, UK, Ungeared 36, 114mm
26.1 mph, Corbin Dunn, Los Gatos CA USA, Geared KH36, 150mm
25.9 mph, (41.7 kph), turtle on “turtle’s V”, Gearded 29", 125mm
24.2 mph, Lars Lottrup, Nivå Denmark, Nimbus 36, 114mm
24.2 mph, John Moriarty, Sarasota FL, 24" Schlumpf muni, 125mm
24.1 mph, Roland Kays, Albany NY, Geared KH36, 165mm
23.5 mph, David Stone, Lobster, 29" Schlumpf, 125mm
22.5 mph Madison Johnston, Portland Oregon, ungeared Nimbus 36 125mm cranks(flat ground)
22.9 mph, Scott Wilton, Madison WI USA, Nimbus 36, 114mm
22.74 mph(36.6kph) Jacob Flansberry Gatineau, Quebec, Canada. KH26 Schlumpf, 137mm
22.6 mph, Spencer Owen, Nottingham UK, Schlumpf 29, 127mm
22.1 mph Tyler Nail, California, ungeared UDC 36er, 125mm
22-ish, John Foss, 45" Unicycle Factory Big Wheel (28 pounds), 6.5" cranks
21.75 mph (35.0 kph) Geoff Houghton, Ashland, Oregon, USA Florian Green
36" with Schlumpf, 165mm
21.43 mph (34.5 kph) Jacob Flansberry, Gatineau, Quebec, Canada. Nimbus Night Rider 36", 137mm.
21.43 mph (34.5 kph) Nathan Hoover, Kenya, Schlumpf KH 36, 150mm
21.1 mph, Øivind Stuan, Trondheim Norway, Nimbus 36, 125mm
20.8 mph, Steve Relles, Delmar NY US, KH36/Schumpf, 165mm
20.8 mph, Nathan Hoover, Norway, Hunter 36, 125mm
20.2 mph, Samuel Farmer, West Sussex England, Qu-ax 36, 114mm
19.9 mph, Peripatet, Jacksonville FL USA, KH36, 125mm
19.0 mph, Joe Sowul, Anaheim CA USA, Nimbus Nightrider 36, 125mm
17.5 mph, John Foss, Max. indicated speed on 24" with 125mm (multiple repeats)
17.0 mph, Rob Northcott, Somewhere on Dartmoor, Mongrel 36er, 145mm
15.9 mph (25.4 kph), Blacky Burny (haha Joey), Millbank, ON, Nimbus/Semcycle 29er, 125 mm
15.5mph, Bob Griffiths, Shrewsbury Cycle Track,UK, Coker 36, 150s
12.8 mph BrianP, Ocala FL US, KH24 w 150s
Oh yeah, it’s been a while since I updated this list. I had hit 27mph during one of the races (Unicon, or UGames, I forget which). I think turtle has gone faster. Madison – 28mph on an ungeared coker? that’s insane!
Speed (mph), Name, Location, Unicycle, Crank size
29-ish, Christian Hoverath, ungeared Coker, 125mm
28.0 mph, Madison Johnston, Portland Oregon, Ungeared Nimbus 36 114mm cranks(downhill)
27.0 mph, Corbin Dunn, Los Gatos CA USA, Geared KH36, 150mm
26.8 mph, Jan Logemann, Remscheid, Germany, Geard KH36, 125mm
26.7 mph Sam Wakeling, Wales, UK, Ungeared 36, 114mm
25.9 mph, (41.7 kph), turtle on “turtle’s V”, Gearded 29", 125mm
24.2 mph, Lars Lottrup, Nivå Denmark, Nimbus 36, 114mm
24.2 mph, John Moriarty, Sarasota FL, 24" Schlumpf muni, 125mm
24.1 mph, Roland Kays, Albany NY, Geared KH36, 165mm
23.5 mph, David Stone, Lobster, 29" Schlumpf, 125mm
22.5 mph Madison Johnston, Portland Oregon, ungeared Nimbus 36 125mm cranks(flat ground)
22.9 mph, Scott Wilton, Madison WI USA, Nimbus 36, 114mm
22.74 mph(36.6kph) Jacob Flansberry Gatineau, Quebec, Canada. KH26 Schlumpf, 137mm
22.6 mph, Spencer Owen, Nottingham UK, Schlumpf 29, 127mm
22.1 mph Tyler Nail, California, ungeared UDC 36er, 125mm
22-ish, John Foss, 45" Unicycle Factory Big Wheel (28 pounds), 6.5" cranks
21.75 mph (35.0 kph) Geoff Houghton, Ashland, Oregon, USA Florian Green
36" with Schlumpf, 165mm
21.43 mph (34.5 kph) Jacob Flansberry, Gatineau, Quebec, Canada. Nimbus Night Rider 36", 137mm.
21.43 mph (34.5 kph) Nathan Hoover, Kenya, Schlumpf KH 36, 150mm
21.1 mph, Øivind Stuan, Trondheim Norway, Nimbus 36, 125mm
20.8 mph, Steve Relles, Delmar NY US, KH36/Schumpf, 165mm
20.8 mph, Nathan Hoover, Norway, Hunter 36, 125mm
20.2 mph, Samuel Farmer, West Sussex England, Qu-ax 36, 114mm
19.9 mph, Peripatet, Jacksonville FL USA, KH36, 125mm
19.0 mph, Joe Sowul, Anaheim CA USA, Nimbus Nightrider 36, 125mm
17.5 mph, John Foss, Max. indicated speed on 24" with 125mm (multiple repeats)
17.0 mph, Rob Northcott, Somewhere on Dartmoor, Mongrel 36er, 145mm
15.9 mph (25.4 kph), Blacky Burny (haha Joey), Millbank, ON, Nimbus/Semcycle 29er, 125 mm
15.5mph, Bob Griffiths, Shrewsbury Cycle Track,UK, Coker 36, 150s
12.8 mph BrianP, Ocala FL US, KH24 w 150s
wow epic fast stuff! Ive hit about 30kph+ gliding down a local hill 
Because he no longer posts here (not sure if he used to) he loses credibility? He was very well known to the unicycling community when he was involved, especially and around the time his club hosted Unicon IX in 1998. His high speed ride was done during a unicycle tour with many other riders we know and who I find credible. I am inclined to believe his relatively undocumented result.
That was posted by a troll who probably isn’t even a unicycle rider.
40 on a uni would be a death wish. 30 would be attempted suicide. 20 would make me piss myself. im plenty happy going 10-15 mph.
Has anyone calculated the rpm’s required to do 29ish w/ 125’s?
I just calculated ~270 rpm, but this might be wrong.. I think I did it right though
Indeed, using a wheel diameter of exactly 36 inch, and a speed of 29 mph, I arrive at an rpm of 271 (rounded). I looked up the world record on the 100 m from http://www.unicycling.org/IUF/records/. It’s from 1996 so it may be somewhat outdated, but hey, it’s around the same time as Hoverath’s claim (which was 1998). Using exactly 24" as the wheel diameter (nowadays the standard is slightly larger), I calculate an rpm of 237 (rounded). Granted, this is with a standing start and so the top rpm will have been higher, but then again, a small wheel is (imho) easier to spin fast than a big wheel. I have a hard time believing that Hoverath spun that much faster than the 100 m world record.
I think I’ve seen an account of Hoverath’s Coker speed record, and I seem to remember a car speedometer was involved. That introduces several potential inaccuracies. My bottom line is that Hoverath has probably not achieved 29 mph, but somewhat less. E.g., at 26 mph, the rpm would come out at 243 which seems plenty fast to me.
What are you asking? To do around 29mph? If you are describing your wheel diameter and crank size, you have forgotten to specify what speed y ou want. Whatever you mean, there is no answer because you have not specified enough.
I’ll post back in a while with a formula for what you need to do for each mph and kph. It’s not rocket science. The crank length has nothing to do with it, it’ll just be a function of wheel diameter (actually the outside of the tyre).
I take it that genbirch referred to Christian Hoverath’s case. As reiterated in this thread, it is claimed that he rode “29-ish” mph on a 36 inch wheel. With 125 mm cranks, but I agree those don’t come into the equation. If that was indeed genbirch’s question, it has already been addressed by Tim3 and by myself.
Multiply 0.002975 by the diameter (inches) of the contacting surface of your tyre and then by the cadence (rpm) to give you the speed in miles per hour.
So, a 24" wheel may have an actual tyre diameter of, say, 26".
Pedaling at a cadence of 120 (2 per sec which is way higher than comp road cyclists) will therefore give you a speed of
0.0.002975 x 120 x 26
9.28mph.
Alternatively, 0.004787 by the diameter of the contacting surface of your tyre and then by the cadence (rpm) to give you the speed in kph.
It should be right, but haven’t checked my workings, so feel free to correct me.