I am currious in comparing exerted pressure on the knees between a road bicycle and a 28" UNi. I am considering purchasing a 28" Uni, but if one rotation is about 88", that’s a
high gear on my touring bike. When I used to tour on level ground, I usally ride somewhere between 64" to 72".
If I calculate the circumference on a Uni with a 28" wheel, I would ride a distance of @ 88" in one rotation
If I ride my 15 speed touring bicycle, with the chain in arrangement that is 88", do my legs have to exert the same amount of pressure on the pedals?
Lets say the 28" UNi has 150mm cranks on it and the bicycle has 170mm cranks on it.
Lets also assume that we are riding on level ground. Is the pressure the same?
if the pressure exerted, is equal on level ground, would it change as I ride up a road that begins to rise? What I mean, is, will the Uni be any harder to pedal, than the touring bike, or still equal?
Gear ratios on a bike are for the diameter of the virtual geared-up rear wheel NOT its circumference.
Hence touring bike wheel is approx 28" diameter and with a ratio of 42 front to 16 rear you get a “gear” of 28x42/16 = 73.5"
The crank lengths do make a difference - so riding with cranks shorter than 170mm you are effectively gearing up your unicycle by a ratio of 170/crank length e.g. 29" wheel with 110 cranks feels like a 29x170/110 = 45" gear.
In article <teachndad.gilbz@timelimit.unicyclist.com>,
teachndad <teachndad.gilbz@timelimit.unicyclist.com> wrote:
)
)I am currious in comparing exerted pressure on the knees between a road
)bicycle and a 28" UNi. I am considering purchasing a 28" Uni, but if
)one rotation is about 88", that’s a
)high gear on my touring bike. When I used to tour on level ground, I
)usally ride somewhere between 64" to 72".
)
)If I calculate the circumference on a Uni with a 28" wheel, I would ride
)a distance of @ 88" in one rotation
As someone else noted, this is the wrong calculation. A 72" gear on a bike
is equivalent to a unicycle with a 72" wheel; it’s not a measure of how
far the wheel travels per revolution. Think about it; one pedal revolution
on a unicycle gives you one wheel revolution. A 1:1 gear ratio on a bike
(say, a 26x26) is a really low gear.
-Tom
Describing bicycle gears in ínches’rather than ratios goes back to the days of the Penny Farthing or órdinary’ bicycle which had a direct drive.
To sell chain driven or ‘safety’ bicycles, they had to convince the traditionalist that it was comparable. So they described the (single speed) safety bicycle as having a '65 inch’gear to compare it with a 65 inch ordinary. The terminology has stuck.
From my keen bicycling days, I recall that most people are happy on the flat cruising in a gear roughly equivalent to their own height. I used to ride in 65 inches or so most of the time and I’m 5’7" or 67 inches tall.
But remember it started as a marketing ploy. Factoring in the crank length would have been confusing for the non specialist customer. WE know as unicyclists that the important ratio is between the distance moved by the feet and the distance moved by the unicycle. So crank length is a vital consideration. A late Victorian semi-numerate customer wouldn’t have realised this.
For reasons of convention, virtually all adult bicycles have 170mm cranks (or 175) and I recall it was a bit unusual to make the effort to buy shorter ones. The best size of crank will vary from rider to rider, depending on leg length and fitness/strength. On a unicycle, there are other considerations - a trade off between speed and control.
So an 88 inch unicycle with 170mm cranks would feel pretty similar to an 88 inch geared bicycle with 170mm cranks - but make due allowance for the different ergonomics of the riding position. In the end, the comparison is not that useful.
Sorry! Couldn’t resist.