comparing climbing ability (the bike's not mine)

[peter stock]

Stop me if you read this on FB, but there are different experts here than there.

Question. How do I compare the "climbing" ability of two different Bike Fridays?

Woohoo! it looks like I can jump away for a week or 10 days cycling in January.

Naturally I will be taking a BF,

when I bought my first BF (a pretty racy AIr Friday with 451 wheels, the sales guy Peter talked me into the IGH by saying "she'll climb like a mountain goat". and she always has.)

But some of tthe destinations on the shortlist - Austin tx, tucson az - might be hilly.

I want to ensure that I can actually make the climbs without walking.

My options are:

1. a Pocket Rocket Pro with a lowest 39tfront-29trear.

or

2. a Pocket Llama with a Dual Drive IGH and a (biggest rear) 28t

I have no idea what a Dual Drive has going on inside its 3speed guts so I don't think I can do the gear inch math.

(But what the heck is Gear Inch anyway?)

In the end I just put them in their lowest gear settings and rolled them across the floor, a full crank turn, and measured the distance covered. (is that distance not "gear inches". if not, it should be)

I measured:

PRP: 83 inches

Llama. 78 inches in lowest IGH (99 in the middle setting and 126.5 in the Highest setting) on a 28t biggest rear cog.

so, can someone explain gear inches to me? is it not the distance a bike travels with a full turn of the crank?

how climbable does the PRP's 83 inches sound?

how should I be gauging this? Peter Stock Toronto Canada

[Joseph Bernard]

Peter, 

I don't know how gear inches are gear inches but I know my Pocket Rocket with DualDrive has a 21" low and if it was much lower I would probably be walking up a hill as fast as it would climb. I need more information to calculate your Llama but I had enough to find the low on your PFR, it's 26.8. Therefore your Llama should be between the two. Here's the charts on my bike and yours, and this is the calculator: 

https://www.sheldonbrown.com/gear-calc.html

To do your Llama I need cassette range (probably 11-28) and chainring size. 

[Eric Daume]

You can find an explanation of "gear inches" here:

https://www.sheldonbrown.com/gain.html

It's an archaic measurement--it results in the effective diameter of your drive wheel, which was the measurement back in the day of the high wheeler bikes. A bigger wheel was faster. Now, instead of giant wheels, we use the gears to achieve the same effect (and quite a bit more: I think high wheelers maxed out at about 60" gear inches, based on how tall of a rider could stretch a leg over the biggest wheel. That's a pretty low top gear, a modern transmission can run from 25~100 gear inches, give or take)

You measured the development--how far the wheel rolls for each gear. That's a more useful measurement, but no one is used to using those numbers, so it's hard to compare.

Sheldon also has a useful gear inch calculator, where you can plug in your crank and hub to get the results:

https://www.sheldonbrown.com/gear-calc.html

Eric

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[Geof Gee]

On Fri, Dec 30, 2022 at 11:33 PM peter stock <lug...@gmail.com> wrote:

In the end I just put them in their lowest gear settings and rolled them across the floor, a full crank turn, and measured the distance covered. (is that distance not "gear inches". if not, it should be)

I measured:

PRP: 83 inches

Llama. 78 inches in lowest IGH (99 in the middle setting and 126.5 in the Highest setting) on a 28t biggest rear cog.

so, can someone explain gear inches to me? is it not the distance a bike travels with a full turn of the crank?

What you did is related to a gear inch which is the diameter of an equivalent penny farthing wheel.  You calculated, with some error, the perimeter/circumference of the equivalent penny farthing wheel.  So divide by pi to get the gear inch. 

~20 gear inches is pretty low. For most people, they would slowly get up just about any hill.  

-G

Arlington, VA 

--

"Sometimes I forget things.  Who I am.  Where I am.  Unimportant things. But I'm not insane. "

[Jon Foraday]

I lived in Austin for 2 years, and Phoenix for too many.  The only really hard climb I can think of is Mt. Lemon in Tucson. As long as you're not looking at doing that, you should be ok with anything 30 gear inches of less.

My 2 cents, and YMMV, but hopefully that should hemp.

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[robert clark]

"Question: How do I compare the "climbing" ability of two different Bike Fridays?" 

OK you got part of it.. tooth count,  --- ratio math .. 

the dual drive the 3 by 7 was using the Sachs 3 speed internals . Sheldon/ [Updated by John Allen] 

has a pull down menu of internal gear hubs.. 

 I am assuming S-ram  used Sachs' internal ratios  

changed the pull chain to a click box  and the driver to take more cogs, 8+

 S-A now is the remaining manufacturer  after S-ram shut down the whole internal gear division 

 to jump on the one by huge cassette range thing..  

maybe you can take that path  12~42t cassettes + the internal triple?  

@ some point spinning a tiny gear or getting off and pushing, the latter lowers your heart rate..

"Is it NOT the distance a bike travels with a full turn of the crank?"  

You are correct, <it is not>, you describe 'Development '

 the roll out of wheel of certain circumference of tire on rim at a given PSI..  in relation to crank rotations

Often spoken of as a distance in Meters.

Gear inches is gear ratio x wheel diameter in inches, as if a penny farthing wheel.

[robert clark]

Other factors:  tire design,  pressure, footprint, Inflation - contributing to rolling resistance..

[robert clark]

FWIW...  I Looked it up  Sachs 3 speed is 0.8/1/1.25,  where Sturmey Archer AW is 0.75/1/1.33..

huddling by the heater 1/1/2023..