Re: [yak] Digest for yak@bikefriday.com - 7 updates in 2 topics

[Alister Sharp]

Dear Peter,

Yes, Gear Inches are the equivalent diameter of a Penny Farthing front wheel. The measure of how far the bike travels with one rotation of the charinring is termed 'Development' by Wikipedia (https://en.wikipedia.org/wiki/Bicycle_gearing). The Gear Inch value is equal to the Development (measured in inches) divided by pi (approximately 3.142).

With derailleur gears, another way of thinking about gearing is to compare the number of teeth on the chainring with that on the sprocket. When these are equal, with one full turn of the cranks the rear wheel will turn exactly once, and the bike will travel a distance equal to the circumference of the rear wheel (about 27 inches for a 700C wheel with touring tyre). So, on a bike with this wheel, when the chain is running over the same number of teeth (say 30) on both chainring and cassette, it has a gearing of 27 gear inches. In other gears, the gear inch value is the distance you'd travel for one turn of the cranks if your bike had a wheel of the gear inch diameter.

I tend to think in gear inches, and when young used to be happy with a lowest gear of 30 gear inches. Now that I'm quite old I like a lowest gear of around 25 gear inches for around town and day rides, and as low as 19 gear inches for my Mountain and Touring bikes. I like the rule-of-thumb that says "Your bottom gear should be so low that you don't need it, but it's there for when you do"!

Cheers, Alister

Alister Sharp

Mob: 0422 468 108, Tel: 02 9879 3664

11 Martin St, Hunters Hill,

NSW 2110, Australia

On Sun, 1 Jan 2023 at 13:26, <y...@bikefriday.com> wrote:

y...@bikefriday.com

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• New bike parts questions - 2 Updates
• comparing climbing ability (the bike's not mine) - 5 Updates

New bike parts questions

Jon Foraday <jon4...@gmail.com>: Dec 31 08:22AM -0800 Thanks folks.   Sounds like the hubs are fine, and the cranks are if forged. One seller says forged, the others (including manufacturer site) say nothing, so probably OK, but not sure. The brakes on the other hand... So If I do this, I need to budget about $100 for new brakes. On Thursday, December 29, 2022 at 8:42:00 PM UTC-7 ro3ert...@gmail.com wrote:

Dirk Bolle <dbol...@gmail.com>: Dec 31 09:36AM -0800 I've got bb7 road's on a custom air (withS ram force brifters.) They work well. Make sure you have good handles. The cheap off brands (which BF will likely supply with the off brand discs) will feel and behave differently than avid or shimano. The avid Speed Dial 7 are a perfect match. The shimano sora and tiagra levers are adjustable via a small cam inside for either caplipers or v/Disc brakes. make sure they are properly set - they work with both, but you MUST set them correctly - lots of mechanics aren't aware, including BF. I bought a basically mint unused PRP with them on H-Bars and they were not set for calipers. they were still in "V" mode. resetting and adjusting the brakes made a world of difference.   *Sent from an IOS Device, iMac, **a MacBook Pro, MacBook Air, Mac Pro, or occasionally (God forbid) a Windows PC. But never an Android device.*

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comparing climbing ability (the bike's not mine)

peter stock <lug...@gmail.com>: Dec 30 11:33PM -0500 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 <joer...@gmail.com>: Dec 31 12:43AM -0800 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 <eric...@gmail.com>: Dec 31 06:05AM -0500 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

Geof Gee <geo...@gmail.com>: Dec 31 11:19AM -0500 > 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 <jon4...@gmail.com>: Dec 31 09:30AM -0700 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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