Touring gears - lowest inch's

[clarion]

I use 50-36-24 with an 11-30.  But the 11t sprocket isn't usable, so it's effectively a 13-30 7-speed.  Works well for all my purposes.

[hbunnet]

Definitely 20" or less if loaded and in hilly places.  I  use my 17" every weekend with only a light load,  I am a spinner though. 

[mcshroom]

Looks like some fettling may be on order then 

[clarion]

Just checked with Sheldon.  My gear range is 21.4-102.9"

[Biggsy]

All you need to remember to work out gear inches is: chainring divided by sprocket, times tyre size.  Hard wire that in your grey matter.

Some popular tyre sizes:

700x20C = 26.1" = (622 + 20 + 20) / 2.54
700x23C = 26.3"
700x25C = 26.5"
700x28C = 26.7"
700x32C = 27"
700x35C = 27.2"

26x1.3"   = 24.6" = (559 / 2.54) + 1.3 + 1.3
26x1.5"   = 25"
26x1.75" = 25.5"
26x2.1"   = 26.2"
26x2.5"   = 27"

(Not accounting for real-world variations and squashage, but near enough for general comparison purposes)

[L CC]

All you need to remember to work out gear inches is:

here: Clicky

Biggsy's sums are hard.

[Biggsy]

It's dead easy with a calculator, and if you approximate the tyre size.  27" will do for 700C.

What about when you wake up in the middle of the nght with a gear customisation idea, but no computer?

Oh, just me, is it?  

[clarion]

It's easiest of all with Sheldon Brown's gear calculator

[dasmoth]

It's dead easy with a calculator, and if you approximate the tyre size.  27" will do for 700C.

What about when you wake up in the middle of the nght with a gear customisation idea, but no computer?

Oh, just me, is it?  

It's just you.  I'd never go to bed without at least a smartphone handy.

[clarion]

I do gear calculations in my head as I ride along sometimes.  And yeah, Biggsy, sometimes when I lie in bed awake.  You're not alone. 

[Biggsy]

You people relying on the internet for simple sums. 

What are you going to when World War III starts and all the interwebs are down? 

I just got a smartphone today, by ze way. 

[L CC]

My link's for an android app. It's not online.

only you can tell us what it's like without t'interweb, you're the one with the BlackBerry, Biggsy

[Biggsy]

Replying from BB now.  

[Efrogwr]

I do gear calculations in my head as I ride along sometimes.  And yeah, Biggsy, sometimes when I lie in bed awake.  You're not alone.

So do I. It distracts me from thinking about the gradient.

[jogler]

Lowest gear on my tourer is 18.5"

[mike]

thank god for this thread, i thought i was going soft cos I was struggling last time out with panniers.  Turns out my lowest gear is 27", I might need to fit a triple

[Wowbagger]

Kim seems to think I pack a solid 19". Rohloff, 42--->16, 26" * 1.5". She might be flattering me a little.

Having said that, Mrs. Wow and I once rode up this hill:-

http://www.streetmap.co.uk/map.srf?X=271037&Y=68730&A=Y&Z=120

on the tandem, which would have been 46--->16, 26" * 1.75", which must be slightly bigger - perhaps 22"?

This just goes to show that I'm more impressive with Mrs. Wow's help than I am on my own. This particular performance was witnessed by a car-full of children who applauded roundly when we climaxed.

[clarion]

Actually about 20"

Oddly, Sheldon's calculator doesn't have a 26x1.75 option, but 1.9 gives 20.9" and 1.5 gives 19.9"  Still bigger than you have by yourself.

[Domestique]

Edit: actually I'm being dumb, isn't a 26" wheel with 1:1 drive give a 26" gear? so you're not far off.

Not sure if it right or not, but isnt it the circumfrance of the wheel rather than the diameter

[Biggsy]

No, the diameter of the wheel (or tyre rather) dictates the gear.  That's why penny farthings have such a large main wheel - to get a usefully large "gear" when there's not the usual chain and sprockets.

The circumference is used by a cycle computer to calculate distance.  I guess this is what you're thinking of.

[Domestique]

No, the diameter of the wheel (or tyre rather) dictates the gear.  That's why penny farthings have such a large main wheel - to get a usefully large gear when there's not the usual chain and sprockets.

The circumference is used by a cycle computer.  I guess this is what you're thinking of.

Thank you Biggsy 

[Biggsy]

Thinking about it.....  Since circumference is of course directly related to diameter, you could use circumference inches as units for comparing gears if you like.  We just commonly use diameter inches because it's easier to visualise, and because it gives nice short chunky numbers (when rounded to the nearest 0.1", which is good enough).

[LEE]

Diameter is used purely to give your brain an easy reference (when compared to a direct-drive wheel, like a Penny Farthing).

An 18" "granny gear" is like pedalling a Penny Farthing with an 18" diameter front wheel (getting close to the radius of your cranks)

You can use circumference as a comparison if you like but it's harder to visualise.

[Kim]

And of course the problem with gear inches is they don't take into account the crank length.  My 19" bottom gear gives a gain ratio closer to 20" with a 170mm crank.

[Biggsy]

A 5mm difference in crank length makes a such a small difference to the gear that I forget about it unless being particularly fussy.  But I would switch to gain ratio units when comparing gears with more crank difference than 5mm.  YMMV.