fatigoworld

so i have been researching which gears are best suited to me and how i ride and ive noticed that the larger the sprockets, the less change there is between gears.

example:

lets assume the front chainring stays at 42

13 changed to 15 = a difference of 11.4 gear inches

31 changed to 33 = a difference of 2.2 gear inches (doesnt seem like much change at all)


i have a few questions about this

1. does this mean i will notice that much less of a difference in gear change between 31/33 than 13/15?

2. or does the change feel almost equivalent considering your most likely are on an incline?

3. would it be more beneficial to have larger differences between sprockets the lower the gear gets? (example skipping from 27 to 34 = a difference of 10.1 which seems more equal to the shifting difference of higher gears)


i am mostly interested in what is beneficial in regard to how these differences between gears feel, not on whether or not it will affect shifting function.

thanks!

BengeBoy 

1. yes.
2. no.
3. yes.

Check out some of the recommended cassettes at the Harris Cyclery website. Sheldon Brown has an excellent gear calculator, and it allows you play with both standard cassettes and a couple of interesting custom cassettes, including one called a "cyclotouriste special," or something like that.

You will see that for recreational/touring application that cog spacing is very tight at the small end (only one tooth difference in the high gears) but in the larger cogs there are more differences. Some people who ride without triples even will put on a giant "bail-out" cog on the rear derailleur just so they can drop into something "easy" when the going gets tough.

R.I.P. Sheldon, who, as always, has the answer...

Speedo

Yes, but see below.

Yes again, but that's kind of what happens with the standard cassettes. If you are looking for "perfection" in gearing then the gears should be evenly spaced when plotted logarithmically. Or, you can think of it as the percentage change from one gear to the next remaining the same. This is difficult to achieve (the perfection that is) in practice, but you can get close enough so that you have a comfortable spacing.

About 15% is a full step between gears. You would prefer nothing larger. About 7.5% is a step that would give you a nice comfortable spacing. Generally, when staying on the same chainring, with a touring spread of gears, the steps will be big. But by interleaving between chainrings, you can achieve a nice step size between gears.

A nice combination for touring 48-36-26 chainrings with an 11x32 cassette. Another nice combination for touring a 46-34-24 with an 11 x 34 cassette. Being a weakling I prefer the latter to the former.

Speedo

fatigoworld

thanks, all this info will be a great help in working out my gearing!

nun

Those are good touring gear combos, however, in my experience anything over 100" isn't really useful. My
favorite combo is a 42-26 with an 11x34.

If I am using a 110/74 triple I'll do 46-36-24 with a 12x34

fatigoworld

would you ever use the 26 x 34 gear? that seems so low....

rm -rf

Using Sheldon's gear calculator:
26 front, 34 rear on a 700c wheel is 5.4 mph at 90 rpm, 4.8 mph at 80 rpm. So you could spin up hills instead of standing up and mashing.

A 26 x 26 would be 6.3 mph at 80 rpm.

nun

Sure its around 21", and I can spin up a hill at between 5 and 6 mph. 24x34 is even lower, but anything much below 20" and its just beter to get off and push. I think the lowest I've seen is 20x34 on a 26" wheeled bike using a MTB crank, that's 15". To me that's just too low and I'd push the bike rather than pedal such a low gear. Gears between 100" and 20" are about right for touring.

fatigoworld

i am planning on using 33" to 102" for my first tour. ill probably be loaded with about 50-80 pounds tops. i weigh 135 and im in pretty good shape, im bike messenger for work so bike lot. do you think 33" is not low enough for my range?

nun

Only you can know if 33" is low enough. Your gear weight is pretty average and I think most tourists would have lower gearing than you're contemplating. I'd advise you to have some lower gears than 33" just in case, there's no harm in having them even if you don't use them. At 135 lbs and a bike messenger you are probably in good shape, but doing long rides day after day with 80 lbs of gear can ware you down so take it easy for the first few days.

fatigoworld

ok, i guess ill try a test trip and see if it low enough and then switch it up if not. thanks for the advice....