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KelOnWheels
06-08-2012, 03:32 PM
Could someone point me in the direction of a good bike gearing 'splanation? :confused:

Preferably one using small words and lots of pictures. I went to art school. Numbers make my head hurt.

For example, the following paragraph confuses and frightens me:

"I have a 50/34 compact double crank with a 9 speed 11/28 cassette on my road bike and struggle up anything over 10% incline. For somebody just starting out who is out of shape, and encounters longer or steeper hills, a 34/28 low gear might not cut it. The thing with road bike derailleurs is that they limit you do a 27-28T granny gear (although that's slowly changing). I'd be inclined to go for the triple crank with a narrower spaced cassette (like a 12/26) on a hybrid if large gear jumps are a concern. On flat ground you'll probably never have to leave the middle chainring and you still have plenty of climbing gears by dropping down to the small chainring."

(I understand the last sentence. There aren't any numbers in it.)

Once people start talking about inches of gears and stuff, I'm totally lost.

An eejit's guide to bike components would be handy too... :)

Greenbelt
06-08-2012, 03:56 PM
My old car struggles on 10% inclines -- I don't even try on my bike!

How about this for starts (others more knowledgeable can correct/add):

Bigger chainring in the front (by the pedals) = faster
Smaller chainring on the cassette (on the real wheel) = faster

and thus, duh:

Smaller chainring in the front (by the pedals) = slower
Bigger chainring on the cassette (on the real wheel) = slower

Most road bikes these days come with 2 gears in the front, and 9 or 10 on the back. Some touring bikes and mountain bikes have 3 gears in the front, the smallest of which is only used for going really slow or up a really steep hill. This smallest front gear in the front is often called a "granny gear".

Most of us leave the front gear in one position a lot of the time, and only use the rear gears for minor gear adjustments when riding around. Switching the front gear is only necessary on occasion when converting from major climbing to faster speeds or vice versa.

There's some overlap in the gears. It's generally not a great idea to crossover the chain -- ie using the slowest(largest) gear on the back in combination with the fast (largest) chainring on the front. When you get the that point, best to move the chain to the smaller gear in the front.

The numbers on chainrings and cassettes refer to the number of teeth (knobby thingies) that grab the chain. Higher number = more cogs, which means a bigger gear. However, you have to remember that bigger = faster in the front and bigger = slower in the back.

-Jeff

KelOnWheels
06-08-2012, 04:24 PM
Oh, so THAT's what crosschaining is! Good to know. I shall try to avoid that.

So what the heck do things like 50/34 and 11/28 and 34/28 and 12/26 mean?

If, for example, a certain hypothetical person chose to enliven their work day by shopping for bikes online, how would they know if one bike might be better than another by looking at these mysterious numbers?

Also, presumably a more expensive bike has "better" components, but is there some handy hierarchical list somewhere for said hypothetical person to refer to, so that they might know if they are looking at apples and oranges, or just different kinds of apples? :D

KLizotte
06-08-2012, 04:41 PM
This is a good easy read on gearing (with pics):

http://coachlevi.com/cycling/complete-beginner-guide-to-bicycle-gears-shifting/

SpokeGrenadeSR
06-08-2012, 05:30 PM
Oh, so THAT's what crosschaining is! Good to know. I shall try to avoid that.

So what the heck do things like 50/34 and 11/28 and 34/28 and 12/26 mean?

50/34= 50teeth in the big front ring, 34teeth in the small front ring
11/28=scale of 11teeth to 28teeth in the rear cassette from smallest to biggest
12/26=same concept of a scale as ^that
34/28=a combination of using the 34tooth small ring in the front with the 28tooth cog in the rear. it's the slowest gear on most road bikes and often only used for climbing

most rear cassettes are a combination of teeth between 11 and 28 (11/28), road racers use 11 to 25 (11/25) in the back and 53/39 in the front (which is non-compact), and mountain bikers use 11 or 12 as the min to 32 max.

for example. this summer i'm going across the country, i'll be experiencing a lot of terrain so i wanted to choose my gearing wisely.
i'm starting in the new england mountainous region and i am bad at hills so i got a mountain bike rear cassette with a scale of 11teeth to 32teeth (with a long cage derailleur to accomodate such a large cog), but i also bought a smaller cassette with 11teeth to 25teeth for the flatter regions. this will be used in combination of a compact front crank (50/34) rather than a 53/39.
my goal is to have close to a 1:1 ratio of the smallest front ring (34 in my case) and the largest rear ring (32 in my case), that's super spinny and makes hills very easy.

vvill
06-08-2012, 06:59 PM
Gearing can be as simple as the ratio between your front gear (chainring) and your rear gear (cassette).

If you are riding with a 34 teeth front gear and a 34 teeth rear gear then it's 1:1, and with each revolution of your pedal, your bike will cover the circumference of your rear tire.

I like using gear inches http://en.wikipedia.org/wiki/Gear_inches because the numbers end up coming out on a convenient scale. 100 gear inches is a high gear, and probably enough for say, most commuters. 35 is a nice low gear enough for non-extreme hills. A bit like 100F is damn hot and 35F is c-c-cold. There are online tools that can calculate the gear range of a given bike (given the front chainrings, rear cassette, and tire size) in various units, including gear inches. e.g. http://sheldonbrown.com/gears/
Incidentally Sheldon Brown's site is a great repository for bike info, although understandably a little out of date with bleeding edge stuff.



The actual number of teeth on each gear in a cassette is sometimes hard to find out, but here's an example (SRAM PG 1050 cassette) from
http://www.competitivecyclist.com/product-components/2011-sram-pg-1050-cassette-%2810-speed%29-7736.22.1.html
The 11/23 includes: 11,12,13,14,15,16,17,19,21,23
The 11/26 includes: 11,12,13,14,15,17,19,21,23,26
The 11/28 includes: 11,12,13,14,15,17,19,22,25,28
The 11/32 includes: 11,12,14,16,18,20,22,25,28,32
The 11/36 includes: 11,12,14,16,18,21,24,28,32,36
The 12/25 includes: 12,13,14,15,16,17,19,21,23,25
The 12/26 includes: 12,13,14,15,16,17,19,21,23,26
The 12/27 includes: 12,13,14,15,16,17,19,21,24,27
The 12/28 includes: 12,13,14,15,16,17,19,22,25,28
The 12/32 includes: 12,13,14,15,17,19,22,25,28,32
The 12/36 includes: 12,13,15,17,19,22,25,28,32,36


You can change out cassettes/chainrings on a bike so as a specification, it's not the most important thing when shopping for a bike. It's more just an indication of the intended audience/use of the bike.

DismalScientist
06-08-2012, 07:22 PM
You can't avoid the numbers. How far you go with one pedal revolution is determined by three things: The number of teeth in the front chain ring, the number of teeth on the rear sprocket you are using and the circumference of the (rear for all you Terry fanatics) wheel. If you are riding a 48/12 combination, the rear wheel spins 4 (=48/12) times for every revolution of the crank. The circumference of the wheel is proportional to its diameter, so a 26" mountain bike moves pi*26 inches, which is about 82 inches, or a little less than 7 feet, for each revolution (there are tire size issues as well, but I digress). Since adult wheel sizes 26", 700 C, 27" are fairly close, when discussing gearing people generally ignore them.

Just to be a general pain in the ass, I would suggest that SpokeGrenade think very hard about getting a triple crank for touring, particularly if he is doing it with full gear. When going cross country, I had something like a 52/48/26 in front and a 14/32 in back. Of course, back in the day, we had canvas tents, glass jugs of wine (rather than lightweight boxes), and had to bike in our own firewood.:rolleyes: You can climb walls with a 26/32, even with gear. Furthermore, the cogs are probably fairly evenly spaced in a 11/32 that there might not be much of an advantage in bringing a more tightly spaced cassette. Back in the stone age, my 14/32 only had 6 cogs, but I felt that sufficient to dial in any gear I needed (although the half-step middle cog on the front helped).

SpokeGrenadeSR
06-09-2012, 11:17 AM
Just to be a general pain in the ass, I would suggest that SpokeGrenade think very hard about getting a triple crank for touring, particularly if he is doing it with full gear. When going cross country, I had something like a 52/48/26 in front and a 14/32 in back. Of course, back in the day, we had canvas tents, glass jugs of wine (rather than lightweight boxes), and had to bike in our own firewood.:rolleyes: You can climb walls with a 26/32, even with gear. Furthermore, the cogs are probably fairly evenly spaced in a 11/32 that there might not be much of an advantage in bringing a more tightly spaced cassette. Back in the stone age, my 14/32 only had 6 cogs, but I felt that sufficient to dial in any gear I needed (although the half-step middle cog on the front helped).fortunately it will be a supported tour for a large group (i'll be one of the people doing the supporting). It's a bit of a stretch to call it a tour too because we're getting free meals 90% of the time and sleeping in churches, dorms, and community centers 98% of the time :)
I do have a 30-39-52 triple set on my "for real touring" bike, but this trip will just be on a road bike with a light rear rack to carry my hammock haha.
and good lord, touring with only 6 speeds for a 14/32 spread? front der must have gotten plenty of use.
kudos to you and your glass jugs of wine sir.

KelOnWheels
06-10-2012, 09:45 AM
Thanks all! As always, you are full of knowledges and smarts, and are very kind to share them.

DismalScientist
06-10-2012, 10:36 AM
fortunately it will be a supported tour for a large group (i'll be one of the people doing the supporting).

To quote Emily Litella, "Oh, never mind."

I checked again and my gearing was 50/45/26 with a 13/28 in back.

MCL1981
06-10-2012, 01:54 PM
A 10% grade a monstrous hill.

On my usual rides, the front is never out 3rd (the big one). The back (8 gears), I never get below 4 even when coming to a stop. It's a mountain bike so the gear ratios are lower than a road bike. I've found that the entire lower 50% of my gear range is totally useless and I never touch them.

KelOnWheels
06-18-2012, 10:27 PM
A 10% grade a monstrous hill.

Well I feel a bit better now that I see the Martha Custis hill is an 8.3% grade :)

I looked up the gearing on my bike (fortunately Bikepedia goes back to prehistoric times so I didn't have to count) and I've got a 7-speed 13/30 with 28/38/48.

One day I'm gonna make it up that hill without stopping! (also preferably without my chain falling off when I try to drop into the granny gear :P)

Arlingtonrider
06-19-2012, 09:24 AM
Is there an easy way to look up the grades of various hills? Or do you have to ride it with a GPS based computer to find out?

DaveK
06-19-2012, 11:14 AM
Is there an easy way to look up the grades of various hills? Or do you have to ride it with a GPS based computer to find out?

Nope. You can compute the average grade yourself if you have Google Earth by hovering over a point at the top and bottom and drawing a distance line between them, but it won't tell you the actual grade of the road, just the grade between those two points.

KelOnWheels
06-19-2012, 11:42 AM
Is there an easy way to look up the grades of various hills? Or do you have to ride it with a GPS based computer to find out?

I cheated - there's a Strava route for the hill ;)

jopamora
06-19-2012, 12:11 PM
I found this calculator (http://veloroutes.org/hillgradecalculator/) this morning. Kids had breakfast later than usual as I plotted various streets in DC.

KelOnWheels
06-19-2012, 12:30 PM
Aw man, the calculator busted mah Doom Hill down to 5.9% :D