MePoocho

What is the difference between 'long cage' and 'short cage' derailleurs?? What are the benefits if any. Will they both work on an inexpensive road bike?

The one below is kinda what I might get.

(I'm still learning..... )

Thanks

Screen Shot 2017-11-29 at 10.09.08 AM.png

Wanderer

You have to count the difference between your front sprockets, and rear sprockets. Then compare against the total difference of the derailleur. You also have to look at the total rear, to make sure it will accommodate your largest rear sprocket.

dsbrantjr

If you are on the fence whether to get a long- or short-cage derailleur, go for the long cage. While there could theoretically be some degradation in shifting if a longer-than-needed cage is used, as a practical matter it is negligible. If you decide to change your gearing down the road, say to a cassette with a larger big cog, the long cage will give you the option without requiring replacement.

Shimagnolo

^This.
I always use the longest cage RD available, and I have never wished for a shorter cage.

MePoocho

Wandere,,,, Man you lost me..... My fronts are 50/34t and my rear cassette is a 7sp 28/12t. Living in Florida without any 'Mt. Pushmoores' I only use the 50t chain ring. Actually, I removed and tossed my front deraileur.

I'll have to give your explanation some more thought. Sorry, sometimes I'm kinda slow on the uptake.

Thanks

MePoocho

Now these recommendations are up to my limited understanding.... dun-deal....

Off to spend more money on my Denali. Please don't laugh, this $199 bike has provided me many hours of maintenance / upgrade fun and has moved me swiftly up the learning curve from motorcycles bicycles along with all the info from you folks on this forum.

kevindsingleton 

The difference between long and short cage derailleurs is in how much chain slack they take up. Your current setup doesn't require a long cage derailleur, but, if you were going to take a trip to somewhere hilly, and decided to use a cassette with larger cogs, you would need more chain, and, thus, a longer cage derailleur. If you will never use a larger rear cog than what you have, now, you will never make use of the longer cage.

TimothyH

Derailleurs come with different cage lengths. The arrow in the first post points to the cage. The cage is made up of two metal pieces which connect the idler pulleys.

A longer cage will allow larger sprockets in the rear such as those found on a cassette with a 32 tooth big sprocket. A shorter cage derailleur is appropriate for cassettes with smaller sprockets and may give marginally better shift performance.

Shimano specifications require a "GS" mid-cage derailleur for a cassette with larger than 28 teeth. Shimano equipped mountain bikes sometimes use cassettes with up to 40 tooth sprockets and these require a true long cage derailleur.

Long (mid) cage is on the left, short cage is on the right. The longer cage in the left allows larger rear sprockets/lower gears.

nfmisso

This is what I have on one of my commuters with 48/38/28 triple and 11-28T 8 speed cassette: https://www.amazon.com/dp/B00FSRVW52...I29MX5HVQHGGSU I am very pleased with it, and not likely to every again purchase the over priced Shimano RDs.

For a project bike that will have a 52/39 double and a 13-28T 7 speed freewheel; I purchased one of these: https://www.amazon.com/dp/B00FSRVW52...I29MX5HVQHGGSU I have not built up the project yet.

Either would function fine on you Denali. If you are replacing RD's, it is probably time to replace the chain - I use KMC X8.93 chains for all my 7 & 8 speed bikes (and X9.93 on my 9 speeds). And possibly the freewheel or cassette, depending on which you have. Denali's came with freewheels.

Homebrew01

You'll need a 7 speed compatible rear derailleur.

SethAZ 

If your area is so flat that you removed your FD because you didn't need it anymore, then you don't need a long cage derailleur either. The long cage derailleur will allow you to use a larger cog than the 28t you're already using. Do you ever find yourself in your 50/28 gearing and think man, if only I had an easier gear?

curbowman

You need to take into account the "Gear capacity". That is the amount of teeth variation between the biggest and the smallest cogs in both the front crankset and rear cassette or freewheel.

Let's see an example. In the attached picture you can read the specifications of the Suntour V derailer that it has a 24T (T is for teeth) capacity, they also offer a typical setup:

rear freewheel difference: 24T - 14T = 10 T
front rings difference: 50 T - 36 t = 14 T
Capacity needed: 10 + 14 = 24 T

Note that the derailleur capacity is independent of how many cogs or rings the bike has. You can have a triple crankset in front with 50/42/36 and its difference will still be 14 teeth.

Now, let's say you install a cassette with 11-32T cogs on the same bike:

rear freewheel difference: 32T - 11T = 21 T
front rings difference: 50 T - 36 t = 14 T
Capacity needed: 21 + 14 = 35 T

Now you'd need a derailleur with 35T capacity. She Suntour V don't have that much, and neither does the VT. That leaves you with the VGT model, with has a 36T capacity.

However, there is a last parameter to consider, and that is the Stroke. The stroke is the horizontal distance the derailleur cage can travel from the smallest cog to the biggest one.

All the Suntour derailleurs models shown have a 31mm stroke even tough they have different cages. That's because they all share the same upper mechanism (the "paralellogram").

If you had to use the Suntour derailleurs with one of the three cassettes shown in the lower picture, you could use only the XCD-6, whose height is 30 mm. The MicroDrive 7 and 8 speed cassettes are too big for the Suntour V, VT & VGT derailleurs.

Hope this somewhat long explanation helps.

JohnDThompson 

The only advantage a short cage derailleur has over a long cage derailleur is that it is slightly lighter.

Retro Grouch 

There's your short answer: A short cage derailleur will suit you fine.

The longer answer is that the derailleur cage has to be long enough to wrap up the chain slack. A chain long enough to cover the big/big combination will have a lot of slack when it's in the little little. For all practical purposes triple crankset = long cage, double or single crankset = short cage.

Bike Gremlin

Explained all here:
Rear derailleur

bike_galpal

fwiw i think there is only one "weird catch" to this and i believe (thought i could be wrong) it's that MTB derailleurs are often longer than long cage road derailleurs, hence one of the pics here withe "Long (mid)"

might be wrong about those details but suffice to say there is more than just "long" and "short", i think there are in fact 3 sizes and which one is "long" often gets confusing.

it's purely semantic though, since if you're coming from a true short cage road derailleur, any of them will be longer.

upon further thought (if anyone cares about my thoughts.... lol) i think older MTB derailleurs are about the length of a newer road "long" so maybe they defined that standard, although they are now longer. older STX derailleurs and stuff tho are shortish maybe even shorter than the modern long cage road.

fietsbob

Books are a good learning tool, many on bike repair have been written..

old ones in the public library and maybe the acquisition department has bought new ones like Zinn's

redlude97

for shimano road there is only short(SS) and mid(GS), mountain there is short(SS, rare), mid(GS) and long(SGS)

bike_galpal

thanks for clarifying. if i may extrapolate, this means that what a lot of roadies may refer to as "long cage" is actually mid, but still longer than short.

Wanderer

A 16 tooth difference on the front, and a 16 tooth difference on the rear, equals 32 teeth difference. You need a derailleur capable of taking up the slack of 32 teeth worth of chain.

MePoocho

Do I ever find myself thinking that I need an easier gear than 50/28? Good question and my answer is no. My riding environment in Florida is flat, flat, boring, and the only real excitement is not getting hit by the snow bird drivers.

But we do have 55' intercostal bridges. Should I ever venture out and need to cross one I'll stop and manually drop from the 50t chainring down to the 34t'er. Climb the bridge and manually go back to the 50t'er. I know that this sounds kinda ********, but I'm not in a race. Besides a good old leg stretch and butt rub now and again isn't so bad.

Actually the front derailleur was cheap and I never could keep it adjusted so I tossed it. Now I think of my drive train as a '1x'. (That was a joke) Also this bike is my cheap 'learning' ride. Someday I'll have a $2 to $4k sexy ride.... My wife tells me to keep on a'dreaming.

Thanks for the input.

MePoocho

curbowman,

Now that is what I call an explanation! Even someone as slow as I am can 'get-it'. Now I even understand the advertising bullet points......

Thanks for taking the time. Your explanation will remain imbedded in my mental database.

Screen Shot 2017-11-30 at 8.34.55 AM.png

robertorolfo

Ummm, don't forget looks! Short cages look better than long cages. I'm only half-kidding...

fietsbob

UBI has classes United Bicycle Institute

MePoocho

Dude, that is what you thought she said.....