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Old 02-09-11, 06:25 AM   #1
hotbike
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Deraileur Guard

A beloved mentor of mine has always been asking me to see if I could come up with a deraileur guard, to keep objects, weeds and sticks, out of a rear deraileur.

Last night, I had an idea. So I put this prototype of the new deraileur guard on the Type 11. Actually, it's a Trek 720 that I added coroplast panniers to, and rebranded it as the NFA Vehicles Type 11.

The deraileur guard is not made of coroplast, it's something else.

Here are the pictures, straight from my Canon camera:







This has not been test ridden yet, but it clears the chain in all gears, including high, and I don't think it will hit my right heel or ankle when I pedal.
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Old 02-09-11, 09:05 AM   #2
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You're guarding against...what?

Taped-on cardboard won't do much at any kind of speed; heck, some Wally bikes come with looped steel derailleur guards, and THEY don't work well (bend too easily).

Good luck with it, hope it works, but I'm dubious.......
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Old 02-09-11, 01:28 PM   #3
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Great concept, but it wont help if you hit a pavement, like I did a while back. I wish the damn cages weren't so long.. *sigh*


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Old 02-09-11, 02:35 PM   #4
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Don't really have a problem with deraillers being damaged but I can see that guard damaging the bike if is strong enough to withstand hits. And if it won't stand a hit- it will still cause a problem.



Why develop something for a use that is not needed? In 20 years of riding I have only ever damaged one derailler by it getting a hit. That puts it about 60,000miles and most of that is offroad.
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Old 02-09-11, 04:01 PM   #5
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Well, this is only a prototype... maybe it's only a mock-up. I'm testing it for clearance, to see if it gets in the way of anything. I could make it out of Fiberglass, or maybe it could be Steel welded to the chainstay.

Myself, with 140,000 miles of riding over 40 years, I have destroyed two deraileurs, and spent many hours skinning my knuckles, to remove stuff that got wrapped between sprockets. And as I said in the introduction, someone (a Professor of Mechanical Engineering) asked me to work on building a deraileur guard. I should have done this twenty years ago, but I was busy building fairings.

This piece is actually TWO layers of foam board, so it is about half an inch thick. It is weak enough that it will sacrifice itself and be destroyed before it can damage the frame of the bike, which should resolve the concerns you all have expressed. I think it will brush weeds and tall grass aside, and if I hit a piece of baling wire, hopefully it will embed itself in the foam before it reaches the deraileur.
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Old 02-10-11, 12:12 AM   #6
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You might consider having them switch over to an internal-gear-hub.

Avoids the hanging-derailler problem entirely, and is a lot more convenient to shift anyways (shifts while standing still). Only downside is the higher cost.
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Old 02-10-11, 08:38 AM   #7
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Most Xmart bikes come with some kind of derailleur guard.

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Old 02-10-11, 11:01 AM   #8
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You might consider having them switch over to an internal-gear-hub.

Avoids the hanging-derailler problem entirely, and is a lot more convenient to shift anyways (shifts while standing still). Only downside is the higher cost.
Yes, an Internal-Gear-Hub would not have the problem deraileurs have. But what about the front deraileur?-The front deraileur relies upon the slack in the chain, and the tension idlers on the rear deraileur, does it not? So Internal-Gear-Hubs are limited to seven or eight speeds, with no front deraileur.
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Old 02-10-11, 11:03 AM   #9
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You might consider having them switch over to an internal-gear-hub.

Avoids the hanging-derailler problem entirely, and is a lot more convenient to shift anyways (shifts while standing still). Only downside is the higher cost.
Really? That's the only downside you can think of?

Often you get fewer gears or a limited range of gears.
If you do get a similar number of gears, the hub is likely really expensive (you did cover that.)
Many hubs are quite heavy.
Hubs are somewhat less efficient than a derailer setup.
Some hubs have a thing sticking out the side that's just as fragile as a derailer.

I do think that your advice is sound -- internal hubs are great -- but there's more downsides than you mentioned.

(Of course, the advantages are there too -- less maintenance required, fewer exposed parts to break, some give you an infinite numbers of gears.)

Last edited by dougmc; 02-10-11 at 12:00 PM. Reason: fixed a typo
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Old 02-10-11, 11:10 AM   #10
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..., some give you infinite numbers of gears.)
I wasn't aware of any hub with "[an] infinite number of gears". Please be more specific, give a link to the manufacturers site?
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Old 02-10-11, 12:00 PM   #11
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I wasn't aware of any hub with "[an] infinite number of gears". Please be more specific, give a link to the manufacturers site?
http://www.sheldonbrown.com/harris/nuvinci.html
http://www.fallbrooktech.com/nuvinci.asp
http://www.bikecommuters.com/2008/02...hat-a-feeling/

People seem to really like them, though they're quite heavy (six pounds or so, order ones were more.)
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Old 02-10-11, 12:43 PM   #12
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Rohloff duplicates an MTB drive train in 14 ratios. range is wider than the NuVinci.

Im running a Sturmey AW3 + a Schlumpf mountain drive planetary
2 speed reduction gear crank in my folding bike.
Mr Schlumpf as 2 over drive hubs 1.6x and 2.5x

Not stepless like the other , but has 6 useful ratios over a wide range.

no front or rear derailleurs needed.

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Old 02-11-11, 01:50 PM   #13
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Anyway, I took the bike for a half mile test ride yesterday, and the Deraileur Guard clears my ankle. It does NOT interfere with pedaling . It clears the chain in all gears on the rear cluster. However, I did not try it with the chain on the largest Chain Ring. Again , the guard is a half inch thick, so it looks like it will clear, from the outside, but I'm not sure about the inside. I have to test ride it again in the big ring. I may have to cut, grind, or file a groove into the material, if it rubs the chain.

Those NuVinci Hubs look interesting, but they must weigh a lot with those huge ball bearings.
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Old 02-11-11, 03:42 PM   #14
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Most Xmart bikes come with some kind of derailleur guard.

I installed this type of guard on both my derailleur equipped bikes saving one of them from a bad fall when I crashed hitting a stone.
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Old 02-11-11, 11:05 PM   #15
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A solution for a problem . . .
Twice a problem in 140,000 miles? Not like a daily occurence, but once every 20 years?!
Have in over 300,000 miles cyling. Only once had a piece of wire wrap into the cog . . .
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Old 02-12-11, 01:51 PM   #16
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A solution for a problem . . .
Twice a problem in 140,000 miles? Not like a daily occurence, but once every 20 years?!
Have in over 300,000 miles cyling. Only once had a piece of wire wrap into the cog . . .
As I said, Someone else told me I should "Invent" a better deraileur guard. I was only fulfilling a request. I built lots of fairings, and someone said I should make a deraileur gaurd, in addition to the fairings. It is kind of a fairing, if you define a fairing as a "protective shield" .
I'm also thinking about chain-guards. Maybe a full length chain guard could be attached to the top of the deraileur guard, perhaps with two screws?
Maybe if I take my rear wheel off, to change a tube, and the bike falls off the park-bench, the deraileur guard will protect the deraileur from the ground?
Maybe I could be running a full-service LBS someday, and someone will walk in , lay $7.00 on the counter, and buy a deraileur guard?
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Old 02-13-11, 09:42 PM   #17
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Yes, an Internal-Gear-Hub would not have the problem deraileurs have. But what about the front deraileur?-The front deraileur relies upon the slack in the chain, and the tension idlers on the rear deraileur, does it not? So Internal-Gear-Hubs are limited to seven or eight speeds, with no front deraileur.
rohloff speedhub IGH has 14 speeds and 500% increase in gearing. No need for a front derailleur.

I'm like the other folks. I have one damaged derailleur in 45 years of riding derailleur equipped bikes and it was caused by a bad adjustment not impact to anything. I also wouldn't be interested in such a device since I don't encounter much that will damage a derailleur as I ride a road bike, maybe mountain bikers would be interested in such a device. As for your scenario of my bike fallingover when fixing a flat, I always lay by bike down on the NDS so the deraileur hangar won't be bent. I have noticed that typically my derailleur hangar will bend before my derailleur is damaged and it is easy to bend back the hangar with the proper tool.

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Old 02-13-11, 09:49 PM   #18
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Come on guys
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Old 02-14-11, 08:57 AM   #19
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Believe it or not, but a cheapo walmart bike i bought came came with a derailleur guard. I dont know what to make of it, because i will most likely convert it to a single speed.
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Old 02-14-11, 12:07 PM   #20
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The more I look at the homemade 'derailleur guard,' the more I realize I have no idea whatsoever what it's supposed to protect against.
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