Short drop deralier for 20" wheel trike

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Tilley
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Short drop deralier for 20" wheel trike

Postby Tilley » 7 Mar 2018, 10:20pm

As the ground clearance on a 20" trike fitted with a long drop rear deralier is minimal, has anyone successfully fitted a short drop rear deralier? If so what limitation did the change impose on cassette choice?

OldBloke
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Re: Short drop deralier for 20" wheel trike

Postby OldBloke » 8 Mar 2018, 3:21am

The style and size of the rear derailleur will impact both the maximum size sprocket and the maximum number of teeth that it can accommodate.

Look at two examples:
Compare this road derailleur http://www.microshift.com.tw/en/product/rd-r42-rd-r42s/
With this MTB derailleur http://www.microshift.com.tw/en/product ... l-rd-m61s/
You'll see they have different max sprockets and max capacities (depending on cage length).

The total capacity is the difference between the smallest and largest sprocket plus the difference between the smallest and largest chain rings. On my trike I have a 11-36 teeth cassette (25T difference) and 22-42T chain rings (20T difference), so my derailleur needs to have 25+20=45T capacity.

A short cage derailleur wouldn't work on my setup unless I eliminated one of the chain rings and restricted the range of gears I have available to me.

To install a short cage derailleur you may have to compromise on range.

I've used Microshift as an example because their info was easy to find. Other manufacturers, like Shimano and SRAM will have different capacities for their rear derailleurs. You may be able to find a short rear derailleur that will fit your situation.

Hope this helps and isn't too much info.

Cheers

Ken

OldBloke
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Re: Short drop deralier for 20" wheel trike

Postby OldBloke » 8 Mar 2018, 3:31am

Another thing to be aware of is that Shimano style rear derailleurs (RDs) for road have different shifter requirements to MTB RDs. If you change between road and MTB RDs you will also have to change shifters. I think this applies to 9, 10 and 11 speed RDs, not to 6-8 speed.

As far as I know SRAM derailleurs don't have the same problem.

:)

Ken

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pjclinch
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Re: Short drop deralier for 20" wheel trike

Postby pjclinch » 8 Mar 2018, 9:29am

This doesn't really answer your question, but I looked at the derailleur on my 8-Freight and my wife's Fiero Tour (both with 20" drive wheels) when they first arrived and thought they looked very vulnerable. Well over a decade later neither of them have sustained any damage from bangs. Just remember to avoid dropping off kerbs with the right hand side of the bike at a close angle and it should be fine (this is not hard in practice IME).

Pete.
Often seen riding a bike around Dundee...

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[XAP]Bob
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Re: Short drop deralier for 20" wheel trike

Postby [XAP]Bob » 8 Mar 2018, 9:53am

Trikes also don’t lean, so ground clearance is almost invariant
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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Neilo
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Re: Short drop deralier for 20" wheel trike

Postby Neilo » 8 Mar 2018, 11:59am

I had a long cage on my 20" rear wheel trike, there was about an inch ground clearance at it's closest to the ground.
The problem I had was that when it was at its closest to the spokes/wheel in the 34 sprocket, there was about 2 or 3mm clearance between the cage and the tyre.
I'd built up the wheel myself, so I removed the dishing of the wheel to give more clearance. I think one of the trike manufacturers does that.
or use a medium cage, and avoid extreme big, big sprocket combinations.
If it aint broke, fix it til it is.

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[XAP]Bob
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Re: Short drop deralier for 20" wheel trike

Postby [XAP]Bob » 8 Mar 2018, 12:19pm

ICE use undished rear wheels in an offset rear triangle.

There is no technical requirement for the rear wheel to be central, but it makes turning behaviours symetrical at the limits.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

Brucey
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Re: Short drop deralier for 20" wheel trike

Postby Brucey » 8 Mar 2018, 12:42pm

Tilley wrote:As the ground clearance on a 20" trike fitted with a long drop rear deralier is minimal, has anyone successfully fitted a short drop rear deralier? If so what limitation did the change impose on cassette choice?


it normally affects the total capacity but not so much the capacity for a large sprocket per se. It is sometimes possible to install a tensioner (or modified rear mech as a tensioner) elsewhere in chain run and then you can use whatever RD you want at the rear wheel, provided it will handle the large sprockets OK.

On a bicycle with a 20" rear wheel the rear mech gets filthy very quickly. This is much less of a problem on a trike, but it is still vulnerable to knocks if you are not careful.

OldBloke wrote:Another thing to be aware of is that Shimano style rear derailleurs (RDs) for road have different shifter requirements to MTB RDs. If you change between road and MTB RDs you will also have to change shifters. I think this applies to 9, 10 and 11 speed RDs, not to 6-8 speed. ....Ken


This is not quite (or perhaps not at all) the case. All Shimano RDs have the same shift ratio for 6,7,8,9s, and 10s road, apart from dura-ace 6,7,8s and RD-4700 10s. 11s road (together with RD-4700), 10s MTB, and 11s MTB each have a distinct and different shift ratio.

So provided you steer clear of 6,7,8s Dura Ace, RD-4700, 11s road, 10s MTB and 11s MTB, everything else will work OK.

cheers
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gaz
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Re: Short drop deralier for 20" wheel trike

Postby gaz » 8 Mar 2018, 4:24pm

Hand wash only. Do not iron.

hercule
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Re: Short drop deralier for 20" wheel trike

Postby hercule » 8 Mar 2018, 8:06pm



I wonder if the same effect (chain wrap) could be achieved with larger than normal jockey wheels? That would have the advantage of only two rather than three bearings and less acute chain bends. Wouldn’t upset babies as much either, I suspect.

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[XAP]Bob
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Re: Short drop deralier for 20" wheel trike

Postby [XAP]Bob » 8 Mar 2018, 8:09pm

Not really, the advantagebit has is that the jockey wheel is ‘wide’ when tucked up, but narrow when dropped down
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

hercule
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Re: Short drop deralier for 20" wheel trike

Postby hercule » 8 Mar 2018, 8:14pm

To return to the original subject, the only trike I’ve had an issue with was my first Kettwiesel which with a delta layout has the rear mech dangling in a very exposed position in the middle of the rear axle. I went crosswise over a very narrow sleepin policeman type hump and bent it. I learned from the experience and cross such obstructions at 90 degrees and look out for rocks, etc. My current Kett has a chain take up mechanism that seems to help, though opinions amongst Kett riders an differ as to exactly what it does!

hercule
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Re: Short drop deralier for 20" wheel trike

Postby hercule » 8 Mar 2018, 8:19pm

[XAP]Bob wrote:Not really, the advantagebit has is that the jockey wheel is ‘wide’ when tucked up, but narrow when dropped down


Ah yes, I see that now. Ideas of becoming a millionaire will have to be shelved for today! :lol:

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Tilley
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Re: Short drop deralier for 20" wheel trike

Postby Tilley » 8 Mar 2018, 9:26pm

Ok so to clearly illustrate why I was considering this option. On road I haven't found any real issue with the current set up. However should I wish to venture onto any track that has anything above a very neatly trimmed grass turf the chain will seek out every long blade and mash it up clogging the rear mech, block, and possibly even dragging material into the chain tubes. I know that the easiest option is to fit a Rohloff hub gear but I don't have that sort of cash.

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[XAP]Bob
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Re: Short drop deralier for 20" wheel trike

Postby [XAP]Bob » 8 Mar 2018, 11:09pm

Yes, running through grass can collect detritus in the gearing.

Never managed to get any into the tubes though - and with a little care the position of the dedangler can be optimised ;)

I have often thought that a tensioner in front of the boom, which swings UP would make an interesting alternative design. The derailleur could then theoretically be a single sprocket (though a very short fixed cage might be good for chain wrap/security)
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.