How to tension chain

[db]

I have obtained a good quality bike. The rear fork points
straight down. I want to use it without a derailleur, just
a single rear sprocket, but then I can't tension the chain
by pulling the rear wheel backward along the fork.

Is there a way to put tension on the chain without a
derailleur?
--
Dieter Britz

[Catrike Rider]

On Sun, 4 Jun 2023 13:14:55 +0200, db <dieterh...@gmail.com>
wrote:

https://duckduckgo.com/?q=bicycle+chain+tensioner+single+speed&t=ffab&ia=web

[funkma...@hotmail.com]

A single-speed chain tensioner is the easiest solution. There are a number of them on the market, pretty much any one of them can do the trick. However, when you do the search there will invariably be chain _guides_ that come up in the results. While these do create tension on the chain, they aren't meant for single speed applications. They are meant for mountain bikes (downhill bikes) in order to keep the chain from popping off the chainring over extreme terrain. Take this list for example.

https://theadventurepub.com/best/bike-chain-tension-idlers/

#1 is a chain guide meant for MTB use. #2 is the type you need.

However, if you want to impress your friends, you could go the route of calculating the length of the chain based on your desired gear ratio and chainstay length (btw, it called 'rear dropout', not 'rear fork', and the ones you have a vertical).

Here are a few good links.
https://www.omnicalculator.com/sports/chain-length
https://math.stackexchange.com/questions/123361/distance-between-two-gears-surrounded-by-a-known-length-belt
https://bicycles.stackexchange.com/questions/8608/what-would-be-the-definitive-formula-to-calculate-chainstay-length-from-sprock

I set up my Giant Team TCR as a single speed, using a chainring/cog of 37/16. I forget how many links I needed. It was a little snug, but worked with a little coaxing.

[AMuzi]

The simplest answer is actually a derailleur.

You don't need a fancy model. Any under-#20-new steel
changer with no cable will be adequate for chain tension if
you're using a freewheel or gearbox. These may often be had
for free.

Style points in selected cultural melieus for a 'chain
tensioner' which is an expensive thing, essentially a
truncated derailleur which cannot shift. They come in bright
colors too.

Neither is useful for fixed gear or a coaster brake.

It is possible to set up your single-point-ends frame by
judicious selection of chainrings. A slack 46x18 may be
functional with a 47x18 for example and the gearing
increment is relatively small (~2%). Using 1/8" chain,
which is dirt cheap, just toss the chain when it seems slack
although note that chain a little slack works fine in
practice but certainly avoid tight chain which eats crank
and hub bearings quickly:
http://www.yellowjersey.org/chainchk.jpg

Other paths include is use of a half link or carefully
cutting out the ends by a millimeter or two.


Unless you're running fixed gear or coaster I recommend a
derailleur.

--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971

[AMuzi]

On 6/4/2023 6:14 AM, db wrote:

p.s. Almost forgot to include the elegant White Eno hub.

[Mike A Schwab]

Use a derailleur style bicycle chain tensioner. Looks like a single jockey wheel.
https://www.amazon.com/s?k=bicycle+chain+tensioner&crid=3IQDKMY76GEUW&sprefix=bicycle+chain+tensioner%2Caps%2C230&ref=nb_sb_noss_1

[Jeff Liebermann]

On Sun, 4 Jun 2023 13:14:55 +0200, db <dieterh...@gmail.com>
wrote:

As others have suggested, a spring loaded chain tensioner is probably
the easiest and best solution. However, if you want something weird
and simple, think about adding a "ghost ring".
<http://rollinginboston.bostonbiker.org/2012/04/08/installing-a-ghostring-on-a-single-speed-or-internally-geared-bicycle/>
<https://www.mtbr.com/threads/interesting-chain-tensioner-idea.202065/>
I've never tried it but suspect it just might work.

--
Jeff Liebermann je...@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

[Frank Krygowski]

On 6/4/2023 3:53 PM, Jeff Liebermann wrote:
> On Sun, 4 Jun 2023 13:14:55 +0200, db <dieterh...@gmail.com>
> wrote:
>
>> I have obtained a good quality bike. The rear fork points
>> straight down. I want to use it without a derailleur, just
>> a single rear sprocket, but then I can't tension the chain
>> by pulling the rear wheel backward along the fork.
>>
>> Is there a way to put tension on the chain without a
>> derailleur?
>
> As others have suggested, a spring loaded chain tensioner is probably
> the easiest and best solution. However, if you want something weird
> and simple, think about adding a "ghost ring".
> <http://rollinginboston.bostonbiker.org/2012/04/08/installing-a-ghostring-on-a-single-speed-or-internally-geared-bicycle/>
> <https://www.mtbr.com/threads/interesting-chain-tensioner-idea.202065/>
> I've never tried it but suspect it just might work.

I've seen that done on the synchronizing chain of a tandem.

--
- Frank Krygowski

[funkma...@hotmail.com]

On Sunday, June 4, 2023 at 3:53:58 PM UTC-4, Jeff Liebermann wrote:
> On Sun, 4 Jun 2023 13:14:55 +0200, db <dieterh...@gmail.com>
> wrote:
> >I have obtained a good quality bike. The rear fork points
> >straight down. I want to use it without a derailleur, just
> >a single rear sprocket, but then I can't tension the chain
> >by pulling the rear wheel backward along the fork.
> >
> >Is there a way to put tension on the chain without a
> >derailleur?
> As others have suggested, a spring loaded chain tensioner is probably
> the easiest and best solution. However, if you want something weird
> and simple, think about adding a "ghost ring".
> <http://rollinginboston.bostonbiker.org/2012/04/08/installing-a-ghostring-on-a-single-speed-or-internally-geared-bicycle/>
> <https://www.mtbr.com/threads/interesting-chain-tensioner-idea.202065/>
> I've never tried it but suspect it just might work.
>

I've never seen a 'ghost' ring set-up before. I'll have to try it.