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PostPosted: Wed Aug 27, 2008 9:07 am 
Retro Guru
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Joined: Tue Aug 07, 2007 12:22 pm
Posts: 2942
Location: Platsa, Messinias, Greece
A half-link isn't a universal panacea for singlespeed chain tension by any means. All it's letting you do is adjust the chain length by 1/2 an inch instead of the normal inch increments - you could fit one and find that your chain was still, for example, 1/4" too long. That equates to one hell of a lot of chain slop, far too much to use on a singlespeed anyway.

For example, something like only a .010" change of chainstay length (or .020" of chain length) affects chain "slop" by around 1/2" - and quarter of an inch change in chainstay length (or 1/2" chain length) will change chain slop by something like 8 inches (yes, really !)

These figures are based on "normal" SS chainring (32T/34T) and sprocket (16-20T) sizes BTW.

As far as tensioners go, the Surly works well especially in "push-up" configuration, but because it is spring loaded does allow some chain slapping around on bumpy downhills etc. I wouldn't rely on one to take up more than about 1/2" of vertical chain free play for this reason.
Another thing to consider is that any tensioner makes the wheel harder to get in and out of the frame - the nut on the QR fouls the arm on the Surly for example and with the Gusset you have to take the skewer out completely to remove the wheel.

So - your options if you don't want to do any frame modifications ( and don't get lucky with a magic ratio) are -

A sprung tensioner like the Surly ( quiet and nicely built), a fixed tensioner like the Gusset Bachelor (noisier, as it just has a plain polyurethane roller), the White Industries Eno hub (best option for rim brakes?) and the "Excentriker" eccentric BB converter. Both are about the same price (£120-ish) - with the hub you have to factor in the cost of the rim/spokes and wheelbuilding and with the Excentriker you need to budget for an external bearing BB crankset ( RaceFace, Shimano HT2) to use with this .


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PostPosted: Wed Aug 27, 2008 9:11 am 
Old School Grand Master
Old School Grand Master
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Joined: Wed Aug 08, 2007 10:35 am
Posts: 12266
Location: Penarth
Interesting...had never heard of them before
http://tinyurl.com/69hvjs


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PostPosted: Fri Aug 29, 2008 12:27 am 
Gold Trader / MacRetro rider
Gold Trader / MacRetro rider
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Joined: Sun May 25, 2008 11:03 am
Posts: 18207
Location: Sunny Glasgow
Problem solved at least for now,i've bought a sram x7 cassette ,chain,shifter and rear mech,so ill put that on for now.
Ive been off the bikes for 2 years so id have to get a bit fitter before going ss
I've also bought a surly tensioner off harry,so i can change if i need to
But thanks to you all for the advice,much to mull over
:D


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PostPosted: Fri Aug 29, 2008 7:37 am 
Retro Guru
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Joined: Tue Aug 07, 2007 12:22 pm
Posts: 2942
Location: Platsa, Messinias, Greece
If you're running a single chainring you may need to look at fitting some sort of chainguide ( like the DH guys use) to stop the chain jumping off over bumpy going - if you look at slo-mo film footage you'll see how much chains whip around under these conditions, it's a wonder they stay on at all ......
Without a front mech. cage to restrain it, you may find it jumps off a lot.
Running the chain as short as possible helps, as does fitting a bash ring in the big ring position - then at least it can only come off on the inside .


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