Fixed wheel build, gearing/ chain tension question.

ross81

Hi,

I'm in need of some advice! I'm trying to put together my first fixed wheel bike. I have a specialized sirrus frame which I want to use however I know that its vertical dropouts are going to make this a little bit of a challenge. I have been reading up and hoping that using the right chainring, rear cog and chain I could get the the correct chain tension and not need to use a chain tensioner and make a single speed. I was hoping to try a few combinations of chainrings and cogs and a half link, will this be possible or more to the point probable to work? I have a 50t and a 52t chainring that I was thinking of using to experiment with a 16t and 17t rear cog (all of which I have except the 16) to see if I can get the correct tension with a new chain before having to buy some ss rings and cogs. However cant seem to find any 52t ss rings so might have to just try the 50t and if no good get a 48t ring to try with the 16 or maybe a 15. Is it not poss to get a 52t ss ring?

So to the chain, can anyone suggest a chain that I can use, possibly with 1 half link and do I need a joining link?

Also if I do find a combination that works how quickly would the chain be likely to stretch too much to be a problem with an un-adjustable set-up?

Many thanks.

yocto

If you google ‘52t track chainring’ you should find what you are looking for. Throw in the BCD you need too to get exactly what you want.

Try this link to work out what length chain you need: http://eehouse.org/fixin/index.php

I have not built a fixed gear bike (yet) but I should imagine any one eighth chain will be suitable. Just make sure the half link you buy is also one eighth. Velosolo have a number of different chains and links that would be suitable.
To bypass these chain length & vertical dropout issues you could use a White Industries Eccentric Eno rear hub. Hubjub have them. They are designed for vertical dropouts and ensure that you can have tight tension for SS or fixed. They are pricey though. Will also tackle the issue of chain stretch. They are shiny too. There was one on ebay the other week (attached to a wheel), was very tempted but I’m not man enough for only one gear! I think modern ones need a special WI fixed cog. They also have the option to run a freewheel on the other side for SS (flipflop style).

An alternative to the WI Eccentric Eno is Tr!ckstuff Excentriker bottom bracket. This allows you to move the bottom bracket slightly so as to achieve correct tension. This looks a lot more finicky to adjust than the Eno but it does come in various colours. Nice. This is also pricey. You also need to use a particular type of crankset (like a hollowtech or something…).

Hope this is of some help! Good luck.

Monty Dog

52x16 drivetrain? That's a pretty big gear for road use - people time-trial on less. I would suggest you start with a 46, or 47 chainring unless you live in East Anglia.
Suggest you only need to look at a 3/32" width drivetrains - cheapy Stronglight chainrings are good for experimentation until you find the right combination. Quick-links are fine for singlespeed/fixed and any regular 7/8 speed chain is plenty strong enough - Connex 808 is good IME.
I have been riding / building fixed gear / singlespeeds before it became 'trendy' and have bikes with both a ENO Eccentric hub as well as a Forward Components eccentric BB - (which is more durable that the Excentriker). The eccentric BB can only be used with 24mm spindle, external-bearing chainsets and has only a limited 'throw' which means you still might need a half-link or swap-around chainring/sprocket combos.

stickman

Is this frame one you absolutely want to use? It would seem easier to sell it and get one with the right dropouts, then you'd never have to worry about all this stuff

ross81

Hi,
thanks for you responses. All really useful, especially the link to eehouse. Seems that there might be a combination that should be close in theory. I presume from your replies though that different cogs and a half link is not likely to work alone with no other adjustment. Eccentric hub and bb are both going to be a route that is too expensive I'm afraid unless there is a cheaper bb out there, I have seen a few cheaper tandem versions would any of these work? Or is there any other way to make a small amount of adjustment, presuming I can get close with a chainring cog combo?
I wasn't meaning to combine a 52 and 16, I meant either 50+16/17 or 52 + 17. A 48 may work well for me I only talked about the 50 and 52 because I already have them and thought could try them out before having to buy new ss rings.

smeat

i dont mean to brag or anything but i have all of those sweet ratios in one in a sweet 3 speed fixed gear sturmey archer. its nothing to drag race with but its real nice on a rando bike

ross81

Hi has anyone any experience of filing rear dropouts. Wondering if I could get close with a gear combo then file the dropouts in order to get correct chain tension and give a bit of adjustment for chain stretch?

yocto

This is something that I would look to avoid in case of the dropouts falling apart. Another option which I once read a bit about (but again would personally look to avoid) is filling of the axle itself. As I understand it, you file the axle where it touches the dropouts to an oval shape. I guess this has to be done symmetrically on both sides. By turning the axle from the shortest to the widest width, it will give you a few mm to gain a bit of tension. This method combined with dropout filing (combined with the eehouse link and using a half link), would probably give you the cheapest method of achieving tight tension. Though it may also provide a sure-fire way for getting you into hospital!

But as they say ‘no fear, no fun!!’.

Monty Dog

Filing drop-out or axles = bodging.
If you're planning on running singlespeed i.e. freewheel, then simply fit a chain tensioner. Whatever you do, don't attempt to use a tensioner with a fixed gear.

ross81

I really wanted to ride fixed that's mainly why trying to avoid a tensioner. Guess I'm going to have to buy a chain and try the couple of gear combos that should be close according to the link previously posted. If this doesn't work ill have to get a tensioner and go to ss. I guess the rings and cogs will be exactly same size as my current road bike gear, just slightly deeper teeth. Thought the filing might be an option after seeing it mentioned by Sheldon Brown, didn't think a small bit of accurate filing would be bodging but I can see what you are saying.

cycleclinic

I would also try a 46T maximium with a 16T rear. Adding or removing 1 tooth from the chain ring or rear sprocket will add or remove 1/4" from the total chain length. So using your existing chain ring and cassette wrap the chain around and find a ratio that the chain will oin up on with giving decent tension.

If you find a 52:20T works then a 46:18T will work by removing 2" from the chain (that is 6 teeth from the front = 1.5" and 2 teeth at the rear = 0.5") . A 44:16T would also work by removing 3" from the chain.

Do it this way and you will find a combo that works. I have done it several times on MTB's, works a charm.