Author Topic: Chain Tension  (Read 630 times)

Chain Tension
« on: January 11, 2017, 08:05:11 pm »
New to riding on fixed. So this is probably a simple or stupid question.
However my chain tension slackens very quickly, set up with tension ok, not overtight nor slack. Chain tug fitted, nuts as tight as I can get them! Ride maybe 50-60 ml and chain is loose enough to cause worries of it coming off, retension required
Bike is 1970's Holdsworth, forward facing drop outs, chain tug Surly!

fd3

Re: Chain Tension
« Reply #1 on: January 11, 2017, 10:28:30 pm »
Check that it is slack for the full rotation, it may vary between slack and tight, which would be based on off-centre chainring.

Re: Chain Tension
« Reply #2 on: January 11, 2017, 10:52:24 pm »
On set up chain set at tight spot and only slightly slack at loosest point. After riding slackest point is really slack.
Chainring set as round as possible as Sheldon Brown! Chainring bolts checked for tightness!

Re: Chain Tension
« Reply #3 on: January 12, 2017, 08:27:38 am »
What sort of nuts are you using?
<i>Marmite slave</i>

Re: Chain Tension
« Reply #4 on: January 12, 2017, 12:01:01 pm »
Miche track nuts with free spinning serrated washers! Changed from those that came with wheel/hub, hub King Kong! Getting really frustrated now, just tightened and reset wheel, went for ride of approx. 30ml and chain slack again!

Re: Chain Tension
« Reply #5 on: January 12, 2017, 12:55:36 pm »
Only two things come to mind:
1) chromed dropouts
2) wheel kinked a bit when you tighten it up.

This is how I used to do it when riding fixed.

Pull wheel back, tighten up both sides with fingers. Using left hand down near the BB, push tyre/wheel back and slightly away from the chain a bit. Tighten up non-drive side.
Chain is almost certainly a tad slack.
with left hand push against side of wheel, shoving it over towards chain. This will tighten the chain and you should have wheel centred. Tighten drive side nut. Check chain tightness, rotating cranks. If chain is ok, do up both nuts bastard tight.
<i>Marmite slave</i>

Re: Chain Tension
« Reply #6 on: January 12, 2017, 01:02:17 pm »
, do up both nuts bastard tight.

This is key, but make sure you take the same length spanner with you in case you need to undo them!
Quote from: tiermat
that's not science, it's semantics.

Re: Chain Tension
« Reply #7 on: January 12, 2017, 02:59:19 pm »
in my experience 3/32" drivetrain needs to be adjusted every 2-300km (depending on weather conditions), 1/8" drivetrain at twice that distance, to compensate for the chain wear. if you need to do it more often it's likely that the axle is slipping - e.g. there might be some play in the chain tug device. if you are using half-link chain I'd swap it to a standard one.
fwiw, i use a closed cam qr skewer on my rear wheel and it doesn't need any additional retention on alloy dropouts - no slippage. i had to use a chain tug on steel dropouts as the skewer did not dig into them to prevent slipping.

Re: Chain Tension
« Reply #8 on: January 12, 2017, 08:13:43 pm »
Thanks Mr Charlie will try that way, what I've been doing is similar, but using chain tug to pull wheel central and tension the chain. I'm thinking of adding another chain tug to further stop any wheel/axle movement. I use a Park Tool which has a C Spanner at the opposite, the end to hex hole, tightening as hard as I can by hand, turning bike over and adding more tightening with my foot. So I would call it Bastard Tight. Frame is Steel, chain, chain ring and sprocket are 1/8", a little concerned I may strip axle threads or nuts at some point!

Re: Chain Tension
« Reply #9 on: January 12, 2017, 08:16:01 pm »
Thanks ZigZag,chain is standard 1/8, no half links!

Re: Chain Tension
« Reply #10 on: January 12, 2017, 08:36:42 pm »
Tugs (which I've never used; they're considered a bit infra dig in snooty fixer circles) usually prevent slippage totally.  Chain wear can be very rapid in wet conditions, and it only takes a small amount of wear to cause visible droop. so this is a bit of a puzzle.
Never tell me the odds.

Re: Chain Tension
« Reply #11 on: January 12, 2017, 09:03:22 pm »
What make/model chain is it? I find the cheap KMC ones stretch pretty quickly.

I agree that with tugs you shouldn't get much movement of the axle - the advantage of these is you no longer have to tighten the bolts so much and can get away with just a 4" adjustable spanner on the road, which I find does for the tugs and mudguards as well.
“That slope may look insignificant, but it's going to be my destiny" - Fitzcarraldo

Re: Chain Tension
« Reply #12 on: January 12, 2017, 09:50:46 pm »
Firstly, you're correct that all is not well. I'm somewhat embarrassed to quote myself, but this is the sort of distance you should expect before a new chain needs retensioning. That's 3/32" chain, so 1/8" should be significantly better.
Your question is very definitely not a stupid one. It is a simple question, and doubtless the answer will turn out to be simple. Nevertheless it's very far from simple finding what that answer is.
 
Various random thoughts: -
Chainring bolts - if they're too long, tightening with an allen key on the outside & the special nut tool on the inside might not have clamped the chainring against the spider. If you can't turn the bolts with an allen key & no nut tool without a lot of force, that looks like an unlikely cause. Is the chainring new?
Axle slippage looks unlikely with a drive-side chain tug & your tightening technique. A 1970s Holdsworth is most likely to have Campag dropouts. If they're not chrome plated, slippage is very unlikely, unless the track nuts are bottoming on something in the axle spacers, or maybe something on the inside of the dropouts. That ought to be visible with careful scrutiny. Symptom... have you checked whether the tyre/rim has moved laterally between the chainstays? RHS slippage can slacken the chain by the amount you describe with only around 5 mm of lateral movement at the rim.
Slippage of LHS of axle looks unlikely. On my 1980 touring frame, the tyre would be rubbing against the RH chainstay with the amount of slack you describe if it were a LH axle issue. Symptom to check is the same as for RH axle slippage.
I've had one chain that measured short of 1/2" pitch when laid out on the workbench. That stretched to a stable length during the usual installation & tensioning routine. That also seems a very unlikely cause.
Bearings... Is bottom bracket tightened securely? Tightness of RH crank on the BB spindle looks unlikely if it's a square taper chainset. Is it? Rear hub bearings look unlikely.. Any lateral play at the wheel rim?

Re: Chain Tension
« Reply #13 on: January 12, 2017, 10:58:35 pm »
Crumbling Nick,
Thanks for your reply, chainbolts fully tight no movement in chainring (chainring centred as much as possible as Sheldon Brown). No obvious obstructions around fork end nuts/hub, nuts seem to fully engage. Chain new, as are rear cog and chainring. Not checked wheel centre, though not noticed any brake rub, will do it all again tomorrow and check. Hopefully it won't change and it's
sorted. If not back to head scratching!!

Re: Chain Tension
« Reply #14 on: January 12, 2017, 11:33:50 pm »
You've reported a loss in chain tension: do you know for certain whether it's movement in the axle/tracknuts, or wear/stretch/elongation of the chain? With a chaintug, axle movement seems unlikely unless you've found a way of using it incorrectly: I'd be inclined to mark or measure axle position so you can eliminate this as a cause.


Re: Chain Tension
« Reply #15 on: January 12, 2017, 11:44:35 pm »
Quote
forward facing drop outs, chain tug Surly

Aren't those chain tugs designed for rear facing dropouts (track ends)?

Re: Chain Tension
« Reply #16 on: January 13, 2017, 12:00:04 am »
Quote
forward facing drop outs, chain tug Surly

Aren't those chain tugs designed for rear facing dropouts (track ends)?

Assuming Tuggnuts, yes - but it's still possible to use them on FF dropouts, and the HurdyGurdy is designed for FF anyway - see 1st and second pics here.

Re: Chain Tension
« Reply #17 on: January 13, 2017, 12:01:06 am »
Brake clearance is minimally altered by axle movements (even asymmetric ones) with traditional horizontal dropouts. The critical measurement is at the chainstays. It's a PITA that brake clearance asseses very small errors (think about lateral accuracy of wheel-building/trueing), but lateral movement of the rim/tyre at the chainstays is less obvious if your frame has space for bigger tyres than the traditional  27"x 1 1/4" (630x32mm in more modern units). Nervertheless, lateral movement at the chainstays is "finger on each side to feel the gap" measurement & definitely not vernier calipers. Since you're in the process of eliminating causes, I'd suggest measuring the distance between the rim & the chainstay on each side with a steel ruler. Repeat after chain has slackened. Result is unlikely to be more precise than +/- a couple of mm, but you're looking for something bigger than that IMHO.

Re: Chain Tension
« Reply #18 on: January 13, 2017, 12:10:10 am »
Maybe the dropouts aren't parallel.

Re: Chain Tension
« Reply #19 on: January 13, 2017, 11:44:29 am »
Thank You All For Your Help/Advice.
Today I've gone through all of your advice, I've checked everything you advised.
However on inspection it appears chain (KMC) is worn, measured over 12" its plus 1/8", which according to Sheldon Brown is excessive. Therefore as drive train has only been ridden some 300 ml
from new.  Chain is going back to Wiggle. What is they say about never assuming!

Which of course means Advice Request Again for Replacement Chain!!

Wheel nuts are open ended.
Drop outs are painted Steel, not chromed. Slightly chewed now especially left side.

With new chain may remove tug, as it seems to be frowned upon.

Re: Chain Tension
« Reply #20 on: March 10, 2017, 07:55:15 pm »
When fitting the wheel, tighten the LH, non-drive, nut (or bolt) first.  For some reason this helps avoid losing chain tension when you tighten the other side.  I can't remember where I read this, but it does work.
Never tell me the odds.