Chain Question

Discussion in 'General Questions' started by Lee_K, Jun 28, 2012.

  1. Lee_K

    Lee_K Member

    I have got my bike done to the point where I can ride it and work on fixing the details.

    The power from the motor and my pedaling all gets transmitted thru a derailleur chain. It seems like this chain is being over worked and I was wondering if anyone has experience with how long this chain will last.

    Also what happens if it fails. Does it also take out the derailleur. I can carry a spare chain, but if it breaks and damages other parts I could still get stranded.

    Thanks for sharing any experiences.

  2. Fabian

    Fabian Well-Known Member

    I'm assuming you have a SickBikeParts shift kit or similar system?

    If you do have a SickBikeParts shift kit and if you have a 9 speed chain, from my experience the chain will last 1,000 kilometers (600 miles) to the point of replacement at 1% stretch.

    So far i have not had a chain "fail" from tension induced stress.
    If the chain does fail, it will most likely end up being wrapped around the bottom bracket and sprocket assembly, stalling the engine.
    If not having a spare chain, you'll most likely be walking home.

    From past experience, my derailleur failures have occurred from elliptical chain resonance, which has caused the chain to jump off the lower derailleur pulley, causing momentary slackness which allows the chain to enter a condition called "chain suck", whereby it drags the lower section of chain (closest to the ground) backwards or opposite to it's normal travel.
    This pulls the derailleur past it's point of minimum takeup and tears it from the derailleur hanger, which promptly has it thrown into the spinning wheel spokes, causing lockup of the rear wheel; a severely bent rear wheel; and a derailleur trapped in the rear wheel, also having the inner and outer derailleur cable ripped in half.

    As i've had to replace 4 rear wheels and about 7 rear derailleurs (after smashing themselves to pieces from chain resonance) when first starting out riding. Consequently i've had to design my own chain stabilisation system, which has completely eliminated this condition, and in almost 3 years, it has never reoccurred; giving trouble free mechanical operation.
    Last edited: Jun 28, 2012
  3. Lee_K

    Lee_K Member

    Fabian--That’s a lot of information. To further explain my set-up, I have an 8-speed cassette with sram pc850 chain. Also a Subaru 35cc engine with home made belt and chain reductions. If you go thru a few calculations starting with the 15.6 in-lb max engine output you will get 210 pounds of tension in the derailleur chain. The only bicycle chain specs I could find were for D.I.D. chain, and they claim 1800 pound tensile strength. So it should be good. The bike pulls so much stronger than I am used to with just muscle power that I wanted to get advice from guys who are more experienced.

    I never thought about chain suck before you explained it. So far I have ridden 125 miles without any derailleur chain problems. My throttle is limited to not open more than 2/3 and I keep the speeds down to where I can keep up with pedaling along. So maybe I have not yet pushed it to a chain speed that will cause suck.

    I just bought a spare pc850 chain and will carry it in my tool kit. After 500/800 miles I will replace the original chain and compare lengths to the new one.

  4. Fabian

    Fabian Well-Known Member

    Chain suck is not caused by bicycle speed as an end effect but by the bicycle bouncing around on uneven surfaces.
    I've never had any problems on smooth bitumen but it all went horribly wrong as soon as the bike bashed and crashed over heavily pot holed dirt roads. That's where eliptical chain resonance really raised it's ugly head, 'every time'.

    In my case (in the early stages) i was towing a conventional two wheeled trailer (used for carting all my tools and spare parts) which meant that the bike had to bear the brunt of the punishment, bashing and crashing over potholes so as to prevent the trailer wheels taking the impact; otherwise resulting in an overturned trailer.
    On a bad road (and in such a situation) you are constantly driving the bike into potholes to give the two wheeled trailer the smoothest path of travel.

    All this bashing and crashing, causes the chain to wildly whip around and induce chain suck, if not carefully stabilised.
  5. Lee_K

    Lee_K Member

    Very interesting, I expect my type of riding will not cause those problems.

    I just took my chain off to measure it so I could cut my new chain to the same length. The original chain is a sram pc870 and with 125 miles it still measures 48.50 inches--no stretch yet. My new spare chain is a pc850 and after cutting, it measured 48.55. Or about 0.1% stretch when it’s brand new. I guess it’s worth a few dollars more for the pc870. Anyway, now I have original lengths so I can monitor chain stretch. Thanks for getting me thinking along these lines.
  6. Fabian

    Fabian Well-Known Member

    Just a note on chain quality: buy the cheapest chain you can get.

    I have tried dirt cheap chain right through to a $150 Wipperman chain. The Wipperman chain lasted the longest. This might sound great but it only lasted 15% longer than a dirt cheap chain.
    The cheapest chain will still get you around 1000 kilometers to 1% stretch. The main difference between the cheap and better quality chain is rust and corrosion resistance.
    Considering that (in a motorized application) the chain only lasts 600 miles, rust and corrosion resistance is of no real consequence and shouldn't be factored into the purchase price.
  7. Fabian

    Fabian Well-Known Member

    Most dirt cheap chain specs in at around 0.25% stretch from brand new whilst a high quality chain like a Wipperman specs in at 0.00% stretch from brand new.
    Although this might sound good, generally all chain rapidly stretches to the 0.35% mark in the first 200 kilometers or 120 miles, with the wear rate significantly slowing down after that.
  8. Lee_K

    Lee_K Member

    That makes sense to me. I expect that the cheap and expensive chains are both made from the same links. Since the expensive chains are plated, they need to allow clearance in pin-bushing fit for the plating. So the unplated chain will start out a bit longer. The plating is softer than hardened steel so it wears away quickly. From now on I am buying cheap chain.
  9. Fabian

    Fabian Well-Known Member

    I asked those same questions when starting out, but one thing is true: the chain stretch gauge does not lie!

    It's very frustrating when spending serious money on a chain, thinking that paying double or triple or 6 times the amount over a cheap chain will get those multiples of extra chain life.
    The reason why i spent $150 on a Wipperman chain is because i was getting tired of chain stretch in the early days before i designed and manufactured my chain tensioners.

    My logic back then was: spend 6 times the amount on the best quality chain money can buy, and get 6 times the life out of the chain over a dirt cheap version.
    This was bitterly disappointing logic as i was to find out.
    Last edited: Jun 29, 2012