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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 05-16-10, 03:08 PM   #1
chucky
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use two chainrings for chain stretch?

Anyone ever try taking up the slack due to chain stretch by switching between two chainrings one tooth apart?

For example, you bolt a 39T chainring on one side of the crank spider and a 40T on the other. The difference in circumference is 1/2" so when the chain stretches 1/2" you move from the 39T to the 40T to take up the slack. Then when it stretches again you remove a link and move back to the 39T (-1"+1/2"). And repeat until it's time to replace the chain.

Or maybe they should be 2 teeth apart since the chain only wraps around half the circumference?

Does it work?

Last edited by chucky; 05-16-10 at 03:12 PM.
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Old 05-16-10, 03:10 PM   #2
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You should get a new chain when it gets about 1/4" longer than it's supposed to be, IMO. Maybe 5/16" tops.

But if, in fact you have a chainring that's 1/2" bigger in circumference, that doesn't mean it's taking up 1/2" slack.

Never tried it, myself.
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Old 05-16-10, 04:21 PM   #3
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Then you could accelerate the wear on two chainrings.

Come on! The real issue is not the change in length but the change in link spacing caused by the chain WEAR that will result in additional friction/wear of the cogs on all used drive gears. But you could keep the worn out chain and just keep adding additional gears.

It's a dillusional solution to a problem that is easily solved by (as LesterOfPuppets said) put on a new chain. Of course you may have already caused 'chainring stretch' by using a worn chain too long and even a new chain won't fix it without all new gears. Chains are vulnerable, expendable, replaceable, and inexpensive.

You sound like a doctor - treat a symptom rather than the cause.

"Now go do the right thing."
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Old 05-16-10, 05:48 PM   #4
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getting a new chainring changes nothing. The chain it stretching between the links, not adding an extra link in the chain.

The teeth in the cog and chainring are still the same distance apart. If you could get a new cog and chainring with teeth spaced a little farther out then that would work, but the chain would snap soon anyway!
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Old 05-16-10, 05:57 PM   #5
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for example, you bolt a 39t chainring on one side of the crank spider and a 40t on the other.
Haha, how exactly would you do this?
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Old 05-16-10, 06:15 PM   #6
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As has been said, by the time the chain is stretched a full tooth the chain is beyond toast and has probably eaten up the cog and chainring. Chains are cheap, much cheaper than replacing cogs and chainrings.
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Old 05-16-10, 06:22 PM   #7
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Come on! The real issue is not the change in length but the change in link spacing caused by the chain WEAR that will result in additional friction/wear of the cogs on all used drive gears. But you could keep the worn out chain and just keep adding additional gears.
No for small amounts of wear the real issue is the slackness caused by a longer chain. That's why singlespeed bikes have had tensioning mechanisms since time immemorial.

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It's a dillusional solution to a problem that is easily solved by (as LesterOfPuppets said) put on a new chain. Of course you may have already caused 'chainring stretch' by using a worn chain too long and even a new chain won't fix it without all new gears. Chains are vulnerable, expendable, replaceable, and inexpensive.
They're really not that inexpensive. Sure the cheap bottom of the barrel ones are cheap, but a decent chain costs more than some entire bikes at wally world and they have much longer usable life spans than the profligate chain wasters like to admit.

As it is written:
"The end of all things is near. Therefore be clear minded and self-controlled so that you can pray. Above all, adjust each others chains tightly, because tension covers over a multitude of sins." 1 Peter 4:7-8

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Haha, how exactly would you do this?
You just sandwich the spider between them, line up the holes, and put in the bolts. Same way you attach a chain guard (you might need slightly longer bolts).

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As has been said, by the time the chain is stretched a full tooth the chain is beyond toast and has probably eaten up the cog and chainring. Chains are cheap, much cheaper than replacing cogs and chainrings.
That's funny because over the years I've taken about three links off the chain on my primary bike due to stretch and it's still going strong. Although it's started making nasty popping and grinding sounds after this last winter, I wonder if it will ever die.

Last edited by chucky; 05-16-10 at 06:44 PM.
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Old 05-16-10, 06:42 PM   #8
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I suppose if you're really gonna go for it, You'll want to get a second rear wheel with a cog you'll use only with wasted chains and a spacer to get said cog inline with the big ring up front.

I still think you're crazy. I do just fine with $13 chains, sometimes I splurge and blow a whole Jackson on one!

They're usually cheaper than tires, but typically last longer, so why not replace 'em when they hit 1/8" over a 12" run?

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Old 05-16-10, 11:47 PM   #9
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You guys are right. This is basically the magic ratio method streamlined for making a quick adjustment. It's not gonna work well.

But the good news is I realised how little adjustment it takes to tension a chain as it stretches (less than 4mm!). You should find that much play in any set of dropouts that aren't completely vertical (certainly mine).
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Old 05-17-10, 09:00 PM   #10
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Old 05-17-10, 09:56 PM   #11
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Old 05-18-10, 07:38 AM   #12
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jaco, my thoughts exactly.
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Old 05-18-10, 08:04 AM   #13
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+1
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Old 05-18-10, 10:25 AM   #14
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A couple of years ago there was a guy that would bring his completely un-maintained road bike into the shop , (on busy saturdays of course) and complain that it was not shifting right or stopping quickly enough.
We would put the bike on the stand and spend 20 min explaining all the things that needed replaced adjusted.
Then we would give him an estimate of the time and cost.
He would say no I don't want to do all that just fix the shifting....another 20 minutes explaining chain wear and why his cog teeth look like shark fins....He would say "I don't care about that, I just want you to fix the shifting"
The shop owner would have to come over, pull his bike from the stand and walk him out back and explain that we don't have time for him today and to come back another time.
Finally, one day his chain breaks and the guy comes in for a new chain. We replace the chain, explain what is going to happen when he tries to ride (because he only wants a chain) and send him off.
He comes back the next Sat and in front of a shop full of customers starts yelling that we ruined his pride and joy.
Fast forward to today on bike forums........

Enjoy
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Old 05-18-10, 06:43 PM   #15
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KMC 410s are 10 bucks. Find a friend with a chain tool and you have no excuse to not replace your chain.

Either that or we all just got trolled.
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