stargazer48

I returned to biking at the beginning of the year and bought a Zizzo 8 speed 20" folding bike. After 3 months, I was primarily using the 8th gear at least 60% - 70% of the time. I even changed out the 48T chain ring for a 52T because I was spinning too often on flats. After 1700 miles, I mistakenly though I needed a new chain because the chain started to slowly drop off. When I installed a new one, it skipped on the 8th gear only when I pushed the pedal hard. I re-installed the old chain and the skipping of course stopped. I got a Park tool chain checker and tested several sections of the old chain and the wear was not at 75% yet. I didn't lube my chain until about 800 miles. My question is, since I use the 8th gear (11 cog) quite a lot, how many miles can one get on that gear before having to replace it? The Zizzo people were kind enough to send me an 11 cog gear so I am ready to install it when the chain is at 75%.

jccaclimber

Total riding miles isn’t a great way to measure individual sprocket lifespan given all the variables in use.
Assuming the correct length chain and proper derailer adjustment, if you are skipping under load with a new chain then it’s time.
While there are plenty of upsides, you have found a notable disadvantage to small wheel sizes. Some have gotten around this with even smaller rear cogs, which hastens the issue. Others do what you have done and gotten a bigger front ring.
The good news is that the 11t is often available separate from the rest of the cassette and is easy to change.

stargazer48

It's time to what, change the 8th gear?

Bill Kapaun

My PARK chain checker reads .25% high. Not uncommon for CC's to read high.
With the chain off, I measure a 3' section with a tape measure (1-37 inch marks to avoid an often inaccurate "hook") and divide by 3 to get an average per foot.
This reduces the reading error of lining up the ends of the tape measure. More than 3' seems to make it disproportionately more difficult to line up the ends.
Compare that to your CC for a "calibration".

That said, if a new chain skips on a cog, that cog is worn. (assuming an undamaged chain/stiff link)
Since it's an end cog, you can get by with either a 7 or 8 speed cog no problem. More/less than that, maybe with/without noise?

For many riders, they seldom use an 11T cog if they have one. They may be a source of lightly used 11T cogs. (or maybe a friendly LBS)

Iride01 

I thought for 11 speed rears it was recommended to replace the chain when it's beyond 0.5% wear which is not quite a 1/16 inch beyond the 12" mark. 75% wear would be 9 inches past the 12" mark so I hope you meant 0.75% wear which will be 12.09" or a tad less than 3/32" beyond 12".

With older stuff 8 speed and less I was thinking some might let it go till at the 0.75% wear or maybe as far as 1/8" out in 12.

KerryIrons

Before you do that (you might not even be able to find that cog) ride it for a couple 100 miles. The new chain might bed in and eliminate the skipping. But the standard way to determine whether you need a new cassette is when a new chain skips.

stargazer48

Actually, the Zizzo people gave me a 11T cog to replace it. I was just going to wait until the chain was at .75 to replace it and the chain but your suggestion seem like a possible solution.

stargazer48

I'm not sure if you went off topic BUT, I have a 8 speed drivetrain NOT an 11 speed. I was referring to my 8th gear which is an 11 cog gear.

Iride01 

Well you mentioned several times about chain wear of 75%.. So it was sort of trying to get you to realize you were using incorrect wear amounts.

If that's off topic, then I suppose your correction of my mistaken understanding of what you related is also off topic! <grin>

Just in fun, relax and don't get your BP too high.

Andrew R Stewart 

Classic example of enough use of the high effort gear (cog) to wear it at a far faster rate than what most maintenance and riding technique books/interweb postings are based on. But very common with riders who don't pay attention to or follow said guidelines.

Warning- the following is satire... When I was a kid I wore out my left knee area on all the pants my mother bought me. It must be because the pants makers used thinner material for the left side... Satire over.

Most current manufactures design their products to be used in a manor that reflects the marketing and feedback they have. Meaning that their cog sets have materials and designs that will hold up to the "normal" use for an acceptable time (miles) frame. What's normal is a great next question. By most published writing normal is to ride at a cadence of about 70-100 RPM. My math has a 20" wheel with an 11/52 combo resulting in about 17mph per 60 rpm. Any idea as to your average cadence, or speed? Andy

stargazer48

Please don't take offense. I know people try to be helpful but if they don't read the thread clearly, they are not. I wrote the following two sentences which say the chain was NOT at 75% and I have an 8 speed cassette not 11 speed as others misread. I wrote, "I got a Park tool chain checker and tested several sections of the old chain and the wear was not at 75% yet" then I wrote "The Zizzo people were kind enough to send me an 11 cog gear so I am ready to install it when the chain is at 75%." I should have wrote 11T cog even though I mentioned 8 speeds several times. Take care.

jccaclimber

Correct. Assuming an otherwise well maintained system, if a gear is skipping under load that gear and/or chain is due for replacement. Since you’ve tried it with a new chain the issue is probably with the gear. I’m assuming your rear derailer is properly adjusted.

Using a new chain until it *maybe* stops skipping is another way of saying “use the worm gear so that the new chain wears out extra fast”. Not a great plan.

A lot of chain checkers aren’t terribly accurate, so your outgoing chain may or may not be due for replacement. If it is, then it’s just wearing all the other gears faster than needed.

The good news here is that 11 tooth sprockets are cheap and easy to replace, plus you already have a spare.

Hondo6

I think you missed one of Iride01's points. He was chiding you about a missing decimal point in your statement.

Your chain is nowhere near 75% elongation. In fact, assuming your chain checker is anywhere near correct it's nowhere near even 1% elongation.

Chain wear is determined by measuring that chain's elongation. This is often but inaccurately termed "chain stretch". The term is inaccurate because nothing on a chain actually stretches; the small gaps between parts simply become larger due to wear and line up in the same direction when under tension, thus making the chain a bit longer.

Elongation is determined by measuring a segment of chain - typically 1 foot, or 12 complete links (inner + outer = 1 complete link). For most accurate results, this should be done with the chain under mild to moderate tension.

When new, 12 complete links should measure exactly 12 inches. On a badly worn chain, it will measure closer to 12 1/8 inches. Divide the measured length by 12, subtract one, and convert the remainder to percentage. For a chain that measures 12 1/8 inches for 12 complete links, that's a bit over 1% elongation.

You can also measure a 3' section, or 36 complete links. In that case, you'd of course divide by 36 instead of 12. Measuring a longer segment of chain is more accurate, but is also a bit more of a pain in the butt.

Chain checkers are a simple mechanical device that are calibrated to eliminate the need for doing the calculations, but are not always perfectly accurate. Moreover, they're calibrated to measure elongation in fractions of a percent - e.g., 0.5%, 0.75%, etc . . . .

That is what Iride01 was chiding you about. To be correct, you should have been saying "0.75%" wherever you said 75%.

A chain that was worn to 50% elongation would measure 18 inches for 12 complete links; a chain worn to 75% elongation would measure 21 inches for 12 complete links. I'd have to look up pin and link dimensions for bike chains and do the calculation to be sure, but off the top of my head I don't think either is even physically possible. I'm pretty sure one or more of the pins or links would be worn completely through (or would have become thin enough to break during normal use) well before a bike chain elongated that much.

70sSanO

Not to nitpick, but the cog closest to the dropout, the 11t in your case, is generally referred to as the 1st position cog regardless of what a shifter may show. Every bike has a first position cog and the counting goes from there until you run out of cogs.

It has been like that for as long as I can remember, which at my age may mean last Tuesday, but nevertheless, a long long time.

John