episodic

I've had my Salsa Casseroll for around 6000 miles now. I'm about to replace my third chain. I replace my chains about a month after they enter .75 stretch - long before they go to 1.0 stretch (per the park tool). Do I necessarily need to replace my rear cassette? I've heard 3 chains = 1 cassette thrown around before - solid advice or YMMV thing? Also - how many miles should I look at getting out of the front rings? It is a Sugino triple. I've recently rewired my bike with fresh cables. Everything seems fine - any other things I should look at? I'm a hundred miles from a LBS - so I have to learn on my own alot. Thanks for any thoughts for things I should double check.

JanMM

If you put a new chain on and it plays well with the cassette, then you are OK. On the other hand, after 6K miles I would tend towards a new cassette to go with a new chain.
I've never measured a chain and replace cassettes approx. every other chain. Chainrings can last a very long time. How do the teeth look? How is the front shifting?

Bill Kapaun

I don't have a Park Tool, but I've heard they can show more wear than you actually have. Readings showing brand new chains to be 1/2 worn out and the like.
You might want to verify the accuracy of your tool on a new chain before considering it to be "gospel".

dsbrantjr

+1 Chain checkers are notoriously inaccurate and can be misleading. Measure your chain with a good steel rule to get a true picture of its wear condition.

ThermionicScott 

The "3 chains per cassette" thing just is a rule of thumb. There's no sense in throwing out a cassette if it doesn't skip yet.

jsdavis

Can cassettes come apart such that individual cogs can be replaced? I tend to ride mostly in one gear combination (somewhere in the middle of the cassette) middle ring so I anticipate significantly more wear in those areas.

furballi

Yes, you can replace individual cog.

ThermionicScott 

It depends -- the older-style cassettes were/are made of discrete sprockets riveted together with spacers. You can drill out the rivets, and swap to your heart's content provided replacing individual sprockets ($7-12 each) is worth the cost. The rivets aren't necessary to hold the cassette together once the lockring is installed.

Some of the fancy new cassettes have multiple sprockets milled out of a single piece of metal, so there's no interchanging those. Look close at yours, and you should be able to tell which kind you have.

If you find that you never use the extremes of your cassette, it may be wise to buy a closer-ratio cassette so that you can spread out the wear a little better.

oldbobcat

I wouldn't call it a hard and fast rule, but it seems to work for me.

Of course some guys insist on getting about 4000 miles out of their chains, and then it becomes one chain per cassette. And the middle chainring.

FBinNY 

There is no rule, only a guideline for expectations.

People who run chains longer might need to replace the cassette after two chains, people who replace chains sooner might have a cassette outlast 5 chains. It also depends how much time you spend on the same few smaller sprockets.

My rule is very simple. I install the new chain, and if it runs fine, then it is. If not, I replace the cassette.

Actually, I replace chains after about 1,000 miles, but save them to be rotated back into service later on. After I've used 3-4 chains I rotate the first back on (cleaned and oiled while on deck) then rotate through the sequence changing every 1,000 miles or so. Doing it this way I typically can get 20,000+ miles out of the set. In 45+ & 100,000+ miles, I've only replaced one freewheel because of wear. The others were retired for other reasons while still functional.

fietsbob

if you preemptively replace the chain then the cassette Will extend its wear life. the balancing act is deciding
how much you want to invest in not wearing one part by investing more in several others..


KMC has a digital chain wear gage , to get more accurate
than the typical ruler check.. a 32nd~16th.. a fraction of an inch over spec in what was 12.0" of chain.. when new.

Looigi

Most chain checkers measure roller wear rather than elongation. The former is much less important than the latter. A ruler is a better instrument for determining when to replace chain. Here's the detailed explanation.

https://pardo.net/bike/pic/fail-004/000.html

BTW, I had the opportunity to discuss this with one manufacturer of a popular chain checker, and they agreed.

GeorgeBMac

OK -- That makes sense...

But, if I were a cassette, would I care WHY the next point of contact is a little further away than it's supposed to be? Wouldn't the effect still be the same?

FBinNY 

The first part of the statement is true, most chain checkers exaggerate wear by including roller wear along with pin wear (stretch). But it isn't true that roller wear doesn't matter as much. Roller wear allows the chain to ride closer to the center of the sprocket effectively reducing the sprocket's pitch which has the same effect as pin wear which increases the chain's pitch. So pin wear vs. roller wear is a case of raising the bridge or lowering the water, both do the same thing.

The issue is that the current guideline for stretch of 1/2% (1-1/6"/12") includes the allowance for roller wear in proportion to pin wear. So including roller wear in the measurement would have you replacing chains prematurely, which is wasteful.

Also, there's roller play in brand new chains, and many (most) chain checkers don't compensate for that and will show even a brand new chain to be worn significantly. I've tested a number of checkers from various makers, and some have shown a new chain to be near the 1/2% replacement point before it was used at all.

DaveSSS 

Don't replace a cassette until you've installed a new chain on it and found that the chain skips on one or more of the most-used cogs. Otherwise, you could be tossing a whole chain's worth of cassette life.

As for chain wear, a precision rule is the very best thing to use for measuring elongation, which is the increase in the pin to pin spacing due to wear on the pins and the bushing formed into the inner side plates.

Elongation is not the only type of wear that can cause new-chain skip, despite what some "experts" contend. Roller wear can be every bit as important. A Campy chain can exhibit very little elongation after 6,000 miles, yet be extremely worn. I've measured as little as .15% elongation over the full length of the chain after 6,000 miles. If that's all you measure then you'll think the chain is in fine shape. If you measure the space between the rollers at that mileage, you may find that the orginal .200 inch length is now .240 inch, which is a large amount of wear. If you measure the side clearance between the inner and outer plates, with feeler gages, you may find the clearance to be twice that of a new chain. When I used a single Campy 10 chain with a cassette for 6,000 miles, I got chain skip on the 19T(steel) cog, when I installed a second new chain. I used another chain with a Record Ti cassette and got far more wear on the 19 and 21T cogs after only 4500 miles.

From that point on, I began using three chains in a rotation, so I will never get new-chain skip and I can use each chain longer. I still toss them if the space between the rollers reach .240 inch.

All chain brands have the same .500 inch pitch, but they do not all have the same space between the rollers, when new. Campy chains tend to measure in the .200-.205 inch range while many other brands measure .210-.215. If you use the space between the rollers a guide for the amount of wear, you need to take into account the measurement when new. I alternate chains before the space increases by .015-.020 and toss them at about .040. If you don't alternate chains, then you'll have to toss them sooner or suffer new-chain skip.

This difference in the space between the rollers is why most chain checkers are inaccurate. A Campy chain might measure zero wear when new, but some of the other brands may show as much as .25% elongation when new. That .25% elongation is totally false and the error is due to the larger space between the rollers. You should subtract the initial false wear from any future readings.

Looigi

Basically, no. The chain rides on the sprocket at the radius where the teeth spacing equaled the pitch of the chain. You could remove the rollers and it would ride at the same radius. (this would be bad, of course, because it would notch the teeth.)