Cassette toast before chain stretch? (Shimano XT 12 spd - 10-51T)

[Jeffsy29]

Can you eyeball this cassette and tell if it's needing replacement? It's got about 750 miles / 49,000 climb ft. on it from new; mixed conditions.

With Shimano's gear machining it's hard to tell "Sharktooth" wear vs. Shimano's normal ramping profiles.

No chain slipping (yet) and chain measures OK per Park Tool CC-3.2 Chain Checker.

But, the chain will drop to the 39T cog from either the 51T or 46T while pedaling backwards. Shifting seems ok, but once and a while seems a bit 'jumpy' like ghost shifting. Adjustments seem about as good as I can get them.

Caveat - I did have an incident where I shifted under-load in Boost (of course) and bent some of the steel teeth outward with a "POP". My LBS just manually re-aligned them and all was fine afterwards. I don't see anything out of alignment.

10-51T 12-speed cassettes and 12spd chains are largely out-of-stock, but I'm planning to order an SLX 10-51T and a chain as soon as they become available so I can have them on-hand when this blows.

Just wondering if this is all pre-mature and keep riding or is it bad to wait until the chain slips?

 

[Mikerb]

Dropping the chain pedalling backwards on a 1x system is one of its weaknesses!! The chain ring is acting as the guide pulley and it is miles away and the chainline is at an acute angle!!
If your chain and cassette are working OK, leave them alone and go ride!!

 

[Jeffsy29]

@Mikerb - I haven't had 1x systems drop a chain going backwards all that often unless they were frankenbuilds or not generation-synched.

On this bike, it never happened but now it's all the time. At least I can pedal forward that's what counts... I can just lube in 4th gear.

 

[steve_sordy]

There is some burring to the teeth on the middle gears, but nothing to worry about. I can't see any elongation of the teeth roots. Looks Ok to me.
Anyway, why does pedalling backwards on an emtb cause shifting problems? My cranks rotate backwards but don't move the ring.

 

[Mikerb]

There is some burring to the teeth on the middle gears, but nothing to worry about. I can't see any elongation of the teeth roots. Looks Ok to me.
Anyway, why does pedalling backwards on an emtb cause shifting problems? My cranks rotate backwards but don't move the ring.

I think he is talking a bout locking the crank to chain ring for lubeing cos as you say there is no back pedal on an Emtb.

 

[Jeffsy29]

I think he is talking a bout locking the crank to chain ring for lubeing cos as you say there is no back pedal on an Emtb.

Yup....this is when lubing and backpedaling with a torx bit jammed into on of the chainring bolts.

Someone should make an e-bike lubing thingy so I don't keep spacing out and leaving my torx bit in there only to be lost later on the trial or in the street somewhere. Getting better at remembering but I've spaced on 2 already.

 

[Mikerb]

no sure why you need to back pedal at all for lubing.........what is wrong with pedaling forward? ( with the battery out or disconnected). .....assuming it is on a bike stand?

 

[Jeffsy29]

no sure why you need to back pedal at all for lubing.........what is wrong with pedaling forward? ( with the battery out or disconnected). .....assuming it is on a bike stand?

Getting my stand out, adjusted and 52lb bike up in there is more of a PITA than sit & spin with the torx bit in reverse (but your way may turn out to be more economical if I keep leaving my torx bits...)

 

[Mikerb]

Except lubeing your chain without first cleaning the chain, chain ring, cassette and jockey wheels is a bit of a waste of Lube!!

 

[Jeffsy29]

Sure, ideally I'd get out some degreaser and do all that proper w/ the Park Cyclone and brushes, but that's a bit much after each ride.

These days I choose to just wipe those parts with a dry (or methanol-sprayed) terry/microfiber to quickly pull off what I can, then use R&R Gold per instructions (they claim it cleans too). I used to do the full-on method every handful of rides, but it would grow to weeks between. I find that it all runs a bit nicer when I clean per ride, even though certainly less thoroughly.

 

[Philly G]

Someone should make an e-bike lubing thingy so I don't keep spacing out and leaving my torx bit in there only to be lost later on the trial or in the street somewhere.

Someone has, Sam Pilgrim helped develop it. I have one and it works a treat. CrankStick E-Bike Tool | CrankStick | E-Bike Tool zur Kettenpflege

 

[Doug Stampfer]

Someone has, Sam Pilgrim helped develop it. I have one and it works a treat. CrankStick E-Bike Tool | CrankStick | E-Bike Tool zur Kettenpflege

I can't for the life of me understand what this does or how it works? You can see why I didn't get into engineering school....

 

[Philly G]

I can't for the life of me understand what this does or how it works? You can see why I didn't get into engineering school....

It goes like this:

Essentially a fancy version of putting a stick or allen key in the chainring to jam the crank arm so the chainring spins backwards.

 

[urastus]

the chain will drop to the 39T cog from either the 51T or 46T while pedaling backwards

This never happens to me because I always rest my rear mech in smallest gear. When I'm working on my bike it is in smallest gear (spring in it's most relaxed position). Yes, I imagine it would drop if it is in the lower gears - this does happen to me when I'm on a track and sessioning a feature. Sometimes, if it's tight, I'll wheel the bike backwards to take another run at something. I have since discovered a good way of lifting the bike without turning around to move back.

Re the jumpy / ghost shifting thing. I use wax - I usually have to adjust cable tension when the chain is newly waxed, and again as the chain loosens up. It's only a click or two; if it hesitates shifting up, I tighten, if it hesitates going down, I loosen. Basically, if the chain has lost it's lube it will be quite a bit different in how it operates, and the drag it creates. This may not be your issue, of course.

I have the same cassette; 2,500km and still going. Same chain not yet .75. Mostly steep climbing and descending - because I predominantly use eco at medium (it comes standard on high), I'm often in the lowest (51tooth) gear. So, I mostly use 1st (lowest) to 9th.

 

[Mikerb]

@Bearing Man ............given that emtb motors are designed to prevent back pedalling what effect does it have on the motor to lock the crank to the chain ring??

 

[Mr President]

Getting my stand out, adjusted and 52lb bike up in there is more of a PITA than sit & spin with the torx bit in reverse (but your way may turn out to be more economical if I keep leaving my torx bits...)

you just need a better stand

 

[Doug Stampfer]

you just need a better stand

Now if that could fit on my towbar....

 

[Mr President]

Now if that could fit on my towbar....

tow bar version coming soonish!

 

[slippery pete]

I've just been investigating my ~800 km SRAM GX Eagle drivetrain. Chain shows 0.3% elongation (measurement excludes roller wear). The cassette slips on the 14, 16, 18 and 24T cogs when fitted with a new chain. I also tried a 0.1% elongated chain and that slips on those cogs too. For now the cassette works OK with the 0.3% elongated chain. The worn cogs are where my cadence usually settles for speeds around the 25kmh limiter.

If you're inspecting a cassette for wear, maybe concentrate on the equivalent cogs in your setup.

Chain going backwards and falling off the bigger cogs is partially affected by chain inner plate wear. The chain becomes more flexible as the inner plates wear. The chain will take up a sharper bend where the top stretch wraps onto the cog. This can be sufficient to derail the chain where it might have stayed on when brand new. (incidentally, an old, worn chain can be twisted easily along its length from the same mechanism; rule of thumb is if you can twist a chain through close to 90 degrees it is worn to a significant degree).

 

[urastus]

@Bearing Man ............given that emtb motors are designed to prevent back pedalling what effect does it have on the motor to lock the crank to the chain ring??

could it be that they are designed that way so that they are more akin to traditional bikes? There is quite a lot of drag back pedalling with the motor locked to the cranks; no such drag with non ebikes. For example, imagine trying to do a fakie with that drag? Wow! We have an advantage with fakies, not having to back pedal or worry about what gear we're in, and can set up for the exit whenever we want ; I didn't realise that.

Just thought of a couple more examples for how I ride. I often have to shift pedal position to avoid obstacles, and sometimes I have to ratchet pedal (partial pedal strokes) to avoid pedal strike. Swapping pedal position through opposing tight switchbacks.

(days later) ahh, I was wrong about the fakie - you still have to pedal backwards, albeit without the drag (on the pedals).