Replacing 50T chainring

[livpoksoc]

Had some pretty aggressive chain skipping going on my road bike a few weeks ago.

I have replaced the chain, cassette and jockey wheels, all fine on the bike stand, but when I take it for a shakedown the skipping replicates immediately. I think the issue is going to be the bigger chainring as it only occurs under load on the 50T, not on the 34T. Only issue is LBS told me earlier this year that parts (particularly chainring) for my drivetrain are harder to come by now. I've had a google and bikeinn and condor have it in stock for wildly different prices.

So, wanting to know before I drop £50 on a chainring - is it worth replacing the whole crank/chainring/bb section at the same time and therefore buy into a newer set of parts that spares will be easier to come by in a few years?

Bike is 2014 Trek Madone 3.1, groupset is shimano 105 10spd, with Sram 6xp(gxp?) Chainrings/cranks.

TIA

 

[fritz katzenjammer]

I’d just get the chain ring.

last year I replaced the 52T chainring on my Panasonic, the rest of the crank set was fine so why bother. I had no problem finding NOS bits and the bike is a 1977 model. I even found a new set of correct SR bolts to fasten it on with. Why spend the money if you don’t need to, the parts will always be out there, you may just have to hunt a bit.

 

[CXRAndy]

Take a picture of the teeth on the chain ring. Unusual to get skipping unless the teeth are absolutely worn down on a large gear. Have you checked derailleur spring tension?

 

[livpoksoc]

Chainrings pictured below. Haven't looked at the springs on the mech, but would be surprised as that is relatively new.

 

[Ajax Bay]

before I drop £50 on a chainring - is it worth replacing the whole crank/chainring/bb section at the same time and therefore buy into a newer set of parts that spares will be easier to come by in a few years?

Chainrings such as these will be 'in stock' for decades, BCD assumed as 110mm. Spa Cycles ftw.
https://www.halfords.com/cycling/bi...10-bcd-5-bolt-50t-outer-chainring-421571.html
https://www.tredz.co.uk/.SRAM-Road-Chainring-5-Bolt-110mm-BCD_69069.htm
https://www.spacycles.co.uk/m8b0s210p3054/SPA-CYCLES-110-BCD-Zicral-Outer-Chainring

 

[Dogtrousers]

Take a picture of the teeth on the chain ring. Unusual to get skipping unless the teeth are absolutely worn down on a large gear. Have you checked derailleur spring tension?

It may indeed be unusual, but it has happened at least once, to me. The underlying cause in that case was lack of maintenance: insufficient cleaning and running an elongated chain well beyond its retirement date.

https://www.cyclechat.net/threads/transmission-slip.177569/

Yes, the teeth were very worn
https://www.cyclechat.net/media/big-ring.7878/

 

[wafter]

Those teeth are toast - must have done a lot of mileage / seen little maintenance to get that far gone.

If it helps I believe the groupset is "GXP".

As @Ajax Bay suggests assuming it's a standard BCD you should be able to get aftermarket replacements.

Alternatively if you're a tart about groupset homogeneity you might be able to pick up the "correct" 5700(?) 105 crankset used / NOS, or potentially fit one of the outgoing 11sp R7000 items (with an 11sp chain) as these are apparently dirt cheap currently.

 

[oxoman]

Definitely toast. Just fit new OEM ring or pattern one, they all look the same after the paint rubs off.

 

[livpoksoc]

Ok thanks, good to know it's the chainring. It's 11 years old, Strava reckons 7.5k miles. I suspect it'll be higher with unrecorded rides on this over the years.

I clean the bike regularly, always make sure to scrape off the gunk on the jockeys/chainrings. Chains and cassettes have been updated a few times, new mech fitted to accommodate a bigger 34t cassette a few years ago too.

So is that wear expected with the above, or am I missing some aspect of maintenance to extend the life of a new component? (Not meant to be a snarky ask, genuinely intrigued).

If I source that new 50t, should I do the 34t at the same time - and so I need to order things like new bolts at the same time?

 

[CXRAndy]

Yes it's not unusual for aluminium chain rings to wear down, when driven by steel chain.

Take a photo of the new chain ring teeth as a reference, they should never look like needles points

 

[cyberknight]

Check out strong light chainrings on spa cycles, I'm assuming you need 50 tooth 5 bolt 110 BCD

 

[oxoman]

If your 34 is hardly used then I wouldn't bother.

 

[wafter]

Ok thanks, good to know it's the chainring. It's 11 years old, Strava reckons 7.5k miles. I suspect it'll be higher with unrecorded rides on this over the years.

I clean the bike regularly, always make sure to scrape off the gunk on the jockeys/chainrings. Chains and cassettes have been updated a few times, new mech fitted to accommodate a bigger 34t cassette a few years ago too.

So is that wear expected with the above, or am I missing some aspect of maintenance to extend the life of a new component? (Not meant to be a snarky ask, genuinely intrigued).

If I source that new 50t, should I do the 34t at the same time - and so I need to order things like new bolts at the same time?

Conventional wisdom suggests that you should expect to get three chains worth of wear from a cassette and considerably more from the crankset. I reckon a conservative estimate for the chain life on my most similar bikes would be maybe 4k miles per chain, so I'd be expecting to replace the cassette at 12k miles and the chainring at some significantly higher mileage... so based on this I'd suggest that ring's worn excessively quickly.

Without wishing to drag everyone down my favourite rabbithole wear is accelerated massively by the presence of abrasive particles; which accumulate on the chain due to use in dirty / dusty conditions and their subsequent adherance to wet chain lube.. so wear is a reflection of operating enviroment and maintenance regime.

As such chain life is extended enormously by regular rigerous cleaning of wet-lubed chains (i.e. periodic removal of the wet lube and re-application) or use of a dry lube such as immersive wax. The former should prolong chainring / sprocket life more than chain life itself since wear of adjacent components will be due to contamination on the outside of the chain (which is easily washed off) while the chain's life will be determined by contamination on the inside (which is much harder to remove successfully).

On top of that running an excessively elongated / worn chain will also accelerate chainring / sprocket wear.

So... if you're not already doing so I'd recommend a more rigerous cleaning regime if wet-lubing, or preferably dry-lubing with immersive wax (I'm a convert, many aren't) and checking your chain regularly for wear (look at the Shimano TL-CN42 tool as this is the gold standard) and replacing at 0.5% wear.

From your photo the 34t doesn't look as badly worn, but certainly is worn. Again potentially a reasonable argument for replacing the crankset en-bloc as this my be cheaper than sourcing two rings for the existing one.

No need to replace the bolts at the same time as long as they're in good nick; however you might want to invest in a proper tool for the nuts as they have shallow notches and are difficult to get a purchase on - this is one occasion where aftermarket tools are better than those from Shimano - I bought their crappy little pressed steel tool and it knackered both the nuts and my delicate little fingers

 

[livpoksoc]

Conventional wisdom suggests that in terms of wear you should expect to get three chains worth of wear from a cassette and considerably more from the crankset. I reckon a conservative estimate for the chain life on my most similar bikes would be maybe 4k miles per chain, so I'd be expecting to replace the cassette at 12k miles and the chainring at some significantly higher mileage... so based on this I'd suggest that ring's worn excessively quickly.

Without wishing to drag everyone down my favourite rabbithole wear is accelerated massively by the presence of abrasive particles; which accumulate on the chain due to use in dirty / dusty conditions and their subsequent adherance to wet chain lube..

As such chain life is extended enormously by regular rigerous cleaning of wet-lubed chains (i.e. periodic removal of the wet lube and re-application) or use of a dry lube such as immersive wax. The former should prolong chainring / sprocket life more than chain life itself; since wear of adjacent components will be due to contamination on the outside of the chain (which is easily washed off) while the chain's life will be determined by contamination on the inside (which is much harder to remove successfully).

On top of that running an excessively elongated / worn chain will also accelerate chainring / sprocket wear.

So... if you're not already doing so I'd recommend a more rigerous cleaning regime if wet-lubing, preferably dry-lubing with immersive wax (I'm a convert, many aren't) and checking your chain regularly for wear (look at the Shimano TL-CN42 tool as this is the gold standard) and replacing at 0.5% wear.

From your photo the 34t doesn't look as badly worn, but certainly is worn. Again potentially a reasonable argument for replacing the crankset en-bloc as this my be cheaper than sourcing two rings for the existing one.

No need to replace the bolts at the same time as long as they're in good nick; however you might want to invest in a proper tool for the nuts as they have shallow notches and are difficult to get a purchase on - this is one occasion where aftermarket tools are better than those from Shimano - I bought their crappy little pressed steel tool and it knackered both the nuts and my delicate little fingers

Interesting to read on mileage. I think this will be the third cassette on this bike. The original from new, then the first 34t was a replacement to improve climbing, this being a like for like 34t after doing the chain and jockey wheels, trying to go through process of elimination, rather than diagnosing it as a cassette issue to begin with.

The whole chain and cassette replacement came after jockey wheels (which were wobbling around excessively), and I had the new spares in the garage.

I wonder if my weight might also be a contributing factor to wear over a featherweight rider? (Just a theory).

I typically use muc-off wet lube, though the last 12mths this bike has had muc off dry lube as it's been my turbo/sunny day bike.

 

[wafter]

Interesting to read on mileage. I think this will be the third cassette on this bike. The original from new, then the first 34t was a replacement to improve climbing, this being a like for like 34t after doing the chain and jockey wheels, trying to go through process of elimination, rather than diagnosing it as a cassette issue to begin with.

The whole chain and cassette replacement came after jockey wheels (which were wobbling around excessively), and I had the new spares in the garage.

I wonder if my weight might also be a contributing factor to wear over a featherweight rider? (Just a theory).

I typically use muc-off wet lube, though the last 12mths this bike has had muc off dry lube as it's been my turbo/sunny day bike.

Cool - so sounds like your parts are wearing at conventional rates relative to each other, if arguably quickly overall (again, this is all relative since, for example in some filthy MTB applications you're looking at chain lifespans in the hundreds rather than thousands of miles).

Weight could be an issue although it's really all about the force you put through the pedals - so assuming you're of average strength I'd not expect this to accelerate wear.

Personally I'm not convinced by Muc-Off stuff (and I don't think it has a great rep in various tests) however really the downfall of any wet lube is the fact that it's wet and collects contamination. Sounds like the drivetrain is having an easier life now, so I imagine the bulk of the wear has occurred before the lubrication / usage changed.