vane171

On this secondhand bike I bought recently is large 53T ring that has what looks like some serious scuffs, even gauges. Maybe I should consider replacing it? The 39T ring looks well preserved.
I can buy locally just the big chainring for $85 CAD but I found on eBay cranks with lightly used chainrings of the same make, only difference is the arms are 170 mm

I have always been riding 172.5 mm cranks and I wonder if I should go for 170 mm on this bike. I am not a big spinner but I find when I try for high rpms near 90 p/m, I can lose rhythm but that could be just what is called spinning out?

For only some 50 $ extra I could have a used but still decent big ring plus shorter cranks. I am 5.8+ (5.8 + 1/2") and the bike is M size (54cm).




This and next picture are the same view, one with flash and the other without







BTW what are those rivets on the big ring for? They are spaced irregularly, maybe they help the chain to move to the small ring or back to the big one?

blamester

What's it like when you ride it?
This and cost are what makes the descision.
If it rides fine why replace it. If it is causing minor issues and you don't mind buying a new one replace it.
If it cause major issues you have to replace it.
Very unlikely it will suddenly fail and leave you stuck at the side of the road.

Andrew R Stewart 

The gouging on the shift gate teeth suggest shifting while powering the pedals. The "rivets" are lift pins, they act like a step stool to help the chain get lifted up to the larger ring. They are located around the ring where the designers think they should be to do this.

Excepting the shift gate teeth tips the rest of the teeth look slightly worn but not worthy of a "Must do" replacement, IMO. How about some additional data like miles ridden, chain replacements, race/hard Training, indoors only or fast recreational use? Andy

Drew Eckhardt 

It's fine if it doesn't skip or downshift when you're cross-chained, noting that you can crash if you're leaning forward during an uncommanded downshift.

vane171

I bought it from previous owner and didn't ride it yet, at least not ride to the extent to uncover problems with chain/rings. I took it partially apart since during cleaning I noticed some BB friction, as I detailed in my other recent post which you maybe saw.

I thought the crank arms didn't spin quite freely and when moving them slowly, I felt bearing balls a little and thought BB was maybe over-tightened. Being new to this modern BB, I assumed it being like the old ones with lock nut that backed off the tension on bearings.
As I said there, the NDS bearing has some friction in it compared to the DS one. With grease making it slippery, you need to get the grip on it to move it, vs the other side, the DS. I bought a new BB and it is still to arrive.

Bike looks exactly like this except handlebars are different, not jutting up as much, but only a little. They were changed to Vision Carbon bars by previous owner.

vane171

The previous owner had it since 2010 (original bought it in 2007). From what he said, he is not a racer, maybe the original owner who had it some three years may have been. I gathered he is fairly accomplished hobby rider, he said due to some hips problems, he stopped using the bike and in his place he had several nice but only recreational like bikes for family outing like. In the selling note, he said,
I don't really have any definite reason to disbelieve what is claimed. I had the impression of honest dealing. The BB is original and I am sure still ride-able, I figured to replace it to start on new leg with the bike. From the looks of it, I have the impression the bike was serviced in a bike shop, by which I mean everything properly greased and tightened and ship shape, so to speak. It feels like I got what I was buying.

The chain marks like you say, are from shifting under the load. Not my style, I don't ride that hard or without regard for chain. The owner didn't look like a brute, just average build, 5.10"

Wheels and the cassette do look newish, chain I have doubts about but could be new last year as claimed, I am no expert to judge chain. I just noticed when closely examining that it has beginnings of rust or what looks like it. But that could be due to standing in garage this whole winter (was long to sell, also you don't bike in winter as a rule anyway). Didn't clean it yet because still waiting for chain tool pliers to come in mail. Just surface wiped it a bit to stop getting dirty whenever I touched it. I suppose I should have ordered a chain gauge for checking chain length, never worried about it on my own bike.










This last image shows the 'grooves' on the round sides are from manufacturer, not worn edges as it might seem from the other pictures, at least to my un-experienced eyes.

Wilfred Laurier

Those chainrings do not look bad at all. I think some of the 'wear' you pictured was actually manufactured tooth profiles to help with shipping. There are a few gouges and nicks, but nothing that should require replacement.

Generally speaking, when chainrings are work the teeth get a asymmetrical profile when viewed from the side, and yours does not as far as I can see.

As for the chain, you cannot see chain wear - the wear happens inside the links where the pins meet the bushings. You can detect wear by measuring a length of chain - put a ruler up against the chain when it is mounted on the bike (big chainring and small cog put the chain in the easiest position for access), and measure the distance from the edge of one pin to the edge of the pin 24 links away. The measurement should be exactly 12" and any amount over that is caused by wear. If 24 links are 12 1/16" or less then you can probably just replace the chain and keep riding. If the chain is worn more than 1/16th of an inch over 24 links, then it is likely the rear cogs have worn to match the wear in the chain and replacing the chain will result in skipping under load.

Chainrings usually last longer than chains and cassettes, so it is common to replace several chains and even cassettes before you have to replace a chainring.

vane171

Thanks a lot for explanation and reassurance. I will check the chain stretch tonight. I believe I can still measure it when the chain is dismounted if I put some tension on it. Cassette looks like new when clean, don't see any wear on it whatever. I think the shifting under load that scuffed the chainring was probably done by the original owner who had it for the first three years.

But last question remains - 172.5 vs 170 mm crank arms. I tried to search if there is thread on crank arms length but didn't find anything, I wonder if I should make new thread on it. I imagine it would have already been discussed and flogged to death (with everybody getting tired of it like the greasing thread) but maybe that should be in other forum sections?

San Rensho 

Pretty straightforward. If you mash, get longer cranks, if you spin, get shorter cranks, also, shorter cranks give you more clearance when leaned over and pedalling in a corner. I can tell the differnce betwee 165mm cranks and 175, but you are not going to feel the diffefence between 172.5 and 170.

tFUnK

Teeth look fine. There's some wear but the more prominent grooves are the shift ramps. Give it a quick tune up and see how it rides. If you're the OCD type then you'll want new components anyway.

Bigbus

That chain needs a serious cleaning if it isn't stretched out. I doubt you can tell the difference of 2.5mm in the cranks. But I would replace the BB and put it together as is and see what you got before I started throwing parts at it that you might not need. Good luck,

robertorolfo

As others have said, the 2.5mm difference in crank length will probably be imperceptible. And, from what I have seen, I think most calculation methods would recommend a 170 for a 5'8" rider anyway.

https://bikedynamics.co.uk/FitGuidecranks.htm

vane171

That's why I am looking at other factors coming into consideration when deciding to buy those 2.5mm shorter cranks - with used BB included (on ebay for some 100 USD). You and the other posts just confirm what I was thinking, how much difference those 2.5 mms can make... but it is move in the right direction

I am thinking I could pass these 172.5 mm cranks to my old bike (with that used BB that would come with those shorter cranks), wouldn't need to put them on shelf or try to sell them. There is a chance it might fit, the frame is from mid seventies (but everything on it is of later date), still decent, with threaded BB (with square tapered axle, cups with balls in them... and 172.5 mm cranks, so that would be no change.

But the new 39T ring would be smaller which would be welcomed, I think I have perhaps 42T small ring on that bike. But finding out if it would fit will have to wait until it is possible to fly back to EU. I would still use that bike when I need to lock it someplace in town, couldn't do that with this new bike.

vane171

I have a follow up question regarding chain rings and I think I should use this thread I made earlier.

My current cranks are 172.5 mm 53/39T chainrings and I found used set on eBay exactly what I have now, except it is 175 mm 46/38T (different one from the one I've seen on eBay as I wrote about in the above posts). That's significantly easier gearing and from the above discussion, the crank length is OK either way. BTW on the back, I have 12/25 sprocket.

I find that tempting and deciding on it, I have a question. In pro races when bike mechanics are changing gears on the front for next day hilly race, do they swap just chainrings, or is it the whole assembly, crank arms with chainrings on them? Maybe some more serious riders around here also sometimes swap front gears once in a while?

I ask because if I should sometimes decide to switch back to the 53/39 (or switch back and forth) and it is all the same which method you choose, I'd rather use the rings swapping, because then I would stick with the shorter, 172.5 mm cranks.

Swapping just the chainrings makes me worry about ring alignment but maybe these 'new' technology rings keep 'true' unless they are bent like in an accident?

Iride01 

Make sure you check the new price at some of the online vendors for what ever crank you are looking at on Ebay. When I was looking, I never found any that were being sold as used for less than what online vendors such as Jensen USA, bikeNashbar, and many others were selling new cranks for.

I've not found Ebay or Amazon a good place to buy most bicycle parts. I find them a good deal for some other stuff, but not bike stuff.

vane171

Interesting, I did notice that Amazon is more expensive, on many, if not all, bike items, than my local shops.
Except that this crank was new in 2007 (Bontrager) and I am not sure right now if they still make and or sell it. But will try to check on it, thanks.

One reason I assumed it would be OK buy was that buying just the big ring from my LBS (if I wanted to replace just that ring, not even Bontrager but some other make) would cost $80 CAD ($90 with tax) whereas the crank with both rings from eBay (used rings but still looking much better than mine) would come to about $145 CAD with shipping and import tax included.

DrIsotope

How has this not been mentioned? Grab the chain at around the 2 o'clock position on the chainring, and try to pull it away from the ring. You should only be able to lift it a tiny amount, if at all. My big ring is so worn, if I pull up on the chain in that way, the whole chain slides off the chainring. Most of what I'm seeing on that ring doesn't look like wear, but damage. Mine has ~9,000 miles or so, looks better than the one in the OP, and is still worn out-- not shark toothed yet, but worn enough to make some krrkrrkrrkrr noises (similar to a chain rubbing against the FD cage) under power (chain slipping on the teeth.)

vane171

I measured it as advised above, 12" on 24 links, also did full length measurement, 4x24 links when it was strung out on a table (I have 105 in total), in which case I would measure the stretch even easier, and it is like new. After all, it is a TT bike and where I got it, was flat country and the guy was no pro, and likely didn't specialize in sprinting either, so the chain was just dirty. I also looked around to buy a new chain but then I was glad I didn't have to, since shopping for a chain is a meh experience. I mean if I was to settle for some 'equivalent' cheap chain, then OK, also if I wanted to pay $60 and up, also OK. Still, this particular chain seems not to be on the market, the HGX, at least not in quite a few places I searched.

Anyway, I gave it a good cleaning, several baths in paint solvent while shaking it in a plastic jar, then another one or two in methyl hydrate and after a week of drying out, I put a drip of that wax in solution on each roller from both sides, then covered all side plates on both sides, including the narrower connections, so it is thoroughly waxed and ready for new life.

thehammerdog

u got couple thousand miles left.
😁