suburbanbeat

Hi all. Ok, so I'm preparing my Novara Randonee tourer for a cross country tour that's set to take place this summer. While taking everything off to clean, I noticed that my crankset is in WAY worse shape than I thought. Never really though to check it, as it hasn't really given me any issues, and shifts well enough. But yeah, this thing is beat up.

The inside of the thing has totally been ravaged by chain rub (I believe this is the result of a local bike shop throwing a standard width chain on there instead of a narrow chain). But more importantly, some of the teeth are just about completely gone. See pictures for the gory details.

Anyway, this is a Shimano SG (SG stands for Superglide - apparently a marketing term Shimano used to refer to pinned chainrings) triple crankset, which I've noticed are not easy to find these days. The chainrings are 50 tooth, 40 tooth, and 26 tooth.

So my questions are:

1) Is it possible to keep the crank arms (I like them a lot) and just switch out the chainrings?

2) If so, what should I be looking for when replacing the chainrings? I know that I should obviously look for 5-bolt ones, but might there be any other criteria that would make the ones I have now different in some way? For example, I compared a 39 tooth Ultegra chainring that I have lying around and noticed that the bolts are spaced differently, making it compatible.

3) I'm not seeing a ton of 40 tooth chainrings, but a lot of 39s. If I had to get a 39, would my experience be noticeably different? I ride in that middle gear most of the time while I'm touring, so I've gotten really used to 40.

Pardon my ignorance - I've never had to replace chainrings before (if you can't tell from the pictures). Thanks in advance!

AnkleWork

If you compare your chainrings to new ones, you might find that the teeth on yours look OK. New ones will probably not function better.

HillRider

No reason to replace the arms and I'm pretty sure that crank has bolt circles of 110 mm and 74 mm so any chainrings of those dimensions will work. It appears the granny ring is in good condition so you should only have to replace the outer rings. Carefully measure the distance between the centers of two adjacent bolts on the outer chainrings. If it's 64.7 mm (say 65 mm) you have a 110 mm bolt circle as I surmised. A 76.4 mm dimension means a 130 mm bolt circle which is Shimano's standard for road cranks and should be the same as the Ultegra chainring you said is different.

The difference between a 40T and 39T middle ring will be negligible and you will never notice the change.

However, the chainrings you show do have the shaped teeth and shifting enhancements and may be intentionally made that way. As AnkleWork noted, they may be fine.

Little Darwin

If the wear on the inside of the rings is what concerns you, I think it is mostly cosmetic.

In case you do decide to replace the rings...

Although you like the crank, I found recently that when I wanted to change rings to modify my gearing, it was actually cheaper to buy a crankset than the three chainrings... just something to consider. I would expect any current square taper crankset with the same crank arm length and similar gearing to feel the same for you and shift well.

FBinNY 

IMO, that crankset is fine with thousands of miles left.

The chain marks on inside faces is normal, and happens because the chain rubs during the shift. And the "damaged" teeth are the normal cut down teeth that modern chainrings have as shift gates, to make shifting easier.

The inner and outer rings are in great condition and the middle ring has more wear, but still has plenty of life.

If you WANT to replace/upgrade the crank, or simply replace rings, that's your option, but IMO you don't have to.

suburbanbeat

Thanks so much for the advice so far, everyone. So yes, I measured the distance between the bolts and the two larger chainrings are indeed 110mm. At first look, these seem to be a lot less common than 130mm chainrings (on eBay at least). Still, I'm seeing some that look promising.

So now that I've surmised the size and bolt spacing of my chainrings, do I need to concern myself with the actual width of the chainrings, or are they all more or less the same in that regard?

suburbanbeat

Thanks much. That seems to be the consensus here, so perhaps I'll hold off and just pick up chainrings when I see them over the next few months and set them aside for when I really need them. Perhaps if I'm still feeling nervous before the trip, I'll throw an extra middle ring in my bag, just in case.

So that being said, is there anything I can or should do to avoid further chain wear, even if it's just cosmetic? If it's just a fact of life, then I'll deal, but I want to make sure I'm not making any problems worse here.

Thanks again.

FBinNY 

IME- a complete crankset often costs less than the sum of two rings. If you decide to replace parts, be sure to cost out the options both ways, new crank complete, vs. the rings only.

If you're replacing the complete set, the BCD isn't an issue except that you need a triple with the ability to mount a small granny, ie. 24 or 26t, which will need an inner BCD of 74mm

fietsbob

You obviously tend to use the middle chainring the Most .. some of what you see is the engineering shortening the teeth
in a portion of the chainring to make it shift a tad quicker ..

if you accept that you have to adjust your shifting technique and expectations , QBP/Surly sells chainrings made in Stainless steel

they are sold as 'single speed' , but are not that much different that what was used on derailleur bikes before the whole index shifting mechanisms

became what all bikes got fitted with .

Jed19

[QUOTE=fietsbob;16764432]You obviously tend to use the middle chainring the Most ../QUOTE]

Yeah, looks like that to me. I'll exchange the middle ring and call it a day.

fietsbob

one of many places that resells those . Surly Stainless Steel Chainring > Components > Drivetrain > Chainrings | Jenson USA Online Bike Shop

110bcd and 40t is amongst the offerings.. (I use a 38t on my IGH bike)

cycle_maven

I don't see appreciable wear on those chainrings. When they wear out, the teeth *all* get like shark fins- pointy and asymmetrical. There are probably tens of thousands of miles left on those chainrings. I wouldn't hesitate to tour on that crankset. I might treat myself to a new chain, though, and maybe a new cassette depending on how worn those are.

Plimogz

While I like my Stainless Surly chain ring as much as the next guy -- I use it on a fixed gear and I see that you use yours on an IGH setup -- My thinking is that given their simple nature and lack of ramps and pins, is it really advisable to install those on a triple crank?

Beyond the possible shifting issues (I expect it would work, but not as well), the multiple rings on a triple only compounds the stainless steel weight disadvantage. Additionally, with the load and wear spread out over 3 rings, I don't know that I'd necessarily crave the durability of SS over aluminum quite as much.

However your remark about a 40t ring gives me pause; given the uneven wear on the OP's chainrings, with the middle being most worn -- if the OP spreads most of the wear over the middle ring, SS durability might be nice, but I still wonder if it would shift alright.

chriskmurray

They shift well enough for most people that are not riding super aggressive like commuters or touring cyclists. Those who NEED a shift to happen quick are also the type to usually complain about the weight so that paired with him clearly preferring his middle ring I think it is a pretty good idea.

Like was mentioned, you do have some life left but I like to start a big trip with fresh gear if possible so I would replace the middle ring, chain and probably cassette if it was me, those parts are relatively cheap and I hate having to work on gear on the road when it is avoidable.

peterw_diy

+1 for FB and cycle mavens' points. The short teeth are deliberate. Your gear looks fine.

fietsbob

Whatever..
I have a chromed steel 110 - 40t in my parts box , used it for quite a while on the triple crank of my touring bike , fitted a 38t also vintage steel 10 speed stock..

Friction bar end shifter user, I dont need shift gate teeth to shift my front derailleur .. was 50 40 24 currently 50 38 24 ..