mowyang

I've searched for info on this crankset but can't find anything. It's a 28/38/48 FC500 from my '97 Fisher Nirvana. It's nothing special, but I'm wondering if it's possible to fit it with a smaller inner chainring. I asked at one shop and they said no, but thought I'd hunt around some more. Thanks!

ThermionicScott 

From the looks of it, you may be able to go a little smaller, but not much. Measure the center-to-center distance between bolt holes, multiply by 1.7 to get the "BCD": https://sheldonbrown.com/harris/chainrings.html

otg 

https://www.ebay.com/itm/Vuelta-Chain...item3389db0a97

This might work for you, you need to find out the BCD for that crankset. Here is a link to help you out.

https://sheldonbrown.com/gloss_bo-z.html

The Golden Boy 

It looks like you should be able to find a 24 or even a 22 tooth chainring in 74. That's pretty tiny.

What are you running for your big rings in the back? I think it would be less hassle to do a different cassette.

28 x 28 is pretty spinny unless you've got some monsterous hills and you're pulling a lot of weight.

clasher

That looks like the rings are all pressed together so I don't think you can swap out the inner ring by itself.

The Golden Boy 

Ewww...

Bianchigirll 

That is what I am wondering, they look more like hollow rivets than hex bolts but a better pic will tell.

dddd

That crankset is good for what it is, so I would say love it or leave it!

I'm puzzled that it's a "500"-level crankset. To my eye, it looks like TY- or maybe 3XX-series.

My 500CX (FC-M500) cranks are 30-40-50t with removable 110/74bcd alloy SG rings. Shown here:

mowyang

I found some old documentation from Fisher that says this crankset has 74/110mm bolt circle diameter. But only the smallest chainring looks to be bolted on, the middle one appears to be attached to the outer ring in some other way. The face of that smallest chainring also has a ridge on it to provide spacing between it and the middle ring. It's not just a flat ring.

Yeah, changing out the cassette might be easier, but I just want to know if changing that inner ring is even an option. I rarely use the inner ring, but there have been some steep rides where I wished for a lower gear. My current cassette is an 12-28. Thanks!

dddd

I have bought a few of the 7sp, 13-34t cassettes over the years. It's not one of those megarange types with just one huge cog tacked on.

And SRAM sells a 12-32t 7sp I believe, that is also very inexpensive.

bobotech

Can you please take a picture of the other side of the crankset? It looks like a standard Shimano crankset that can go down to the 22-24t chainrings.

The other side is what matters.

mowyang

OK, here ya go

dddd

Those two small holes either side of the chainring bolts look like crimping or spot welds to me.

I'd guess that it would be hard to remove the small ring without damaging the larger ones that it's attached to.

A grinder might easily take it off, and then you'll need the new chainring and an appropriate set of spacers.

That bolt pattern won't accept anything smaller than 24t, I'm sure of that.

bobotech

Very interesting. I have never seen a Shimano crankset like that even in our pile of random cranksets at my co-op.

I have seen crimped cheap cranksets setup like yours where there is only 1 set of chainring rivets but never on somewhat decent triple cranksets with removable chainring bolts. Your set with the steel chainrings (they look like typical steel stamped rings but I maybe wrong) look like somewhat entry level quality. I wonder though if someone had drilled out rivets and replaced them with chainring bolts?

I doubt that you will find a smaller chainring easily considering the oddness of the crankset.

Usually on Shimano triples, you find the outer chainring nuts and bolts which are exposed to the outside of the crankarm and then there is another set of chainring bolts that hold the small chainring in place and are hidden by the backside of the crankarm.

mowyang

I never would have thought that this crankset would be so unusual. I bought this bike new back in 1997, so I know that the crankset's odd construction originated with Shimano. I remember reading somewhere years ago that this FC500 crankset was typically used on hybrid bikes. The 1997 Nirvana was essentially a 26" steel MTB-based hybrid. It retailed for about $500.

Sounds like a new chainring is out of the question. Thanks for the info!