gossamer crank - 130bcd outer + 110bcd inner?
 

i hardly ever use my small ring on my tt rig but i'm swapping cranks out and just realized the inner ring is 110 bcd. i don't exactly understand how the inner can use the same bolt and be smaller. any how if i were to buy a chainring kit is there a way to use a 130 inner instead or am i stuck with the 130/110 setup? i've never come across this before and i haven't taken them apart yet so i'm not real sure what's going on. thanks.

I got an email from fsa about this. they say it's not possible to have a mix of bcd's, which sounds right to me. however I am looking at my crank and the outer is 130 with a 110 inner. I also saw a few on eBay like this so either it is possible or they labled their small rings wrong.

should I just go with the outer measurement on this and get 2 130's?

Is the 110 bolt circle part of the large chainring? Other than MTB cranks I've never seen what you describe and the only two bolt circles I've ever seen are 135/74 (Campy), 130/74 (Shimano road) and 110/74 (Older MTB and touring/trekking cranks).

I'm not sure you have the facts straight. Normally double cranks mount both chainrings using the smae bolt with oneinside the arm and the other outside. If yours is that way than both chainrings must have the same bolt circle (BCD), be it 110 or 130mm.

Triples usually use 2 diameters, with the outer 2 sharing the same mount the way doubles do, and the inner having it's own smaller BCD and mounting directly to the arm. A typical triple would be 110/74.

Check your cranks and look at the arrangement, then measure to determine the BCD of the rings you need. If measuring bolt to bolt, refer to these charts to find the BCD

Brain669- How did you come to the conclusion that there are two different bolt circle diameters? Actually see two sets of bolts and measure their c-c or circle diameter? Or just read a lable on the rings? I don't know the FSA product line well enough to say from memory if they did produce a crank with two sets of mounting holes, but this design has been done before. Usually to get a much smaller ring (for granny/triple) so the inner bolt set is usually more like a 74mm diameter allowing a 24T inner ring. Do you have a link to a discription or a photo of your crank? I will say that parts are miss marked all the time. While I believe every thing i read on the interweb i don't believe everything i read marked on bike parts:) Andy.

Did you count the number of teeth on the small ring?

Why are you concerned with the markings. You have both rings and the crank.

Put one ring on top of the other and see if the bolt holes line up or not, then count teeth.

You can also see how they mount and measure the crank BCD point to point, and use Sheldon Browns to convert that to BCD. (link sent earlier).

So you don't have to assume or guess whether the chainring is mis-marked, if the marking doesn't match what it actually is then it is. For all we know they mis-marked a bunch, but decided to use them on OEM cranksets because it wouldn't matter.

One thing is certain, if the small ring is really 34T it CANNOT fit on a 130 mm bcd.

there are chainrings with 10 holes in them in 2 different bolt circles ,
but I think they are for wider chains ..

Is this the SRM FSA Gossamer? Looks like it uses a non-standard ring mounting method - like the crank spider arms are threaded and the chainring bolts do not go through both rings. Various online stores list it as 130/130 or 130/110 compact.

this was my other thought.

I didn't count teeth yet, had to run after the first post and won't be back till late. so as of now I have to assume anything bc i'm not with the bike. but again, I was basically making sure fsa didn't do something weird and somehow use 2 different sizes. that's a pretty bad **** up on their part either way because one of those is wrong (the inner I'm sure, I know I'm spinning a 53/11 by power/computer). I didn't think that big of a mistake could happen. but I suppose if it were a whole batch it'd be easiest to throw them on oem bikes.

This really seems like a whacky post. #1 FSA Gossamer double cranks use the same BCD for both CR as they are attached with the same chainring bolts; just because you see what you think are different numbers does not mean the laws of physics have been altered.

#2)You previously said,I would like to see these cranks you are talking about. I am wondering of you are confusing the 53/39T marking with the BCD. I also question your ability to measure a BCD when you don't even know how many teeth you have on your chainrings..This could be easily settled if you posted a photo of your crank or a link to a Gossamer crank on ebay setup the same way you say yours is setup.

I've got an FSA Gossamer crank and used to have an FSA Energy compact. On the standard crank both rings are 130 bcd and both 110 bcd on the compact. Only difference from other cranks is that the FSA ring fixing bolts are Torx rather than hex bolts.

As Gonzo Bob has pointed out it seem to be the SRM-Powermeter unit with comes with various crankarms such as FSA Gossamer or others. All the compact SRM powermeters are using 130BCD for the large chainring ring and a 110BCD for the small ring. So for everybody who does not know, or has not seen, (or does not underrstand), just look at Gonzo Bob's picture and description above or study the SRM site. http://www.srm.de/index.php/us/power...ssamer-compact