rynpaulbert

Hello all, I've been searching around all day trying to find an answer to my question but I can't
seem to find what I'm looking for. I hate to create a new post since I'm pretty sure a lot of
people get annoyed by newbies posting new threads, but this is my last resort >_<

Apologies in advance!

So recently, I purchased a 12-speed 1989 Bianchi Sport SX and I've been trying to do my homework
on converting it into a fixed-speed. On the internet, I see a common set-up of having a
Sugino RD Single Speed Armset in conjunction with a Sugino Zen Messenger chainring.
I was planning on purchasing these two tonight ( have a little $ left over from the current
'economic stimulus check' here in the states (: ) but I ran into a little confusion.

Here is what I was about to order:

- Sugino Single Speed Armset: 170mm, Black, 130mm. Melt forged.
https://www.bikemannetwork.com/biking...PCRNKSS/CR8971

- Sugino Zen Messenger Track Chainring - 144 BCD - 42t
https://shop.vendio.com/benscycle/ite...727/index.html

The 42t on the description of the chainring threw me off.
I can't find an answer to what that exactly means and I was worried that it might not be
compatible with the crankset I was looking at.

If anyone could give me a little hand, it would be greatly appreciated.

KevinF

They won't work together.

The "42t" refers to the number of teeth on the chainring.

However, the problem is this: the crankarms you linked to have a BCD of 130mm. The chainring you linked to has a BCD of 144mm. The BCD's need to match, or you won't be able to bolt the chainring onto the crankarm.

BCD = Bolt Circle Diameter (Distance?). It's essentially a measure of the distance between the bolt holes. (Not technically accurate, but it should give you an idea of what BCD means). Basically, the BCD needs to match between the crankarms and the chainring.

Jeff Wills

"42 teeth". It really has nothing to do with compatibility. On the other hand, your armset is described as "170mm" and "130mm". I assume the last is a description of the bolt circle diameter. The chainring is described as having a bolt circle diameter (BCD) of 144mm, so the two are not compatible. These chainrings will work, though:
https://www.bikemannetwork.com/biking...30SALSA/CR3713
https://www.bikemannetwork.com/biking...CR130SG/CR4942

Combine this with a 16-tooth sprocket on your rear wheel, and you will have a "typical" fixie. That's what I have on my single-speed, and it's a good all-around flatland gear.

frankstoneline

Those messenger chainrings come in both 144 BCD (track standard) and 130 BCD (road standard). Also, be careful when you buy chainrings if you use a 3/32" chain (like a road chain) because it wont work with a 1/8" chainring.
Also, you will probably want to get the matching 103mm bottom bracket to maintain a chainline, and you can get the cranks w/ a messenger chainring from benscycle.com for about 95 and save yourself some cash.

Edit: you might look into 165's for the arm length to maintain a little more clearance, especially if you are converting a bike.

rynpaulbert

Ah! Thank you for the super quick response.
I understand now, thank you for putting that into terms I can understand (:

Instead of ordering a chainring with a 144mm bcd, I need to find one that has a 130mm bcd.

roadfix

Have you thought of using the crankset that's on the bike and using one of its rings?

frankstoneline

Out of cuiriosity, what cranks are on that bike? You might be better off using them and just buying a new bottom bracket to achieve a straight chainline with a single chainring in the outer position. Sugino RD's are essentially road double cranks marketed as track cranks, they even have the tabs to be set up as doubles, so unless you are purchasing new cranks for shorter arms, there is a good chance the current cranks on your bianchi are nicer than RD's

rynpaulbert

The bike is sitting in my room right now and on the crank a sticker says,
"Exage 400EX" and on the chainring, "Shimano Biopace".


EDIT>> I'm also planning on buying some new wheels as well. I've been told
that another thing I should do is find a fixed-gear / single-speed wheel.

ultraman6970

Hmm.... exage is an old shimano model cant even remember when that thing was discontinued. I remember were like shimano 105 sc but cheaper... swuared tapper and stuff.

Biopace, biopace is a series of chainrings that OVAL, not rounded. Probably if you take a look u'll notice the chainrings are oval, the nice about biopace is that will help you to do not fell dead spots while pedaling, your pedaling is more rounded but the big issue is that u cant make big changes in the pace like accelerations not even thing in a long sprint. For "pacing" were ok, but road racing... quite bad idea to use them, in the mountains worked very well.

If you want to make a single speed with those cranks the anser is "u cant" why? because the chainrings are oval, u need rounded chainrings.

The conversion of that bike to single speed it is too simple...
nites.

Deanster04

This is the purpose of this thread...no apology necessary. I have been working on my own bikes for more years than I like to admit but, I always learn a lot about equipment that I normally don't ride or use and am grateful for viewing the questions and responses. If a person gets or seems to get irritated then there is probably a little too much ego involvement. This is the discovery channel of bike mechanics.

frankstoneline

I believe you are mistaken sir. By tightening the chain when the cranks are in the position where they take up too much slack i think it can be done (I believe sheldon brown did so).
https://www.sheldonbrown.com/biopace.html
If you want to try using the biopace rings, give it a shot, thought they are less suitable for use if you ride stop and go, like in traffic.

Deanster04

I think you would have to use one of those thingies that take up the slack like a little single wheel derailluer, nes pas?

frankstoneline

no sir, a little bit of chain play is acceptable in fixed and single speeds, and some claim it makes them faster machines. By adjusting the chain so it's tight at its tightest point, when it is at it's loosest it should be about right. The argument is whether or not the OP is better off with a standard round ring, which really depends on his plans for the bike (ie. long commute etc would be good with a biopace setup, city navigation probably not so much) I've been meaning to set up a fixed with a biopace ring just to check it out, seems like it might be fun for long rides in the country.