Converting to Compact Double?

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05-11-2007, 11:44 AM
melissam

Converting to Compact Double?

Hi,

I have an old (1984) Bianchi Limited that I've recently reclaimed from the garage. It's currently on bike trainer duty, but I'm considering greater things for my fine, trusty steed.

My bike currently has a 52/39 in the front on a Takagi crankset (I think), with a Suntour derailleur. It's also got a 6 speed freewheel (remember those?) in the back. Downtube mounted friction shifters, thank you very much!

What's involved in converting to a compact double? Is it as simple as changing out the chainrings?

Thanks!

-- Melissa

PS I know that some of you are probably thinking that this is the *perfect* bike to convert to a fixie. Don't think that the thought hasn't crossed my mind. ;)
05-11-2007, 01:13 PM
SadieKate

Hey, "Deanna"!

Since you have friction shifting, you don't need to worry about the shifters.

Chain rings - you have to know number of arms on the spider (crank set) and the BCD (the bolt hole diameter). I suspect Sheldon has a huge article on this.

Front Der - the curve of the front derailleur needs to match. Frequently, the front derailleur for a standard double is too shallow an arc. Plus, the back plate of the front der may need to be deeper. Again, because of the friction shifting you may be able to get away with more.

I'll go see what I can find on Sheldon's site.
05-11-2007, 01:15 PM
SadieKate

Start here.

http://sheldonbrown.com/gloss_bo-z.html#bcd
05-11-2007, 01:25 PM
SadieKate

Sizing and curvature of the front derailleur

http://sheldonbrown.com/gloss_ca-g.html#capacity

You may not be able to get small enough chainrings on that crankset and you may be able to get a new crank for less than the cost of chain rings. I suspect you have a square taper bottom bracket on that bike.
05-11-2007, 01:31 PM
DebW

To replace the whole crankset, if that what you decide to do, you either need to match the spindle of the old bottom bracket or replace the bottom bracket. You almost certainly have a square-tapered spindle. You can still get Sugino and possibly other cranksets that take a square-tapered spindle. Even if you can use the same bottom bracket, you may get a better chainline by going with a slightly shorter spindle since the smaller inner ring of a compact can sit closer to the frame, which would give you more usable cogs with the big ring.
05-11-2007, 02:16 PM
KnottedYet

My compact double was a used double crankset for a mtb. Suntour. With labor and a new small chainring, switching cost me $50 in all.
05-11-2007, 02:42 PM
melissam

Thanks everyone!

This is great info -- I'll have to take some time when I'm not @ work to peruse Sheldon Brown's site. Thanks for the links, SK!

Knot, I'll keep the MTB crankset in mind. Sounds like you got a great deal!

Deb, your expertise is always welcome. I'll keep the bottom bracket in mind.

-- Melissa (AKA "Deanna")
05-22-2007, 02:09 PM
melissam

Compact Double is on hold, for now

What I *really* wanted was to get the Bianchi back on the road. I think it will be a nice bike to do flat, social rides on. No need for a compact double, yet.

In order to get the Bianchi roadworthy, it's getting a tune-up. I have no idea when the last time the grease in the hubs was changed. Ditto for the headset. We're holding off on the bottom bracket overhaul in case I end up going with a compact double.

The Bianchi is also getting new short reach brake levers. If this doesn't give me sufficient stopping power, we'll look into upgrading the brake calipers.

Brake & derailleur cables will also be replaced, as well as the handlebar tape. I had the handlebar tape redone back in 1988, and it has the scrapes & smudges to prove it!

I'm also the high bidder of a 7-speed freewheel with a 34T sprocket. Not sure if it will get me up Nemesis Hill....If not, there's always that Compact Double.

-- Melissa
05-22-2007, 04:37 PM
ridebikeme

Converting to compact double

Everyone here has definitely given you some good advice. As Deb mentioned, the chain line will undoubtedly be better with a new crank and bottom bracket.. and then of course you'll also need a new front derailleur. However the other problem is that a compact double is made for 9/10 speed rear wheels... which means it needs a much narrower chain than your current 6 speed rear wheel.

Another choice is to check on a touring crankset.. they usually run 50/42/30 but you can also get 48/38/28... so you definitely have plenty of options. This make work out better for you in the long run..

Good luck!
05-22-2007, 04:58 PM
Popoki_Nui

I recently converted my Bianchi Limited to a MTB triple (48/38/28). I was able to simply change out the old BB for a new XT cartridge as the original was worn out anyway, and the XT crankset bolted right on. The spindle length was same as, and the chainline is perfect.
The stock Shimano 600 front derailleur works perfectly (just needed to adjust the limiting screws), but I did change the rear derailleur to a Shimano 700CX as the 600 cage didn't have quite the length needed. The conversion went much easier than I anticipated. Cost: $50 for the BB, $60 for the rear derailleur. I had the cranks already. About an hour's work start to finish including adjustments.
Then for fun, I added MTB flat bars, vintage XT brake levers, and fatter all-terrain tires. Now it's a lightweight go-almost-anywhere ride that I really enjoy.
05-22-2007, 05:34 PM
melissam

Popoki_Nui,

Do you have any pics of your Bianchi Limited? That sounds like quite the bike!

ridebikeme,

The touring crankset could be an option too. I did "win" the 13-34T freewheel on eBay, so I would have a low gear of 39-34, which should be sufficient.

At this point, my plans are to take the Bianchi out for nice, flat, social rides. The Trek will get to go out on hillier rides or longer rides. I love my Trek, but there's something that tickles me about taking my old college bike out on the road.

Just call me a sentimental fool.... ;)

-- Melissa
05-22-2007, 06:15 PM
Popoki_Nui

2 Attachment(s)

Quote:

Originally Posted by melissam

Popoki_Nui,

Do you have any pics of your Bianchi Limited? That sounds like quite the bike!

Just call me a sentimental fool.... ;)

Hey...nothing wrong with being sentimental! Lots of us here have/ride bikes from our younger years. Go ahead...be sentimental! :D
Here are a couple of pix, hastily taken just now, of my Bianchi Limited converstion. Hope it gives you some ideas! It was my winter project in Dec 05/Jan 06. I took couple of weeks to strip, paint, re-decal, and do the mechanical restoration, then the conversion later in 06.
05-23-2007, 10:28 AM
melissam

Popoki_Nui,

That looks fantastic! Thanks for posting the pics!

What kind of handlebars are those?

How wide are the tires? 28s? Do they fit on the original rims?

What color is your bike? It looks black in the pictures, but that could be the lighting. My bike is burgundy, but it can look brown or black.

Thanks again for posting the pics. Man, maybe we should start a "vintage" bike pic thread.

-- Melissa
05-23-2007, 05:02 PM
Popoki_Nui

1 Attachment(s)

Quote:

Originally Posted by melissam

Popoki_Nui,
What kind of handlebars are those?
How wide are the tires? 28s? Do they fit on the original rims?
What color is your bike? It looks black in the pictures, but that could be the lighting. My bike is burgundy, but it can look brown or black.

Not sure about the bars and stem, I had them in a box of parts in my workshop. They are basically 1" quill mountain bike stem and bars with bar ends. The tires are Continentals marked 700x28, but they actually measure 31mm wide. Yes, they fit right on the original rims. The bike's color now is gloss black, the original color was a kind of brownish~black (as far as I could tell: most of the paint was gone). The pic below shows what she looked like the day I brought her home. Tires rotted, cables seized, anything not alloy was rusted tight.